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Flashcards in Anaesthetics III Deck (97):
1

Cerebral blood flow

Cerebral blood flow (CBF) is approximately 50 ml/100 g of brain tissue per minute and is maintained at this constant rate over a wide range of mean arterial pressures (not systolic blood pressures). This phenomenon is called autoregulation and occurs between mean arterial pressures (MAP) of 60-130 mmHg.
The autoregulation curve for cerebral blood flow is shifted to the right (not left) with hypertension and is lost around areas of diseased brains.
Hypothermia is defined as a core temperature below 35°C and is associated with a reduction in CBF.
Hypercapnoea causes cerebral vasodilatation which increases CBF. In hypocapnoea the CBF falls due to cerebral vasoconstriction, for example, a reduction in PaCO2 from 5 kPa-4 kPa (40-30 mmHg) results in a 30% fall in blood flow.
CBF increases when the PaO2 falls below 6.7 kPa (50 mmHg) and is doubled at a PaO2 of 4 kPa (30 mmHg).

2

Cervical plexus

The cervical plexus is formed by the anterior primary rami of C1 to C4 and divides into superficial and deep branches.
The superficial branches pierce the deep fascia at the middle of the posterior border (not anterior) of the sternocleidomastoid, and provide sensation from the lower border of the mandible (not maxilla) to the level of the second rib.
The deep branches supply motor fibres to the neck muscles and diaphragm and are located in the sulci of the transverse processes.
Complications of a cervical plexus block include
• Injection of local anaesthetic into the vertebral artery, subarachnoid and epidural spaces
• Blockade of the phrenic nerve, recurrent laryngeal nerve and cervical sympathetic plexus.

3

Thrombosis risk

Patients with deep venous thrombosis usually present with physical signs that are unreliable or non-specific, and frequently require investigation to confirm the diagnosis.
Some calf vein thromboses can be asymptomatic.
Risk factors associated with DVT and pulmonary embolism (PE) include hypercoagulable states, such as deficiencies of
• Protein C
• Protein S
• Antithrombin III
• Plasminogen.
Other risk factors are
• Malignancy
• Prolonged immobility
• The oral contraceptive pill
• Pregnancy
• Obesity
• Previous DVT
• Varicose veins
• Polycythaemia
• Myocardial infarction
• Cardiac failure
• Connective tissue diseases.

Lumbar (not thoracic) epidurals and spinals have been associated with a reduced incidence of DVT. This has been attributed to the increased blood flow to the lower limbs, reduced venous stasis and reduced blood viscosity (from intravenous fluid loading).

4

Pulmonary embolism

A pulmonary embolus can present with
• Dyspnoea
• Pleuritic chest pain (with an audible pleural rub)
• Haemoptysis
• Cyanosis
• Pulmonary hypertension
• Right ventricular failure
• Cardiac arrest.
They can also be asymptomatic.
A pleural rub may be found on auscultation in pneumonia, so it cannot be used to confirm a PE.
A positive V/Q scan will show persistent ventilation in a region with absent perfusion (not ventilation). The presence of co-existing pulmonary pathology reduces the sensitivity of this investigation.
The associated ECG changes in a PE are not diagnostic, but include signs of right (not left) ventricular strain with right axis deviation, right bundle branch block and the S1, Q3, T3 pattern (S wave in lead I, Q wave and inverted T wave in lead III).
The classical findings on arterial blood gas analysis show
• Hypoxia
• Hypocarbia (not hypercarbia)
• An increased alveolar-arterial oxygen gradient.
Treatment of a PE requires systemic anticoagulation (heparin followed by warfarin), and in selected cases only (central PE) surgical embolectomy may be performed.

5

helps to prevent the development of multiple organ dysfunction syndrome (MODS) in trauma patients? Early nasogastric feeding

Multiple organ dysfunction syndrome (MODS) is defined as 'the presence of altered organ function in an acutely ill patient such that homeostasis cannot be maintained without intervention' (1992 American College of Chest Physicians/Society of Critical Care Medicine consensus panel). It is a frequent complication of the systemic inflammatory response syndrome (SIRS) and sepsis.
Enteral feeding via a gastric tube should be started as soon as possible in all trauma patients. In the absence of enteral nutrition, the gut mucosa atrophies and bacteria may 'translocate', which is thought to be the cause of sepsis and MODS.
Selective decontamination of the digestive tract (SDD) may reduce the incidence of nosocomial infection, but there is little evidence to suggest it reduces the incidence of MODS. The use of broad spectrum antibiotics will merely encourage the development of resistant bacteria.
Fractures should be stabilised as soon as possible. Using propofol for long term sedation on the ICU is no longer popular; however this is not associated with the development of MODS.

6

Treating pain in trauma patients

Decreases muscle spasm, does not increase identification of clinical signs

Appropriate analgesia should be given to all trauma patients. Pain will usually cause immobilisation of the patient and thus increases the risk of developing venous thrombosis and venous thromboembolism.
When in pain, patients have shallow respirations and usually are reluctant to cough or sigh. This causes atelectasis and increases the risk of pulmonary infections. When adequate analgesia is provided, tidal volumes are greater with less atelectasis and a reduced incidence of pulmonary complications is seen.
Pain causes adrenergic stimulation and this increases metabolic responses, for example,
• Gluconeogenesis
• Glycolysis
• Lipolysis
• Production of free fatty acids.
Treatment of pain will decrease this response.
Pain associated with fractures can cause skeletal muscle spasm, which if left untreated not only helps to maintain the pain but can also make the reduction of fractures very difficult.
Although analgesia improves patient co-operation during examination and radiological investigation, some important clinical signs and symptoms can be masked. The interpretation of an abdominal examination may be more difficult and some cervical spine fractures have also been missed following the administration of analgesia.

7

Traumatic rupture of aorta

Widened mediastinum
The thoracic aorta is at risk in any patient sustaining a significant decelerating force, for example, fall from a height or high speed road traffic accident (not penetrating injuries).
Widening of the mediastinum may have been overlooked on the original AP radiograph. This is a sensitive sign of aortic rupture, though not very specific: 90% of widened mediastina are due to venous bleeding.
Other features frequently associated with aortic rupture are:
• Fractures of the upper three ribs
• Deviation of the trachea to the right
• Depression of the left mainstem bronchus
• Deviation of the nasogastric tube to the right
• Loss of the aortic knob
• Pleural capping.

8

Interscalene block Can cause ipsilateral horners syndrome


An interscalene block anaesthetises the brachial plexus at the level of the roots, and reliably blocks the shoulder and radial aspect of the forearm. It is often associated with sparing in the ulnar nerve territory (not radial).
The key landmark for performing this block is the interscalene groove which is located between the anterior and middle scalenus muscles. At least half of patients having an interscalene block develop Horner's syndrome on the same side (ipsilateral).
One of the main advantages of the interscalene block is that pneumothorax is avoided, and the supraclavicular block is associated with the highest risk of pneumothorax.

9

Nerves to be blocked in an ankle block

In order to perform an ankle block, five nerves need to be anaesthetised.
They are the saphenous nerve (the terminal branch of the femoral nerve) and four nerves derived from the sciatic nerve:
• Tibial nerve
• Sural nerve
• Superficial peroneal nerve
• Deep peroneal nerve (not common peroneal nerve).

10

Muscle of inspiration

Scalenus anterior
The internal intercostals are muscles of expiration.
Latissimus dorsi has no role in either inspiration or expiration.
The rectus abdominus aids expiration by pushing the relaxing diaphragm upwards and pulling the ribs down and in.
In deep forced inspiration, every muscle that can raise the ribs is brought into action, including the scalenus anterior and medius and the sternocleidomastoid muscle.

11

Femoral nerve

Supplies part of foot but not in femoral sheath, and doesn’t share origin with sciatic nerve

The femoral sheath contains the femoral artery and vein as well as lymphatics, but not the nerve. The femoral nerve lies behind and lateral to the sheath.
The femoral nerve gives off three cutaneous branches
• Two from its anterior division (medial and intermediate cutaneous nerves of thigh which supply the skin of the medial and anterior surfaces of the thigh)
• One from its posterior division (saphenous nerve).
It has no branches to the scrotum.
The saphenous nerve runs down the medial side of the leg and supplies the medial side of the calf as far as the medial malleolus. It terminates in the region of the ball of the big toe and may supply the medial side of the dorsum of the foot.
The femoral nerve is the largest branch of the lumbar plexus and comes from the same lumbar nerves as the obturator nerve, L2, L3 and L4.

12

Hyperkalaemia treatment

When electrocardiogram abnormalities are present, treatment of hyperkalaemia is an emergency. The treatment includes
• Calcium chloride
• Sodium bicarbonate
• Dextrose/insulin
• Beta agonists
• Loop diuretics
• Drugs to bind potassium in the gastro-intestinal tract
• Dialysis.
The underlying condition must also be sought and treated.
Amiloride, atenolol, magnesium and phosphate have no role in the management of hyperkalaemia.

13

Causes of hypokalaemia

Causes of hypokalaemia can be divided into the following:
• Transcellular shifts
o Alkalosis
o Insulin
o Beta-agonists
• Renal losses
o Diuresis
o Diabetic ketoacidosis after therapy
o Conn's disease
• Extrarenal losses
o Diarrhoea
o Nasogastric suction
• Decreased intake
o Malnutrition
o Alcoholism.
Angiotensin converting enzyme inhibitors and rhabdomyolysis tend to cause hyperkalaemia.

14

Regarding burns

Full thickness are painless
Chemical burns should be brushed off (if dry substance) and irrigated. Using an alkaline substance to neutralise the acid may result in an exothermic reaction (generating heat), which could exacerbate the injury.
Superficial partial thickness burns are painful and erythematous, deep partial thickness burns are blistered and very painful, and full thickness burns are white, leathery and painless.
The anterior trunk is 13% of body surface area (Lund and Browder chart). The 'rule of nines' is just a simple approximation.
The half-life of carboxyhaemoglobin in 100% oxygen is approximately 30 minutes; in air it is four hours.

15

Principles of traumatic head injury

Principles in the management of a head injury include
• Nursing the patient in a head up tilt of 30 degrees (not down)
• Avoiding hypoglycaemia and hyperglycaemia
• Using normal saline (0.9%) as the primary maintenance fluid
• Maintaining normocapnoea (not hyperventilation to a pCO2 of 3.0 kPa)
• Active treatment of fever and seizures.
The prophylactic treatment of seizures has not shown to be of benefit.

16

Severe traumatic brain injury Loss of autoregulation


Primary brain injury is usually irreversible and occurs at the time of injury.
Causes of secondary brain injury include
• Hypoperfusion
• Hypoxia
• Reperfusion injury.
The factors that determine the cerebral perfusion pressure (CPP) include the mean arterial blood pressure (not systolic blood pressure) and the intracranial pressure (ICP) as shown in the following equation:
Cerebral perfusion pressure = mean arterial pressure - intracranial pressure.
The cerebral perfusion pressure is usually maintained above 70 mmHg.
In severe traumatic brain injury, the autoregulation of cerebral blood flow is lost.
Cerebral oxygen consumption should be minimised following head injury (not maximised).

17

GCS

The Glasgow coma score (GCS) provides a score from 3 to 15, depending on the best response observed in three different parameters. The minimum score is 1 in each of these.
• Eye opening
• Verbal response
• Motor response.
The pupil response to light is not included.
The GCS was originally developed for use in brain trauma but is now used when evaluating other cerebral insults.
A modified version is used in young children.

18

Hypovolaemic shock

CVP pressure is reduced
False:

Hypovolaemic shock occurs when the intravascular volume is depleted as a consequence of blood or fluid loss.
The commonly encountered haemodynamic findings include
• A decrease in stroke volume, cardiac output and filling pressures (that is, central venous pressure and pulmonary capillary wedge pressure)
• An increase in heart rate and systemic vascular resistance.

19

Invasive arterial measurement complication

False aneurysms
Complications of arterial cannulation include
• Haematoma formation
• Distal ischaemia
• Infection
• Embolisation
• False aneurysm
• Arteriovenous fistula
• Blood loss.
Flush volumes must be limited in children, otherwise fluid overload may occur. Replacing the pressure bag with a syringe pump may provide some protection against such an occurrence.

20

Inappropriate cannulation site

Brachial artery
Commonly used sites for the insertion of arterial cannulae include the radial, femoral, axillary and dorsalis pedis arteries.
Short catheters should be used for the radial and dorsalis pedis arteries.
Longer, softer and more flexible cannulae should be used for the femoral and axillary arteries (to minimise injury).
The brachial artery should be avoided because the collateral circulation is limited.

21

ARDS

ARDS is diagnosed when all the following are present
• Acute onset of impaired oxygenation
• Severe hypoxia where the paO2:FiO2 ratio is <18 mmHg.

22

Life threatening asthma features

Asthma may be classified as
1. Moderate exacerbation
2. Acute severe
3. Life-threatening
4. Near fatal.
The features of life-threatening asthma are
• A peak expiratory flow rate (PEFR) <8 kPa
• Normal or raised pCO2
• A silent chest
• Cyanosis
• Feeble respiratory effort
• Bradycardia
• Exhaustion.

23

Metabolic acidosis causes

The causes of a metabolic acidosis include
• Renal failure
• Gastrointestinal bicarbonate loss
• Drug poisoning (for example, salicylates, diabetes mellitus, starvation and lactic acidosis).
The other options all cause a metabolic alkalosis (hyponatraemia/kalaemia, calcium antacids, hypochloraemia)

24

Increased pulmonary capillary wedge pressure

Fluid overload and left ventricular failure (LVF) cause an increase in pulmonary capillary wedge pressure (PCWP).
The PCWP may misrepresent the left ventricular end-diastolic pressure (LVEDP) in
• Pulmonary venous obstruction (pulmonary fibrosis, vasculitis, atrial myxoma)
• Valvular heart disease (mitral stenosis, mitral regurgitation and aortic regurgitation).

25

Steroid use

Not in LVF
Yes in:
ARDS
Asthma
Sepsis
Meningitis
Steroids decrease the incidence of deafness following Haemophilus influenzae type B (Hib) meningitis. They are used as a first line treatment in asthma.
Steroids are in the guidelines for the management of sepsis, and decrease the incidence of fibrosis if given at 10-14 days in ARDS.

26

Use of tourniquets

Tourniquets may be used in the elderly and in diabetics who do not have peripheral neuropathy.

They are contraindicated in patients with sickle cell disease, any peripheral vascular disease (including deep vein thrombosis) and limb infections.

27

APACHE II scoring system

The APACHE II score is a form of physiological scoring system which devises a score by taking the following three factors into consideration:
1. Acute physiological score
2. Age of the patient
3. Previous health condition.
The acute physiological score takes into account the following factors:
• Rectal temperature (°C)
• Mean blood pressure
• Heart rate
• Respiratory rate
• Alveolar-arterial oxygen gradient if FiO2 >0.5, or PaO2 if FiO2 75 years with 75 scoring '6' points.
One of the factors in previous health condition (chronic health points) includes immunocompromised status. There are also scores for
• Post-operative admission
• Non-operative admission
• Emergency operation.
Higher APACHE II score is associated with a higher risk of hospital death.

28

Complications of laparoscopic surgery

Endobronchial intubation may result from cephalad displacement of the trachea during high pressure peritoneal insufflation. The position of the endotracheal tube should always be checked intra-operatively once gas insufflation has commenced.
Aspiration of gastric contents may occur from
• Increased intra-abdominal pressure
• Changes in position
• Gastric manipulation.
A tension and simple pneumothorax may be caused by
• Gas tracking along tissue planes
• Pulmonary barotrauma
• Undiagnosed diaphragmatic hernia
• Damaged pleura
• Ruptured bulla.
Venous gas embolism, which is extremely rare, is usually caused by accidental intravascular injection of gas into a vein. It may also, very rarely, arise from the tip of a cooled laser.

29

Effective preoperative anti-emetic

Ondansetron

Atropine, an anticholinergic, is seldom used for its anti-emetic effects which are weak, as it causes tachycardia and is preferentially used to dry up secretions.
Midazolam and lorazepam are benzodiazepines and are anxiolytics.
Metoclopramide is used pre-operatively to stimulate gastrointestinal emptying, but is rather ineffective due to short duration of action as a pre-operative anti-emetic in standard doses (10 mg).
Ondansetron is an effective anti-emetic.

30

Sickle cell pt with ?appendicitis

The initial management of the patient with abdominal pain, whether it is due to appendicitis or a sickle crisis, is to provide oxygen, intravenous opioid analgesia and fluids.
Sickle cell anaemia is a haemoglobinopathy caused by substitution of valine for glutamic acid at position 6 (from the N-terminal) of the beta chain. Homozygotes contain only abnormal haemoglobin (HbSS) which depolymerises at a PO2 of 5-6 kPa, which is found in normal venous blood. Thus, sickle cell disease (HbSS) patients are continuously sickling.
Heterozygotes contain both normal and abnormal haemoglobins (HbAS) and are said to have sickle cell trait. These patients only sickle at extremely low PO2 values of 2.5-4 kPa.
Sickle cell crises are caused by acute vascular occlusion, which is associated with severe pain, which can mimic an acute abdomen. In addition to hypoxaemia, sickling can be precipitated by
• Hypothermia
• Dehydration
• Infection
• Exertion
• Stress.
Thus the peri-operative management of sickle cell disease patients involves keeping them well oxygenated, warm, well hydrated, providing adequate analgesia by PCA (patient controlled analgesia) and avoiding acidosis (venous stasis).
Exchange blood transfusions may be required by HbSS patients before major elective surgery, the aim being to lower the HbS concentration to 30-40%, which would be impossible to organise before emergency surgery.
Haemoglobin electrophoresis is the only investigation which can determine the nature of the haemoglobinopathy, but is rarely performed out of hours.
A Sickledex test will detect HbS but provides no information on other haemoglobins.
An FBC will usually show a low haemoglobin in sickle cell disease, but it can be normal in sickle cell trait and a blood film will show sickle cells.

31

Pancreatitis

Acute pancreatitis is an autodigestive process which is commonly associated with biliary tract disease or excessive alcohol intake. Other recognised causes include
• Abdominal trauma
• Mumps
• Hypothermia
• Diuretic
• Steroid therapy.
The classical laboratory findings include
• A raised serum amylase
• Leucocytosis
• Hyperglycaemia
• Hypocalcaemia
• Hypoproteinaemia
• Hyperlipidaemia.
An abdominal x ray may reveal a 'sentinel loop' of small bowel overlying the pancreas. The chest x ray can show a wide range of pathology.
Poor prognosis may be indicated by:
• Age >55 years
• Systolic blood pressure 15 x 109/l
• Temperature >39°C
• Glucose >10 mmol/l
• PaO2 15 mmol/l
• Calcium <2 mmol/l
• Haematocrit reduced by over 0.1
• Abnormal liver function tests.
Surgery may be required for drainage of an abscess or pseudocyst but the resection of a necrotic pancreas early in the disease has a high mortality.

32

PA CXR

Rotation of the patient causes the lungs to have a difference in translucency

The PA chest x ray is performed in the radiology department and is a high quality radiograph which differs from the portable anteroposterior (AP) chest x ray which is of inferior quality.
The technique of taking a PA chest x ray involves a patient standing with their back to the x ray source, with the anterior chest wall against the film plate. It should ideally be taken at full inspiration, otherwise the appearance of abnormal lung base shadowing and cardiac enlargement may be seen.
When the x ray penetration is sufficient the thoracic vertebrae can be visualised on the radiograph, which ensures that the pulmonary vessels behind the heart are well seen. In an adequately centred x ray the medial ends of the clavicles should be equidistant from the spinous processes in the midline of the thoracic spine. If the patient is rotated then it can cause the lungs to have a difference in translucency, which can mimic pulmonary disease. The hilum and heart may also look enlarged.
Normally the right hemidiaphragm is higher than the left by 1.5-2 cm and a difference of more than 3 cm may be significant. In hyperinflation they may be at the same level and when the stomach or splenic flexure is distended the left hemidiaphragm may be higher than the right.
As a normal variant, bowel may be interposed between the liver and the right hemidiaphragm; this is known as Chilaiditi's syndrome.

33

Horners syndrome

Horner's syndrome results from interruption of the sympathetic innervation to the head. It was originally described with cervical lesions causing damage to the T1 contribution to the cervical sympathetic chain, but may be due to lesions anywhere along the sympathetic pathway.
The features of Horner's include
• Partial ptosis
• Myosis (contraction)
• Apparent enophthalmos
• Lack of sweating
• Nasal stuffiness on the affected side.
Myosis occurs due to paralysis of the dilator pupillae and ptosis is due to paralysis of the sympathetic muscle fibres transmitted via the oculomotor nerve to the upper eyelid.
Horner's may follow
• Operations on, or injuries to, the neck in which the cervical sympathetic chain is damaged
• Malignant invasion from lymph nodes or adjacent tumour
• Spinal cord lesions at the T1 segment.

34

Lap chole for a rh arthritis patient

Rheumatoid arthritis is a systemic connective tissue disease which presents as a symmetrical arthropathy involving any joint (except the terminal interphalangeal joints).
Lung involvement usually causes fibrosis and hence a restrictive pattern on lung function testing.
Atlanto-axial ligament laxity, together with odontoid peg erosion, may result in cervical subluxation and possible cord compression.
Twenty five per cent of rheumatoid arthritis sufferers have cervical instability, but only 7% have clinical signs. Cervical spine x rays are required and a gap of more than 3 mm between the odontoid peg and the posterior arch of the axis is diagnostic of subluxation.
Cricoarytenoid involvement may cause hoarseness, stridor and airway obstruction. A normochromic normocytic anaemia plus anaemia from chronic gastrointestinal loss (NSAIDs) are often found on a pre-operative FBC.
Bone marrow suppression is a side effect of gold therapy and penicillamine can cause thrombocytopenia.
Pancytopenia associated with hepatosplenomegaly is termed Felty's syndrome.

35

A 20-year-old male has sustained 15% burns in a house fire.

Colloid is the principal agent used for fluid resuscitation in the Mount Vernon formula

The rule of 9s is used to approximate the body surface area (BSA) burnt.
Adults
• Head: 9%
• Upper limbs: 9% each
• Lower limbs: 18% each
• Trunk: 18% front and 18% back
• Perineum: 1%.
Adults can compensate with oral fluids for up to a 15% burn but children can only compensate for a burn <10%.
The Mount Vernon formula uses colloid at 0.5 ml per kg x %BSA of burn every four hours for the first 12 hours following injury, then every six hours for the next 12 hours.
Carbon monoxide poisoning is common in fires within enclosed spaces. Symptoms range from a throbbing headache with nausea and vomiting (10-30% carboxyhaemoglobin), to convulsions, coma and cardiac arrest (more than 60% carboxyhaemoglobin).
Treatment of carbon monoxide poisoning is with high inspired concentrations of oxygen. The half life of carboxyhaemoglobin is four hours but this falls to 30 minutes when breathing 100% oxygen.

36

A 65-year-old male is two days post-operation following an elective repair of an abdominal aortic aneurysm. Surgery was uncomplicated and the aortic cross clamp time was below average.
He has a low dose epidural infusion for analgesia. The patient complains that he feels paralysed below his waist.
Ischaemic damage to the spinal cord occurred during aortic cross clamping

The main differential diagnosis in this scenario is whether his symptoms are
• Related to the epidural
• A consequence of aortic cross clamping.
Low dose epidural infusions are weak concentrations of local anaesthetic agents delivered by a syringe pump. They are popular because they block sensory fibres but spare motor function, thus could not be totally responsible for his symptoms.
Direct spinal cord injury from the epidural Tuohy needle is rare. The risk can theoretically be further reduced if the epidural technique is performed on patients who are awake using local anaesthesia.
Epidural haematoma formation with spinal cord compression is extremely rare with normal coagulation. The presence of such a haematoma is unlikely to be masked by low dose local anaesthetic infusions in the epidural space. Permanent neurological damage may occur if surgical decompression is delayed.
Epidurals can also be safely inserted into patients scheduled for anticoagulation, but are contraindicated in patients who are already anticoagulated.
The spinal cord is supplied by an anterior spinal artery, two posterior spinal arteries and several radicular branches that feed the spinal arteries. The most important radicular branches are located at T1 and at the lower thoracic/upper lumbar levels. The latter is called the artery of Adamkiewicz.
Cord ischaemia can occur, but anterior spinal artery syndrome usually only occurs with severe hypotension, and since surgery was uncomplicated this option is unlikely. The actual location where the artery of Adamkiewicz supplies the spinal arteries is not known. Therefore, aortic cross clamping exposes patients to the potential risk of distal spinal cord ischaemia even when the cross clamp time is short.
Secondary damage to the cord can also occur during reperfusion.

Ischaemic damage to the spinal cord occurred during aortic cross clamping

The main differential diagnosis in this scenario is whether his symptoms are
• Related to the epidural
• A consequence of aortic cross clamping.
Low dose epidural infusions are weak concentrations of local anaesthetic agents delivered by a syringe pump. They are popular because they block sensory fibres but spare motor function, thus could not be totally responsible for his symptoms.
Direct spinal cord injury from the epidural Tuohy needle is rare. The risk can theoretically be further reduced if the epidural technique is performed on patients who are awake using local anaesthesia.
Epidural haematoma formation with spinal cord compression is extremely rare with normal coagulation. The presence of such a haematoma is unlikely to be masked by low dose local anaesthetic infusions in the epidural space. Permanent neurological damage may occur if surgical decompression is delayed.
Epidurals can also be safely inserted into patients scheduled for anticoagulation, but are contraindicated in patients who are already anticoagulated.
The spinal cord is supplied by an anterior spinal artery, two posterior spinal arteries and several radicular branches that feed the spinal arteries. The most important radicular branches are located at T1 and at the lower thoracic/upper lumbar levels. The latter is called the artery of Adamkiewicz.
Cord ischaemia can occur, but anterior spinal artery syndrome usually only occurs with severe hypotension, and since surgery was uncomplicated this option is unlikely. The actual location where the artery of Adamkiewicz supplies the spinal arteries is not known. Therefore, aortic cross clamping exposes patients to the potential risk of distal spinal cord ischaemia even when the cross clamp time is short.
Secondary damage to the cord can also occur during reperfusion.

37

Postoperative ileus

Can occur after most abdo ops
Intestinal atony occurs to some extent after most abdominal operations. However, even in the presence of this post-operative ileus, small bowel activity can continue despite gastric and colonic stasis.
The aetiology is thought to include
• Intra-operative bowel manipulation
• Sympathetic overactivity
• Peritoneal irritation (for example, from blood)
• Electrolyte imbalances, especially hypokalaemia.
The presence of increased bowel sounds and colicky abdominal pain suggest mechanical obstruction, which can follow an ileus.
The ileus usually resolves within 48 hours, although the presence of bowel sounds is not a reliable indicator.

38

Hypokalaemia

Hypokalaemia is defined as a serum potassium of less than 3.5 mmol/l, and symptoms usually occur below 2.5 mmol/l.
A common cause of post-operative hypokalaemia is inadequate potassium intake, for example, intravenous fluid therapy without sufficient potassium supplementation. The daily maintenance potassium requirement is 0.5-1.0 mmol/kg per day.
ECG changes are common and include
• T wave inversion
• S-T segment depression
• Q-T and P-R prolongation
• U waves.
Cardiac arrest may occur if attempts to raise the serum potassium are delayed and hypokalaemia is a cause of pulseless electrical activity (PEA).
Treatment of hypokalaemia in this patient should be with intravenous potassium, as he may still be on restricted oral intake or even be nil by mouth. Up to 40 mmol of potassium chloride can be added to each litre bag of fluid, but this method may not raise the serum potassium quickly enough. Therefore, it should be given by intravenous infusion at a rate not exceeding 40 mmol/hour.
In severe cases this upper limit may be exceeded with ECG monitoring, for example, in critical care areas, as there is a high risk of dysrhythmias, especially ventricular fibrillation.

39

Haematrocrit

The haematocrit is the total red blood cell volume as a proportion of blood volume, and it is expressed as a fraction not as a percentage.
Normal values are 0.4-0.54 (male) and 0.37-0.47 (female).
Venous blood has a higher haematocrit than arterial blood, because of the entry of chloride ions into red cells (chloride shift) which is followed by water entry by osmosis.
A fall in haematocrit decreases the viscosity and thus increases the flow. Therefore, a haematocrit of about 0.3 after acute blood loss is thought to be optimal; in addition to reducing the viscosity and improving tissue blood flow, the hazards of blood transfusion and deep vein thrombosis are reduced.
However, a value below 0.3 is undesirable because of reduced oxygen carrying capacity.

40

Hypercalcaemia causes

MASH IT Hypercalcaemia is commonly caused by hyperparathyroidism and malignant tumours (especially bone secondaries).
Less common causes include
• Milk-alkali syndrome
• Hyperthyroidism
• Sarcoidosis
• Adrenocortical insufficiency
• Immobilisation
• Thiazide diuretics.

41

Paediatric shock

The initial crystalloid bolus is 20 ml/kg
Children's cardiovascular systems initially compensate well in shock. Hypotension is a late and often sudden sign of decompensation, and if not reversed will be rapidly followed by death.
A formula for calculating normal systolic blood pressure is 80 + (2 x age in years).
Capillary refill time is a more useful test of perfusion in children than blood pressure measurement. The skin on the sternum or a digit held at the level of the heart should be pressed for five seconds. After blanching pressure has been released the time for the colour to return to normal is measured. A normal capillary refill time is less than two seconds.
Hypoglycaemia and shock may co-exist as the sick child or infant has poor glucose producing reserves. Urgent blood glucose estimation must always be performed to exclude this common condition.
Fluid resuscitation in paediatric shock is based on crystalloid boluses of 20 ml/kg, which can be repeated up to three times.
Blood is the colloid of choice, although 4.5% albumin may have a role in septicaemia.

42

Magnesium

Magnesium is largely an intracellular cation present mainly in bone and skeletal muscle. Only 1% is in the extracellular fluid (ECF), and normal plasma levels are 0.75-1.05 mmol/l. Its effect can be described as antagonising the actions of calcium.
Magnesium sulphate is used in pre-eclampsia as an anticonvulsant but it also relaxes vascular smooth muscle, causing vasodilatation, thus lowering the mean arterial blood pressure. It is also an effective tocolytic drug, helping to decrease uterine contractions. It acts at the neuromuscular junction, decreasing acetylcholine release, thus neuromuscular function is weakened.
Therapeutic plasma levels of magnesium are 2.0-3.5 mmol/l, but side effects may occur above 4.0 mmol/l. Increasing plasma levels of magnesium causes deep tendon reflexes to gradually diminish until they become absent. Thus tendon reflexes are frequently used as a bedside measurement of hypermagnesaemia.

43

Hypothermia

Hypothermia is defined as a core temperature of less than 35°C.
Children have a relatively large body surface area to weight ratio and even though they have a higher basal metabolic rate, they are very susceptible to hypothermia.
Alcohol and anaesthetic gases cause vasodilatation, thus increase heat loss. As the core temperature continues to fall, the cardiac rhythm becomes increasingly unstable, sinus bradycardia tends to give way to atrial fibrillation, followed by ventricular fibrillation and finally asystole.
In hypothermic patients, J waves are frequently seen on the ECG.

44

General pain management

The half life of naloxone is shorter than the half life of morphine

Intravenous morphine is the gold standard opiate analgesic, against which the potency of other drugs is compared. The dose of intravenous morphine is 0.1-0.2 mg/kg.
It is an agonist at the various opioids' receptors and its actions are antagonised by naloxone (especially pain and respiratory depression). However, the half life of naloxone is shorter than the half life of the metabolites of morphine and this should be remembered when treating an opioids overdose.
Entonox is a gaseous mixture of oxygen and nitrous oxide in equal proportions (50:50). It provides moderate analgesia but the effects are short-lived and its use is contraindicated in patients with pulmonary disease.
Codeine is unlicensed for intravenous use and should only be given intramuscularly, orally or rectally.
Ketamine increases salivation and pretreatment with an anti-sialogogue such as glycopyrrolate is useful.

45

70 year old with hyponatraemia

Could be due to thiazide diuretic

Hyponatraemia is a serum sodium <115 mmol/l.

46

PEA

Pulseless electrical activity (PEA) has numerous causes that can be summarised into the four Hs and four Ts.
These are
1. Hypoxia
2. Hypovolaemia
3. Hypothermia
4. Hyper/hypokalaemia

1. Tension pneumothorax
2. Cardiac tamponade
3. Thromboembolism
4. Toxic/therapeutic disorders.
Hypothermia is defined as a core temperature below 35°C.
A small pneumothorax is unlikely to cause hypoxaemia at sea level, unless it becomes a tension pneumothorax.
Atenolol is used in the management of hypertension and angina, and is frequently prescribed in doses up to 100 mg daily, which does not constitute an overdose.
A low serum potassium is a recognised cause of PEA.

47

On-table positioning can affect which nerve can be affected

The length of time spent in an abnormal position will increase the likelihood of problems.
Nerves at risk during the peri-operative period include
• Optic nerve
• Ulnar nerve
• Radial nerve
• Saphenous nerve
• Common peroneal nerve.
The eyes and optic nerves are at risk from direct pressure from surgical instruments and elbows resting over the face.
The brachial plexus and its terminal branches are at risk from stretching or external pressure, particularly in the lateral position.
The lithotomy position can damage the saphenous and common peroneal nerves by pressure from the poles.
Neuronal injury is usually temporary and function returns with time, but occasionally damage is permanent.

48

Homologous blood transfusions are associated with Mast cell degranulation

An homologous blood transfusion is the administration of blood to a patient that has been obtained from donors.
It usually consists of concentrated or packed erythrocytes suspended in a storage solution such as SAG-M (saline, adenine, glucose and mannitol), which has been stored between 2-6°C.
Transfusions of homologous stored blood will in general terms render the patient cold, acidotic (metabolic acidosis) and hyperkalaemic. This is because stored blood has a low pH 6.7-7.0, a high lactic acid content and an increased potassium concentration (up to 30 mmol/l). The blood should be given via a fluid warming device to avoid adverse cooling of the patient and hypothermia.
Whole blood obtained from screened donors is collected into bags containing citrate, phosphate and dextrose (CPD) which acts as an anti-coagulant. During rapid or large transfusions the citrate may cause hypocalcaemia, which can be treated by giving intravenous calcium. Alkalosis may follow citrate metabolism to bicarbonate, but this is unlikely to be of clinical significance.
Blood products can potentially trigger an anaphylactic reaction following IgE mediated mast cell degranulation, releasing histamine and other vasoactive compounds.

49

Anuria

The pigments urochrome and uroerythrin give urine its yellow colour

Urine is coloured yellow by the pigments urochrome and uroerythrin, but urine darkens on standing due to the oxidation of urobilinogen to urobilin.
Oliguria is defined as a urine production <100 ml/day.
The urine of patients on long term sedation using propofol is frequently coloured green.
Abnormal constituents of urine include
• Glucose
• Ketones
• Bilirubin
• Erythrocytes
• Large numbers of leucocytes
• Casts.
Normal urine output in temperate climates is 800-2500 ml/day, which is about 1 ml/kg per hour. Despite the concentrating ability of the kidney, a minimum of 500 ml/day is required to eliminate the urea and other electrolytes.

50

Emphysema patient having 4th operation

FBC/electrolytes
The main point to note in this question is that the patient is about to have his fourth operative procedure in a six week period.
The patient is known to have emphysema and he will undoubtedly have been extensively investigated before his previous operations. Therefore, unless his pulmonary function has changed or deteriorated over the last six weeks, then the only appropriate preoperative investigations would be to repeat his full blood count and urea and electrolytes.
To repeat the chest x ray and lung function tests would be totally unnecessary, as it is unlikely to change his management.
The 12 lead ECG and arterial blood gases taken prior to the previous operations should provide sufficiently up to date information, thus repeating them would not be required.

51

IV cannulas

With a 20 gauge have a flow rate of approximately 60 ml per minute

The Hagen-Poiseuille equation is used to calculate flow through tubes and cylinders:

Where P is the pressure gradient across the tube of length l and radius r to the power of 4. π is, of course, Pi and η the viscosity of the fluid or gas.
Thus wider and shorter cannulae have faster flow rates. The flow rate through intravenous cannulae varies between manufacturers, but a 14 G and 20 G cannula have approximate flow rates of 300 ml/min and 60 ml/min respectively.

52

Hyperkalaemia management 10mls of 10% calcium gluconate


Hyperkalaemia is a serum potassium over 5.0 mmol/l, which, if left untreated, may lead to arrhythmias and cardiac arrest.
It can be treated in a number of ways. Giving calcium gluconate 5-10 mmol intravenously (IV) is effective. This can be repeated every 10-20 minutes until the ECG becomes normal. It does not reduce potassium but reduces myocardial excitability so protects the heart against arrhythmias.
50-100 ml of 8.4% sodium bicarbonate (not carbonate) over 30 minutes IV results in the exchange of potassium ions for hydrogen ions across cell membranes and is also an effective treatment.
Subcutaneous insulin will take too long to work.
50 ml of 50% dextrose with 5 units of insulin given as an infusion over 15-30 minutes will drive the potassium back into the cells. This will be effective for several hours.
Oral or rectal calcium resonium (an ion exchange resin) and dialysis are also recognised methods but clearly take much longer to be effective.
250 mg furosemide or 5 mg bumetanide IV over one hour is also effective

53

Tramadol

Tramadol is a commonly used, centrally-acting opioid analgesic. It is a non-selective pure agonist at mu, delta and kappa receptors with a higher affinity for the mu receptor.
Other mechanisms which contribute to its analgesic effect are
• Inhibition of neuronal reuptake of noradrenaline
• Enhancement of serotonin release.
Small quantities of tramadol and its metabolites are found in human breast milk.

54

Alteplase is used on thrombolysis

Alteplase (tissue type plasminogen activator) is a thrombolytic and acts by activating plasminogen to form plasmin, which degrades fibrin and so breaks up thrombi. It is used in the treatment of myocardial infarction and life-threatening venous thrombosis.
Aprotinin is an enzyme inhibitor acting on plasmin and kallikrein and is classed as an anti-fibrinolytic, thus inhibiting fibrinolysis. It is indicated in patients at high risk of blood loss.
Warfarin is an oral anticoagulant and it inhibits the synthesis of vitamin K dependant factors II, VII, IX and X. Hepatic enzyme inducing agents, for example, carbamazepine and phenobarbitone reduce its effect. Enzyme inhibitors, such as valproate, enhance the effect of warfarin. If the enzyme-inducing drug is withdrawn without reducing the dose of warfarin, haemorrhage may occur.
Factor VIIa (recombinant) is a purified coagulation factor used to treat patients with inhibitors to factors VIII and IX. It has been used successfully in patients with serious trauma in whom haemorrhage has been difficult to control surgically. Thus it can be classed as a procoagulant.
Heparin is an anticoagulant and its effects are monitored by measuring the activated partial thromboplastin time (APTT), although thrombin and clotting times are also prolonged. It accelerates the action of antithrombin III, which inhibits activated factors XII, XI, X, IX and thrombin.

55

Postop hypotension

Post-operative hypotension is most commonly due to epidural or spinal anaesthesia due to a reduced systemic reduction. However, it is important to exclude ongoing bleeding.
The most common cause of post-operative hypertension is inadequately controlled pain. A full bladder due to urinary retention or a blocked catheter can also cause agitation and pain.
Hypercapnoea, due to alveolar hypoventilation, can cause hypertension. This may be due to respiratory depression following a general anaesthetic or excess opioids used for analgesia.
Malignant hyperpyrexia (MH) is an inherited disease (autosomal dominant) affecting skeletal muscle contraction and metabolism. It follows exposure to triggering agents, particularly volatile anaesthetic agents and suxamethonium.
• Cardiovascular instability
• Cyanosis
• Hypercapnoea
• Hyperkalaemia and
• Hyperthermia
are features of this life threatening condition which usually presents early during an anaesthetic but can be delayed for several hours.

56

Paediatric abdominal trauma

Diagnostic peritoneal lavage (DPL) should not be performed

A diagnostic peritoneal lavage (DPL) should not be performed in children as the presence of intraperitoneal blood per se is not necessarily an indication for laparotomy.
Rectal examinations should only be performed on children by the operating surgeon and even then it should only be done if the results of the examination will alter the management.
Fluid resuscitation is based on boluses of 20 ml/kg of crystalloid not albumin.
A double contrast CT scan of the abdomen (with intravenous and intragastric contrast) is the radiological investigation of choice in children but should only be performed in cardiovascularly stable patients.

57

Hartmanns

A bag of Hartmann's solution (compound sodium lactate) contains:
• Sodium 131 mmol/l
• Chloride 111 mmol/l
• Potassium 5 mmol/l
• Calcium 2 mmol/l
• Lactate 29 mmol/l.
The lactate is subsequently metabolised to bicarbonate, which otherwise would have formed a precipitate of calcium carbonate with the calcium ions in the bag.
The osmolality of Hartmann's is 278 mOsmol/kg, which is greater than the 154 mOsmol/kg in a litre of 0.45% saline.
As a solution, it causes a shift in fluids from extracellular to vascular, thus temporarily replacing lost blood volume (but not oxygenation) and sustaining the blood pressure until whole blood can be transfused.

58

Regarding NBM

The nil by mouth (NBM) policy may vary slightly between hospitals, but safe practice is as follows.
• No solid food for six hours prior to a general anaesthetic or procedures involving sedation.
• Milk is classed as solid food and so the same six hour rule applies.
• Water or clear fluids can be consumed up to two hours preoperatively (small volumes only).
• Chewing bubble gum or eating any type of confectionery should be avoided, as this promotes gastric acid secretion.
• Patients having regional or local anaesthetic procedures should follow the same NBM policy as the general anaesthetic patients.

59

MAO inhibitors preop


Monoamine oxidase inhibitors, which are occasionally used in the treatment of depression, should be withdrawn at least two to three weeks prior to elective surgery. Psychiatric assistance is recommended in order to select an alternative antidepressant.
Chronically anaemic patients scheduled for major surgery should be cross-matched and warned about the possibility of receiving a blood transfusion but this is usually not necessary.
A spinal or regional anaesthetic block if appropriate, avoids the need for a general anaesthetic.
Infected patients or those with dirty wounds should always be operated on at the end of the list, or in a separate theatre, to avoid possible contamination of other patients.
Pregnant women who have a general anaesthetic are exposing themselves and their unborn baby to significant risk. During the first and second trimester the risk is from the teratogenic potential of anaesthetic agents and premature delivery of their fetus. As a rule, surgery should be delayed until after 32 weeks gestation to improve survivability of the neonate, should premature labour be induced.
Emergency surgery, for example an acute abdomen, obviously cannot be delayed but fetal monitoring and obstetric assistance should be available in case delivery of the neonate is indicated.

60

ABG

Arterial blood gas analysis requires knowledge of the inspired oxygen concentration (FiO2) before interpretation is possible.
Arterial blood is aspirated from a superficial artery into a heparinised syringe. Local anaesthetic infiltration renders the procedure relatively painless.
Normal values taken on air are
• PaO2 of 13.3 kPa (100 mm Hg)
• PCO2 of 5.3 kPa (40 mm Hg).
A high plasma pH is an alkalaemia and a low pH is an acidaemia.
Obtaining a pre-operative blood gas on patients with pulmonary disease is not always indicated. Providing a result is available from within three months and the symptoms remain unchanged, then a repeat test is unnecessary.
Covering the sample syringe with ice reduces the inaccuracy which may result due to ongoing blood cell metabolism. However, this is only necessary when a delay between obtaining the sample and analysis is anticipated.

61

Lactic acidosis

Not in chlorpropamide treatment

Lactic acidosis may be either type A or type B.
Type A occurs in association with poor tissue perfusion such as shock, and includes
• Infections
• Cardiac/hepatic/renal failure
• Hypotension.
Type B occurs in the absence of shock and may be drug related, such as
• Biguanide therapy
• Methanol (metformin).

62

Tetanus features

Includes carpopedal spasm
Tetanus is caused by the Gram positive bacillus Clostridium tetani and is associated with tetanic contractions due to neuromuscular blockade by the tetanus toxin.
Tetanic contractions and respiratory arrest are seen but the level of conciousness is typically unimpaired.

63

Malignant hyperthermia

In suxamethonium

Malignant hyperthermia is a serious autosomal dominantly acquired condition linked with other myotonic disorders.
Intracellular calcium transport is deranged and generalised muscular contractions generating heat may be precipitated by anaesthetic agents.
It is treated with dantrolene.
Propofol is used in the management of malignant hyperthermia patients.

64

LA

Local anaesthetics produce a reversible block of conduction along peripheral nerves.
They enter the nerve in lipid soluble form and once in the nerve become protonated and bind to a receptor in the sodium channels.
Maximum safe dose of plain lidocaine is 3 mg/kg.
If accidental IV administration occurs local anaesthetics may cause central nervous system and cardiovascular toxicity resulting in restlessness, convulsions, hypotension and cardiorespiratory arrest.
Local anaesthetics with adrenaline are absolutely contraindicated in areas supplied by end arteries (for example, fingers, toes, and penis) due to risks of prolonged ischaemia and necrosis.

65

Acute osteomyelitis in kids

Joint fluid aspiration may be an essential investigation

Acute osteomyelitis is commonly caused by Staphyloccus aureus infection.
It may be acquired by haematogenous route, direct skin puncture following injury or from infection spreading from adjacent soft tissues.
It usually commences in the metaphyseal region of long bones, but at later stages could affect the growth plate and epiphyseal cartilage.
The child with acute osteomyelitis usually presents after several hours of pain, malaise and fever. The child refuses to walk or to move an affected limb. There is invariably local tenderness over the inflammation; local redness, swelling and oedema are late signs, but joint movement is often painful. Blood cultures may be positive in about 60% of cases.
A sequestrum and involucrum are features of chronic osteomyelitis; a sequestrum is a necrotic nidus of bone within a focus of chronic osteomyelitis while an involucrum is a cloak of new bone produced by the periosteum around the infection.
If the child is refusing to move the limb/joint, then a joint fluid aspiration may be necessary to distinguish acute osteomyelitis from septic arthritis.

66

Blood transfusion complication

Overall the mortality associated with transfusion of blood products is 1 per 100000.
ABO incompatibility is the commonest cause of transfusion related death.
Incompatible white cells result in a febrile reaction shortly after commencing the transfusion; there is response to slowing the transfusion and paracetamol or aspirin.
Transfusion related lung injury (TRALI) presents with fever, dyspnoea, cough and infiltrates on chest x ray. It is due to incompatibility between donor antibodies and host granulocytes.
Urticaria results from a patient's IgE antibody complexing with a protein present in the donor's plasma.
Massive transfusion may cause
• Hypothermia
• Hyperkalaemia
• Hypocalcaemia
• Acid load
• Coagulation factor depletion
• Adult respiratory distress syndrome (ARDS) and
• Disseminated intravascular coagulation (DIC).

67

Polycythaemia

Polycythaemia is an increase in the concentration of red blood cells above the normal level.
Polycythaemia may be
• Primary
• Secondary (chronic hypoxia stimulates erythropoetin)
• Relative (reduced plasma volume, normal red cell mass) or
• Inappropriate (inappropriate erythropoetin production).
Polycythaemia leads to increased blood viscosity and sluggish blood flow, resulting in increased risk of myocardial infarction, stroke, ischaemic limbs and DVT.
Approximately 75% of patients will have splenic enlargement.
Peptic ulceration is common in polycythaemia rubra vera (primary).
Haemorrhagic lesions may be a feature of the condition, especially of the gastrointestinal tract.

68

Micro, macro, normocytic anaemia

The patient illustrated has a microcytic hypochromic anaemia.
Causes include
• Iron deficiency and
• Thalassaemia.
Macrocytic anaemia may be caused by
• Folate deficiency
• B12 deficiency and
• Alcoholism.
Normocytic, normochromic anaemia may be caused by
• Acute blood loss
• Haemolytic anaemia
• Chronic disorders and
• Leucoerythroblastic anaemias.

69

Postop pain

Increases the risks of post-operative cardiac ischaemia

Pain increases sympathetic output leading to increased myocardial oxygen demand and therefore the risk of myocardial ischaemia, especially in patients with pre-existing heart disease.
Poorly managed post-operative pain results in delayed mobilisation and in turn increased risk of DVT.
Poor management of post operative pain impairs the patient's ability to cough and deep breathe leading to retention of secretions, atelectasis and pneumonia.
Effective analgesia improves respiratory function.
PRN regimes rely on the patient requesting analgesia when in pain and there may be considerable time delay between request and administration.
In addition peak plasma levels obtained by IM opiod injections and the time taken to reach these levels varies between patients. The standard regime is therefore optimal for only a small number of patients.
The plasma concentrations of opiods required to provide effective analgesia may vary up to fourfold between patients.

70

Adult vs paediatric airways

Adult intubation requires the tip of the laryngoscope to be anterior to the epiglottis and in a child behind the epiglottis

Anatomical differences between adults and children must be considered during intubation.
For instance the angle of tracheal bifurcation is greater and the main bronchi come off at the same angle in children, whereas in adults the right main bronchus is more vertical and therefore more prone to inadvertent intubation.
However, children have comparatively larger soft tissues including a floppy epiglottis.
The larynx of a child is higher and more anterior than in the adult.
In paediatric intubation a straight bladed laryngoscope (that is, McCoy) is placed behind the epiglottis holding it in position, so that it may be lifted to expose the slightly more anterocaudal placed cords.
In adults a curved Macintosh blade, with the tip in the vallecula, anterior to the epiglottis is used.

71

Lidocaine

Lidocaine blocks fast sodium channels.
Most local anaesthetics, with the exception of cocaine, cause dilation of blood vessels.
Toxic effects associated with local anaesthetics usually result from excessively high plasma concentrations. Other signs of toxicity include inebriation and light-headedness followed by sedation, circumoral paraesthesia and twitching.
Lidocaine is an alkaline solution and the pH of the surrounding tissues influences both the pharmacokinetics and pharmacodynamics of lidocaine.
0.5% solution = 5 mg/ml
1% solution = 10 mg/ml
100 ml of solution = 1000 mg or 1 g of lidocaine.

72

Laryngoscopes

Laryngoscopes are used to perform direct laryngoscopy and can be classed as curved or straight, according to the shape of the blade.
Straight blade laryngoscopes include the following types:
• Miller
• Soper
• Wisconsin and
• Seward.
They are designed to be advanced over the epiglottis which is then lifted in order to view the larynx.
Straight blades are commonly used for intubating neonates and infants but can just as easily be used in adults.
Curved bladed laryngoscopes (not straight) are designed so that the tip is placed into the vallecula; examples include the
• Macintosh
• Polio and
• McCoy.
The standard Macintosh blade used in adults is the right-sided version. The left-sided blade may be used in patients with facial deformities that make the use of the standard blade difficult.
The Macintosh Polio blade is at an angle of 120 degrees to the handle, and was designed to intubate patients in the iron lung.
The McCoy laryngoscope is based on the standard Macintosh blade (not Robertshaw's), with a lever operated hinged tip, which can improve the view at laryngoscopy.

73

Epidural

19G Tuohy needles have 0.5 cm markings

In the United Kingdom 16G and 18G Tuohy needles which are commonly used in adult practice are 10 cm in length with an 8 cm shaft (which has 1 cm markings).
A 15 cm version exists for obese patients and a 5 cm 19G needle (with 0.5 cm markings) is available for paediatric use.
The catheter is made of biologically inert Teflon or nylon and is transparent. The distal end has a rounded tip which is closed (not open) to reduce the risk of dural or vascular puncture. Two or more side ports are also found in the distal end.
Catheters are usually 90 cm in length. There are markings at 5 cm intervals at the distal end and from 5-15 cm there are additional 1 cm markings. The filter has 0.22 micron mesh (not 0.55) that acts as a bacterial, viral and foreign body filter.

74

APACHE II scoring system

Involves the assessment of 11 physiological measurements

The APACHE scoring system (Acute Physiology And Chronic Health Evaluation) is used on ICU to assess the severity of illness in individual patients, which allows stratification of patient groups in order to compare different therapies.
APACHE scores may be weighted according to illness to give a mortality prediction for a specific patient.
The APGAR scoring system is used to evaluate the condition of newly born neonates.
In 1981 the APACHE I system was introduced, and then in 1985 this was replaced by the APACHE II system. The APACHE II score is the sum of the acute physiology score (APS), the numerical assessment of chronic health and the points allocated for increasing age.
The acute physiology score:
• This assesses 11 physiological variables, with each being awarded points from 0 to 4 depending on their deviation from the normal range. The greater the deviation the greater number of points allocated.
• The sum of these 11 variables is then added to a numerical assessment of neurological function (15 minus the Glasgow coma score), which is the 12th variable, to make up the APS.
Therefore, the APACHE II score assesses 12 physiological variables (the APACHE I assesses 34).
Points are assigned to age in the following manner
Years Points
75 6
Note that points are allocated at the age of 45 years or above (not 50 years).
Chronic health points are awarded for:
• Organ insufficiency (cardiovascular, respiratory, renal and hepatic), or
• Immunosuppression (pharmacological, radiation and disease states, for example, lymphoma, AIDS)
which were documented prior to the present hospital admission.
The points assigned are greater for non-operative or emergency postoperative patients than for elective postoperative patients.
The mean arterial pressure (not systolic) and heart rate are the cardiovascular measurements included in the physiological assessment of the APS.

75

Effect of local anaesthetics on nerve fibres?

Nerve fibres with diameters less than one micrometer are blocked first

Local anaesthetic agents block the smaller (<1 micrometer in diameter) unmyelinated C fibres first, then the B fibres (1-3 micrometers) and finally the larger A fibres (1-20 micrometers).
Temperature and pain sensation are carried by the small C fibres, whereas proprioception is carried by A-alpha fibres, hence temperature is blocked before proprioception.
Preganglionic class B fibres are myelinated, whereas the postganglionic class C fibres are unmyelinated, hence unmyelinated fibres are theoretically blocked first.
Motor function is provided by the largest diameter nerves (A-alpha) which are blocked after the C fibres that carry temperature sensation.

76

Invasive arterial cannulation

Right atrial pressure

Invasive arterial cannulation provides accurate beat-to-beat blood pressure monitoring.
Other parameters can be measured and estimated such as
• Myocardial contractility
• Stroke volume
• Vascular tone (systemic vascular resistance)
• Pulse pressure and
• Heart rate.
The presence of a respiratory swing (during mechanical and spontaneous ventilation) can also be detected from the arterial pressure trace.
Specific software is available which allows measurement of this systolic pressure variation (SPV) which gives an indication of the volaemic status of the patient. In hypovolaemia the SPV is high and when the patient is over filled the SPV is low.

77

ABO blood groups

Soluble forms of the antigens are found in sweat

The ABO blood group system consists of three allelic genes: the A, B and O.
The A and B genes control the synthesis of specific enzymes that are responsible for adding a carbohydrate to a glycoprotein or a glycolipid that has a terminal L-fucose (known as the H substance).
The O gene is an amorph and does not transform the H substance.
There are six possible genotypes (OO, AA, AO, BB, BO, AB), but the absence of a specific anti-O allows the serological recognition of only four phenotypes (O, A, B, AB).
In the United Kingdom blood group O is the commonest and AB the rarest.
The frequency of the blood groups is
• O (46%)
• A (42%)
• B (9%)
• AB (3%).
The A, B and H antigens are present in most body cells including white cells and platelets.
In 80% of the population that have secretor genes these antigens are also found in soluble form in body fluids and secretions (for example, saliva, sweat, plasma and semen).

78

Lung function

The vital capacity is equal to the difference between the total lung capacity and the residual volume

The total lung capacity (TLC) is the sum of the inspiratory reserve volume (IRV), tidal volume (TV), expiratory reserve volume (ERV) and the residual volume (RV).
Alternatively it is the sum of the inspiratory capacity (IC) and the functional residual capacity (FRC).
The vital capacity (VC) is equal to the difference between the TLC and the RV. It is also the sum of the ERV, TV and the IRV.
The IC is the sum of the TV and the IRV.
The RV is the volume of gas remaining in the lungs at the end of forced maximal expiration, whereas the FRC is the volume of gas remaining in the lungs at passive end-expiration.

79

VTE

Venous thromboembolism (VTE) is a life-threatening complication in patients undergoing surgery. The risk is greatest following orthopaedic surgery to the lower limbs, and when no prophylactic measures are employed, the incidence is 50 - 70%.
Associated risk factors for the development of VTE include
• Previous VTE
• Hyperviscosity
• Obesity
• Prolonged immobility
• The presence of a specific thrombolytic condition
• Pregnancy
• The combined oral contraceptive and
• Malignancy.
Dipyridamole is an antiplatelet drug which decreases platelet aggregation and may inhibit arterial thrombus formation. It has been used as prophylaxis against VTE in patients with prosthetic heart valves.

80

Preop medication

Not propofol

Ketamine given intramuscularly is effective at sedating patients with mental retardation, dementia or uncooperative patients, however the issue of consent for surgery must be established prior to administering the drug. An intravenous induction is usually possible when the level of consciousness has reduced.
Chloral hydrate given orally is a useful sedating premedication used in paediatric practice (smaller children and infants) and can provide acceptable conditions for either an intravenous or inhalational induction.
Atropine and glycopyrrolate are both anticholinergic drugs and have antisialogogue properties.
Atropine is administered to infants and neonates prior to anaesthesia and surgery (particularly ENT and ophthalmic surgery) primarily to reduce the risk of inducing a bradycardia.
Glycopyrrolate has a greater drying effect on airway secretions than atropine and it is given intravenously prior to topically anaesthetising the airway for an awake fibreoptic intubation.
Propofol is a short-acting intravenous sedative agent used for the induction and maintenance of general anaesthesia.
Metoclopramide increases the rate of gastric emptying and it is often given to patients at risk of regurgitation and aspiration perioperatively.

81

Premedication

The objectives of premedicating patients preoperatively are to:
• Reduce anxiety and fear
• Reduce secretions and salivation
• Produce sedation and amnesia
• Reduce postoperative nausea and vomiting
• Reduce the volume and increase the pH (not decrease the pH) of gastric contents
• Attenuate vagal reflexes (not increase vagal tone) and sympathoadrenal responses and to
• Enhance the hypnotic effect of general anaesthesia.

82

Increase gastric empyting

Pro-kinetic drugs increase the rate of gastric emptying and intestinal motility. Metoclopramide, cisapride and erythromycin have all been successfully used in this role.
Loperamide is an opioid agonist which reduces intestinal motility.
Dopexamine increases splanchnic perfusion but does not have pro-kinetic properties.
Vancomycin similarly has no therapeutic effect on intestinal motility.

83

LMA mask

Reinforced laryngeal masks have a higher flow resistance

The laryngeal mask airway (LMA) is a widely used device and provides an alternative to the face mask or tracheal tube during anaesthesia. Seven different sizes of LMA are available that are designed for use in infants to large adults.
The recommended cuff inflation volumes on LMA sizes 1, 2, 2.5, 3, 4, 5 and 6 are 4, 10, 14, 20, 30, 40 and 50 ml respectively.
In order to reduce the flow resistance to a minimum LMAs have wide internal diameters (for example, the internal diameter of sizes 2, 3, 4, and 5 are 7, 10, 10 and 11.5 mm respectively).
Reinforced LMAs are longer and have smaller internal diameters than standard LMAs causing an increase in flow resistance.
At the junction of the tube and the cuff on the LMA, there are slits that prevent the epiglottis from obstructing the airway. However, 10% of patients still develop an obstructed airway due to down folding of the epiglottis.
Rotation of the LMA can result in complete obstruction of the airway.
A black line is present along the length of the tube and when an LMA is correctly orientated, the black line should face the upper lip (not lower lip).

84

Tracheal tubes

Uncuffed RAE tubes have two Murphy eyes
Tracheal tubes can either be made of disposable plastic or red rubber which are reusable.
The tube size refers to the internal diameter in mm not the external diameter. The internal diameter (ID) is marked on the outside of the tube (some manufacturers also have the external diameter marked on the outside).
Plastic tubes have a radio-opaque line running along their entire length (rather than the entire tube being radio-opaque), which allows their position to be identified on x rays.
The internal diameter of the tube is marked in millimetres on the outside (not the external diameter).
The bevel located at the end of the tube is usually oval in shape and is left-facing (not right), which improves the view of the vocal cords during intubation.
Oxford tubes are L-shaped and have a bevel that faces posteriorly. They have thick walls which increase the external diameter, making them wider for a given internal diameter (not narrower).
RAE (Ring, Adair and Elwyn) tubes are preformed and can be either north or south facing, cuffed or uncuffed. The cuffed RAE tubes have one Murphy eye, whereas the uncuffed version has two eyes.
Uncuffed tubes are mainly used in paediatric anaesthesia and two Murphy eyes ensure adequate ventilation should the tube be too long.

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Cannabinoids

They are opioid sparing
Cannabinoids are derived from the resin of the plant Cannabis sativa. The most active constituent of the resin is 9-tetrahydrocannabinol, which is highly lipid soluble and has a large volume of distribution.
Bioavailability following oral ingestion is 6% (not 60%) and it is metabolised to polar water soluble compounds before being excreted by the kidneys.
Cannabinoid receptors have been identified in the central nervous system and also the spleen. Agonism at these cannabinoid receptors reduces the amplitude of voltage-gated calcium currents, which reduces excitability and neurotransmitter release.
Cannabinoids also have an agonistic action at opioid receptors and have been shown to exert an opioid sparing effect in chronic pain.
Naloxone and other opioid antagonists block the antinociceptive actions, but not the behavioural effects.
Prostaglandin production may also be reduced

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Electrolyte abnormalities in ARF

The typical plasma electrolyte abnormalities associated with acute renal failure (ARF) are
• Hyperkalaemia
• Hypocalcaemia
• Hypermagnesaemia
• Hyperphosphataemia
• Normal or reduced sodium concentration and
• High urea and creatinine concentrations.

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Urine analysis in ARF

A high urine:plasma osmolality ratio in intrinsic renal failure

Pre-renal causes of acute renal failure (ARF) are associated with the following urinary findings:
• Low urinary sodium and chloride concentration (400 mosmol/kg)
• High urine:plasma osmolality ratio (>1.8)
Intrinsic causes of acute renal failure (ARF), for example, acute tubular necrosis are associated with the following urinary findings:
• High urinary sodium and chloride concentration (>40 mEq/l)
• Low urinary urea and creatinine concentrations
• Low urine osmolality (<350)
• Low urine:plasma osmolality ratio (1.2)
It is important to note that the findings listed above may change when prerenal causes of ARF become superimposed on chronic intrinsic renal failure or following diuretic therapy.
The presence of red cell casts suggests acute glomerular damage.
Epithelial casts occur in acute tubular damage and forms of acute glomerulonephritis.
White cell casts appear in pyelonephritis.
Granular casts may indicate tubular damage, but they can also be found in the urine of normal individuals.
Hyaline casts may be found during any febrile illness and after loop diuretic therapy.

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In drowning

Pulmonary oedema may occur days after the submersion

Drowning refers to submersion in water and the pronouncement of death within 24 hours of the event. If death does not occur then the event is described as a 'near drowning'.
Submersion (head below the water) leads to a short period of breath holding, and when a breath is finally taken the entry of water causes laryngospasm and apnoea (at post mortem up to 20% of fatal drowning victims have no water in their lungs).
A period of involuntary breathing may follow, during which time water enters the lungs causing a respiratory arrest and finally a cardiac arrest. Therefore, cardiac arrest is usually a secondary event, but it may also be a primary event (for example, exercise induced myocardial ischaemia).
The clinical presentations of near drowning in salt water and fresh water are similar.
Hypothermia (not hyperthermia) is common and this offers some protection (especially neurological) against the effects of hypoxia.
Electrolyte abnormalities do occur but they are rarely significant or common.
A severe permeability pulmonary oedema can occur up to three days following a near drowning event in both salt and fresh water.
All unconscious patients removed from water should have cervical spine immobilisation until an injury can be excluded clinically and/or radiologically.

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Hypovolaemic shock

Hypovolaemic shock is a clinical state in which there is reduced organ perfusion and tissue oxygenation due to loss of blood or plasma after injury or trauma.
This is generally classified into four classes (I to IV) depending on the amount of blood loss (ATLS):
• Class I: 2000 mls; >40%
This case is Class II.
In class I the signs and symptoms are very minimal.
In class II the systolic blood pressure is normal but the diastolic is raised (reduced in classes III and IV).
The heart rate is about 100 beats/min in class II shock, increasing to >120 beats/min in class IV shock.
The respiratory rate is normal in class II shock and the patient becomes tachypnoeic (>20) in classes III and IV.
The urine output is 20-30 mls/hr in class II shock (10-20 in class III and 0-10 in class IV).
The patient is anxious and aggressive in classes II and III, and becomes drowsy, confused and unconscious in class IV shock.
In reality patients do not fit into these convenient boxes. Some consider the pulse rate is the most reliable factor.

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Intensivist

The following are indications for seeking an intensivist's review
Airway:
• Threatened airway
Breathing:
• Respiratory arrest
• Respiratory rate >40 or < 8
• Sa02 140
• Systolic BP <90 mmHg
• Metabolic acidosis
Disability:
• Sudden fall in level of consciousness
• Repeated or prolonged seizures.

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In critical care

Only patients with a potentially reversible condition should be admitted

Critical care units require a nurse : patient ratio of 1:2 or fewer.
Patients with single organ failure can be monitored or treated in HDU. However, if a patient requires ventilation they will require transfer to ICU.
Mortality is higher in patients admitted from general wards as these patients have usually received suboptimal basic treatment before admission.
Patients with no hope of improvement should not be admitted to a critical care area.
Higher ICU throughput is associated with significantly lower mortality rates.

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Blood cultures

Blood cultures are frequently negative or grow commensal organisms.
Bacteraemia can be intermittent and transient. Episodes of bacteraemia are usually associated with chills and fever.
Two culture specimens (one aerobic one anaerobic) should be obtained from at least two different sites. Ideally, blood cultures should be obtained before commencing antibiotic therapy.
A preliminary report can be issued at 24 hours, however, 48-72 hours are required for growth and identification of the organism.

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Bactericidal abx

Both penicillins and the aminoglycosides such as gentamicin are bactericidal whereas the others are bacteriostatic.
Bacteriostatic: Clindamycin, Erythromycin, tetracycline and trimethoprim

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Anxiolytic

The benzodiazepines are anxiolyic drugs such as midazolam, lorazepam and diazepam. These act upon GABA neurones.
Fentanyl is an opiate analgesic.
Ondansetron an antiemetic and hyoscine an anticholinergic that is used as a mild antiemetic and for drying up secretions.
Propofol is an anaesthetic.

95

Dental extraction-who doesn’t need abx prophylaxis

Patient with severe osteoarthritis doesn’t
Patients who have undergone splenectomy are at risk of overwhelming sepsis and require lifelong antibiotic prophylaxis.
Patients who have previously undergone an abdominal aortic aneurysm repair require antibiotic prophylaxis to prevent infection of the synthetic graft.
Patients with septal defects, patent ductus, heart valve lesions and artificial valves require prophylaxis.
Patients with severe rheumatoid arthritis1 (not osteoarthritis) are usually treated with steroids or other immunosuppressives.

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Abx prophylaxis

In adults the full dose of the chosen antibiotic should be administered unless there is a concern regarding excretion, for example, renal failure.
In prolonged procedures, a second dose is advised. Otherwise, single-dose prophylaxis is effective in most clinical situations.
Clean procedures where synthetic material is implanted require antibiotic prophylaxis.

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Physiological effects of surgery

Physiological effects of surgery include
• Antidiuresis (increased antidiuretic hormone (ADH) secretion in an effort to retain water and increase BP)
• Increased catecholamine, cortisol and aldosterone release (increased sodium retention and increased potassium losses) and
• Increased nitrogen excretion.
There is decreased utilisation of glucose as a consequence of the excess secretion of cortisol/catecholamines.