Flashcards in Critical Care Kanani II Deck (39):
What are the risk factors for post-operative atelectasis?
Upper abdominal and thoracic surgery: reduced lung expansion from pain and diaphragmatic splinting leads to retention of secretions and distal airways collapse
- Body mass index of
What is continuous positive airway pressure (CPAP) ventilation, and what are its physiological effects
on the respiratory system?
CPAP is an oxygen delivery system that relies on a closed cir- cuit to provide positive airways pressure throughout all phases of spontaneous ventilation. The circuit can be attached to a tracheal tube or to a tight fitting mask, which means that it may be used on the ward under supervision. Some of the physiological methods by which it improves alveolar ventilation are:
- Recruitment of collapsed alveoli, and prevention of their collapse on expiration
- Increase in the functional residual capacity (FRC): in the elderly and critically ill, collapse of the airways occurs close to the volume of the FRC. By increasing the FRC, atelectasis can be avoided or overcome
- Increased lung compliance, reducing the work of breathing
- Consequently the V/Q ratio increases, improving oxygenation
What are the disadvantages of CPAP ventilation?
The tight fitting mask is uncomfortable and may be poorly tolerated
- Causes gastric dilatation due to swallowed air
- Barotrauma to the alveoli due to high pressures (more common in neonates)
Define the blood pressure.
Blood pressure is defined as the product of the cardiac out- put and the systemic vascular resistance. The cardiac output is the product of the heart rate and stroke volume.
In which ways can blood pressure be measured?
Blood pressure can be measured non-invasively with a sphyg- momanometer, or invasively by direct cannulation of a periph- eral artery. This latter method gives a continuous waveform trace after attachment to an electronic pressure transducer.
The ‘dicrotic notch’ is a momentary rise in the arterial pressure trace following closure of the aortic valve.
How is the mean blood pressure calculated?
The area beneath the arterial pressure wave tracing represents the mean arterial pressure. For the purposes of simplicity, it may be calculated by the formula
Pd + (Ps = Pd)/3
where Pd = diastolic pressure and Ps = systolic pressure.
What are the complications of arterial lines, and what are the contra-indications to their insertion?
The complications include
- Most commonly:
- Haematoma formation
- Digital ischaemia due to vascular injury or accidental
injection of drugs
- Less commonly:
- Pseudoaneurysm formation
- Arteriovenous fistula formation
- Exsanguination from a disconnected line
It is contra-indicated in those with digital vasculitis, and in those patients who are going to have the artery of that side harvested as a conduit for bypass surgery.
What is meant by the term ‘swing in the arterial line’ during continuous measurements, and what is its significance?
This term refers to a variation of the amplitude in the arterial tracing with the respiratory cycle. It is an indicator that the patient is underfilled and requires more fluid resuscitation.
How does the arterial pressure at the radial artery compare to that at the aortic root, what accounts for this difference?
Both the pressure values and waveform change at different levels of the circulation. In the radial artery, the systolic pressure is about 10mmHg higher and the diastolic pressure about 10 mmHg lower than in the aortic root. Consequently, although the pulse pressure is higher in the radial artery, the mean arte- rial pressure is about 5 mmHg lower than in the aortic root.
These differences are, in part, due to changes in wall stiffness along the arterial tree, and its consequent effects on the trans- mission of the pulse wave along the vessel.
How does the arterial pressure waveform differ with diseases of the aortic valve?
Aortic stenosis: Anacrotic pulse – slow to rise and of low
- Aortic incompetence: Waterhammer pulse – rapid rise and decline, attaining high amplitude
- Mixed aortic valve disease: Pulsus bisferiens – a large amplitude pulse with a ‘double peak’, often felt as a double pulse at the brachial artery
What is pulsus paradoxus?
Pulsus paradoxus is an exaggerated (10mmHg) reduction of the arterial pressure brought on by inspiration, and may be seen in cardiac tamponade. The normal increase in the venous return brought on by inspiration coupled with a tight pericardial space leads to a reduction of the left ventricular end diastolic volume, and hence, stroke volume.
What is pulsus alterans?
Pulsus alterans is a random variation in the amplitude of the arterial pressure tracing with each cardiac cycle, and is seen with left ventricular failure.
What blood products do you know of other than red cells?
What blood products do you know of other than red cells?
The other major blood products are:
The other major blood products are
- Fresh frozen plasma (FFP)
- Human albumin solution
- Individual factor concentrates, e.g. factors VII,VIII, IX, X,
prothrombin complex, antithrombin III
Note that FFP may be fractionated into the products listed below it.
- Platelet concentrates
How are platelets stored once collected?
Platelets do not function at low temperatures, so that once collected, they are stored at room temperature of 20–24°C on a special agitator.
How many platelets are obtained from each
Each platelet donation contains 55 x 109 platelets. When pooled together to form an adult dose, about 240 x 109 platelets can be obtained.
Give some indications for a platelet transfusion.
These are basically
- Any cause of thrombocytopenia, when the count falls below 50 x 109/l
- Note that the above includes disseminated intravascular
- Post cardiopulmonary bypass: It is known that this has a direct detrimental effect on platelet function. Also, patients coming off bypass may still have a low body temperature, which reduces platelet function. They may also have taken aspirin up to the time of surgery. Platelets may in these instances be required to control bleeding even though the platelet count may not be that low
What are the problems associated with platelet transfusion?
Risk of infection: as for a transfusion of packed red
- Rhesus sensitisation: Rh negative females under the age of 45 should receive Rh-D negative platelets
- Alloimmunisation: this is due to development of antibodies to HLA class I antigens. It can lead to a febrile transfusion reaction and ‘refractoriness’ to therapy, when the platelet count rises less than expected following a transfusion
What are the two main components of FFP?
The two main components are cryoprecipitate and cryosu- pernatant. Taken together, they are a rich source of all of the clotting factors, von Willebrand factor, f ibrinogen, and other plasma proteins.
How is FFP stored and what is the shelf life?
FFP is stored at -30°C for up to 12 months. Once thawed, it should be transfused immediately to prevent the loss of the labile factorsV andVIII.
What is the dose of FFP?
The dose of FFP is weight-dependent, and a typical starting dose is 10–15 ml/kg.
Give some indications for its (FFP) use.
Reversal of warfarin effect
- Help control intra-operative/post-operative bleeding,
e.g. after cardiac surgery
- Following massive blood transfusion
- Disseminated intravascular coagulation
- Those with antithrombin III deficiency and resistance to heparinisation
What components is cryoprecipitate particularly
Cryoprecipitate is a rich source of fibrinogen, fibronectin, factors VIII,XIII (fibrin-stabilising factor),and vonWillebrand factor.
What is the management of warfarin overdose?
The management of warfarin overdose depends on the severity of the blood loss and the international normalised ratio (INR).
If the INR is >4.5 with no haemorrhage, the warfarin
can be omitted for 1–2 days followed by a review
- If haemorrhage is not severe, warfarin may again be
omitted, and if indicated clinically, reversed with a slow
i.v. infusion of vitamin K, 0.5–2.0 mg
- In the face of severe haemorrhage, 5 mg of vitamin K is
given by slow i.v. infusion together with prothrombin complex concentrate (PCC), containing factors II, IX and X with factor VII. Alternatively, FFP can be given, but may be less effective than PCC
- These guidelines are based on the advice of the ‘Handbook of Transfusion Medicine’ published by Her Majesty’s Stationery Office (HMSO)
What types of human albumin are available?
Human albumin solution is available as either a 4.5% or 20% solution. The latter is also known as ‘salt-poor albumin’ since it contains less sodium.
What is the use of this blood product?
Some uses for human albumin
- Management of ascites in portal hypertension
- Oedema due to other causes of hypoalbuminaemia such
as the nephrotic syndrome
- As a plasma expander in hypovolaemic shock: there is no
evident superiority over other colloids or crystalloids in this situation
For which infections is donated blood screened?
HIV 1 and 2
In special circumstances, e.g. for use in the immunocompromised, CMV is screened.
Which coagulation factors are most affected by storage?
The most labile of the coagulation factors areV andVIII.The reduction of factor VIII may be offset by the metabolic response to stress, which stimulates factor VIII production.
What infective complications may be seen following transfusion?
Hepatitis B and C
Yersinia enterocolitica: Gram negative organism often
implicated in red cell transfusions
Gram positive infections, especially staphylococcal
Infections associated with endemic areas: Malaria, Chaga’s
Which immune reactions may occur following transfusion?
Immune reactions seen are
-Febrile reaction: Occurs within an hour of commencement
as a reaction to white cell antigens in the donated blood
-Acute haemolytic reaction following ABO-incompatibility. This is usually due to a clerical error
-Delayed haemolytic reaction: The patient is immunised to foreign red cell antigens due to previous exposure. Can lead to jaundice and haemolysis days later
-Post transfusion purpuric reaction: Occurs 7–10 days following transfusion due to reaction to platelet PIAI antigens
Graft vs. Host disease: A rare but almost-uniformly fatal reaction. Immunocompetent donor lymphocytes mediate an immune reaction to the recipient
What are the signs and symptoms of an immediate haemolytic transfusion reaction?
Pyrexia and rigors
Abdominal and loin pain
Facial f lushing
Hypotension, progressing to acute renal failure,
disseminated intravascular coagulation (DIC) and acute lung injury
Name the hormones involved in controlling serum calcium.
Major hormones are
- Parathormone (PTH): of 84 amino acids, produced by the
- Vitamin D3 (cholecalciferol) metabolites: this is obtained via the diet and from the skin by conversion of 7-dehydrocholesterol
- Calcitonin: a 32 amino acid molecule produced by the thyroid’s parafollicular (C) cells
- others, e.g. parathormone-related peptide
PTH: In the bone, increases the synthesis of enzymes that breakdown the matrix to release calcium and phosphate into the circulation. Also stimulates osteocytic and osteoclastic activity. Thus leads to progressive bone resorption. At the kidney, increases renal phosphate excretion, while reducing renal calcium loss. It also stimulates 1-alpha hydroxylase activity in the kidney, thus indirectly increasing calcium absorption
Vitamin D3 metabolites: The active metabolite is 1,25(OH)2 D3 formed by renal hydroxylation of 25(OH)D3. This acts to increase the serum calcium while increasing the calcif ication of bone matrix. It acts on the bone to stimulate osteoblast proliferation and protein synthesis. At the kidney, it promotes calcium and phosphate reabsorption. It also enhances gut absorption of calcium and phosphate
Calcitonin: This act to reduce the serum calcium if the level rises above 2.5 mmol/l. This inhibits bone resorption through inhibition of osteoclast activity. At the kidney, it stimulates the excretion of sodium, chloride, calcium and phosphate
ECg changes in hypercalcaemia
The ECG changes are related to alterations in the membrane potential and cardiac conduction. They are
- Shortened QT interval
- Increased PR interval, progressing to heart block
- Flattened or inverted T waves
Give some examples of non-invasive investigations of cardiac function.
- Pulse: rate, rhythm, volume and character
- Blood pressure using a pressure cuff: measuring the absolute values, mean, and pulse pressure
- ECG recording: rate rhythm, intervals, axis and waveforms
- Trans-thoracic echocardiography: measuring systolic function, cardiac f illing and valve function general morphology and blood f low
- Indicators of the cardiac index and peripheral organ perfusion
- Level of consciousness: marker of cerebral perfusion
- Peripheral capillary refill
- Urine output: also a marker of renal function as well as
Which invasive investigations do you know, and what information do they provide?
- Blood pressure monitoring with arterial line: exhibits a
continuous arterial waveform and beat to beat variation
- CVP monitoring with central line: measuring the absolute value of the CVP or its response to f luid challenges and inotropes. The waveform may also be displayed continuously on a monitor
- Pulmonary artery flotation catheter: providing both direct and derived measures of left heart function. Also measures other parameters of cardiovascular function, such as systemic and pulmonary vascular resistance, and oxygen delivery/demand
- Trans-oesophageal echocardiography: Gives a more
detailed picture of the left heart and thoracic aorta than trans-thoracic echo
Markers of the cardiac index and peripheral organ perfusion:
- Blood gases: to assess the acidosis and base excess associated with anaerobic metabolism following poor tissue perfusion
- Serum lactate: rising levels indicate a poor cardiac index
- Gastric tonometry: Adequacy of splanchnic perfusion is estimated from gastric intramucosal pH measurements using a gastric probe. This is based on the belief that the gut is the first organ system to reflect a poor peripheral perfusion
- Mixed venous oxygen saturation (SvO2): Using a pulmonary artery catheter. A fall of the SvO2 is suggestive of a fall in the cardiac output
- Arterial-venous oxygen difference: This is increased in cases of poor organ perfusion where relative stagnation of blood leads to greater oxygen extraction
What are the findings from the pulmonary artery catheter in cardiogenic shock?
Elevated central venous pressure
- Cardiac index of 16 mmHg
- Decreased mixed venous oxygen saturation