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Flashcards in Critical Care Kanani Deck (41)
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1

Which abdominal organs are most commonly injured?

The three most commonly injured organs are the liver, spleen and kidneys.

2

Investigating abdominal trauma

The initial investigations performed to assess the abdomen as a whole are:
-Plain radiography: also assesses the bony pelvis
-Ultrasound: particularly good for the presence of free
fluid in the abdomen, or haematoma around solid organs. There is a 10% risk of missing a significant injury
-Diagnostic peritoneal lavage (DPL): this is 98% sensitive for intra-peritoneal bleeding
-CT scanning: this can be used if the results of the DPL are equivocal, and may also be performed at the same time as a brain scan. Very good for retroperitoneal injury, less so for hollow viscus injury such as the bowel

3

Under which circumstances would you perform a diagnostic peritoneal lavage (DPL)?

Some of the indications are:
- A suspicion of abdominal trauma on clinical examination
- Unexplained hypotension: with the abdomen being the
source of occult haemorrhage
- Equivocal abdominal examination because of head injury
and reduced level of consciousness
- The presence of a wound that has traversed the
abdominal wall, but there is no indication for immediate laparotomy, e.g. a stab wound in a stable patient

4

When is DPL contraindicated?

The most important contraindication for DPL is in the situation which calls for mandatory laparotomy, e.g. frank peritonitis following trauma, abdominal gunshot injury or a hypotensive patient with abdominal distension.

5

What are the positive criteria with DPL?

- Lavage f luid appears in the chest drain or urinary catheter
- Frank blood on entering the abdomen
- Presence of bile or faeces
- Red cell count of

6

Acid base balance organs

The main organ systems involved in regulating acid-base balance are:

- Respiratory system: this controls the pCO2 through alterations in alveolar ventilation. Carbon dioxide indirectly stimulates central chemoceptors (found in the ventro-lateral surface of the medulla oblongata) through through H+ released when it crosses the blood-brain barrier (BBB) and dissolves in the cerebrospinal f luid (CSF)

- Kidney: this controls the [HCO3-], and is important for long term control and compensation of acid-base disturbances

- Blood: through buffering by plasma proteins and haemoglobin

- Bone: H+ may exchange with cations from bone mineral. There is also carbonate in bone that can be used to support plasma HCO3 levels

- Liver: this may generate HCO3 and NH4 (ammonia)
by glutamine metabolism. In the kidney tubules, ammonia excretion generates more bicarbonate

7

How does the kidney absorb bicarbonate?

There are three main methods by which the kidneys increase the plasma bicarbonate:

- Replacement of filtered bicarbonate with bicarbonate
that is generated in the tubular cells
- Replacement of filtered phosphate with bicarbonate that
is generated in the tubular cells
- By generation of ‘new’ bicarbonate from glutamine that is
absorbed by the tubular cell

8

Define the base deficit.

The base deficit is the amount of acid or alkali required to restore 1l of blood to a normal pH at a pCO2 of 5.3kPa and at 37°C. It is an indicator of the metabolic component to an acid-base disturbance. The normal range is -2 to +2

9

What are the major ‘renal’ causes of acute renal failure?

- Acute tubular necrosis
- Glomerulonephritis
- Interstitial nephritis
- Bilateral cortical necrosis
- Reno-vascular: vasculitis, renal artery thrombosis
- Hepatorenal syndrome

10

What is acute tubular necrosis?

Acute tubular necrosis is renal failure resulting from injury to the tubular epithelial cells, and is the most important cause of acute renal failure. There are two types:

- Ischaemic injury: following any cause of shock with resulting fall in the renal perfusion pressure and oxygenation

- Nephrotoxic injury: from drugs (aminoglycosides, paracetamol), toxins (heavy metals, organic solvents), or myoglobin (from rhabdomyolysis)

11

What are the major ‘post-renal’ causes?

Acute obstruction from calculi
- Obstruction from tumours arising from the renal
parenchyma or transitional epithelium of the
pelvi-calyceal system
- Extrinsic compression from pelvic tumours
- Iatrogenic injury, e.g. inadvertent damage to the ureters
during bowel surgery
- Prostatic obstruction
- Increased intra-abdominal pressure (>30 cmH2O)

12

Which part of the kidney is the most poorly perfused?

The renal medulla is more poorly perfused than the cortex. This ensures that the medullary interstitial concentration gradient formed by tubular counter current multiplication is preserved and maintained.

13

Which part of the nephron is the most susceptible to ischaemic injury, and why?

The cells of the thick ascending limb are the most susceptible to ischaemic injury for two important reasons
- The cells reside in the medulla, which has poorer oxygenation than the cortex
- The active NaKTPase pumps at the cell membrane have a high oxygen demand.

14

Name some common drugs of surgical importance that may exacerbate or cause acute renal failure.

- Paracetamol: overdose is a known cause of acute tubular
necrosis
- Non-steroidal anti-inflammatory drugs: can lead to renal failure by reducing the renal protective effects of prostaglandins during renal ischaemia
- Aminoglycosides: a potent cause of acute tubular necrosis
- Penicillins: can cause interstitial nephritis
- Furosemide: can lead to interstitial nephritis
- Dextran 40: a colloid used during f luid resuscitation

15

What are the two most important life-threatening complications of renal failure?

- Acute pulmonary oedema: due to fluid retention with
over-hydration
- Hyperkalaemia: leading to metabolic acidosis and cardiac arrhythmias
Both may require urgent dialysis as part of the management.

16

ARDS definition

ARDS is a syndrome of acute respiratory failure with the formation of a non-cardiogenic pulmonary oedema leading to reduced lung compliance and hypoxaemia which is refractory to oxygen therapy. The changes are seen as:
Diffuse pulmonary infiltrates seen on chest radiography
- Pulmonary wedge pressure of of

17

How does it relate to ‘acute lung injury’ and the ‘systemic inflammatory response syndrome’?

Acute lung injury (ALI) comprises of a number of non-specific pathological changes in the lung in response to a specific insult.

These changes are like that of ARDS, but of decreased severity in that the PaO2/FiO2 is

18

Causes of ARDS

The triggering factors can be organised into a number of groups:
- Pulmonary insults:
- Trauma
- Pneumonia
- Aspiration
- Smoke inhalation
- Fat embolism
- Multiple trauma
- Generalised sepsis
- Others: massive transfusion, disseminated intravascular
coagulation (DIC), acute pancreatitis, cardio-pulmonary bypass

19

What is the mechanism of action of nitric oxide?

Nitric oxide, (‘endothelium-derived relaxing factor’) is an activator of the cytoplasmic enzyme guanylyl cyclase. This increases the intracellular cyclic guanosine monophosphate (cGMP) levels, which stimulates a cGMP-dependent protein kinase. This activated protein kinase stimulate the phosphoryla- tion of key proteins in a pathway that leads to a relaxation of vascular smooth muscle cells.

20

Ramsay scoring system for sedation

There are a number of techniques in routine clinical use to determine the level of sedation attained. The most com- monly employed of these is the Ramsay scoring system that describes six levels of sedation

21

Sedation drugs

The most commonly used classes of drugs are
- Benzodiazepines: e.g. diazepam and midazolam
- Intravenous (i.v.) anaesthetic agents: such as propofol and ketamine
- Inhalational anaesthetic: nitrous oxide (70%)
- Opiate analgesics: morphine and the synthetic opioids pethidine and fentanyl are popular choices. They may be combined effectively with benzodiazepines
- Trichloroethanol derivatives: such as chloral hydrate
- Butyrophenones: e.g. haloperidol. As a group they are
neurotransmitter-blocking drugs
- Phenothiazines: e.g. chlorpromazine. They also act on neurotransmitter receptors

22

The most commonly used sedative drug

The most commonly used sedative drugs are propofol, benzodiazepines and the opioid analgesics.

23

major physiological side effect of propofol?

major physiological side effect of propofol?
The important side effect of propofol is hypotension on induction, and is caused by a fall in the systemic vascular resist- ance and/or myocardial depression. As with many of the other sedatives, it also leads to respiratory depression.

24

Give some examples of the opiates in common use. Which are the synthetic and non-synthetic agents?

The commonly used opiates are
- Non-synthetic: morphine, codeine (10% of this is
metabolised to morphine)
- Semi-synthetic: diamorphine, dihydrocodeine
- Synthetic: pethidine, fentanyl

25

Which receptor do opiate analgesics act on?

The majority of the effects of the opiates are carried out through the mu-receptor. They may also have some action through the other two types of opiate receptors, kappa and delta.

26

What are the systemic effects of the opiates?

The effects of the opiates are
- Analgesia: they are good for moderate to severe pain of
any cause and modality. Less effective for neuropathic pain, such as phantom limb pain, or allodynia (pain from a non-painful stimulus)
- Respiratory depression: with blunting of the ventilatory response to rising pCO2. Also causes suppression of the cough ref lex, both of which encourage sputum retention, atelectasis and pneumonia in the critically ill
- Sedation: with a reduction in the level of consciousness with higher doses, so beware in those with head injuries
- Nausea and vomiting: following stimulation of the chemoreceptor trigger zone in the area postrema
- Reduced GI motility: which leads to constipation
- Euphoria
- Dependence and tolerance: there is a progressively reduced effect from the same dose of drug
- Histamine release from mast cells: producing pruritis and reduced systemic vascular resistance

27

Why is morphine not advocated for use in
abdominal pain of biliary origin?

Why is morphine not advocated for use in
abdominal pain of biliary origin?
Morphine increases the tone of the sphincter of Oddi (as well other sphincteric muscles), while stimulating contraction of the gallbladder. Therefore, it can exacerbate biliary pain.

28

What are the therapeutic effects of paracetamol (acetaminophen)?

What are the therapeutic effects of paracetamol (acetaminophen)?
This is an analgesic and anti-pyretic with minimal anti- inf lammatory properties.

29

By what mechanism does overdose cause liver injury?

By what mechanism does overdose cause liver injury?
The cause of liver injury lies with the metabolism of para- cetamol. Normally it is conjugated in the liver, with the production of a small amount of the toxic metabolite N-acetyl- benzoquinoneimine. Binding to hepatic glutathione renders this metabolite harmless.With overdose, glutathione is depleted, leading to hepatocyte injury. Acetylcycteine, the drug used to treat overdose, is a glutathione precursor.

30

How do the non-steroidal anti-inflammatory
drugs (NSAIDs) work?

How do the non-steroidal anti-inflammatory
drugs (NSAIDs) work?
These agents act to reduce prostaglandin formation by the inhibition of the enzyme cyclo-oxygenase which acts on arachidonic acid. This leads to a modif ication of the inf lam- matory reaction and its effects on the stimulating nociception.