Table of Contents

Cardiac arrest following cardiac surgery is surprisingly uncommon, considering the fact that the heart was already quite diseased (hence it needed the surgery) and then it has been cut, grafted, manually handled and perfused with perverse fluids. Apparently in America the rate is about 0.7-0.8%, which means in a large hospital with a minimum turnover of 200-300 post-op cardiac surgical patients you'll end up doing this at least once or twice a year. This seems consistent with local experience. Given the frequency and importance of these events, it is surprising that the college has not thought to ask about it until Question 30.2 from the second paper of 2017. 

The use of pulmonary vasodilators in ARDS is an attempt to manipulate pulmonary bloodflow in a way which improves gas exchange and right heart function. Unfortunately, it does not seem to improve survival, and only prostacycline improves oxygenation. The college showed some interest in these therapies (specifically in nitric oxide) in Question 14 from the first  paper of 2006 and Question 2 from the first  paper of 2004, but not in the subsequent decade.

Management of ARDS is not all flashy physiology and pressure-volume circus tricks. There are numerous supportive strategies which help the ARDS patient, working quietly in the background. Minimization of dead space ventilation improves CO₂ clearance, and low-carbohydrate high-fat nutrition decreases CO₂ production. Neuromuscular blockade improves both survival and gas exchange (according to solid trial evidence). Good sedation decreases energy expenditure and improves ventilator synchrony, and neutral-to-negative fluid management improves gas exchange.

In summary, crystalloid is currently “in”, and colloid is “out”. Recent guidelines (eg. Scandinavian guidelines) recommend crystalloid over colloid, and this reflects the broad trend in critical care over the last 20 years. All available evidence (eg. meta-analysis with n=16,000) points to there being no difference in mortality. Theoretical benefits in the use of colloid (eg. defence of the glycocalyx with albumin) or even known practical benefits (eg. a more rapid achievement of haemodynamic goals) have thus far not translated into measurable hard outcome advantages. Some colloids have a propensity to cause renal failure (eg. hydroxyethyl starch) or coagulopathy (eg. gelatins); all are more expensive then crystalloid (particularly human albumin).

The history of the glass electrode enjoys a thorough and well-developed exploration in a 2011 article by Fritz Scholz, from which much of this information is derived. Generally speaking, the explanation of a concept like this probably benefits from an exploration of its origin, so that the trains of thought can be followed from early observations all the way to the modern era (so that one can understand how the current state of the art ABG analytic technology performs its basic functions).

In days gone by, people relied on the CVP as a simple means of predicting fluid responsiveness. But it turns out the CVP is really bad at predicting the patients' responsiveness to fluid challenges. There are too many variables governing central venous pressure. This has become evident from some high-quality evidence, and it has been known for some time. Indeed, so obvious the uselessness of CVP in this scenario, and so entrenched the practice of its use, that prominent authors have described a recent meta-analysis as a plea for common sense.

Apart from fancy ventilation strategies and cheating with pulmonary vasodilators, there are some pharmacological agents which are thought to be helpful in ARDS.Though the evidence for them is weak, there is some argument that many of the trials were perfomed prior to the era of low tidal volume ventilation, and that in this new enlightened age some sort of previously obscured subtle mortality benefit might surface.

The question of what to do with the patient who has presented within 4 hours of having a cerebral infarct is brought up in Question 22 from the first paper of 2013, "A 60-year-old male presents 2 hours after the onset of vertigo and loss of consciousness. CT brain is performed and shows right basilar and vertebral occlusion with no evidence of infarction. Discuss two possible definitive treatment strategies for this condition, including the indications and contra-indications of each."

Questions about PE are frequent. Usually, they ask about the acute management of a haemodynamically unstable pulmonary embolism. The examiners seem to have a particular interest in thrombolysis. The best references for answering such SAQs are probably the 2014 ESC guidelines and 2012 ACCP Guidelines.

Tricyclic antidepressant overdose is generally neglected by the college examiners.  Question 28.2 from the second paper of 2009 was the one and only time TCA overdose has ever made it into the SAQs in any major way. Even then, the college asked not about the management of TCA overdose but rather about the specific role of bicarbonate in the management thereof. Similarly, Question 7 from the second paper of 2017 asked about the specific antidote to TCA overdose, and the mechanoism of its action. Consequently, this chapter dedicates an undue attention to this specific issue. Otherwise, TCA overdose is well covered in such resources as the LITFL toxicology conundrum. Generally speaking, one may safely limit their exam reading to the  LITFL page. If one has unlimited time resources, one may also wish to explore this 2001 BMJ article by Kerr et al.

Mechanical ventilation for pulmonary oedema has never come up in the CICM Fellowship Exam, perhaps because it is something clearly indicated and well supported by the evidence. High flow nasal prongs do not improve clinically significant outcomes, but may be an option in cases where CPAP (NIV) is contraindicated. NIV decreases mortality and intubation rates, and is the standard of care. Invasive ventilation has the added benefit of decreasing the distribution of cardiac output to the respiratory muscles 

Mechanical ventilation for pneumonia has never come up in the CICM Fellowship Exam, though this condition is sufficiently ubiquitous in the ICU that one can step into any unit and reasonably expect to find one. The examiners appear to be more interested in hot sexy topics like ARDS and severe status asthmaticus. However, this may not be for long. At some stage, a pneumonia question will arise, and the trainees will be expected to suggest some ventilator settings and other strategies for it.