The anion gap is a mathematical test performed on laboratory electrolyte values to determine the cause of a metabolic acidosis. It is defined as the sum of serum anion concentrations subtracted from the serum cation concentrations. Specifically, by convention the cations are sodium and potassium, and the anions are bicarbonate and chloride. These measured anions account for only about 85% of the total anionic charge of the extracellular fluid. The gap affords us an estimate of the concentration of this unmeasured 15%, the "miscellaneous" anionic electrolytes which are present in the bloodstream. The "normal" expected value is around 12, though it is adjusted for the serum albumin, which - being a negatively charged protein - contributes to the anionic charge of the extracellular fluid.
Mixed venous blood is blood sampled from the pulmonary artery which is mixed in the RV and which represents a weighted average of venous blood from all tissues and organs. It is usually said to have a haemoglobin saturation of around 70-75%, which corresponds to a PO2 of around 40 mmHg.
Primary adrenal insufficiency is the state of adrenal malfunction due to genuinely disorderly adrenal glands. Secondary hypoadrenalism is the state of being adreno-suppressed, for whatever reason (be it drugs, critical illness or hypothalamic-pituitary malfunction)- but in the presence of normal adrenal glands. Lastly, one might have completely normal hypothalamic-pituitary-adrenal axis, and it might be secreting normally, but one might have a "relative adrenal insufficiency" if this volume of secretions happens to be inadequate to sustain the magnitude of the stress response which is required.
Cardiac reflexes are reflex loops between the heart and central nervous system which regulate heart rate and peripheral vascular resistance. Some of these have homeostasis-maintaining roles, for example the baroreceptor reflex which maintains stable cardiac output and blood pressure. Others, such as the oculocardiac reflex and the vasovagal reflex, are not homeostatic in their function, but still have various protective roles. The efferent arms of these reflexes are inevitably the vagus nerve and the sympathetic nervous system.
For a critical care college in a country with this much shoreline and such a vibrant beach culture, the CICM is strangely unconcerned with drowning. Certainly, the author can conceive of a seaside ICU where perhaps half of the inpatient population is recovering from a near-drowning, but this pathology does not seem to form a very large proportion of our daily workload out here in the Western Suburbs of Sydney, where the people are too poor to afford pools. Uneducated social remarks aside, the drowning SAQs consist of Question 25 from the second paper of 2012 and Question 1 from the first paper of 2009. Thus far, the issues examined have been acute management of the drowning victim, potential complications of near-drowning, and risk factors for severe neurological injury arising from the hypoxia of submersion.
The question of futile or non-beneficial care is a constant feature of day-to-day work in the ICU, and it is surprising that it receives so little attention in any forum (be it the media, the college exams, or even in the core business of most hospital specialties). Unfortunately "futile" is a term loaded with unnecessary emotional content which lacks any standard medical definition, and in any given scenario a group of clinicians will disagree as to what futile care is. However, it is widely acknowledged that often we use "considerable resources without a reasonable hope that the patient would recover to a state of relative independence", with death being viewed as treatment failure.
Encephalitis had come up in Question 21 form the second paper of 2019, and with no previous exposure to this question, many trainees were caught unprepared. The aetiology of this diverse group of conditions can be divided easily into "infectious", "autoimmune" and "misc". The treatment is usually tailored to the cause and usually consists of some CNS-penetrating antiviral drugs like aciclovir, some steroids such as dexamethasone, and potentially some sort of hardcore immunosuppressant drugs such as rituximab and cyclophosphamide.
Question 9 from the second paper of 2012 asked vaguely about "clinical and organisational issues involved pre-transfer" in the context of trying to ship a subarachnoid haemorrhage survivor out of a backwater dungheap and into a neurosurgical unit. The answer to all such questions can be found in college policy documents. ANZCA also have a policy document- Guidelines for Transport of Critically Ill Patients- which has been endorsed by CICM. Additionally, CICM have a policy document - Minimum Standards for Transport of Critically Ill Patients (IC-10, 2010) which is referred to in the college answer. This document provides a reasonable systematic framework for a good quality answer.
Prone ventilation, the technique of flipping a patient over to manipulate their V/Q matching, has numerous advantages. Its cheap, widely available, relatively safe, and it increases FRC, improves the drainage of secretions, decreases oxygen requirements and improves mortality. The PROSEVA trial demonstrated a mortality improvement from 32% to 16%. We should all be prone, all the time.
In Question 21 from the second paper of 2005, the candidates are nvited to explore the statement, “The absence of evidence of effect does not imply evidence of absence of effect”. This is a rebuttal to the Argument from Ignorance, which (put simply) states that if something has not been proven true, then it must be false. The rebuttal addresses the third possibility, that the currently available evidence has failed to detect a phenomenon. In the interpretation of medical literature, this means that a study that has failed to demonstrate the evidence of a risk has not succeeded in demonstrating the absence of risk. Similarly, a study which has failed to demonstrate a significant difference between two treatments has not demonstrated the absence of difference, only the absence of evidence of a difference.
This is a brief discussion of the reasoning behind the tests of coagulation function. Additionally, one may wish to review the coagulation cascade, if one (like myself) is unable to reliably recall its various details. An excellent resource for this information is PracticalHaemostasis.com
The ICU is a specialised area where the sickest patients and the expertise to manage them are both concentrated. The patients are high-maintenance, as they have the need of special beds, numerous large machines which keep them alive, as well as towering stacks of drug pumps and complex monitoring equipment. All this stuff needs lots of electrical outlets and an uninterrupted power supply. Moreover, the expert staff who look after these patients are also high maintenance and require offices, break rooms, family conference lounges, overnight on-call beds, education facilities, and an uninterrupted coffee supply. Clearly, to meet the demands for both of these groups of organisms an artificial environment (functionally equivalent to a terrarium) must be constructed, which is complicated and expensive.
The causes of DIC are numerous. An excellent review article produces an extensive list, and delves deep into their pathophysiology and management. The college has show some interest in this condition, but usually it appears as the answer to a data interpretation question ("What's wrong with these coags?"). Examples include Question 13.1 from the second paper of 2013, Question 29.1 from the second paper of 2012 and Question 6.1 from the second paper of 2008. Apart from these, DIC comes up frequently in the past papers as an important complication to mention (eg. in the discussion of amniotic fluid embolism, etc etc).
Antiphospholipid syndrome is a state of autoimmune-induced hypercoagulability. The uncharacteristically hyperbolic term "catastrophic" is used to describe a case of antiphospholipid syndrome which involves both excessive clotting and excessive bleeding, with consumption of coagulation factors. Like most medical conditions with the words "catastrophic" in the title, the ICU trainee should want to be familiar with this syndrome, even though it has thus far never appeared in the fellowship exam papers.