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Propofol

Tuesday, July 27 (2021); Nervous system

Miraculous pale fluid, tincture of calm, friend to the swollen brain, the bringer of immediate improvement into any nurses' night shift. Propofol, 2,6 diisopropylphenol, is an extremely oily GABA agonist which completely replaced older dirtier agents when it appeared on the market in the late 1970s. Its only disadvantage is its tendency to completely switch off the sympathetic nervous system, with predictable haemodynamic consequences.

Ketamine

Tuesday, July 27 (2021); Nervous system

Ketamine is a unique dissociative anaesthetic with a distinctive mechanism of action. It is an NMDA receptor antagonist, which produces sedation and analgesia without inhibiting cardiovascular stability or airway reflexes. From a pharmacodynamic perspective it has it has no equal in routine medical use. Its complex modulatory effects have multiple uses, including the management of acute and chronic pain, depression, and severe asthma.

The "ideal" sedative or anaesthetic agent

Tuesday, July 27 (2021); Nervous system

The ideal anaesthetic drug should be chemically stable, presented without excipients, and available by a variety of routes. It should distribute to molecular targets which only produce sedation, with a rapid onset and offset time, and it should not accumulate with prolonged use. There should be no effects other than anaesthetic effects, and it should not rely on any specific organ system for elimination. There should be no withdrawal or rebound effects, and it should not have active metabolites.

Response to 1L of normal saline

Monday, July 26 (2021);

These are the physiological effects of infusing one litre of 0.9% sodium chloride solution into a patient.

Midazolam

Sunday, July 25 (2021); Nervous system

This drug is a short-acting variation on the general benzodiazepine theme. Like the rest of them, it acts as an allosteric modulation of the GABA_A receptor, increasing the frequency of its opening and thereby hyperpolarising the neuron cell membrane. Its unique qualities lay in its versatile methods of administration and in quick distribution/elimination, which produces its desirable rapid offset and recovery characteristics.

Common respiratory equations

Sunday, July 25 (2021); Respiratory system

The 2017 CICM Primary Syllabus expects the exam candidates to be able to "Understand the common respiratory equations", but does not elaborate as to what these are. This list is compiled from past paper questions and from the syllabus document, but represents pure speculation on the author's part. The only essential equation is the alveolar gas equation.

Physiology of normal sleep

Saturday, July 24 (2021); Nervous system

Sleep is a normal active physiological state which serves a poorly understood but apparently vital function. It can be described as a resting state in which behavioural signs of consciousness are absent, threshold for response to sensory stimuli is increased, and from which there is a rapid reversal to wakefulness. Sedation does not seem to have the same restorative function.

Formation, circulation and function of cerebrospinal fluid

Saturday, July 24 (2021); Nervous system

CSF is a protein-poor fluid that serves as a mechanical buoyancy cushion and chemical waste clearance system for the CNS. It is secreted mainly from the choroid plexus by a two-stage process (combination of ultrafiltration and active secretion). It then circulates around the CNS and is reabsorbed from multiple sites, mainly arachnoid granulations. Its chemical composition is distinct from plasma; particularly, it has intentionally poorer buffer capacity, so that it can act as a conduit for pH changes between the blood and the medullary chemoreceptor regions.

Ionic basis of spontaneous electrical activity of cardiac muscle

Friday, July 23 (2021); Cardiovascular system

The pacemaker cells are distinct from normal cardiac myocytes, in that they do not have a resting potential: instead, their membranes depolarise gradually via the "funny" current (If), allowing them to cyclically self-depolarise.  

Sleep disturbance in ICU patients

Friday, July 23 (2021); Miscellaneous Topics

The topic of sleep disturbance in the ICU has been of some considerable interest, considering how many articles pop up when you look up "sleep disturbance in the ICU". Much of the information I used to generate the discussion section for  Question 25 from the first paper of 2008 has been derived from this excellent article from the The Open Critical Care Medicine Journal. The LITFL page on sleep in the ICU also offers an excellent brief overview, perfect for pre-exam cramming.

Response to 500ml of concentrated (20%) mannitol

Friday, July 23 (2021);

As one might expect, injecting a large amount of a hyperosmolar chemical into somebody has some unusual effects. The physiological consequences of mannitol infusion are complex, and there are several distinct stages. First, there is a brief period of (potentially undesirable) plasma volume expansion. After that, there is intracellular dehydration, including brain parenchyma (i.e. the desired effect of mannitol). After this, the mannitol will drag the fluid out of the circulation and into the urine; volume depletion and hypernatremia will follow.

Definition, causes and differential diagnosis of ARDS

Wednesday, July 21 (2021); Respiratory Medicine and Mechanical Ventilation

Many past paper questions ask about the causes and differential diagnosis of " a diffuse bilateral infiltrate on CXR." There are many scenarios available.

 Question 20 from the first  paper of 2014 asks about the causes and differential diagnosis of " a diffuse bilateral infiltrate on CXR." There are several scenarios available.  Question 17 from the second paper of 2011 puts the infiltrates into a patient recovering from a bone marrow transplant. Question 10 from the second paper of 2010 puts this radiological finding in the context of a recent cardiac arrest.  It is important to be able to generate a lot of differentials in this sort of question.

Renal handling of water

Monday, July 19 (2021); Renal system

The proximal tubule reabsorpbs 65% of filtered water using sodium reabsorption to generate a concentration gradient. Then, 15% is reabsorbed in the thin limb of the loop of Henle, using the osmotic pull of the medullary interstitium. Lastly, a variable amount (8-19%) is reabsorbed by the collecting duct, where vasopressin can exert some regulatory control.

Conflict resolution in the setting of professional medicine

Sunday, July 18 (2021); Communication and Ethics

Conflict is a complex behaviour where one party perceives that its interests are being opposed or negatively affected by another party. Dysfunctional conflict hinders individual and organisational performance. The objective here is not to add to the (massive, overwhelming) ocean of published literature on this subject, or to offer any novel insight into the process (which the author can not claim to have). Instead, this chapter prepares the ICU exam candidate in near-final stages of their training to answer viva and interview questions about conflict resolution.