Table of Contents

Formally, this is an interrogation of the third, fourth and sixth nerves, However, examination of the eye movements tends to also reveal cerebellar pathology (as nystagmus). The gaze palsies are a difficult bunch of disorders, and for the purposes of the CICM fellowship exam one should become familiar with the main ones, but one should not feel compelled to become a master of this area. One should be able to recognise a third nerve palsy, a fourth nerve palsy and a sixth nerve palsy. If one is able to recognise internuclear ophthalmoplegia, one is ahead of the herd. Gaze palsies have been interrogated in Question 24.4 from the first paper of 2009, Question 21.3 from the first paper of 2014 and Question 26.2 from the second paper of 2011.

The PAWP should be equivalent to the LA pressure. So, if the mitral valve is competent, the LA pressure should be equivalent to left ventricular end-diastolic pressure (and thus, to left ventricular preload - supposedly). This is only true for a catheter tip positioned in the most dependent portion of the lung (Wests Zone 3), where pulmonary arterial pressure is greater than alveolar air pressure (otherwise air pressure influences your measurement)

The microcirculation is the terminal vascular network of vessels smaller than 100 μm in diameter, where the exchange of substances between the blood and the tissues occurs. It consists of arterioles, capillaries and venules. Its main characteristics are its vast surface area and the low velocity of flow, which allows enough transit time for gas exchange and solute diffusion.

Context-sensitive half time  is the concept which relates the drug distribution into and out of tissue compartments to the change in plasma concentration after sustained infusion. If the infusion has not achieved a steady-state of concentration, the context-sensitive half time will more closely resemble the α half-life (distribution half-life).  If the infusion is at steady-state and the tissue compartment is well-saturated with drug molecules, the context-sensitive half time will resemble the β half-life (elimination half-life). The context-sensitive half time is not expressed as a number like a half-life would normally be, but is rather a constant.

The proximal tubule reabsorbs 55% of filtered potassium, which is absorbed by means of solute drag (along with water). The thin descending and ascending limbs of the loop of Henle exchange potassium by a countercurrent mechanism. Then, the thick ascending limb reabsorbs a further 30% via the NKCC2 co-transporter. Finally, in the distal convoluted tubule and the collecting duct some potassium excretion occurs, mainly by an aldosterone-regulated mechanism which maintains electroneutrality in the tubular fluid while sodium is reabsorbed.

After years of neglect, this fascinating topic has finally founds its way into the fellowship exam in the form of Question 22 from the first paper of 2016.

Like the thoracocentesis chapter, the purpose of this summary is to unite the information which is otherwise contained in numerous widely spread-out sources. The main audience would probably be the CICM supervisor of training who would need something akin to a reference manual in order to be able to assess the trainee who needs their WCA form filled out. Alternatively, the trainee doing the WCA might benefit from the bibliography at the end of this chapter (but probably not from the chapter itself). 

The proximal tubule reabsorbs 65% of filtered sodium, mainly by the combined action of basolateral Na/K ATPase and apical NHE3 exchanger. Then, an additional 25% is reabsorbed in the thick ascending limb by the frusemide-sensitive NKCC2 co-transporter protein. The distal convoluted tubule contributes 5-10% to the total absorption by the action of the thiazide-sensitive NCC co-transporter. Lately, the collecting duct reclaims the least 2% via the aldosterone-regulated ENaC channel.

This is a hygroscopic filter which replaces the normal warming, humidifying and filtering functions of the upper airways when these structures are bypassed during anaesthesia and intensive care. Much of the material presented here is derived from an excellent series of articles by A.R Wilkes, published in 2010.

LITFL has an excellent synopsis of the current BTF guidelines, which is a well-referenced revision resource. The BTF guidelines also form the basis of the summary detailed below.  An extensive rambling discussion of these recommendations is also available at the end of this chapter, but it  has diminished relevance in the context of pre-exam panic. Links to discussions with greater detail are made available for those who are interested. Specific SAQs interrogating this topic consist of Question 15 from the first paper of 2013; however there are numerous questions which inidrectly address this issue by asking about the management of raised intracranial pressure.

To quote Casley-Smith (1980), "In brief, the tissue lymphatic system is a leaky swamp through which material flows due to the vagaries of adjacent pressure changes". 

With the recent publication of the new BTF guidelines (at bloody last) the topic of severe brain injury becomes more likely to appear in the fellowship exam. The aim of this page is to have a list of the BTF directives collected in one spot to allow rapid revision. Wherever possible, the normal urge to explore to the nth degree of fine detail has been suppressed in favour of brevity.

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.