A free online resource for Intensive Care Medicine.
An unofficial Fellowship Exam (CICM Part 2) preparation resource.
Deranged Physiologyis a slowly growing archive of discussions and study notes relevant (or if not relevant, then at least interesting) to the practice of intensive care medicine. The content provides an introduction to the fundamental themes in intensive care: mechanical ventilation, vasopressors, electrolyte management, hemodynamic monitoring, dialysis, and so forth. Attention is directed at equipment in intensive care, and there are attempts to revisit interesting pharmacology and physiology. The aim of this resource is to supplement the bedside teaching of senior staff, and to consolidate resources for intensive care trainees in the initial stages of their training.
Toxicology of childhood differs from adult toxicology on several key issues. In both scenarios, the patient is frequently uncooperative and history is often cluded, leading to empirical decisionmaking. In children, the situation is complicated by their tendency to compensate readily up to a certain cliff's edge, and then to collapse in a spectacular manner. Most of the routine toxicological primary survey is valid in the paediatric setting.
This chapter answers parts from Section D(iii) of the 2017 CICM Primary Syllabus, which expects the exam candidate to "describe alterations to drug response due to physiological change, with particular reference to ...
In brief, old age affects drug absorption, distribution and elimination in a manner which can be suimmarised by the term "worse". Rarely is anything pharmacologically better in the elderly. They are reluctant to absorb drugs enterally, they are sluggish metabolisers, they more susceptible to side effects and their renal clearance is usually delayed, increasing the half life of most drugs. To say nothing of the tendency of physicians to challenge these physiologically fragile individuals with polypharmacy cocktails.
One cannot increase in body mass to three or four times the expected norm and still expect to have a normal response to drugs. The pharmacokinetic and pharmacodynamic changes associated with obesity are often surprisingly in the direction of increased function, for instance increased gastric emptying rate, increased hepatic clearance, increased GFR and renal clearance, and increased soluble enzyme activity. A large volume of adipose tissue increases the apparent volume of distribution for lipophilic drugs and increases their half-life. Everything is pharmacokinetically different, and dosing is made more difficult by the fact that the equations which predict lean body mass and ideal body weight become less and less accurate with increasing BMI.
Pregnancy results in several pharmacokinetic and pharmacodynamic changes. Oral administration is affected by delayed gastric emptying; distribution is affected by changes in the fat and water content of the body, and metabolism is afected by changes in hepatic blood flow and enzyme activity. Clearance of many substances is increased by the increased glomerular filtration rate. Pharmacodynamic changes are also numerous, eg. increased sensitivity to both local and general anaesthetics. Discussion of adverse effects and dosing adjustments must take into account toxicity to the foetus.
The College, in their model answer to Question 1 from the second paper of 2014, have constructed an excellent resuscitation protocol, which does not afford this author very much room for improvement.One can merely summarise their model, and expand upon it with references. To be clear, this approach is not "Early Goal-Directed Therapy". Protocolised sepsis management may not be especially effective in reducing mortality (ProCESS, ARISE). Rather than a protocol, this is a stepwise method to tailor a bespoke response to septic shock for individual patients, which branches from simple to advanced management options.
For the patient whose inspiratory flow rate exceeds even the generous threshold of Venturi masks, high flow nasal oxygen is an excellent option. Though the first paper to describe these devices (Dewan & Bell, 1994) gave us this terminology, subsequent authors have occasionally referred to these devices as "high flow nasal cannulae" or "high flow nasal oxygen", because presumably the word "prongs" is somehow uncivilized or intrinsically comical. All CICM trainees will be familiar with the device - it is a single-limb circuit which connects a gas blender to a heater/humidifier, and then funnels a mixture of oxygen and air into the patient, essentially using their respiratory system as a PEEP valve.
Toxicology of pregnancy comes up agains three main issues: altered pharmacokinetics, teratogenicity and the toxicity to the foetus. There is only a handful of drugs (valproate, salicylates, carbon monoxide) which are more harmful to the foetus than to the mother. Othwerise, management of the mother's toxycology takes priority- what's good for the host organism is good for the parasite.
Idiosyncrasy is an abnormal reactivity to a chemical that is peculiar to a given individual. It could be an abnormally exaggerated response, or an abnormal lack of response, or an abnormal extension of the normal physiological drug effect, or a reaction which is completely unrelated to the expected physiological effect. Common lifethreatening idiosyncratic drug reactions include DRESS syndrome, toxic epidermal necrolysis and Stevens-Johnson syndrome.
Organ system failure and critical illness can affect drug response. The exact effect will be highly individual, and it is safe to say that the majority of the effects will be due to pharmacokinetic changes. The main issues are usually related to impairment of metabolism and clearance.
Addiction is a behavioural pattern of preoccupation with the use of a drug, associated with use-related satiation, loss of control and continued use despite evidence of harm. Dependence is behaviourally distinct from addiction, and is characterised by tolerance and the development of a withdrawal syndrome. Withdrawal is the physiological syndrome which occurs when there is tolerance to a drug and it is discontinued.
Transpulmonary dilution cardiac output measurement techniques differ from dilutional techniques which use the pulmonary artery catheter. Cold fluid is poured into the venous circulation. It mixes with blood in the cardiac chambers before making its way into the arterial circulation. A thermistor is dangling in the arterial circulation, and it measures the change in blood temperature. The resulting temperature over time curve is used to make all sorts of comments. This method has advantages over PA catheter thermodilution, as well as unique disadvantages.
This chapter is relevant to Section G7(iii) of the 2017 CICM Primary Syllabus, which asks the exam candidate to "describe the invasive and non-invasive measurement of blood pressure, including limitations and potential sources of error". It deals with the ways in which the shape of the arterial waveform can be correlated with the pathology affecting the cardiovascular system. This matter has never enjoyed very much attention from the CICM examiners, and for the purposes of revision can be viewed as something apocryphal. Certainly, one would not spend the last few pre-exam hours frantically revising these waveforms. In fact it has been abundantly demonstrated that a person can cultivate a gloriously successful career in Intensive Care without any appreciation of this material.