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.
The acidity of your precious bodily fluids is a carefully guarded parameter. To allow this parameter to deviate out of a very narrow range would massively impair your capacity to continue living. Basic molecular services would break down. Cellular anarchy would ensue. In order for the ICU physician to wrest a form of order from this chaos, a reasonable grasp of basic acid-base chemistry is expected. An excellent medically themed foundation for acid-base chemistry is laid by Kerry Brandis in a highly acclaimed series of online articles, to which I will constantly refer. It is not my intention to supercede this resource, as it remains canonical for all critical care trainees.
Lets face it, we don't really care about venous oxygenation (or arterial, for that matter). The real issue is how much oxygen is in the cells? How are those cells using it? The intracellular environment is a place of massively heterogenous oxygen demands. Some organelles are involved in enzymatic metabolism of drugs or maintenance of electrolyte gradients - these areas require a higher oxygen tension than, for example, mitochondrial ATP synthesis.
Central and mixed venous blood gases offer us a glimpse of whole-body oxygen extraction.
A mixed venous blood gas is a sample aspirated from the most distal port of the PA catheter, offering a mixture of inferior vena cava blood, superior vena cava blood, and the coronary sinuses. Thus, the result is an average of venous blood. But what if I don't have a PA catheter, you might ask? A central venous gas may be almost as good.
Dobutamine is a synthetic catecholamine. As well as a well-defined catechol group, it possesses a humongous amine substituent group, which confer upon it a high level of beta-1 selectivity. This is the result of "intelligent drug design". The first paper to describe its properties (1975) is an amazing piece of work. The authors systematically produced a whole bucketfull of catecholamines with different side chains, amine substituents, hydroxyl group arrangements, etc etc - and then tested them for cardiovascular effect. Indeed, much of what we know about the structure and function relationship of catecholamines comes from such experiments.
This chapter is a summary of the pharmacological properties of milrinone. My main focus will be the differences between milrinone and dobutamine. These are the two major old-style inotropes in our arsenal; and there are situations which favour the use of one over the other.
Noradrenaline is an endogenous catecholamine, a sympathomimetic drug with a strong alpha-1 receptor selectivity. This chapter is a tribute to it, as it is the true workhorse of intensive care, and a drug with which one ought to become intimately familiar. It is the gateway drug to understanding the effects of catecholamines.
The principle of measuring left atrial pressures through the pulmonary capillaries rests on the premise that capillary resistance is very low, and with the baloon inflated there is no flow, leaving only the capillary pressure to act on the transducer.
The relationship of pressure, flow and resistance
Behold the Tube.
In it, a nameless fluid flows, with a flow rate of Q.
It flows because there is a difference in pressure from one end of the tube to the other.
One may feel an understandable reluctance to subject one's fragile patient to an investigation which has received such terrible publicity. However, one must remember: PACs don't kill people, people kill people.
In the wrong hands even a peripheral cannula is a lethal weapon.