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Definition, causes and differential diagnosis of ARDS
Friday, August 25 (2023); 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.
The utility of routine physical examination in the ICU
Friday, August 25 (2023); Miscellaneous Topics
Question 12 from the first paper of 2003 asked whether or not there is any merit to the routine practice of examining ICU patients. Specifically, it was a "critically evaluate" question. In answer to it, one can crudely say that physical examination has a role to play (particularly in the investigation of neurological phenomena) but is neglected by ICU staff and is generally viewed as having little importance by the senior ICU staff.
Applications of VAD in brief summary
Friday, August 25 (2023); Cardiothoracic Intensive Care
Indications for a VAD
In order to qualify for a ventricular assist device, one must have serious problems:
- Cardiogenic shock
- Cardiac arrest
- Fulminant myocarditis
- Failure to wean off bypass
There are also situations in which you might anticipate a VAD might be needed, and would have one on standby:
Pharmacology of opioids
Friday, August 25 (2023); Nervous system
Opioids are analgesic agents which act on opioid receptors, G-protein coupled receptors mainly situated on the presynaptic membrane. Activating these receptors increases potassium conductance and decreases calcium conductance. The net effect of their activation is to hyperpolarise the membrane and prevent neurotransmitter release. Their mechanism of analgesic action is mainly related to the inhibition of glutamate release from primary pain afferent neurons in the spinal cord.
Constipation and ileus in the critically ill
Thursday, August 24 (2023); Gastroenterology and Hepatology
Broadly speaking, constipation is associated with inadequate nutrition due to pooor feed tolerance, delayed ventilator weaning and slower ICU progress, with some authors reporting an increased length of ICU stay and increased mortality. The therapy scales up from simple things (stopping the constipating drugs and mobilising the patient) all the way to neostigmine infusion and manual disimpaction.
Causes of diarrhoea in the ICU
Thursday, August 24 (2023); Gastroenterology and Hepatology
The written paper (as well as clinical life in general) occasionally gives us cause to generate a broad list of differentials for diarrhoea.
The alveolar gas equation
Tuesday, August 22 (2023); Respiratory system
This equation describes the concentration of gases in the alveolus, and thus allows us to make educated guesses as to the effectiveness of gas exchange. One can use this to calculate the tension-based indices of oxygenation, such as A-a gradient or the a/A ratio (which is expressed as a percentage). The ABG machine frequently does this work for you, provided you have entered the FiO2 and have specified that your sample is "arterial". The result is usually reported as pO2(a/A).
Fast voltage-gated sodium channels of cardiac muscle
Tuesday, August 22 (2023); Cardiovascular system
Fast voltage-gated sodium channels are a necessary element of cardiac excitation; they open to conduct a rapid and short-lived influx of sodium, causing the depolarisation of the membrane, and then enter a refractory inactive state which prevents sustained depolarisation and allows the myocyte to "reset", waiting for the next contraction. They are an important drug target (eg. for Class I antiarrhythmic agents) and the site of various clinically relevant mutations (eg. Brugada syndrome).
Normal processes of cardiac excitation and electrical activity
Sunday, August 20 (2023); Cardiovascular system
The action potential of a cardiac myocyte has five distinct phases: Phase 0 (rapid depolarisation), Phase 1 (early repolarisation), Phase 2 (plateau), Phase 3 (repolarisation) and Phase 4 (resting membrane potential). The main ionic players are voltage gated sodium channels (Phase 0), transient outward potassium channels (Phase 1), voltage gated calcium channels (Phase 2), and inward rectifying potassium currents (Phase 3). The latter also maintain a stable membrane resting potential (-90 mV) during Phase 4.
Adrenaline
Thursday, August 17 (2023); Cardiovascular system
Adrenaline is an endogenous catecholamine, a sympathomimetic drug with little receptor selectivity. In its role as a haemodynamic support infusion, adrenaline acts as an inodilator, increasing cardiac output and increasing blood pressure while decreasing the afterload (mainly by its effect on the arterioles of the skeletal muscle). It also has several unpleasant side effects (hyperglycaemia, hypokalemia, lactate elevation) which decrease its popularity somewhat.
Vasopressin
Thursday, August 17 (2023); Cardiovascular system
Vasopressin is an endogenously available vasoconstrictor with antidiuretic effects. "Vasopressor effects are exerted by V1 receptors, which are Gq-protein coupled receptors. Similarly to alpha-1 receptors, they increase intracellular calcium by means of increasing cAMP concentrations. V2 receptors are Gs-coupled receptors and produce the insertion of aquaporins into the apical membrane of principle cells of the collecting tubule, promoting the retention of watr.
Unlike catecholamine receptors, vasopressin receptors do not lose their affinity for vasopressin with changing pH."Pharmacology of neuromuscular blocking drugs
Thursday, August 17 (2023); Musculoskeletal system
Neuromuscular junction blockers act by depolarising and inactivating the motor endplate, or by competitive antagonism of acetylcholine. They are a group of small molecules which are generally highly water soluble, poorly protein bound and generally unstable (breaking down spontaneously). Most of them are cleared by a combination of renal and hepatic mechanisms. The speed of onset of these agents is inversely proportional to their potency.
Influence of pregnancy on respiratory function
Thursday, August 17 (2023); Respiratory system
The changes in respiratory physiology associated with pregnancy can be summarised as "higher minute volume and lower FRC", as those are the most important changes which have clinical relevance. The airway also becomes more oedematous, there is a progesterone-associated chronic respiratory alkalosis, the chest wall undergoes some remodelling, and respiratory resistance decreases.
Physiology of pituitary and hypothalamic hormones
Thursday, August 17 (2023); Endocrine System
The hypothalamus and pituitary are small CNS endocrine organs that are involved in the regulation of numerous processes, among them the autonomic nervous system, temperature, body water volume, reproductive function, emotion, metabolic rate, satiety, and stress responses.