Homepage | Deranged Physiology

Time 2020-09-21 15:04:31

Web Name: Homepage | Deranged Physiology

WebSite: http://derangedphysiology.com

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A free online resource for Intensive Care Medicine.An unofficial Fellowship Exam (CICM Part 2) preparation resource.Deranged Physiology is 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. Regional skeletal muscle blood flow Tuesday, September 15 (2020); Cardiovascular system Skeletal muscle is unique among organ systems, in that it can vary its blood flow by a factor of 1,000. It can go from a maximaly vasoconstricted state in haemorrhagic shock (flow of 0.1-0.4ml/min/100g) to a maximally vasodilated state during peak exercise (400ml/min/100g). This vascular responsiveness is mediated by intrinsic myogenic mechanisms and metabolic byproducts which act as vasodilators. Under normal circumstances, the sympathetic nervous system maintains a high resting vascular tone, limiting flow to resting muscle. A comparison of renal replacement therapy modalities Monday, September 14 (2020); Renal Failure and DialysisThe candidates have been asked to compare different CRRT modalities in numerous past paper questions. Typically, the college has expected the answers to be presented in a tabulated format. The table in this chapter makes an attempt to combine all these tables into a single reference. Factors which affect peripheral vascular resistance Sunday, September 13 (2020); Cardiovascular systemSystemic vascular resistance is one of the major regulatory mechanisms which control blood pressure, and its main determinants are the length of the blood vessels, the viscosity of the blood and the radius of the vessels. Arterioles of around 200μm diameter tend to produce most of the resistance in the systemic circulation. Their radius is under control by systemic events (eg. the arterial baroreceptor reflex) as well as a host of locally acting mechanisms. Splanchnic blood flow Wednesday, September 9 (2020); Cardiovascular systemThe splanchnic circulation by definition consists of blood vessels which supply and drain the liver, spleen, stomach, pancreas, and the amall and large intestine. Owing to their low oxygen extraction ratio, these organs tend to have no need of blood flow autoregulation to support their metabolism, as they can just extract more oxygen instead. Thus, the splanchnic circulation mainly regulates its blood flow according to demands made by digestion, and after a meal intestinal blood flow can be up to 35% of the total cardiac output. Blood transfusion in the ICU Wednesday, September 9 (2020); Haematology and OncologyThis chapter deals with the indications, contraindications and complications of blood transfusion in the ICU. The contents and properties of packed red blood cells, the physiology of acute haemorrhage and the physiological responses to blood transfusion are detailed in other chapters. The National Blood Authority of Australia has issued a series of practice guidelines which can be helpful in guiding the shaking bloodied hand of the ICU practitoner. The guidelines have been endorsed by our college, which means that at least some of the Australian intensivists must agree with them. The following entries are a summary of these clinical practice guidelines. Renal blood flow Wednesday, September 9 (2020); Cardiovascular systemRenal blood flow is massive (400ml/100g/min), and most of this is for the purpose of filtration rather than renal metabolism. The kidneys autoregulate their own blood flow within a wide range of MAP values (60 to 160 mmHg) by two main mechanisms. Myogenic autoregulation is an intrinsic property of vascular smooth muscle and accounts for most of this. Tubuloglomerlar feedback is a negative feedback loop which is controlled by the rate of sodium delivery to the tubule. Addiitonally, the sympathetic nervous system manages renal blood flow, and steps in to drastically decrease it in states of shock and hypovolaemia. Ketamine Wednesday, September 9 (2020); Nervous systemKetamine 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. Hyperthyroidism and thyrotoxicosis Tuesday, September 8 (2020); Endocrinology Metabolism and NutritionThe management strategy for thyroid storm revolves around preventing peripheral effects of raised thyroid hormone levels, and preventing the ongoing increase of said levels by inhibiting the synthesis and release of thyroid hormone. The mainstay agents are propylthiouracil, carbimazole (or methimazole), potassium iodide and a beta-blocker such as propanolol. One cannot forget to mention corticosteroids, as there is always some relative adrenal insufficiency. Other potentially useful agents include lithium and cholestyramine. Severe refractory disease may call for extracorporal clearance of thyroid hormone by plasma exchange or charcoal haemoperfusion. Ventricular pressure-volume loops Tuesday, September 8 (2020); Cardiovascular systemA PV loop plots the changes in ventricular pressure associated with the changes in volume which occur during the cardiac cycle. Multiple pieces of information can be extracted from such a loop, including volumes (eg. stroke volume), pressures (eg. end-systolic pressure), and area (which represents myocardial work). The PV loop can also be used to represent the relationships of contractility preload and afterload to cardiac function, and to model the effects of changing these variables. Coronary blood flow Sunday, September 6 (2020); Cardiovascular systemThe coronary circulation consists of three main arteries (LAD, LCx and RCA) and one main vein (the coronary sinus). The most exciting feature of this regional circulation is its ability to autoregulate its blood flow in a way which permits the heart to massively increase its metabolic demand. As myocardial oxygen extraction is already quite high (60-70%), coronary blood flow needs to increase to match demand. Mediators implicated in this autoregulation include variou metabolic substrates and bytproducts, such as ATP, adenosine, potassium, oxygen, carbon dioxide, lactate and hydrogen ions. Heating and humidification in the normal respiratory tract Thursday, September 3 (2020); Respiratory system The upper airway is structurally designed to humidify the respiratory gas mixture by increasing the turbulence of inspired gas. The mucosa and the air exchange heat and moisture with each other, such that the air at the level just below the carina becomes 100% humidified and heated to body temperature. This process remains highly efficient within a broad range of ambient temperatures and humidity values; however pathological states (tachypnoea, increased cardiac output) can increase the rate of heat and water loss via the respiratory tract Myocardial oxygen supply and demand Tuesday, September 1 (2020); Cardiovascular systemCoronary blood flow is biphasic (mainly diastolic), and scales significantly with myocardial oxygen demand, which is the main determinant of blood flow. It needs to do this because the myocardial oxygen extraction ratio is already quite high, around 75%. This is mainly regulated by changes in coronary vascular resistance, which result from autonomic and autoregulatory paracrine signals. Thiamine deficiency as a cause of lactic acidosis Tuesday, September 1 (2020); Thiamine participates as a cofactor in oxidative phosphorylation, and its absence is sorely missed. Historically, this is a cause of lactic acidosisin the malnourished patient in who there is no other apparent cause of lactic acidosis. Hypomagnesemia Saturday, August 29 (2020); Electrolytes and FluidsIn short, hypomagnesemia is associated with hypokalemia and hypocalcemia, and the clinical features closely resemble the features of an extremeyl low calcium- with tetany, seizures and postive Trousseau and Chvostek signs. You have either failed to absorb enough magnesium somehow, or (more likely) there is some sort of magnesium-wasting illness, with diarrhoea and renal tubular loss being the usual culprits. In epidemiological terms, 99% of all hypomagnesemia seen in hospital will be the consequence of loop diuretics, but many other classical causes would need to be mentioned in the exam answer, including hyperaldosteronism, hyperparathyroidism, alcoholism and pancreatitis.

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