ABC of intensive care: Renal support

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Abstract
Oliguria and renal dysfunction are common in critically ill patients. In most cases the kidney is an innocent bystander affected secondarily by the primary disease process. As patients with acute renal failure usually have multiple organ dysfunction and often require respiratory or circulatory support, they are increasingly referred to intensive care units rather than to specialist renal units. Nevertheless, close liaison with nephrologists is advisable, particularly when primary renal disease is suspected. It is rare for patients to develop acute renal failure after admission to intensive care unless a new problem has occurred or the primary process has not been controlled. Renal failure is not an acceptable cause of death unless a conscious decision has been made not to treat it in the face of another non-recoverable disease Urine is produced by glomerular filtration, which depends on the maintenance of a relatively high perfusion pressure within the glomerular capillary and an adequate renal blood flow. #### Role of kidneys in maintaining the internal environment Glomerular blood flow is autoregulated by the pre-glomerular arteriole until the mean arterial pressure falls to 80 mm Hg. Below this pressure the flow decreases. The autoregulation is achieved by arteriolar dilatation (partly mediated by prostaglandins and partly myogenic) as pressure falls and by vasoconstriction as pressure rises. If perfusion pressure continues to fall glomerular filtration pressure is further maintained by constriction of post-glomerular arterioles, which is mediated by angiotensin II. Diagram of nephron and position within kidney The proximal tubules reabsorb the bulk of the filtered solute required to maintain fluid and electrolyte balance, but elimination of potassium, water, and non-volatile hydrogen ions is regulated in the distal tubules. As renal perfusion and glomerular filtration …

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