[The preanaesthetic care of patients with renal disorder]

The preoperative evaluation of patients with renal disease does not begin with the anaesthesiologist's visit, but with the evaluation and care given by the primary physician. To decrease postoperative morbidity and mortality, an optimal preoperative preparation is essential. The kidney is highly sensitive to perioperative hypoperfusion. Basically the medullary oxygenation with its high rate of oxygen extraction (about 79% of the delivered oxygen) is vulnerable to hypoxia, which may lead to acute tubular necrosis. The main goal of perioperative care is to avoid hypoperfusion and therefore hypoxia of the kidney. A perioperative equalized intravascular fluid balance (normovolaemia) seems to be the most effective strategy to prevent postoperative renal dysfunction. On the other side, the anaesthesia management depends on the renal function. The dosage of anaesthetics must be adapted to an impaired renal capacity. Accurate assessment of the renal function relies on laboratory determinations. The most useful laboratory tests are those related to the glomerular filtration rate (GFR), which represents the renal function. The measurement of the creatinine clearance is the most precise method available for clinically assessing overall renal function (really GFR). Measurement of creatinine clearance by 24-hour urine collection is uncomfortable and highly error-prone. For the estimation of GFR, the use of the Cockroft-Gault or the MDRD (Modification of Diet in Renal Disease) formula is recommended. The renal impairment is grouped according to the glomerular function, estimated by the named formula. Other important parameters to estimate the effects of an advanced renal dysfunction are the haemoglobin and the serum concentration of potassium and sodium. If possible, elective operative interventions should be carried out during a stable phase of the disease. Appropriate treatment of concomitant symptoms, such as hypertonia, is essential and contributes to a reduction of post operative renal dysfunction. Timely consultation with the responsible anaesthesist can prevent unnecessary delay of the intervention.