The role of the anaesthetist in the management of acute renal failure

Cholinesterase phenotyping: clinical aspects and laboratory applications

The measurement of cholinesterase activity in human serum is an important investigation, especially in patients suspected of poisoning with organophosphate insecticides, or those experiencing prolonged paralysis following treatment with the short acting muscle relaxant succinylcholine. Appropriate clinical management of affected individuals can only be instituted if enzyme activity is measured using a method capable of clear interpretation and phenotypic ascription of cholinesterase, ascertained by use of selected enzyme inhibitors, is reliable. This review considers factors which lead to significant cholinesterase abnormalities and advises on the techniques most appropriate to their investigation. It is concluded that no one method is suitable both for measurement of activity and determination of genotype. The use of propionyl thiocholine is recommended for the first procedure and benzoyl choline for the latter. Those laboratories in which a request for the assessment of cholinesterase status is an unusual event should make greater use of assistance from colleagues whose experience with the problem is greater.

Anaesthesia and the kidney

Applied anatomy and physiology of the kidney are briefly reviewed. This includes an account of renal blood flow, glomerular filtration rate, juxtaglomerular apparatus, renal autoregulation and intra-renal blood flow distribution, tubular transport mechanisms, solute handling in proximal tubule, function of loop of Henle and distal tubule system. This section concludes with a summary of changes in tubule fluid along the length of the nephron. Acute effects of anaesthesia are reviewed in detail. Indirect effects include those on circulatory and sympathetic nervous systems, autoregulation, endocrine systems such as those involving anti-diuretic hormone, adrenaline and noradrenaline, renin-angiotensin and aldosterone. Direct effects of anaesthesia on renal function have now been confirmed both in vitro and in vivo. Delayed direct nephrotoxicity of anaesthetics relates predominantly to methoxyflurane (MOF) and its metabolism to inorganic fluoride. Other factors are MOF dose, genetics, age, enzyme induction, obesity, other nephrotoxic drugs. Clinical implications are presented. Enflurane nephrotoxicity is rare but aetiologic factors are similar to the foregoing. Isoflurane and halothane are not nephrotoxic. A consideration of the influence of anaesthetic management on the incidence and severity of postoperative acute renal failure concludes the review.