Blood serum fluoride levels with methoxyflurane anaesthesia

Abstract

in 1905, reported that diethyl ether and chloroform anaesthesia respectively reduced urine output, and Smith, Rovenstine and associates, ~ in 1939, reported in a similar effect with spinal anaesthesia, close attention has been paid to the effect of all anaesthetics, surgical trauma, and analgesics on the function of the kidney. [4][5] Until approximately 10 years ago, inhalational and parenteral anaesthetics administered judiciously and even in moderate overdose had not been found to cause a direct adverse effect on the renal parenchyma in animals or man unless they accompanied or followed severe surgical trauma and multiple blood transfusions. Nevertheless, urine output is almost invariably reduced during surgical anaesthesia, with reductions in renal blood flow, glomerular filtration rate and osmolar clearance. These effects usually respond to forced diuresis with intravenous fluids (dextrose, saline or balanced salt solutions in water). In our practice, an osmotic diuretic such as mannitol is also given, usually when the urine output falls below 40 ml/hr. These manoeuvres usually increase urine output promptly2 The oliguria which occurs during anaesthesia is followed frequently by a moderate postanaesthetie compensatory polyuria, as glomerular filtration rate and renal blood flow are restored, or the liberation of antidiuretie hormone ceases. These effects may be contingent upon many other factors such as the amount of analgesics administered postoperatively, the presence of preexisting renal or eardiopulmonary disease under drug therapy, and the use of antibiotics or other therapeutic agents that may be nephrotoxie. 5,7Following the clinical introduction of methoxyflurane in 1960, the question of a toxic effect on the kidney arose again, especially in centers where operations were often prolonged. 8,~q,'~ Methoxyflurane anaesthesia produces a similar renal response to that described above. The reduction of glomerular filtration rate with this anaesthetic may result as a consequence of a fall in renal pcrfusion pressure or of constriction of the afferent renal arterioles, all of which cause retention of salt and water. 4 After extensive animal and clinical evaluations, our recommendation was that 1.5 per cent methoxyflurane should never be exceeded and this agent should only be used with nitrous oxide for maintenance of anaesthesia for major or prolonged operations, after induction of anaesthesia with a rapid-acting anaesthetie.11,1~Clear-cut evidence of nephrotoxicity of methoxyflurane vapour itself had still