Pre-stretched cuffs on tracheostomy tubes.

in labour. It was subsequently calculated that less than half this amount of methoxyflurane was required for Caesarean section when using a 0.1% supplement. Cousins and Mazze (1972) qualified the findings that there was no evidence of nephrotoxicity following the use of 0.35% methoxyflurane in labour by stating: "The agent appears not to be nephrotoxic under most conditions of low dosage administration". It would certainly appear prudent to avoid the use of this agent in patients who have grossly impaired renal function or who are receiving nephrotoxic agents, such as tetracydine. Wilson, Marshall and Hodgkinson (1972) noted that elevated levels of free fluoride ion and oxalic acid appeared in urine following the administration of small quantities of methoxyflurane at Caesarean section. No clinical evidence of renal dysfunction was noted, however, and no direct measurements of renal function appear to have been made. Work is at present in progress in Cardiff to determine whether there is any evidence of renal calculus formation as a result of the oxalic acid excretion which follows methoxyflurane analgesia. N o cases of renal dysfunction have been reported in the literature following the use either of 0.1% methoxyfluranc as part of a balanced anaesthetic technique for Caesarean section or of 0.35% methoxyflurane for analgesia in labour. Since the nephrotoxicity following methoxyflurane is dose-related it would appear desirable to limit the quantity administered to a minimum. The use of a balanced anaesthetic technique with a 0.1 % methoxyflurane supplement for a limited period appears to be the optimum method of administering the drug providing that it is also efficient in preventing awareness. It can indeed be argued that this is the only justifiable method of administering the agent and that the use of high concentrations in patients breathing spontaneously should be avoided. We agree both with Cousins and Mazze (1972) and Wilson, Marshall and Hodgkinson (1972) that the effect of these metabolites on the foetus should be assessed. I. P. LATTO. Cardiff A. C WAINWRIGHT Bristol