Femoral nerve palsy has been reported after percutaneous ilioinguinal field infiltration with general anaesthesia for inguinal herniorrhaphy. The mechanism whereby this could occur was studied in cadaver dissections. It was found that the plane between the transversus abdominis muscle and the transversalis fascia was continuous laterally with the tissue plane deep to the iliacus fascia, which is the plane containing the femoral nerve. Injection of methylene blue 1 ml into this plane resulted in pooling of dye around the femoral nerve. Femoral nerve palsy may result from infiltration of a sufficient volume of local anaesthetic into the plane between the transversus abdominis muscle and the transversalis fascia with tracking of the injectate deep to the iliacus fascia to affect the femoral nerve. This finding has important implications for the performance of a percutaneous ilioinguinal field block particularly in day surgery provision.
We have investigated the effect of four doses of remifentanil on the incidence of respiratory depression and somatic response at incision. Remifentanil was administered as a loading dose of 0.125, 0.25, 0.375 or 0.5 microgram kg-1 and at a maintenance infusion rate of 0.025, 0.05, 0.075 or 0.1 microgram kg-1 min-1, respectively, with an infusion of propofol 6 mg kg-1 h-1. Responses occurred in 88% of patients with remifentanil 0.025 microgram kg-1 min-1 compared with 30-40% in the other groups. Respiratory depression after incision increased from 6% with remifentanil 0.025 microgram kg-1 min-1 to 73% with 0.1 microgram kg-1 min-1. Increases in propofol infusion rate to 7.2-8.4 mg kg-1 h-1 produced adequate maintenance of anaesthesia. Reductions in remifentanil doses to 0.025-0.05 microgram kg-1 min-1 resulted in adequate respiration at the end of surgery in 88% of patients. Maintenance infusions of the two drugs for spontaneous ventilation are likely to be in these ranges. However, the ideal loading doses and infusion rates for induction remain to be established.
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