Sciatic nerve block: a new lateral approach.

The currently available methods for local anaesthetic block of the sciatic nerve are difficult to perform. Here we describe a new and easier technique for the block. The sciatic nerve is approached from the lateral side of the thigh with the patient lying supine and is identified by simple anatomical landmarks with the help of a nerve stimulator. The technique was found to be safe and effective in over 100 cases. It can be learnt quickly and is easily remembered.

Ketamine hypertension and the renin-angiotensin system.

Renin and angiotensin II have been measured before and 10 minutes after anaesthesia, in 23 patients undergoing minor gynaecological surgery. Twelve were anaesthetised with ketamine 2 mg/kg i.v. and the remainder with thiopentone 5-10 mg/kg i.v. Arterial blood pressure was monitored automatically throughout. The arterial blood pressure rose significantly in the group given ketamine and plasma AII concentration fell. In the group given thiopentone there was no significant overall change in blood pressure but an increase in AII. Plasma renin concentration and activity showed significant increases following the administration of ketamine but were unchanged following thiopentone. Overall, there was a significant inverse relationship between the change in blood pressure and the change in AII. This is compatible with a negative feedback being exerted on the renin-angiotensin system by the raised blood pressure, which has itself been evoked by some quite different factor or factors. We conclude that the renin-angiotensin system is not concerned in the pressor response to ketamine.

Effects of ketamine on the pregnant uterus.

Intra-uterine pressure was recorded by placing a Foley catheter in the extra-amniotic space before the termination of pregnancy in 25 patients, and Caesarean section in 12 patients. The effects of administration of i.v. ketamine 2 mg/kg body weight, sodium thiopentone 4 mg/kg body weight and ergometrine 0.5 mg, and intra-cervical 0.5% lignocaine 20 ml were measured in the first trimester of pregnancy, and i.v. ketamine and sodium thiopentone in late pregnancy. Ketamine was found to cause uterine contraction (mean increase 16.1 mm Hg) equal to ergometrine (mean increase 14.8 mm Hg) in early pregnancy, but exert no effect (mean decrease -- 1.33 mm Hg) in late pregnancy. Lignocaine in early pregnancy given as a paracervical block had no significant effect on intrauterine pressure (mean increase 0.33 mm Hg). Sodium thiopentone (mean decrease -- 4.28 mm Hg first trimester and -- 2.22 mm Hg at term) in late pregnancy had no significant effect on intra-uterine pressure.

Anaesthesia for Caesarean section. Analysis of blood concentrations of halothane using 0.2% or 0.65% halothane with 50% nitrous oxide in oxygen.

In 15 patients anaesthesia for elective Caesarean section was maintained with 50% nitrous oxide in oxygen and a 0.65% halothane supplement. In a further 15 mothers a 0.2% halothane supplement was used. In those mothers receiving 0.65% halothane intermittent measurements were made of maternal arterial halothane concentrations during the uptake and the excretion of the agent. At delivery the foetal umbilical venous concentrations were measured also. The mean time between administering halothane and delivery was 10.5 min (SD 3.5). The mean maternal arterial halothane concentration at delivery was 6.03 mg/100 ml (SD 0.75) and the mean umbilical vein concentration was 2.13 mg/100 ml (SD 0.69). The regression of Apgar scores at 1 min after delivery on umbilical vein halothane concentration at delivery was not significant. In the mothers receiving 0.2% halothane measurements of halothane concentration were made in five patients only. The mean maternal arterial halothane concentration at delivery was 1.56 mg/100 ml (SD 0.52) and the mean umbilical vein and artery concentrations were 0.8 and 0.38 mg/100 ml respectively. The use of 0.2% and 0.65% halothane supplements prevented awareness in all the mothers. However, dreaming occurred in two patients given a 0.2% halothane supplement. Studies are required to establish the minimum halothane supplement required to prevent awareness in a larger series of patients.