The use of di-isopropyl phenol (Diprivan) for induction of anaesthesia was assessed in doses ranging from 1 to 3 mg kg-1. With less than 1.75mg kg-1 not all patients were anaesthetized; 2.0 mg kg-1 appeared to be a satisfactory induction dose. Involuntary muscle movement, cough and hiccup at induction were rare with any dose studied. However, the frequency of hypotension and respiratory depression were related to the dose given. Pain on injection was uncommon when the drug was given into an antecubital vein, but occurred in 39% of patients when injected to the back of the hand or wrist. Recovery was rapid, and characterized by lack of emetic sequelae. Di-isopropyl phenol 1.5 - 2.0 mg kg-1 given rapidly during reactive hyperaemia can produce anaesthesia in one arm-brain circulation time. A reaction involving flush, hypotension, cough, laryngospasm and bronchospasm occurred in one patient receiving 2.5 mg kg-1 given over 20 s.

SummaryWe have previously demonstrated in a rat model that the lumbar intrathecal injection of 0.02 ml 6.3% magnesium sulphate, a concentration iso-osmolar with rat plasma, produces a state of spinal anaesthesia and general sedation which reversed completely after 6 h, without evidence of neurotoxicity, immediately or during the week thereafter. Using the same model and five groups of six animals in each, we administered the same volume and concentration of magnesium sulphate and compared its clinical effects with those of 0.02 ml 12.6% magnesium sulphate, 0.02 ml 2% lignocaine and 0.02 ml 0.9% sodium chloride solution, given as a series of 15 injections on alternate days for a period of 1 month. The animals were then killed and their spinal cords and meninges examined histologically. No significant differences were noted in the times of onset, durations of sensory and motor blockade and the times to full recovery throughout the entire period of 1 month's observation in the animals receiving intrathecal 6.3% magnesium sulphate. In the group receiving 12.6% magnesium sulphate, the time of onset of sensory and motor blockade was shorter and the duration of both parameters was significantly longer than in the former group. Full clinical recovery and resumption of normal eating and drinking took place in both groups throughout the entire series of 15 successive intrathecal injections. Identical, mild, uniform histopathological changes in the spinal cord were seen in all the five groups, including the group in which only the intrathecal catheter was implanted. The complete recovery and benign consequences of repeated intrathecal injections of iso-osmolar magnesium sulphate in a rat model indicate a lack of neurotoxicity and provide an impetus for further trials in larger animal species, before initial clinical trials of this substance, given intrathecally, in humans.Keywords Anaesthetics, local; lignocaine. Ions; magnesium. Anaesthetic techniques, regional; intrathecal. ...................................................................................... Correspondence to: Dr M. Bahar Accepted: 22 September 1996 The recent increased interest in the neurological effects of magnesium deficiency and a renewed concern with magnesium metabolism [1] prompted us to examine the results of intrathecal administration of magnesium sulphate (MgSO 4 ) in an animal model previously described by us [2]. We have also previously demonstrated in this same rat model that the intrathecal injection of a 0.02-ml bolus of 6.3% MgSO 4 , a concentration iso-osmolar with human and rat plasma [3][4][5], produced a state of spinal anaesthesia and general sedation lasting approximately 1 h. This

An animal preparation has been developed to test therapeutic agents in the extradural and intradural spaces. Under anaesthesia a hole was drilled in the penultimate lumbar vertebra of male Wistar rats and the appropriate space cannulated. The catheter was tunnelled subcutaneously to emerge at the neck. There was no spinal cord or meningeal reaction after 1 month. Catheters remained patent for 3 months. The method of cannulation allowed free rostral spread of drugs. Using plain 2% lignocaine, paralysis and anesthesia of the hind limbs required an intradural volume of 32 +/- 3 mulitre: the required volume on extradural injection was 46 +/- 2 mulitre (P less than 0.01). Paralysis of all limbs required an intradural volume of 115 +/- 12 mulitre. Respiratory arrest and death required a mean intradural volume of 179 +/- 15 mulitre.

The response to somatic pain with sub-hypnotic doses of ICI 35, 868 (diisopropyl phenol in cremophor) and thiopentone was compared using tibial pressure algesimetry. Studies were also carried out following recovery from larger doses of both drugs. The patients underwent gynaecological procedures using only one of the two i.v. agents and nitrous oxide in oxygen. The studies confirmed the known antanalgesic action of thiopentone and demonstrated that diisopropyl phenol has an analgesic action which is an attractive feature in an i.v. anaesthetic agent.

Summary Pain caused by intravenous injection in