A reply

Abstract

Correspondence 1085was excessive in 12.5% overall. Three patients exhibited abnormal movements after premedication, one following the smaller dose. There were no significant changes in heart rate, blood pressure or arterial oxygen saturation. Ketamine alone has a foul taste, but it was well accepted when disguised in orange juice, although one vomited 45 minutes later.The pharmacokinetics of oral ketamine and its metabolite norketamine are interesting. Although the bioavailability of oral ketamine is low at 16.5%, the peak plasma norketamine levels are much higher than those after the same dose intramuscularly.' Norketamine probably has anaesthetic and analgesic properties and this possibly accounted for the remarkable lack of response to venepuncture or arterial cannulation.We were attracted by the analgesic and sedative effects of oral ketamine, but the salivation, hypocarbia and dreaming were undesirable side effects in our patients. Eventually, we returned to more conventional premedicant drugs because of disquiet due to the passivity and abnormal movements, but not before combining oral trimeprazine and oral ketamine which rectified the salivation and hyperEdinburgh Royal Infirmary, Ketamine and propofol for TIVAWe would like to comment on the paper by Guit et al.(Anaesthesia 1991: 4 6 24-7). The infusion rates of propofol and ketamine are similar to the rates that we have used in the spontaneously breathing patient for peripheral surgery, such as debridement of wounds, below knee amputation and formation of arteriovenous fistulae. Because of the low infusion rate of ketamine and the interpatient variability to the effects of most drugs, how did they know that they did not have inadequate analgesia or hypnosis in a paralysed patient? Following premedication with oral lorazepam, our patients were given glycopyrroninm to reduce secretions and anaesthesia was induced with ketamine 1 mg/kg and initially propofol 2 mg/kg, which we have now reduced to 1 mg/kg. Ketamine was then infused at 3 mg/kg/hour, and the propofol as per the regimen of Richards et a!. ' An air/oxygen mixture was breathed through a medium concentration oxygen mask.A transient apnoea occurred at induction but on recovery from this the patients were able to maintain their airway. Heart rate increased slightly after the glycopyrronium (a mean of 7 beats/minute), but increased by a mean of 18 beats/minute after induction of anaesthesia. Subsequently the heart rate remained stable.Mean arterial blood pressure fell on average by about 5 mmHg. In two patients nonspecific limb movements occurred, unrelated to any surgical stimulus, and could not be controlled by additional propofol. The time taken to full recovery was very variable and independent of patient factors or duration of surgery. All patients were comfortable in the immediate recovery period and some felt intoxicated. Two patients experienced dreams, but they were not unpleasant. We have further refined this technique using other nonopioid analgesics (nefopam and tenoxicam) and this has i...