Negative extradural pressure may not be caused by tenting of the dura.

Sir,—We read with interest the review article on anaesthesia and myotonia [1]. Myotonia dystrophica is an uncommon disorder with as yet no consensus of opinion regarding the ideal anaesthetic for these patients. Propofol has been used in this disorder with variable responses, including prolonged recovery, altered dose–response curves and precipitation of the myotonia. We report three additional cases where propofol was used successfully for induction and maintenance of anaesthesia. The first case was a 53-yr-old man with moderate myotonia dystrophica, ischaemic heart disease (including myocardial in-farction 1 yr previously) and marked peripheral vascular disease. He presented with an acute on chronic ischaemic leg, requiring urgent exploration of his femoral artery. Temazepam 10 mg was administered orally 1 h before operation. After preoxygenation, anaesthesia was induced with fentanyl 250 ␮g, propofol 50 mg (the effect noted), followed 1 min later by another 25 mg. A propofol infusion was then given at a rate of 6 mg kg 91 h 91 for 15 min, then 4 mg kg 91 h 91 for another 10 min and finally 2 mg kg 91 h 91 [2] for the remainder of the operation. Atracurium 20 mg was also given. No other sedative or analgesic drugs were used. The patient underwent femoral embolectomy without any major problems. The propofol infusion was discontinued 55 min after induction. Within 3 min his respiratory efforts were adequate and the trachea was extubated. However, although respiration was satisfactory and the airway was well maintained, it was a further 65 min before verbal contact was made with the patient. The immediate postoperative period was uneventful but on day 7 he began to develop increasing weakness, including bulbar weakness, and he died on day 14. The second case was a 27-yr-old female with moderately severe myotonia dystrophica causing cataracts, marked muscle weakness, slurred speech and swallowing difficulties. However, she was mobile and had no respiratory or cardiovascular system involvement. She was admitted for laparoscopic cholecystectomy. The patient was premedicated with temazepam 10 mg, and heparin 5000 u. was administered s.c. After preoxygenation, fentanyl 100 ␮g was given and the effect observed. Three 25-mg increments of propofol were given at 1-min intervals to assess the patient's sensitivity to propofol. When it was evident that the patient was not sensitive, propofol 125 mg was given followed by atracurium 15 mg. Anaesthesia was maintained with 0.5–1.0 % isoflurane and nitrous oxide in oxygen. The operation …