A reply

Abstract

[3] RICE EH, SOMBROTTO LB, MARKOWITZ JC, LEON AC. Cardiovascular morbidity in high-risk patients during ECT. American Assistance for the Anaesthetist. The treatment of postoperative shiveringThe recent study by Alfonsi and colleagues (Anaesthesia 1995; 5 0 214-7), whilst interesting, has features that make it difficult to support the conclusions offered by these authors.Alfonsi and colleagues have deliberately chosen to study hypothermic patients, thereby ignoring the 50-60% of shivering patients who, in our practice at least, are normothermic with core temperatures greater than 36°C. Indeed the lack of correlation between postoperative shivering and body temperature appears to be the norm rather than the exception [I, 23. The paper cited by Alfonsi and colleagues in support of their contention that shivering is related to core hypothermia refers to an experimental study in a small group ofvolunteers [3] and given the predominance of normothermic patients amongst those who shiver the relevance of this study to clinical anaesthesia is not clear. Alfonsi and colleagues do not comment on the number of shivering patients that they observed who were not included in the study because they were normothermic.The aetiology of postoperative shivering appears to be multifactorial. We are concerned that in Alfonsi's study the treatment groups differ markedly from each other in relation to their gender ratio, since males exhibit more postanaesthetic shivering than females, [4, 51 although we have no evidence that males and females differ in their response to treatment and so the difference may not matter in this study. Alfonsi and colleagues do not comment upon the frequency of spontaneous remission of shivering in the saline-treated group. We are aware that postoperative shivering is episodic in nature and that given the small group sizes employed in this study, it is possible that the apparent effect of fentanyl was in fact due to spontaneous remission. This would explain why the apparent rate of recurrence after fentanyl was higher than after pethidine, in that it perhaps reflects the episodic nature of postoperative shivering rather than pharmacokinetic or pharmacodynamic differences between the treatments.In our practice the treatment of choice remains low dose pethidine. We were surprised at the size of the doses of both pethidine and fentanyl employed by Alfonsi and colleagues since low doses of pethidine are well established as treatment for postoperative shivering [4,67]. Furthermore, the doses of pethidine and fentanyl employed are not equipotent with respect to analgesic activity. In a study that is attempting to investigate the mechanisms underlying the effect of pethidine this introduces a further variable which makes meaningful comparisons between treatment groups difficult.The logic that leads these authors to consider lignocaine for inclusion in the study is intriguing, but pethidine also has antimuscarinic effects in addition to its local anaesthetic effects. Anticholinergic premedication increases the incid...