Randomized clinical trial ASGBI Paper Randomized clinical trial of perioperative systemic warming in major elective abdominal surgery P. F. Wong, S. Kumar, A. Bohra, D. Whetter and D. J. Leaper Professorial Unit of Surgery, University Hospital of North Tees, Stockton-on-Tees TS19 8PE, UK Correspondence to: Mr P. F. Wong, Department of General Surgery, The James Cook University Hospital, Martan Road, Middlesbrough, Cleveland TS4 3BW (e-mail: pwong23@hotmail.com) Background: Hypothermia is common in the operating theatre and may increase susceptibility to postoperative complications. Intraoperative systemic warming has been shown to improve outcomes of surgery. This study aimed to examine the effects of additional perioperative systemic warming on postoperative morbidity. Methods: All patients admitted for elective major abdominal surgery and fulfilling the inclusion criteria were randomized into control or warming groups. Both groups were warmed during surgery, but patients in the warming group were additionally warmed 2 h before and after surgery using a conductive carbon polymer mattress. Results: The trial recruited 103 patients (56 in the control group, 47 in the warming group). Both groups were well matched for age, sex and clinical state. Patients in the warming group had lower blood loss (median 200 (range 5–1000) ml versus median 400 (range 50–2300) ml in the control group; P = 0·011) and complication rates (15 (32 per cent) of 47 versus 30 (54 per cent) of 56 in the control group; P = 0·027). There were three deaths; two in the control group (P = 0·566). Conclusion: Extending systemic warming to the perioperative period had additional beneficial effects, with minimal additional cost and patient discomfort. Preliminary data were presented to the Annual Meeting of the Association of Surgeons of Great Britain and Ireland, Harrogate, UK, April 2004, and published in abstract form as Br J Surg 2004; 91(Suppl 1): 18 Paper accepted 19 February 2007 Published online in Wiley InterScience (www.bjs.co.uk). DOI: 10.1002/bjs.5631 Introduction Hypothermia, defined as core temperature below 36° C 1–3 , is common in the operating theatre and has often been disregarded as an inevitable consequence of general anaesthesia and surgery 2,4,5 . The body’s core temperature is determined by the balance between heat loss and heat gain. Exposure to a cold operating theatre environment and anaesthetic-induced impairment of thermoregulatory control are two of the commonest contributing factors that tip the balance in favour of heat loss, leading to hypothermia in surgical patients 1,6 . Hypothermia confers distinct benefits as well as severe complications. Potential benefits include protection against the deleterious effects of cerebral ischaemia as well as malignant hyperthermia 7 . Hypothermia may, however, increase susceptibility to perioperative wound infection by causing vasoconstriction and impaired immunity. Vasoconstriction decreases the partial pressure of oxygen in tissues, which lowers the resistance to infection 8 . The other commonly recognized adverse effects of hypothermia include shivering 9 , prolonged duration of drug action 10 , coagulopathy 11 , myocardial ischaemia 12 and decreased resistance to surgical-site infections 8 . Intraoperative localized and systemic warming have been shown to reduce perioperative complications 13,14 . The aim of this randomized clinical trial was to examine the effects of extending the warming duration to include the pre- and postoperative periods and the potential benefits in reducing postoperative complications. Methods All adult (over 18 years old) patients admitted for elective major abdominal surgery were considered for entry into the trial. The inclusion criteria were major open abdominal Copyright  2007 British Journal of Surgery Society Ltd British Journal of Surgery 2007; 94: 421–426 Published by John Wiley & Sons Ltd