The effectiveness of strategies for the management and/or prevention of hypothermia within the adult perioperative environment: systematic review.

BACKGROUND: Inadvertent hypothermia is common in patient's undergoing surgical procedures. Hypothermia within the perioperative environment may have many undesired physiological effects that are associated with significant postoperative morbidity. Patient's temperature drops to below 35°C during the first hour of anaesthesia because of impaired thermoregulatory mechanism and patient getting cold in the operating theatre. For this reason, health care professionals working in the perioperative environment need to know what are the most effective strategies for treating or preventing hypothermia to improving patient outcomes following surgical procedures. However, to date there has been no systematic review of effectiveness with high quality randomised controlled trials to identify effective strategies for the prevention and/or management of hypothermia in the perioperative environment.

OBJECTIVE: The objective of this systematic review was to identify the most effective strategies for the prevention and/or management of hypothermia in the intraoperative and postoperative phases of surgical care.

DATA SOURCES: A comprehensive search was undertaken on electronic databases from their inception to October 2008, including Cochrane library, MEDLINE, PubMed, CENTRAL, CINAHL, Current contents connect, DARE, Dissertations Abstract International, EMBASE, Scopus, and TRIP. The search was restricted to English language.

REVIEW METHODS: Randomised controlled trials or clinical controlled trials were sought, which evaluated the effectiveness of active or passive warming techniques in the prevention and/or treatment of inadvertent hypothermia. Critical appraisal of study quality was undertaken using Joanna Briggs Institute critical appraisal instruments. Data extraction was via the Joanna Briggs Institute standard data extraction form for evidence of effectiveness.

RESULTS: Eighteen studies with a combined 1451 patients were included. The results were classified into three categories with a further sub classification within the active warming techniques category.Forced air warming was effective in maintaining intraoperative normothermia when compared to passive warming, routine thermal care and no form of warming. Forced air warming in pregnant women scheduled for caesarean delivery under regional anaesthesia prevented maternal and foetal hypothermia. In contrast, passive warming with tight elastic bandages wrapped around the legs (passive insulation) in the same patient population had no significant benefits in preventing maternal hypothermia.However, in arthroscopic knee surgery patients, forced air warming did not result in a decrease in the incidence of postoperative shivering indicating that it was not effective or feasible to extend active warming into recovery in this patient population. Forced air warming was effective than circulating water mattress in preventing hypothermia in patients who underwent repair of infrarenal aortic aneurysms. Forced air warming was effective against radiant warming in maintaining intraoperative normothermia in lengthier surgical procedures.Prewarming in different patient populations prevents redistribution hypothermia, especially after one hour of anaesthesia induction. Intravenous and irrigating fluids warmed (38-40°C) to a temperature higher than that of room temperature by different fluid warming devices (both dry and water heated) proved significantly beneficial to patients in terms of stable haemodynamic variables, and higher core temperature (core T) at the end of the surgery (transurethral prostatectomy and orthopaedic surgery). However, prewarming irrigation fluids in knee arthroscopy patients did not prove beneficial in maintaining normothermia.Water garment warmer was significantly (P < 0.05) effective than forced air warming in maintaining intraoperative normothermia in orthotopic liver transplantation patients. Extra warming with forced air compared to routine thermal care was effective in reducing the incidence of surgical wound infections and postoperative cardiac complications, as well as shorten the length of hospital stay.Passive warming with reflective heating blankets or elastic bandages wrapped around the legs tightly were found to be ineffective in reducing the incidence or magnitude of hypothermia. Low-flow anaesthesia with active forced air warming was effective in stabilising patient's core T during surgical procedures when compared to low-flow anaesthesia alone or low-flow anaesthesia with passive insulation.Phenylephrine i.v. infusion resulted in a significantly less reduction in core T after first hour of anaesthesia and patients were warmer until the end of the surgery (minor oral surgery).

CONCLUSION: Active warming with forced air warming units keeps all patients warmer in the intraoperative and postoperative periods. Forced air warming compared with alternate forms of warming reduces the incidence of shivering and wound infections, increases thermal comfort and reduces morbid cardiac events.

IMPLICATIONS FOR PRACTICE: Our review indicates that active warming techniques (forced-air warming) are effective in preventing and managing hypothermia in the perioperative environment and based on the results from the review there are several recommendations to guide clinical practice: IMPLICATIONS FOR RESEARCH: Future research should focus on large, high quality randomised controlled trials looking at long-term clinical outcomes, operating temperature forced-air warming devices (not just maximum set temperature), different body sites and percentage of body coverage area of active warming for efficient management of intraoperative hypothermia.