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PERIOPERATIVE PRACTICE
Warming can improve patient outcomes
Kate Woodhead RGN DMS provides an insight into the latest evidence and guidance on patient warming to improve outcomes following surgery.
Since the publication of the NICE guideline for maintaining perioperative normothermia in 2008, practice has changed and a great deal more evidence is available. It is to be hoped that fewer than the 40% of patients who are said to suffer perioperative hypothermia,1
experience it nowadays,
with better information, education and more devices available to mitigate the effects. It is not just unpleasant for patients to be cold intra and post operatively, being hypothermic reduces their ability to heal optimally and there are numerous other poor outcomes. These include increased likelihood of surgical site infections, increased blood loss intraoperatively, reduced ability to metabolise post operative pain control medications, longer hospital stays and potentially delayed wound healing. Hypothermia is defined as a core body temperature of below 36˚C and can be classified as: mild hypothermia (34-36˚C); moderate hypothermia (30-34˚C); and severe hypothermia (less than 30˚C). Symptoms of perioperative hypothermia can be reduced by active warming. The two most common causes of perioperative hypothermia are exposure to the cold environment of the operating theatre and anaesthetic induced impairment of thermoregulatory control; known as redistribution hypothermia where core warmth is redistributed to the periphery, where it may be lost.
The redistribution of heat may cause patients to lose up to 1.5˚C at the beginning of their anaesthetic, often within the first 45 minutes. This initial drop is followed by a continuing reduction in core temperature which plateaus after around four hours of anaesthesia.2
Once a patient becomes hypothermic it is difficult to get them back to normothermia again. It is therefore implicit that we should ensure preventive measures are in place for as many patients as possible. Inadvertent non-therapeutic hypothermia is considered to be an adverse effect of general and regional anaesthesia. Pre-warming a patient has demonstrated that this effect can be reduced considerably.
MARCH 2017
NICE guidance updated
The clinical guideline responsible for fundamentally changing practice was published in 2008 and received a review in December 2016. Changes made in 2016 are minimal but significant. New recommendations have been added on patients with communication difficulties,
Once a patient
becomes hypothermic is difficult to get them back to normothermia again.
measuring temperature, warming patients before induction of anaesthesia and warming patients after induction of anaesthesia. See Table 1 for changes. Further changes made to the text of the clinical guideline refer to advice on measurement of core temperature. The revised guideline suggests that a site used for temperature measurement should produce either a direct measurement of core temperature or a direct estimate of core temperature, which has been shown in research studies to be accurate to within 0.5˚C of direct measurement. At the time of publication, these sites are pulmonary artery catheter, distal oesophagus, urinary bladder, zero heat – flux (deep forehead) sublingual, axilla rectum (the last being an addition for 2016. Also new in this section is
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