External patient temperature control in emergency centres, trauma centres, intensive care units and operating theatres: A multi-society literature review
Timothy Hardcastle, a
trauma surgeon at Inkosi Albert Luthuli Central Hospital and
the University of KwaZulu-Natal, Durban, South Africa, is
President of the Trauma Society of South Africa and Chair:
Peer Review and Professional Practice Sub-committee,
Association of Surgeons of SA. Melanie Stander is an emergency
medicine specialist at Tygerberg Hospital and Stellenbosch
University, Parow, Cape Town, and President of the Emergency
Medicine Society of SA. N
icola Kalafatis, a
critical care specialist at IALCH and UKZN, is
Regional Chairperson KZN – Critical Care Society of Southern
Anaesthesiologist at IALCH and a Clinical Lecturer in
anaesthesia at UKZN.
Dean Gopalan is
Specialist and Head: Anaesthesiology and Critical Care,
University of KwaZulu-Natal, Durban, is also a council member
of the SA Society of Anaesthesia.
The paper is endorsed by the Trauma Society of SA, the Emergency Medicine Society of SA, the SA Society of Anaesthesia, the SA Society for Endoscopic Surgery, and the Association of Surgeons of SA.
Corresponding author: T C Hardcastle (firstname.lastname@example.org;
Here we review the available literature supporting the routine
and timely use of external patient warming devices of all
possible types during emergency department and peri-operative
situations, including the role of best ambient temperature, and
provides a best-practice statement on the need for such devices.
It aims to present a guideline document endorsed by the major
South African professional societies in the field of emergency
and peri-operative care.
S Afr Med J 2013;103(9):609-611.
This literature review was initiated to ensure best practice in
the use of external patient warming devices and appropriate
ambient temperature control during emergency and peri-operative
care, to prevent adverse events and increases in morbidity or
mortality due to unintended hypothermia.
To provide an evidence-informed, best-practice guideline on the
appropriate timing and use of external patient warming devices
(all possible types) in the emergency centre and during the
peri-operative care of emergency or elective trauma and surgical
patients. Other relevant adjuncts may be mentioned for
A literature search was performed reviewing existing evidence and guideline publications addressing the external or ambient maintenance of normothermia in emergency, trauma and peri-operative patients undergoing resuscitation, imaging or peri-operative procedures, specifically where the risk of unintentional hypothermia exists. The literature review further examined the consequences of inadequate control of temperature in terms of physiological and septic complications, but did not aim to exhaustively review intentional therapeutic hypothermia after cardiac arrest or for severe neurological (non-traumatic) pathology.
The authors asked four questions to evaluate the content of the retrieved literature, namely:
• Which patients require warming?
• For procedures of what minimum duration is warming recommended, and what temperature should be used?
• What external devices are available, and what are their advantages and disadvantages? This includes maintenance of optimal ambient room temperatures.
• What consequences
and complications occur more readily when temperature is poorly
controlled, and at which human core temperatures do these
The Medline search with the Medical Subject Headings (MeSH) terms ‘patient warming system’ and ‘peri-operative OR trauma AND hypothermia’ resulted in 80 possible references. These were screened for articles that constituted research studies examining either type of device or reporting complications or consequences of hypothermia, and consensus or position statements from other international professional organisations. Twenty-seven relevant articles that addressed the topic were retrieved, and a further three articles were identified by direct reference review of the retrieved articles. Six further items were located by means of a Google Scholar search with the same search terms.
Regarding the first question, namely who should be warmed, the literature clearly demonstrates that most adult patients and all children require temperature maintenance at normothermic levels to optimise outcome.1 , 2 Patients at particular risk of hypothermia are those undergoing resuscitation in most emergency situations, especially trauma (including burns),3-6 those undergoing surgical procedures with combined regional/general or general anaesthesia, and those who have procedures outside the operation suite (interventional radiology or emergency department).2 , 7-9 While the role of therapeutic hypothermia in selected specific medical and surgical treatment strategies is acknowledged, it should be noted that this is not the focus of this review and that our aim is not to discourage this practice in appropriate selected patients. A recent Cochrane review of traumatic brain injury found no benefit to cooling and recommended normothermia.10
With regard to timing of warming device activation, there appears to be reasonable evidence supporting the use of prewarming in both adults and children for any procedure expected to last longer than 2 hours, and also for any procedure where the time of anaesthesia and surgery combined will exceed 30 minutes. Warming should also be maintained during the procedure.7 , 11 For neonates and infants (<1 year of age), routine warming is recommended. All the literature suggests a peri-operative or emergency department target core body temperature of 36°C both pre-operatively and before discharge from the recovery room or delivery to the intensive care unit (ICU).
More recent literature also recommends that the ambient temperature in the emergency department, operation suite and ICU to be kept at a minimum of 21°C, and ideally around 24°C, to ensure reduction in convective heat loss by patients, including those undergoing orthopaedic surgery.2 , 7 , 11-14
There appears to be little evidence from the available comparison studies that any particular external warming device has significant advantages or disadvantages over others. The recommendation is that whatever device is utilised (convective forced-air warming, warm-fluid circulation blankets or carbon-fibre devices), the temperature should be adjusted to ensure a core temperature at or above 36°C at all times.15-19 Most South African health facilities currently use forced-air warming devices, as these are simple to use and cost-effective. What is clear, however, is that simply keeping patients covered with conventional fabric blankets, whether warmed or unwarmed, or foil/plastic ‘space-blankets’ does not provide any warming and may not even adequately maintain the patient’s temperature at application, especially in colder climates or air-conditioned hospital rooms.7 , 11 , 19 In addition, all fluids should ideally be administered through a fluid warming device, although this is not the focus of this review.
What is the rationale for aggressive prevention of hypothermia? The requirement for normothermia has been researched extensively over the past 15 years, and the consequences of overt or occult mild to moderate hypothermia on outcome have been well documented. These include cardiovascular consequences (myocardial ischaemia and dysrhythmias), increased inotrope requirements11 , 19 , 20 and haemorrhagic consequences (clotting abnormalities, and increased transfusion requirements and intra-operative blood loss).4 , 11 , 20 , 21 All are associated with the need for longer ICU and hospital stay, thus adding to the cost of healthcare provision and justifying the minimal expense of the warming device.22
Furthermore, the fact that hypothermia is associated with an increased risk of surgical site sepsis as a result of a number of immunomodulatory and pathophysiological mechanisms3 , 11 , 23 , 24 has been confirmed in a number of recent studies, evidence-based reviews and consensus documents.12 , 23 , 25 , 26 This holds true for elective and emergency surgery, across the spectrum from vascular to trauma and even including orthopaedic procedures (both emergency and implant related),21 , 23 , 24 , 26-28 and applies equally to surgery for burns. Burns patients presenting to the hospital hypothermic, despite no active cooling having been administered, and those experiencing hypothermia during excision surgery, have an increased mortality rate.29 , 30
The seminal work by Kurz et al.,21 , 28 who examined the effect of mild hypothermia (<36°C) in general surgical and orthopaedic operations, showed a reduced surgical site sepsis rate for normothermic patients in both groups. Subsequent studies have confirmed these findings, despite concern over increased cell shedding with forced-air warming devices in orthopaedic surgery. 31 Currently there appears to be little evidence that using forced-air warming devices (the most common available) increases the risk of wound and implant sepsis. 26 , 27 , 32-35 The important implications of increased sepsis associated with mild hypothermia are the potential need for ICU readmission, prolonged hospital stay and potential requirement for secondary procedures, all of which would increase the cost of healthcare.
The evidence overwhelmingly
supports the need for liberal use of warming devices and other
measures to prevent mild to moderate hypothermia.
Hypothermia in the emergency and peri-operative patient is defined as a core temperature (measured by an indwelling central temperature catheter or tympanic measurement) of less than 36°C. Patients with major trauma frequently arrive at the emergency centre with core temperatures below this level. This has profound effects on outcome, including higher rates of acute coagulopathy of trauma and higher mortality.3 , 6 , 35
External patient warming devices are standard of care in emergency centres throughout the world, and there are no time limits assigned to their use. There is no consensus on which type of external warming device is best. Cotton blankets and ‘space’ blankets do not actively warm patients, and at best maintain existing temperature and reduce heat loss somewhat.19 Other modalities for maintaining normothermia include removal of soaked clothes and drapes, warming of intravenous fluids, and humidification of inspired gases through the use of heat-moisture exchange filters.19 , 36 , 37
There is good evidence that maintaining normothermia in children and adults in the emergency centre is associated with improved outcomes and reduced morbidity, (including after head injury or other trauma, and after burns).3 , 6 , 35
There is evidence that peri-operative prewarming, even before surgery starts, is associated with improved tolerance of both the anaesthesia and the surgical procedure. Prewarming reduces the gradient between the periphery and core, thus reducing core heat loss, which occurs through redistribution after induction of general and/or major regional anaesthesia.
Ongoing intra-operative warming in both emergency and elective surgery, irrespective of type, extent or duration, is associated with improved rates of postoperative normothermia and more rapid recovery. In addition, intra-operative normothermia significantly reduces postoperative sepsis rates and wound complications. For any procedure, warming must span the period of the surgery and of anaesthesia induction and recovery. A cost benefit for the use of patient warming devices has been demonstrated at ≥30 minutes total procedural time.7 , 11 , 22 Finally, the availability and use of warming devices are highly recommended in international and local expert guidelines.1 , 2 , 5 , 7 , 12 , 13 , 23 , 32 , 37-40
The consensus from South Africa and around the world, including the World Health Organization, is that normothermia is essential for optimal patient outcome during emergency care and peri-operative management, reducing both morbidity and mortality.
Recommended practices locally should therefore routinely include:
• Routine measurement of core temperature, with either intra-oesophageal or tympanic temperature probes.
• The ambient temperature in the emergency department or operation room should be kept at 21°C - 24°C by limiting cool air-conditioner settings, as this is strongly associated with a reduction in septic complications.
• Active warming must be instituted for any patient with a core temperature of <36°C.
• Routine use of external warming devices for all emergency and peri-operative patients who do not have a high temperature at presentation is advised.
• Routine use of external warming devices for all children is advised.
• These devices should be used in association with fluid warming devices, heat-moisture exchange filters in breathing circuits, and other methods to prevent heat loss.
• If hypothermia is
identified, rewarming should be undertaken.
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Accepted 2 August 2013.
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