Transient hypothermia (i.e. low body core temperature) is common in burns. All patients risk a decrease in body temperature between the scene of trauma and admission to the burn unit. At the burn unit repeated procedures under anaesthesia mean that the risk of hypothermia is not reduced for a long part of the patient's stay. Despite this risk, little progress has been made to resolve the issue.
In our burn unit the typical approach to combat hypothermia would be increased ambient room temperature, resuscitation with warm fluids, warm blankets, radiators in the ceilings, and hot air. These techniques are often easily available and technically less demanding but often not effective enough and slow working as well as influencing the staff's work environment.
For hypothermic trauma patients a number of rewarming modalities have been described and can be divided in three main strategies; passive rewarming
(optimizing the environment thus allowing endogenous heat production), active external rewarming (adding heat to body surfaces), and active core rewarming (adding heat to internal body surfaces) [1
Even though passive rewarming could be considered the basic first step in rewarming a cold patient it alone is seldom efficient enough in burn care and should be combined with other modalities. Active external rewarming by e.g. convective air blankets is routinely used in burn care. However, peripherally vasoconstricted patients are often less susceptible to active external rewarming and can also sustain thermal injuries by intense local heat build-up, especially in already traumatized (burned) skin. Probably the most frequently, and easiest, used active core rewarming technique in burn care is intravenous infusion of warm fluids. There are, though, more elaborate examples such as e.g. body-cavity lavage and airway rewarming available.
Any of the three rewarming strategies may be appropriate in certain settings and in situations where resource availability varies.
However, hypothermia during admission and procedures are still reported [2
], even though numerous (new) rewarming approaches, including invasive techniques, have been described [5
Invasive techniques using e.g. intravascular thermal regulation catheters have been proposed to be effective and reliable [13
]. However, invasive techniques are not commonly available and certainly more technical challenging at least regarding burn patients. Catheters need to be introduced centrally in highly bacterial susceptible patients and its safety and efficacy is still to be investigated in burn patients.
Hypothermia is associated with several deleterious effects and increased morbidity and mortality. Complications such as myocardial ischaemia, arrhythmias, vasoconstriction, and coagulopathies are associated with hypothermia, as is impairment of wound healing, and abnormalities of the immune-, stress-, and neurological systems [8
The patient's core temperature is defined as the temperature in the central circulation, and is regulated by the hypothalamus. The core temperature in a healthy human being is fairly constant (36.5-37.5°C) despite fluctuating ambient temperatures, and this allows the biochemical processes to function unaffected by the outer conditions [5
]. However, patients being anaesthetised in general, and injured patients in particular, face an inherent risk of hypothermia during procedures [5
]. Hypothermia is technically recognised as a core temperature of less than 36.5°C, but a usual threshold for healthy subjects is < 35.0°C [8
Hypothermia is further commonly divided into three groups depending on the core temperature (ranges for injured patients in brackets) [8
]: mild 35-32°C (36-34°C); moderate 32-30°C (34-32°C); and severe < 30°C (< 32°C).
To prevent and combat hypothermia in burned patients in our unit we use Bair Hugger™, radiator ceilings, bed warmers (warm air), and Hotline® or Fluido®- infusion heaters. However, we still encounter hypothermia occasionally in patients, both during and after procedures. Because of the warming technique used, the ambient room temperature is often negatively affecting the staff while working close to patients for long periods of time. We have also noticed that even though warm air is circulating around the patient from the bed warmers, patients with leaking wounds (and thus wet bandages) become even more hypothermic, probably as a result of strong convection effects cooling the patient.
This spurred us to investigate other ways of preventing and combating hypothermia in burn patients, while keeping the staff's working environment tolerable.
Many methods of heating have been reported in the quest for the optimal and most efficient technique [9
], and two relatively new techniques appealed to us: the Allon™2001 Thermowrap (a temperature-regulating water mattress-fluid-convection), and Warmcloud (a temperature-regulating air mattress-air-convection).
The fluid-convection technique has been studied during thoracic and abdominal surgery and has been reported to increase (and maintain) body temperature more efficiently than traditional methods [12
]. Extended details about the Allon™ 2001 Thermowrap are given by Nesher et al. 2001 [12
]. There are fewer scientific reports about the KanMed Warmcloud [21
We could find no reports of the use of either the fluid- or air-convection techniques for patients with burns, and so have investigated them in burned patients, and compared them with our ordinary heating technique.
The aim of this study was to investigate whether either the fluid-convection or the air-convection technique could prove to be more efficient in preventing and combating hypothermia in burn patients as compared to our conventional method.