Patient warming: improving outcomes

 Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions, which is defined as 35°C (95°F). The very young and the very old are more susceptible to hypothermia, while certain medical conditions can also affect patients’ thermoregulation. Trauma patients are particularly at risk and studies have shown that there are serious consequences associated with injured patients who are hypothermic (<35°C), including coagulopathy, acidosis, decreased myocardial contractility and increased risk of mortality. Addressing the risk of hypothermia, even before the patient arrives at hospital, is critical, therefore. A French study, recently published in the journal Critical Care (July 2012), found that patients who suffered a traumatic injury were at greater risk of mortality from hypothermia. The researchers advised that patients receiving emergency medical services should remain clothed when possible and temperatures of IV fluids and ambulances should be controlled.1 The researchers analysed cases of adults with traumatic injuries who received pre-hospital care before being taken by ambulance to one of eight hospitals included in the study. The patients’ body temperatures were monitored continuously using an infrared tympanic thermometer – 14% of patients had hypothermia by the time they arrived at the hospital. “As expected, the severity of hypothermia was linked to the severity of injury,” said Dr. Frederic Lapostolle, of Avicenne Hospital in Bobigny. “Blood loss and spine or head injury impair body temperature regulation, and, in our study, we found that head injury and intubation to aid breathing were independently associated with hypothermia.” Although the temperature outside had little effect on patients’ risk for hypothermia, the temperature of the IV fluids they were given and temperatures inside their ambulance were significant risk factors for the condition. “The temperature of infused fluid for 75% of our patients was below [70°F] and usually at ambient air temperature,” Dr Lapostolle added. “We suggest that, to reduce the incidence of hypothermia, the temperature of infusion fluids needs to be controlled, and that as small a volume as possible is used. Temperature of infusion fluids can be easily and rapidly measured in pre-hospital settings.” “We also recommend that ambulances be heated and that, as much as possible, the patient should remain clothed, because attempting to warm the patients did not compensate for the effect of them being undressed even if it can make examination more difficult,” he concluded. The need for improved temperature management for trauma patients was also highlighted by the findings of an earlier study on ‘The incidence and significance of accidental hypothermia in major trauma’ – conducted by Ireland et al, in Melbourne, Australia.2 A review of 732 medical records of major trauma patients presenting to an adult major trauma centre was undertaken between January and December 2008. Overall mortality was 9.15%, while the incidence of hypothermia was 13.25%. However, the mortality of patients with hypothermia was 29.9% with a threefold independent risk of death. Independent determinants for hypothermia were pre-hospital intubation, Injury Severity Score (ISS), Arrival Systolic Blood Pressure (ASBP) <100 mm Hg: 3.04, and winter time. The authors concluded that seriously injured patients with accidental hypothermia have a higher mortality independent of measured risk factors. For patients with multiple injuries a coordinated effort by paramedics, nurses and doctors is therefore required to focus efforts toward early resolution of hypothermia – aiming to achieve a temperature >35°C.

Surgery

Temperature management in the hospital setting is also vital. In 1994, Blackburn suggested that as many as 70% of all patients undergoing surgical procedures develop inadvertent hypothermia.3 Studies undertaken by Flores-Maldonado et al, in 2001, also showed that 40% to 60% of patients suffer from pre-operative hypothermia.4 Factors contributing to inadvertent hypothermia include patients lying on cold operating theatre tables, heat loss from open body cavities, exposure to cold ambient temperatures in the preoperative and surgical suites, a reduction in metabolic heat production (i.e. no muscle activity), room-temperature antimicrobial skin preparations and IV fluids, various forms of anaesthesia (vasodilation) and various pharmacological agents. To combat these factors, numerous clinical studies have evidenced that patients benefit from being actively warmed prior to, during and after surgery. It is now widely acknowledged that perioperative hypothermia is associated with poorer patient outcomes – including increased risks of surgical site infection, cardiac complications, and bleeding; as well as an associated increase in treatment costs, prolonged hospitalisation and mortality. Following a study of 262 patients having aortic aneurysm surgery, Bush et al found that hypothermia is associated with significantly increased morbidity and mortality rates – 12% of the hypothermic patients died, compared to 1% of the normothermic patients.5 Similarly, in a study of 562 patients by Mahoney, 6% of hypothermic patients died, compared with almost 3% of normothermic patients. Hypothermia can also increase the risk of the patient suffering a myocardial infarction (MI). After surgery, when the body temperature begins to return to normal, the metabolic rate increases with shivering and vasoconstriction occurs, which increases arterial blood pressure, putting extra demands on the heart. The Bush and Mahoney studies prove this point – 7.5% of hypothermic patients in the Bush study had an MI compared to 4% of normothermic patients. In the Mahoney study, 4% of hypothermic patients had an MI compared to 2% of normothermic patients.6 Studies undertaken by Bush, Mahoney and Kurtz7 all demonstrate that hypothermic patients take longer to recover – spending an average of 10 days longer in hospital. At the Infection Prevention Society’s recent annual conference (2012) Judith Tanner, professor of clinical nursing research, De Montford University, also reported that patient warming was found to be one of the most significant factors in reducing surgical site infection, following an initiative to reduce infections at her Trust. Judith Tanner and colleagues at Leicester found that patients who had no pre-op warming had a superficial SSI rate of 22%. For patients that were pre-op warmed, the superficial SSI rate was 0%. Hypothermia also appears to have a significant effect on patient satisfaction, anxiety and pain management. A recent study highlighted the fact that active warming leads to a reduced requirement for pain relief after surgery. Benson et al conducted a prospective, randomised controlled trial to determine the efficacy of a patient-controlled active warming gown in optimising patients’ perioperative body temperature and in diminishing postoperative pain after total knee arthrosplasty (TKA).8 Thirty patients who would be undergoing TKA received either a standard hospital gown and prewarmed standard cotton blanket (n=15) or a patient-controlled, forced-air warming gown (n=15). Although pain scores were not significantly different in the two groups (P=0.08), patients who received warming gowns had higher temperatures (P<0.001) in the post-anaesthesia care unit, used less opioid (P=0.05) after surgery, and reported more satisfaction (P=0.004) with their thermal comfort than patients who received standard blankets. The authors concluded that patientcontrolled, forced-air warming gowns can enhance perioperative body temperature and improve patient satisfaction. Patients who use warming gowns may also need less opioid to manage their postoperative pain. They recommended that nurses should ensure that effective patient warming methods are employed in all patients, particularly in patients with compromised thermoregulatory systems (such as older adults), and in surgeries considered to be exceptionally painful (such as TKA).