Pre-operative warming: a look at the benefits

While it is already standard practice in the UK to warm a patient during surgery which lasts longer than 30 minutes there is still often little consideration given to the temperature of the patient before they actually reach the operating theatre. This was the subject of a presentation by Professor Judith Tanner, who believes that many patients will have already suffered from peripheral shutdown by this point because of the effects of the journey to theatre, the effects of the anaesthetic and stress. She believes that prevention of this temperature dip should be more widely addressed through the use of preoperative warming devices to maintain patient normothermia. During her presentation Prof. Tanner referred to studies undertaken by Flores Maldonado A et al, in 20011 which showed that 40% to 60% of patients suffer from pre-operative hypothermia. Temperature is routinely measured on the ward before the patient is taken to surgery and then again in the recovery unit. However, temperature is rarely measured in the anaesthetic room prior to induction. This is a crucial measurement as the NICE Guidelines for the prevention of inadvertent perioperative hypothermia state that inducing hypothermic patients should be recorded as a critical incident. If patients become hypothermic during transfer from the ward to the theatre the effects are difficult to reverse. Patients are cooled further inside the theatre, where there is generally a low ambient temperature to make conditions more comfortable for the clinical team. Patients are also prone to heat loss through evaporation from the surgical site and from the use of cold fluids during the procedure – such as skin preparation solutions, washouts and irrigation – and the use of IVs during surgery which add to the cooling effect.

Regulating temperature

General anaesthesia also impacts the ability of the body to regulate temperature by the inhibition of vasoconstriction of the blood vessels, which minimises heat loss and shivering to help generate heat. The use of some sedatives and analgesics can also further impair the patients’ temperature regulatory response. Having discussed why it is so easy for surgical patients to become hypothermic, Prof. Tanner went on to explain that patients suffering from hypothermia are at a much higher risk of developing postoperative complications. She presented the results of two studies that show that hypothermic patients have a greater risk of mortality. Bush et al2 studied 262 patients having aortic aneurysm surgery. 12% of the hypothermic patients died, compared to 1% of the normothermic patients. Similarly, in a study of 562 patients by Mahoney3 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 Bush2 and Mahoney3 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. The studies undertaken by Bush2 Mahoney3 and Kurtz4 all demonstrated that hypothermic patients took longer to recover and spent an average of 10 days longer in hospital. However, it is not just about a patients increased length of stay on the ward. As well as an increased risk of MI, hypothermia can cause increased mortality, morbidity and surgical site infection (SSIs), increasing the length of hospital stay. Bush2 and Mahoney3 both reported increased length of stay in ITU for hypothermic patients – If a patient is cold their internal systems take longer to remove anaesthetic agents. With one hospital day costing around £400 and one ITU bed day costing around £900, this presents a large cost consideration.