Patient warming practices explored

The importance of patient warming was highlighted by anaesthesiology professionals taking part in the on line event, Warming Update. Experts discussed best practice, current evidence and the latest patient warming approaches. A presentation by Dr Dan Sessler, from the Department of Outcomes Research, Cleveland Clinic in Ohio focused on aspects of thermoregulation during anaesthesia and on the substantial consequences of mild inadvertent hypothermia. According to Dr Sessler, the major complications of hypothermia include increases in morbid myocardial outcomes, the promotion of bleeding and increased transfusion requirements, decreased drug metabolism and prolonged recovery times. His advice was to carefully monitor the core temperature of the patient whenever general anaesthesia is administered for more than 30 minutes and with large procedures under neuraxial anaesthesia. Dr Sessler said he believed that prewarming is the only way to prevent initial post-induction hypothermia. “Evidence from large randomised trials has shown that hypothermia causes severe complications and, although not every patient is susceptible to all hypothermiarelated complications, it is rare to find a patient who is not susceptible to at least one of them,” he commented. Greater attention from anaesthesiologists regarding the issues surrounding patient warming began with the publication of two articles in 1996. Dr Sessler explained further: “Our study of wound infection published in the New England Journal of Medicine, and our study of hypothermia and blood loss transfusion requirements published in the Lancet, drew considerable attention, as did an article on hypothermia and morbid cardiac outcomes by S.M. Frank in 1997 published in the Journal of the American Medical Association.” However, despite the overwhelming evidence linking intraoperative hypothermia to serious adverse effects, including increased morbid myocardial outcomes, increased transfusion requirements, risk of wound infections and prolonged hospitalisation, it is still hard to say what the real incidence of perioperative hypothermia is, pointed out Dr Sessler. “There are no good recent cross-sectional studies. Many of the complications related to hypothermia do not occur during the anaesthetic period, but after. Take, for example, wound infection: it is often attributed to surgical problems. Surgical technique certainly contributes to infection risk, but too many people forget about the contribution of hypothermia – which might be just as important. In fact, maintaining normothermia is more effective than administering antibiotics. “Heart attacks are another example. They usually occur one to three days after surgery and are rarely linked to intraoperative hypothermia. By the time a heart attack occurs, it is no longer considered an anaesthesia problem – although anaesthetic management may have been a key contributor.” According to Dr Sessler, there is also reason to believe that the current incidence of hypothermia is much lower than it used to be. “In the past it was not unusual to see patients come into the recovery room with a temperature of 34.5°C. Today, temperatures are rarely below 35.5°C. Also, the studies that evaluate complications of hypothermia rely on a population that shows a higher risk of hypothermia. That makes sense if you are designing a trial, but you cannot just extrapolate the results to all patients,” he said. So what is best practice to maintain patient normothermia? “Most anaesthesiologists use insulating covers. It is understandable, safe, effective, easy to use, and relatively inexpensive,” said Dr Sessler. “Whatever works is fine. You do not absolutely need to use an active system: Heating the room could also be a solution,” he said. In Japan, for example, operating-room temperature is kept near 25°C and hypothermia is less of a problem there than in other countries. Pre-warming is a useful strategy for short procedures in particular. “Counterintuitively, it is more difficult to keep normothermia during a short intervention,” explained Dr Sessler. “The initial hypothermia results from the internal redistribution of heat following the vasodilating effect of the anaesthesia. Pre-warming can reduce this redistribution because it is an active system that regulates the temperature difference between the periphery and the core. Pre-warming is an interesting technique but it has not been used widely because of procedural and technical reasons – although efficacy of the methods is well-documented in many randomised trials,” he said. In conclusion, Dr Sessler said that the best approach to avoid initial postinduction hypothermia during the first hours of an intervention is a combination of pre-warming and intraoperative temperature management. “Pre-warming is a highly attractive option and it should be used more often. It is probably the only way to avoid the initial core-to-periphery redistribution of body heat,” he said. He also mentioned the results of a study on the prevention of intraoperative hypothermia by pre-operative skin-surface warming of hip-surgery patients,1 which showed significantly higher core temperatures during the operating room procedure for pre-warmed patients (Figure 1). The next webinar presenter was Dr Johan Raeder, a professor in anaesthesia at Oslo University Hospital in Norway. He focused on the initial drop in patient temperature after administering anaesthetic drugs and explained how prewarming the periphery of the patient can help during the redistribution phase of the anaesthesia period.

Low levels of awareness

Dr Raeder highlighted the low level of awareness of the benefits of pre-operative skin-surface warming. “We need to give anaesthesiologists a better understanding of the physiology of impaired thermoregulation and resultant core-toperiphery thermal redistribution to make them better understand the importance of pre-warming the patient,” he said. “Emergency care is probably the only field of care that has always been conscious of the importance of keeping the patient within the limits of normothermia. There is a consistent focus on the ‘golden hour’, the time span we have to prevent the patient from suffering severe hypothermia and take them into normothermia,” he said. In Scandinavia there is pre-warming equipment in the ambulances because patients often are already cold when they enter the ambulance. Beyond trauma care and major surgery, normothermia has not been an issue of much interest. Dr Raeder believes that this is because it is quite cumbersome to take warming measures and, traditionally, the impact of hypothermia was never considered to be substantial, as patients will recover from it, eventually. “The result is that many anaesthesiologists do not know the specific physiology related to prewarming. Most of the tools available have, traditionally, been marketed as perioperative tools, rather than related to pre-warming issues.” Today, however, there are simple and cheap devices available to manage pre-warming in the operating theatre. Dr Raeder is convinced that the key to higher implementation of pre-warming strategies is education of anaesthesiologists and nurses. “We need to show them the physiology, so that they understand that it is not just a matter of keeping the body warm during the period of anaesthesia. They need to understand the core-to-periphery thermal redistribution of body temperature at the very start of a procedure,” he said. Dr Raeder believes that the best strategy to maintain normothermia starts with pre-anaesthetic skin-surface warming to avoid the initial postinduction temperature drop and continues by keeping the patient warm and measuring their temperature consistently during the procedure. He went on to state that pre-warming is the only way to avoid post-induction hypothermia, and is also the best way to reduce the risk of perioperative hypothermia. “Skin-surface warming is the only way to keep the patient warm preoperatively, as they are usually dressed in just a patient shirt and often have to wait in a cold corridor or room prior to the intervention. There are some conventional ways to try to keep the patient warm prior to the anaesthesia, but they are more for the comfort of the patient, rather than to maintain normothermia,” he said. “Pre-warming will prevent the initial temperature drop and will also keep the patient comfortable,” maintained Dr Raeder. “This goes for procedures with general anaesthesia or spinal or epidural anaesthesia. Also, if the patient is sedated, they have a lower threshold to start shivering and the body cannot tell that it is cold. The issue may become bigger, in terms of prolonged waking up and recovery time.” Dr Raeder went on to speak about the single-use Barrier EasyWarm active selfwarming blanket. “The cost of this device is not high, it is effective, easy to use and our patients like it. We are currently in the process of gathering data to have more structured feedback relating to its use.” Contamination concerns require the blankets to be kept in a clean environment prior to taking them into the operating theatre. “However, the use of the blankets does not change the way a patient is handled, but you need to make sure they do not get in the way of the surgeon so, during the procedure, we keep the blanket on the patient as much as possible, on parts of the body not involved in the procedure. We measure the patient’s temperature and have found that, when using the blanket, it is sufficient to keep the patient within normothermia limits.” The Warming Update webinar session also included a presentation by Karin Ganlöv, medical director at Mölnlycke Health Care, who looked at practical uses of the company’s single-use Barrier EasyWarm active self-warming blanket. She provided details of a study undertaken to access the safety and efficacy of an active warming blanket to maintain normothermia during the perioperative period in the prevention of hypothermia. The main results of this study are highlighted in Figure 2.