If you warm patients during surgery and they emerge from anesthesia normothermic, you’ve done all you can to prevent hypothermia-related complications, right? It may be time to rethink that approach and to focus more on active intraoperative warming. By focusing on core temperature readings taken as patients begin to emerge from anesthesia, we may be overlooking the importance of temperature fluctuations during the hours leading up to that point. The fact that a patient is normothermic at the end of surgery doesn’t tell us much about temperature changes that might have occurred during surgery, or how long they might have lasted.
More common than you think
Many randomized studies show that hypothermia increases the risk of various serious complications, including coagulopathy, wound infection and prolonged hospitalization. This explains why active intraoperative warming is now the standard of care. A reasonable question, though, is how well active warming maintains core temperature in typical clinical environments.
We evaluated core temperatures in more than 50,000 adults who had non-cardiac surgery at the Cleveland Clinic (results presented at the 2013 annual meeting of the American Society of Anesthesiologists). None were pre-warmed, and all were warmed intraoperatively with forced air. Nearly all patients were at 36°C or higher at the end of surgery. But what we found was that hypothermia was surprisingly common during surgery.
- 29% of the patients were less than 35.5°C at some point during surgery.
- Nearly half of the patients had continuous core temperatures below 36°C for more than an hour, and 20% were below 35.5°C for more than an hour.
- 20% of patients had continuous core temperatures below 36°C for more than 2 hours, and 8% were below 35.5°C for more than 2 hours.
These results are sobering, since most clinicians assumed that forced-air warming kept nearly all patients normothermic. A more accurate statement is that patients warmed with forced air are usually normothermic at the end of surgery — but may be quite hypothermic during surgery. The reason for this is redistribution.