When patients kept at a body temperature of 37C with aggressive warming during surgery, there was no reduction cardiac complications compared to patients kept at 35.5C, finds a large new study reported in The Lancet. No differences was seen in number of infections or required blood transfusions in patients kept at cooler body temperatures.
An unintentional drop in body temperature is a normal side effect during surgery, due mostly to anaesthetic medications’ interference with the body’s temperature regulation processes. In Western countries, nursing staff typically use forced-air heaters to keep patients warm during surgery, with a target temperature of 36C. This trial, one of the largest to date, sought to determine whether even greater warming, to 37C, would reduce the risk of cardiac complications, a major cause of mortality in the first 30 days after surgery.
Results showed no significant differences between groups for the trial’s primary endpoint, a composite of troponin elevation due to ischemia (an indicator of heart injury), non-fatal cardiac arrest or death from any cause within 30 days after surgery. Researchers also reported no differences for any of the trial’s secondary endpoints.
“This trial tells us that there is no benefit to aggressively warming patients to 37 C during surgery. It is simply unnecessary, and it doesn’t improve any substantive outcomes,” said Daniel I. Sessler, MD, Michael Cudahy professor and chair of the Department of Outcomes Research at Cleveland Clinic and the trial’s lead author. “Also, the results show that 36C should not be considered the threshold for defining mild hypothermia since there was no harm at 35.5C.”
The researchers enrolled 5050 patients, mostly in Chinese centres. Participants had various major noncardiac surgical procedures, with a minimum duration of two hours and an average duration of four hours. Half of the patients were randomised to routine care, with a target body temperature of 35.5C, and the other half randomised to aggressive warming, with a target body temperature of 37C.
For patients assigned to routine care, nursing staff put a warming cover in position but did not activate it until the patient’s body temperature decreased to less than 35.5C, resulting in an average group body temperature of 35.6C. With the more aggressive warming protocol, nurses covered patients with a heated blanket for 30 minutes before surgery and then used two forced-air heaters to keep patients warmed to a mean of 37.1 C during surgery.
In addition to seeing no benefit in terms of the composite primary endpoint, the trial reported no significant differences between groups in terms of serious wound infections, length of hospitalization, hospital re-admissions or the need for blood transfusions. The investigators were surprised that rates of wound infections and transfusions were similar to previous studies, which suggested that both were more common in patients maintained at lower body temperatures.
While most patients were enrolled in China, Dr Sessler said, the results should still be generalisable to patients and health care settings in other countries.
“This study shows that it is reasonable to keep patients warm, but we saw no evidence whatsoever that it makes a difference if they’re just above or just below 36C,” Dr Sessler said. “Surgical patients should still be warmed, but there’s no need to be super-aggressive about the warming.”
Less serious or non-medical outcomes, such as patient comfort or shivering was not assessed. Dr Sessler said that patients maintained at a lower body temperature may shiver or feel cold after surgery, but both are temporary and unlikely to have a meaningful health impact.
Source: American College of Cardiology
