Hypothermia And Wound Infection In Trauma
For the most part, hypothermia is a bad thing for trauma patients. Its impact on bleeding and mortality has long been known. A paper just out now implicates it in surgical site infections as well. This fact has already been shown for some types of elective surgery (colorectal), but it appears to be a factor in trauma laparotomy as well.
A retrospective review of 524 patients who underwent a trauma lap looked at the correlation of surgical site infection (SSI) and the depth and duration of hypothermia. The mean low temp across all cases was 35.2° C (!). Nearly a third had at least one measurement below 35° C. About 36% of all patients developed an SSI.
- Hypothermia is a common problem in these patients!
- 35 C was the nadir temp most predictive of developing an infection
- Every degree below 35 C more than tripled the risk of SSI
Bottom line: Yet one more reason to avoid hypothermia in our trauma patients! This effort begins with prehospital providers doing their best to insulate and keep patients warm. The trauma team also has a responsibility to heat up the room and keep the patient covered as much as possible. Baseline temp should be obtained in all major trauma patients. And if they do end up in the operating room, anesthesia needs to monitor the temp closely and keep the surgeon apprised of any concerning drops.
Reference: The Effects of Intraoperative Hypothermia on Surgical Site Infection: An Analysis of 524 Trauma Laparotomies. Annals of Surgery 255(4):789-795, 2012.
Hypothermia and Massive Transfusion
Tuesday, I talked about a new notion of using profound hypothermia to save critically injured trauma patients. Since this concept is not yet ready for prime time, we still have to treat hypothermia as our enemy. Most trauma centers have established massive transfusion protocols that detail the use and ratios of specific blood components to avoid fatal anemia and coagulopathy. But do we pay enough attention to hypothermia?
A multicenter study was carried out that will be reported at the upcoming EAST meeting in January. They looked at patients who received massive transfusion (>= 10u PRBC in 24 hours) and looked at their lowest temperature during that 24 hour period.
They found that as temperature decreased, shock parameters, coagulopathy, injury severity and transfusion requirements increased significantly. Specifically, if a temperature of <34C doubled mortality risk, and this effect was most pronounced in patients who received relatively less plasma.
Bottom line: Temperature is still very important, and hypothermia must be avoided at all costs. This is true in the ED and the OR. Allowing temperature to drop below 34C significantly increases mortality and is at least as important as giving enough FFP to correct coagulopathy from dilution.
Reference: Hypothermia in massive transfusion: are we not paying enough attention to it? Poster 2, EAST 25th Annual Assembly, Jan 2012.
Induced Hypothermic Arrest In Patients Bleeding To Death?
Here’s an interesting note out of the University of Pittsburgh. They are preparing to engage in a study to look at the role of hypothermic arrest as a way to salvage trauma patients who are bleeding to death. Sometimes we encounter catastrophic injuries that are exceeding difficult to stop the bleeding. Some vascular injuries within the abdomen come to mind, particularly retrohepatic vena cava injuries.
So what would happen if you rapidly reinfused the patient with cold preservative instead of more blood? The idea is to stop the heart and induce profound hypothermia that would essentially put the brain and other key organs into suspended animation. This might provide a period of time to do the needed repairs, but not worry about the imminent danger of brain death.
Sam Tisherman, the principal investigator, terms this scenario EPR or “emergency preservation and resuscitation” instead of CPR. The desired temperature after cardiac arrest is 50 degrees F, or 10 degrees centigrade. Animal trials have shown promise.
Bottom line: It will be interesting to see how this goes. We’ve tried hypothermia for heart attacks, head injury, and a number of other clinical problems. Unfortunately after initial enthusiasm, they’ve generally not lived up to their billing. It seems counterintuitive to use a maneuver guaranteed to produce coagulopathy to save somebody who is bleeding. But sometimes this type of bold thinking results in life-saving breakthroughs.
Trauma 20 Years Ago: CAVR For Hypothermia
Hypothermia is the bane of major trauma resuscitation, causing mortality to skyrocket. A number of rewarming techniques have been developed over the years. These are classified as passive (the patient generates their own heat) or active (we deliver calories to them), and noninvasive vs invasive. Rewarming speed increases as we move from passive to active and from noninvasive to invasive.
Continuous arteriovenous rewarming (CAVR) is one of the invasive techniques used today. Its use in humans was first reported 20 years ago this month. Larry Gentilello at Harborview in Seattle had experimented with this technique in animals, and reported one case of use in a human who had crashed his car into icy water. After a 20 minute extrication, the patient was pulseless with fixed and dilated pupils, but he regained pulse and blood pressure at the hospital.
The initial core temperature was 31.5C. Peritoneal, bladder and gastric lavage were carried out for warming, as was delivery of warm inspired gas via the ventilator. However, after an hour the temperature had dropped to 29.5C. CAVR was initiated as a last-ditch effort using a jerry-rigged Rapid Fluid Warmer from Level 1 Technologies. The core temperature was raised to 35C after 85 minutes.
The patient did have typical complications (ARDS, acute renal failure), but survived with recovery of his renal and pulmonary function, and a normal neurologic exam. At the time, the authors were unsure whether the complications were due to the near-drowning or the rapid rewarming.
Reference: Continuous arteriovenous rewarming: report of a new technique fo9r treating hypothermia. J Trauma 31(8):1151-1154, 1991.