Tag Archives: hypothermia

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Hypothermia For Treatment of Severe TBI?

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We’ve been trying to figure out therapeutic hypothermia for a long time. Although we know that accidental hypothermia, especially in trauma patients, is not a good thing, it seems to be protective in certain circumstances. The most significant areas of interest center around the neuroprotective effects, especially after ischemia or hypoxia.

But with the good always comes the bad. Every intervention has side effects, and hypothermia is no exception. Decreased cardiac efficiency, blood viscosity increases, pulmonary dysfunction or edema, coagulopathy, decreased tissue oxygen availability, and changes in drug pharmacodynamics are but a few of the problems that may arise. But as long as the benefits outweigh the risks, such an intervention may be acceptable.

We’ve been looking at the possible protective effects of hypothermia on the brain after severe head injury for quite some time. As with most neurotrauma studies, hypothermia ones are tough to do well. Patient selection, adequate numbers of subjects and good randomization and/or blinding are very difficult. It requires assembling all the relevant studies and scrutinizing this whole body of work to figure out if it works or not.

And the answer is, it doesn’t. The Cochrane Library updated their previous work in this area in 2009. They combined 23 studies and over 1600 patients to try to determine if hypothermia (35C for at least 12 hours) is protective in patients with severe TBI. After whittling the field down to good quality studies, they found that there may be a trend toward fewer unfavorable outcomes (death, severe disability, vegetative state), but it was not statistically significant. There were variable results with respect to the incidence of pneumonia after hypothermia, and these, too, did not meet statistical significance.

Bottom line: Therapeutic hypothermia for treatment of severe TBI is still not ready for prime time, and may never be. The studies thus far are small and flawed. Don’t implement your own protocol for this technique unless you are involved in a very high quality, multi-center study that will add to the literature!

Reference: Hypothermia for traumatic head injury. The Cochrane Library 2009, Issue 4.

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Trauma 20 Years Ago: CAVR For Hypothermia

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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 for treating hypothermia. J Trauma 31(8):1151-1154, 1991.

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Rapid Noninvasive Rewarming Using a Hubbard Tank

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It’s that time of year again in Minnesota. We’re getting 5 inches of snow tonight, so hypothermia season is officially here! I’m republishing a technique for rewarming patients faster than just about any other method. Most burn centers have large tanks for handling burn wounds, and many hospital have smaller therapy tanks that can be used for the same purpose.

Hypothermic patients need to be rewarmed using the most appropriate method. Patients with mild hypothermia (32-35 degrees centigrade) generally only require removal of wet clothing and surface warming. Moderate hypothermia (28-32 degrees C) to severe hypothermia (<28 degrees C) is very serious and requires more aggressive central rewarming techniques.

Basic central rewarming techniques, such as warm inspired gases, warm IV fluids, and gastric or peritoneal lavage can raise the temperature about 3 degrees per hour. 

Rapid central rewarming techniques, like thoracic lavage (6 degrees/hr), AV bypass devices (1-4 degrees/hr), and cardiopulmonary bypass (18 degrees/hr) are typically used on patients with severe hypothermia.

A technique that we use at Regions Hospital involves the use of the Burn Center’s Hubbard Tank. Patients are carefully immersed, torso first, then one extremity at a time to avoid rebound hypothermia. It is possible to increase core temperature using this method faster than bypass (>20 degrees centigrade/hr)! Typical time in the tank is an hour or less for any degree of hypothermia.

Patients can be immersed with EKG monitors and IV lines in place. Temperature monitoring should be performed using a thermistor tipped urinary catheter. Many hospitals don’t have a full Hubbard tank, but do have smaller therapy baths that work nearly as well.

Tips:

  1. A physician must stay with the patient while immersed in case arrhythmias develop.
  2. Position the urinary catheter and collecting bag in such a way that urine in the tubing does not backwash into the bladder. This will falsely and rapidly increase the temperature reading.

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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.

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Reference: The Effects of Intraoperative Hypothermia on Surgical Site Infection: An Analysis of 524 Trauma Laparotomies. Annals of Surgery 255(4):789-795, 2012.

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Hypothermia and Massive Transfusion

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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.

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Reference: Hypothermia in massive transfusion: are we not paying enough attention to it? Poster 2, EAST 25th Annual Assembly, Jan 2012.