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    Turn up the Heat for Better Patient Outcomes

    By Jennifer Decker Arevalo, MA, contributor.  

    The results from a new study, published in the January 2008 issue of Anesthesiology, add to the growing body of evidence supporting the importance of maintaining normothermia in surgical patients to avoid the many complications caused by mild perioperative hypothermia, defined as a core body temperature between 33°C and 36°C.

    “Although our study focused on increased blood loss and transfusion requirement, it’s just one of many major complications, including a three-fold increase in the incidence of morbid myocardial outcomes and surgical wound infections, nitrogen wasting and a 20 percent increase in the duration of hospitalization,” said Daniel I. Sessler, M.D., p rofessor and chair of the department of outcomes research at the Cleveland Clinic in Ohio and senior author of the study. “Other complications include delayed drug metabolism, prolonged post-anesthetic recovery, shivering and thermal discomfort.

    “Inconsistent results from more than a dozen published studies on blood loss and intraoperative core temperature prompted us to do a formal systematic review and meta-analysis of the published medical literature between 1966 and 2006,” continued Sessler.

    According to Sessler and his co-authors, anesthetic-induced hypothermia in unwarmed surgical patients impairs platelet function by interfering with the release of thromboxane A2, which is necessary for the formation of an initial platelet plug, and impairs enzyme function in the coagulation cascade that normally promote clotting. This effect is often unrecognized clinically because coagulation tests, including the prothrombin time and the partial thromboplastin times remain normal, as they are most often performed at 37°C regardless of the patient’s actual core temperature. However, these same tests are markedly prolonged by hypothermia when they are performed at the patient's actual core temperature.

    “Our meta-analysis confirmed that even mild hypothermia of less than one degree Celsius significantly increases blood loss by approximately 16 percent and increases the relative risk for transfusion by approximately 22 percent,” said Sessler. “Reducing transfusion is especially important now that increasing evidence suggests that transfusions are far more harmful than previously believed.”

    As the authors point out, this may not be an enormous treatment effect, but these data add to those from other studies to demonstrate that preventing hypothermia decreases the risk of morbidity and is thus indicated for reasons other than just reducing blood loss.

    “Perioperative hypothermia can easily be avoided with treatments that externally warm patients,” said Sessler. “There is simply no excuse for letting patients become hypothermic these days.”

    Although there are several ways to maintain normothermia, including 30 to 60 minutes of pre-warming, control of ambient operating room temperature, administration of warmed intravenous fluids and surface warming with blankets, forced hot air or circulating water, forced-air convection warming systems are often the method of choice since they are simple, effective, inexpensive and essentially risk free.

    “The standard of care these days is to maintain intraoperative normothermia (>36°C) unless therapeutic hypothermia is specifically indicated,” said Sessler. “However, the American Society of Anesthesiologists (ASA) Temperature Monitoring Standards relate only to monitoring and don’t actually address maintaining normothermia.”

    “This may change though, as one of the first pay-for-performance and anesthesiology quality incentive measures pertains to intraoperative hypothermia and will be based on maintaining perioperative normothermia. It has not yet been officialy promulgated, but the process is well along towards completion. The measure will initially pay for reporting, but soon thereafter, require performance for supplemental payment.”

    “For this measure, payment incentives would be based on either using effective intraoperative warming, specifically, forced-air or actually maintaining normothermia which is a body temperature of at least 36°C within plus or minus 30 minutes of the end of anesthesia,” added Sessler.

    The Management of Postoperative Hypothermia measure proposed in October 2007 by the   ASA Committee on Performance and Outcomes Measurement states that forced-air convection warming systems are effective for restoring body temperature to greater than or equal to 36°C postoperatively. Consultants and ASA members agree that both the perioperative maintenance of normothermia and the use of forced-air warming reduce shivering, and improve patient comfort and satisfaction.

    “There are few things in medicine that are so clearly demonstrated to improve outcome as maintaining perioperative normothermia,” said Sessler.



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