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For the first time ever, clinical practice guidelines on managing patient temperature during cardiopulmonary bypass (CPB) surgery have been published, appearing in the .

The guidelines were jointly issued by , the , and the .

"Numerous strategies are currently invoked by perfusion teams to manage the requirements of cooling, temperature maintenance, and rewarming patients during cardiac surgical procedures. To date there have been very few evidence-based recommendations for the conduct of temperature management during perfusion," according to the guideline authors, led by , of Baystate Medical Center in Springfield, Mass.

"Basically we are trying to protect the brain," Engelman told 乌鸦传媒. "The rest of the body can deal fairly well with heat and cold, but the brain is the most adversely affected by temperature, especially overheating. So we have detailed an approach during the conduct of cardiopulmonary bypass to prevent overheating and potential injury to the brain."

Engelman and colleagues reviewed 615 abstracts and 153 full papers published between 2000 and 2014 to come up with recommendations in four areas: the optimal site for temperature monitoring, avoidance of hyperthermia, peak cooling temperature gradient and cooling rate, and peak warming temperature gradient and warming rate. The authors made the following recommendations:

Class I Recommendations:

• The oxygenator arterial outlet blood temperature should be utilized as a surrogate for cerebral temperature measurement during CPB.
• To monitor cerebral perfusate temperature during warming, it should be assumed that the oxygenator arterial outlet blood temperature underestimates cerebral perfusate temperature.
• Surgical teams should limit arterial outlet blood temperature to <37 degrees C to avoid cerebral hyperthermia.
• Temperature gradients between the arterial outlet and venous inflow on the oxygenator during CPB cooling should not exceed 10 degrees C to avoid generation of gaseous emboli.
• Temperature gradients between the arterial outlet and venous inflow on the oxygenator during CPB rewarming should not exceed 10 degrees C to avoid outgassing when blood is returned to the patient.

Class IIa Recommendations:

• Pulmonary artery or nasopharyngeal temperature recording is reasonable for weaning and immediate post-bypass temperature measurement.
• To achieve the desired temperature for separation from bypass when arterial blood outlet temperature ≥30 degrees C, it is reasonable to maintain a temperature gradient between arterial outlet temperature and the venous inflow of ≤4 degrees C; and also to maintain a rewarming rate ≤0.5 degrees C/min.
• To achieve the desired temperature for separation from bypass when arterial blood outlet temperature <30 degrees C, it is reasonable to maintain a maximal gradient of 10 degrees C between arterial outlet temperature and venous inflow.

The authors made no specific recommendation for an optimal temperature for weaning from CPB "due to inconsistent published evidence."

"Our new guidelines will help improve understanding of the relationship between temperature management and clinical outcomes, particularly its impact on brain function," Engelman said in a press release. "The guidelines also will increase patient awareness about the issue and help begin a dialogue between the patient and the cardiothoracic surgical team prior to surgery."

"We would like to make patients part of the discussion," Engelman told 乌鸦传媒. "For example, a patient might ask, 'Will you be following an appropriate guideline for managing my body temperature to avoid potential brain injury?'"

Engelman and colleagues are working on two other sets of guidelines which may be published next year. One is on reducing the inflammation associated with use of a heart-lung machine to avoid complications related to blood utilization and reduce the need for transfusions. The other details the optimal devices to use within a heart-lung machine for measuring blood temperature and flow.

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