Temperature Management on Cardiopulmonary Bypass LORRAINE BROWNE TRAINEE PERFUSIONIST CORK UNIVERSITY HOSPITAL

Introduction Important variable in cardiac surgery “The safe conduct of CPB requires the clinical perfusionist to measure and control…. blood temperature…. during the period of bypass” – Guide to Good Practice Neuroprotection, myocardial protection, etc AIM: To understand current temperature measurement and monitoring practices, during adult cardiac surgery, using CPB, in Great Britain and Ireland

Our Research Survey Temperature measurement sites Temperature management Minimum/maximum temperatures reached on bypass Rewarming techniques We developed a survey using a web-based programme (Google Forms). The questionnaire consisted of multiple choice and short answer questions referring to routine adult cases (CABG/AVR) undergoing cardiac surgery using CPB.

Temperature Monitoring Sites Sites typically used to monitor temperature and determine the target temperature for patient cooling and rewarming are shown here. Every centre used more than one monitoring site, be it naso and bladder or naso and aterial outlet, etc. 74% - Significant difference between monitoring sites As you can see, there is a wide variation between the many centres in their temperature monitoring sites. NASOPHARYNGEAL TYMPANIC VENOUS INLET PROBE BMU 40 BLADDER OTHER (SKIN) OXYGENATOR OUTLET PROBE SPECTRUM OESOPHAGEAL CDI 500 OTHER

Research carried out by Nussmeier et al explains the differences in monitoring sites. They found that the JB is a reasonable approximation of global brain temperature. This may be due to the rapid cerebral blood flow during rewarming, and the proximity of the carotids to the aortic cannula. They found that when cooling, it was overestimated, suggesting that the brain may not be as cool as we think, and when rewarming, it was underestimated, meaning we could possibly be over heating our patients. Found significant differences between JB venous temp and temperatures in the np and oesophageal, and there were even larger differences between JB temperature and temperatures in the rectum and bladder. Monitoring bladder or rectal temp to estimate “core” temp is standard practice in many institutions. if bladder or rectal temperatures are brought to 37C, brain temp is likely to be 2-4C higher. Np and oesophageal sites were consistently better than the rectal or bladder sites, just ~2C off. Nussmeier and colleagues recognised the importance of the arterial outlet blood temperature from the oxygenator. They found that this temperature site was the most accurate in reflecting cerebral temperature, as it correlated the best with the JB temperature. JB AND ART OUTLET = CEREBRAL, THE NEAREST WE HAVE IS ARTERIAL OUTLET. JB IS GOLD STANDARD MENTION <37

Temperature Management Hypothermia Mild: 32-35°C Moderate: 28-32°C Deep: <28°C (Saad & Aladawy, 2013) 62.5% % CENTRES -protect the brain -reducing the oxygen requirements Even a relatively small degree of hypothermia, 2-3C, can offer significant brain protection. ACTIVELY COOL: our job to control temperature and have a heater cooler unit to control it ALLOW TO DRIFT: ensure equalisation of temperature throughout the body rather than aggressive cooling targeting a specific area. If doing a cabg, by the time the mammary is down and they’ve cannulated, the chest is open, so patient has already drifted to ~34C. % CENTRES COOL & DRIFT COOL DRIFT LOWEST CORE TEMPERATURE (°C)

Rewarming Detrimental effects of hypothermia Post-op neurocognitive dysfunction Hyperthermia Faster rewarming - neurocognitive dysfunction (Grigore et al, 2009) Limit arterial temperature to 37°C (Shann et al, 2009) MEAN REWARMING TIME % CENTRES -Avoid detrimental effects… -Can exacerabate post-op… Hyperthermia, even if mild (2-3C), is deleterious during cerebral ischaemia. Those rewarmed faster endured higher peak temps with a mean greater than 37 than those rewarmed slower and at lower peak temps THI (Nussmeier, 2005)- Mean rewarming time 38 min ART OUTLET 37 REWARMING TIME (MINUTES)

Minimum temperature deemed acceptable to separate from CPB NASOPHARYNGEAL BLADDER 36.5°C 35°C In most centres, patients are typically rewarmed to a target temperature between 36-37C, at the target monitoring site before separation from CPB Limiting the arterial line temperature to 37C might be useful for avoiding cerebral hyperthermia during CPB.

PARTIALLY REWARMED PRIOR TO CROSS CLAMP REMOVAL Rewarming PARTIALLY REWARMED PRIOR TO CROSS CLAMP REMOVAL Neuropsychological injury – microemboli (Pugsley et al, 1994) High % emboli – early/late CPB phase Cannulation Initiation of CPB Cross-clamp (Van der Linden & Casimir-Ann, 1991) So when do we start to rewarm? While this may seem advantageous, as the patient will be separated from bypass sooner than if rewarming was started after cross-clamp removal, there is one issue… Therefore, by initiating rewarming prior to cross clamp removal, are we really protecting the patient’s brain from neurological damage? YES NO

Heater Cooler Unit MAXIMUM TEMPERATURE SET ON HCU % OF CENTRES These machines are efficient and do not need to be set at exceedingly high temperatures to reach a target temperature for full rewarming. When you set the temperature on your HCU when you’ve started rewarming, you’ll notice that it only takes a short amount of time for the arterial temperature to shoot up, often times above 37C. Remembering back to what was discussed earlier, arterial temperature should go no higher than 37C, as in doing so, one may be exposing the brain to higher temperatures. One paper recommended setting the HCU no higher than 37 (PAPER?) MAQUET HCU 30 SORIN 3T (LIVANOVA) MAXIMUM TEMPERATURE SET ON HCU (°C) MAQUET HCU 40 MAQUET HCU 20

Has this temperature protocol been changed in the past ten years? ENGELMAN’S RECOMMENDATIONS: CLASS I RECOMMENDATIONS: The oxygenator arterial outlet blood temperature is recommended to be used as a surrogate for cerebral temperature measurement during cardiopulmonary bypass. 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 <37C to avoid cerebral hyperthermia. Temperature gradients between the arterial outlet and venous inflow on the oxygenator during CPB cooling should not exceed 10C to avoid generation of gaseous emboli. Temperature gradients between the arterial outlet and venous inflow on the oxygenator during CPB rewarming should not exceed 10C to avoid outgassing when blood is returned to the patient. CLASS IIA RECOMMENDATIONS: Pulmonary artery (PA) or nasopharyngeal temperature recording is reasonable for weaning and immediate postbypass temperature measurement Rewarming when arterial blood outlet temperature is greater than or equal to 30C: To achieve the desired temperature for separation from bypass, it is reasonable to maintain a temperature gradient between arterial outlet temperature and the venous inflow of less than or equal to 4C. To achieve the desired temperature for separation from bypass, it is reasonable to maintain a rewarming rate of less than or equal to 5C/min. YES NO

Conclusion Temperature management & monitoring practices are evolving Mild-moderate systemic hypothermia Significant variation between centres Target temperatures (cooling/rewarming) Monitoring sites Lack of definitive evidence & lack of uniformity Research recommendations: Arterial outlet Limit to < 37°C to avoid hyperthermia REWARMING

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