Patients undergoing cardiac surgery can experience significant thermal changes during the perioperative period and, for that reason, it is essential to monitor temperatures with adequate accuracy and precision during cardiopulmonary bypass (CPB). The primary aim of the current study was to measure the discrepancies between temperatures at different body sites during normothermic or mild hypothermic CPB.
48 patients undergoing cardiac surgery participated in our study. Simultaneous temperatures were measured at nasopharynx, pulmonary artery, arterial outlet, venous inlet, forehead using a heat flux sensor, and urinary bladder at 5-min intervals throughout surgery. The Bland-Altman plot for repeated measures was used to assess concordance between methods.
The duration of surgery was 360 min (interquartile range (IQR) 300–412), while the median cross-clamp time was 135 min (IQR 101–169). During the CPB time, the average difference between arterial outlet and nasopharyngeal temperature was −0.16°C (95% limits of agreement of ±0.93). The bias between arterial outlet and the venous inflow was 0.16°C and the 95% limits of agreement were −0.63 to 0.95°C. The Bland-Altman analysis showed an average difference between oxigenator arterial outlet and bladder probe of −0.62 (95% limits of agreement of ±1.3). The average difference between arterial outlet and Tcore™ temperatures was 0.08°C (95% limits of agreement of ±1.46). 25 patients (52.08%) presented nasopharyngeal temperatures higher than 37°C in the post-CPB period, but none of them exceeded 38°C.
Perfusionists should be cautious when using the nasopharyngeal site as the only surrogate of brain temperature, even in normothermic cardiac surgery because the precision of measurements is not entirely adequate.