Zero-heat flux skin temperature tracks nasopharyngeal temperature during cardiac surgery with cardiopulmonary bypass: a prospective observational study

Background Monitoring both nasopharyngeal temperature (T NP ) and arterial blood temperature at the CPB arterial outlet is routinely used in cardiac surgery with cardiopulmonary bypass (CPB). We examined the agreement and temperature tracking ability of zero-heat-flux skin temperature (T ZHF ) compared with T NP in cardiac surgery. Methods Of 40 patients scheduled to undergo cardiac surgery with CPB, paired T ZHF and T NP measurements were recorded for 33 patients, yielding 8610 measurements across pre-CPB, CPB-cooling, CPB-maintenance, CPB-rewarming, and post-CPB. Results In the final, trimmed dataset, T ZHF and T NP at 30 min after CPB weaning, the primary endpoint, showed similar mean values (35.57 ± 0.69 °C vs. 35.69 ± 0.61 °C; P = 0.181), with a mean difference of –0.12 °C (95% Confidence Interval: –0.29 to 0.06). Bland–Altman analysis showed a small mean bias between T ZHF and T NP across all intraoperative phases, ranging from − 0.55 to 0.28 °C. However, the limits of agreement (LOA) exceeded the clinically acceptable ± 0.5 °C during CPB-cooling and CPB-rewarming. Mixed-effects modeling showed considerable between-patient variability in the difference between T ZHF and T NP measurements during periods of rapid temperature change. Consistent with the Bland–Altman results, correlation coefficients between T ZHF and T NP measurements remained high (ranging from 0.798 to 0.958), and their intraclass correlation coefficients were high (ranging from 0.82 to 0.99) across all intraoperative phases. Conclusions Our results indicate that T ZHF tracked T NP trends, but its large LOA limits its accuracy and reliability. Simultaneous blood temperature monitoring would enhance T ZHF ’s effectiveness, as is currently done in cardiac surgery, where both blood temperature and T NP are monitored. Trial registration ClinicalTrials.gov Identifier: NCT04160845.