Accuracy of Nasopharyngeal Temperature in Comparison to Oesophageal Temperature for Core Body Temperature Measurement: A Cross-sectional Observational Study

Abstract

Introduction: Temperature monitoring intraoperatively is standard of care for almost all surgical cases and is necessary due to the important role that temperature plays in maintaining body homeostasis, anaesthetic drug metabolism, and recovery. However, invasive and user-unfriendly methods like measuring temperature in the oesophagus, tympanic membrane, or rectum have limitations. An alternative site for measuring core body temperature could be the nasopharynx, as its mucosa is supplied by branches of the internal carotid artery. Aim: To determine the accuracy of the nasopharyngeal probe in comparison to oesophageal temperature probe and to identify appropriate insertion depths for measuring core body temperature. Materials and Methods: Sixty patients scheduled for elective non-cardiac surgery under general anaesthesia lasting 60 minutes or more. A nasopharyngeal probe was inserted past the nares to a depth of 20 cm, and an oesophageal temperature probe was inserted to a depth of 40 cm past the incisors. The nasopharyngeal probe was gradually pulled out after induction, and temperatures at various depths were recorded at regular intervals. The observed depths of the nasopharyngeal probe that correlated with the oesophageal temperature were considered as the endpoints. Data was entered into Microsoft Excel and analysed using Statistical Package for Social Sciences (SPSS) version 25.0. Results: The study population consisted of 60 patients, with 31 males and 29 females, a mean age of 50 years, mean body mass index of 26 kg/m2 , American Society of Anaesthesiologists (ASA) (physical status) of 1 (n=27) and 2 (n=33). The insertion depths of 10 to 20 cm for the nasopharyngeal probe showed a mean temperature difference of ±0.3°C compared to the reference oesophageal temperature. This difference fell within the clinically acceptable accuracy range of 0 to 0.3°C (temperature mean difference ±1.96 SD) for both probes. Conclusion: The nasopharyngeal probe offers a minimally invasive method for measuring body temperature and is easily accessible for probe placement. However, the optimal depth of insertion past the nares has not been well established. Based on the results, which showed that the mean temperature difference between the two probes fell within the specified accuracy range when the nasopharyngeal probe was inserted to a depth range of 10 to 20 cm from the nares, it is advisable to use this depth range for core body temperature measurement in non cardiac surgeries.