Agreement Among Three Methods of Intraoperative Core Temperature Monitoring: Nasopharyngeal Probe, TaiDoc TD-1261 Infrared Tympanic Thermometer, and 3M SpotOn™ Skin Sensor

Overview

Keeping a patient's body temperature normal during surgery is an important part of safe anesthetic care. When the body temperature drops below 36°C (called inadvertent perioperative hypothermia), patients face higher risks of bleeding, wound infection, heart problems, and a slower recovery. To prevent these complications, anesthesiologists monitor core body temperature continuously during surgery. Three monitoring methods are commonly used in clinical practice: (1) a nasopharyngeal probe - a small soft sensor inserted through the nose and placed at the back of the throat, which provides continuous readings and is considered the gold standard; (2) an infrared tympanic thermometer (TaiDoc TD-1261) - a handheld device that measures ear temperature in about one second; and (3) the 3M SpotOn™ sensor - a non-invasive adhesive patch placed on the forehead that continuously estimates core temperature without requiring insertion into any body cavity. Although all three methods are used interchangeably at Srinagarind Hospital, no study has directly compared all three simultaneously in the same patient to determine how well they agree with each other. If significant differences exist between methods, a clinician who switches from one device to another may unknowingly under-detect or over-estimate hypothermia. This study will enroll 92 adult patients scheduled for elective surgery under general anesthesia at Srinagarind Hospital, Khon Kaen University. All three temperature sensors will be applied at the same time, and readings will be recorded simultaneously every 15 minutes throughout the operation. The main goal is to determine whether each device gives results close enough to the nasopharyngeal probe to be safely used as an alternative. The study is observational - no medications or procedures will be added to routine care.

Background: Inadvertent perioperative hypothermia (IPH), defined as a core body temperature \< 36.0°C, affects 20-90% of patients undergoing general anesthesia and is associated with coagulopathy, surgical site infection, morbid cardiac events, and prolonged drug metabolism. Accurate intraoperative temperature monitoring is mandated by professional society guidelines. Study design: Prospective, single-center, triple-method observational agreement study at Srinagarind Hospital, Khon Kaen University, Thailand. All three thermometry modalities are applied simultaneously in each participant. No intervention is assigned; temperature monitoring is additional to standard perioperative care. Methods: After induction of general anesthesia and tracheal intubation, the nasopharyngeal (NP) probe (reference standard), TaiDoc TD-1261 infrared tympanic thermometer (test method 1), and 3M SpotOn™ zero-heat-flux forehead sensor (test method 2) are placed. Simultaneous temperature readings are recorded at 15-minute intervals from 15 minutes after induction until surgery end. For the TD-1261, two consecutive readings are taken at each time point and averaged; pinna retraction and fresh disposable probe cover are used at every measurement. The SpotOn™ sensor requires a 10-minute equilibration period before the first recorded value. Statistical analysis: Primary analysis uses repeated-measures Bland-Altman analysis (Myles \& Cui, 2007 framework) to estimate bias and limits of agreement (LoA) for each method pair against the NP probe. Pre-specified clinical acceptability criterion: LoA within ±0.5°C (Sessler, 2008). Variance of differences is decomposed into between-subject (σ²\_B) and within-subject (σ²\_W) components. Secondary analyses: proportional bias assessment, sensitivity/specificity for hypothermia detection (NP \< 36.0°C), intraclass correlation coefficient (ICC, two-way mixed-effects model), and multivariable linear mixed-effects regression for clinical covariates. Sample size: 92 patients (Lu et al., 2016 method; 80% power; α = 0.05; SD of differences = 0.30°C for NP vs. TM; LoA acceptability threshold ±0.50°C; 15% dropout allowance). This study provides the first institution-specific, population-specific evidence on temperature monitoring agreement in Thai surgical patients and constitutes the first published intraoperative validation of the TaiDoc TD-1261 infrared tympanic thermometer.