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

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.

Inclusion criteria

• Age ≥ 18 years
• We will include 3 independent groups of patients receiving general anesthesia with tracheal intubation:

Group 1: Cardiac surgery Group 2: Thoracic surgery Group 3: General surgery, including neurosurgery

• Expected surgical duration ≥ 60 minutes
• ASA Physical Status Classification I- III
• Able to provide written informed consent

Exclusion criteria

• Prior nasal surgery, nasal polyps, deviated nasal septum, or significant epistaxis history precluding safe nasopharyngeal probe insertion
• Otitis media, tympanic membrane perforation, significant cerumen impaction, or external auditory canal deformity that would prevent reliable infrared tympanic temperature measurement
• Facial or forehead skin lesions, burns, or known adhesive hypersensitivity at the planned 3M SpotOn™ application site, craniotomy, and head and neck surgery.
• Baseline core temperature < 35.0°C or > 38.5°C at preoperative assessment
• Planned use of neuraxial anesthesia as the primary or adjunct technique
• Emergency procedures, pregnancy, or procedures involving deliberate hypothermia or cardiopulmonary bypass.