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.
Age ≥ 18 years
Expected surgical duration ≥ 60 minutes
ASA Physical Status Classification I- III
Able to provide written informed consent
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
Adult patients scheduled for elective surgery under general anesthesia with tracheal intubation at Srinagarind Hospital and Queen Sirikit Heart Center of the Northeast, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand, with expected surgical duration ≥ 60 minutes and ASA Physical Status I-III.
Cohort
Prospective
Not listed
Limits of Agreement Between Each Test Method and the Nasopharyngeal Probe
The 95% limits of agreement (LoA = Bias ± 1.96 × SD\_total) between (i) the TaiDoc TD-1261 infrared tympanic thermometer and the nasopharyngeal probe, and (ii) the 3M SpotOn™ sensor and the nasopharyngeal probe, estimated by repeated-measures Bland-Altman analysis. Pre-specified clinical acceptability criterion: LoA must be contained within ±0.5°C with both 95% CI limits of the upper and lower LoA falling within this range.
Systematic Bias (Mean Difference) of Each Test Method vs. NP Probe
Mean difference (°C) with 95% CI between each test method and the NP probe across all paired observations, estimated from the repeated-measures Bland-Altman model
Proportional Bias Assessment
Linear regression of the difference (test - reference) on the mean of both methods, with cluster-robust standard errors; Pitman's test for correlation between sum and difference
Sensitivity and Specificity for Hypothermia Detection
Sensitivity, specificity, PPV, and NPV of each test method for detecting intraoperative hypothermia defined as NP temperature \< 36.0°C, with AUROC estimated by DeLong's method
Intraclass Correlation Coefficient
ICC (two-way mixed-effects model, absolute agreement) with 95% CI for each method pair
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