• Clemens Miller, Anselm Bräuer, Thomas Asendorf, Marielle Ernst, Philipp von Gottberg, Juliane Richter, Leif Saager, and Marcus Nemeth.
• Department of Anesthesiology, University Medical Center Goettingen, Goettingen, Germany.
• Paediatr Anaesth. 2022 Sep 1; 32 (9): 1054-1061.

BackgroundCore temperature monitoring is indispensable to prevent children from perioperative thermal perturbations. Although nasopharyngeal measurements are commonly used in anesthesia and considered to reflect core temperature accurately, standardized target depths for probe insertion are unknown in children.AimsOur primary goal was to determine a target depth of nasopharyngeal temperature probe insertion in children by measuring distances on magnetic resonance imaging (MRI). Secondary aims were to correlate these measurements with biometric variables and facial landmark-distances to derive formulas estimating target depth.MethodsWe conducted a prospective observational study in children ≤12 years undergoing cranial MRI with anesthesia. We documented patient characteristics and measured the landmark-distances nostril-mandible, nostril-tragus, and philtrum-tragus on patient's faces. On MRI, the target point for the probe tip was considered to be the site of the nasopharyngeal mucosa with the closest proximity to the internal carotid artery. After its determination in the transverse axis and triangulation to the sagittal axis, we measured the distance to the nostril. This distance, defined as target insertion depth, was correlated with the patient characteristics and used for univariate and multiple linear regression analysis.ResultsOne hundred twenty children with a mean age of 4.5 years were included. The target insertion depth ranged from 61.8 mm in infants to 89.8 mm in 12-year-old children. Height correlated best (ρ = 0.685, 95%-CI: [0.57-0.77]). The best-fit estimation in millimeters, "40.8 + height [cm] × 0.32,″ would lead to a placement in the target position in 67% of cases. A simplified approach by categories of 50-80, 80-110, 110-130, and >130 cm height with target insertion depths of 60, 70, 80, and 85 mm, respectively, achieved similar probabilities.ConclusionsHeight-based formulas could be a valuable proxy for the insertion depth of nasopharyngeal temperature probes. Further clinical trials are necessary to investigate their measurement accuracy.© 2022 The Authors. Pediatric Anesthesia published by John Wiley & Sons Ltd.

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