Target insertion depth of nasopharyngeal temperature probes in children: A prospective observational study analyzing magnetic resonance images

Background Core 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. Aims Our 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. Methods We 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. Results One 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 (rho = 0.685, 95%-CI: [0.57-0.77]). The best-fit estimation in millimeters, 40.8 + height [cm] x 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. Conclusions Height-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.

Automated summary

This study aimed to determine the target depth of nasopharyngeal temperature probe insertion in children by measuring distances on magnetic resonance imaging. The results showed that height had the strongest correlation with insertion depth, and a formula of 40.8 + height [cm] x 0.32 could achieve the target position in 67% of cases. Categorizing height ranges and corresponding insertion depths also achieved similar probabilities.