Optimal Positioning of Nasopharyngeal Temperature Probes

Core temperature is of greatest interest in terms of temperature monitoring as it is thought to represent the temperature of the vessel-rich groups that are instrumental in thermoregulatory control. The nasopharynx is among the recommended temperature monitoring sites for core body temperature. It is the part of the pharynx that lies above the soft palate. Anteriorly it opens to the nasal cavities through the choanae; inferiorly it communicates with the oropharynx through the pharyngeal isthmus. Nasopharyngeal temperatures are accurate in adults when probes are inserted between 10 and 20 cm. The optimal depth for insertion of nasopharyngeal probes remains poorly defined in infants and children. While some data suggest that anthropometric measurements are well correlated with endoscopic measurements in infants based on weight, the accuracy of temperature measurements at these and other distances has yet to be quantified. The investigators thus propose to determine the insertion depth (or range of depths) for nasopharyngeal temperature proves that best approximate core temperature as measured in the distal esophagus in infants and children of various sizes. The comparison site will be the distal esophagus since there is broad consensus that the distal third of the esophagus it at core-body temperature. For the two groups of infants aged up to twelve months, the nasopharyngeal probe will be marked with indelible ink from 2-10 cm in 1-cm increments and inserted 10 cm. For the two groups of children between 1 and 5 years, the nasopharyngeal probe will be marked with indelible ink from 2-15 cm in 1.5-cm increments and inserted 10 cm. For older children, a nasopharyngeal probe will be marked with indelible ink from 2 to 20 cm at 2 cm increments from its tip, and inserted 20 cm. Both nasopharyngeal and esophageal temperatures will initially be recorded 30 minutes after induction of anesthesia. Nasopharyngeal probes will then be withdrawn at the designated increment for e