Methodological investigation of measuring nasopharyngeal temperature as noninvasive brain temperature analogue in the neonate

Objectives: (a) To investigate in a newborn animal model whether nasopharyn geal temperature is more closely related to epidural brain temperature than rectal temperature and (b) to investigate in human neonates whether measur ement of nasopharyngeal temperature is dependent on the measurement site an d other conditions. Design and setting: (a) Animal experiment in newborn piglets, at an institu te for surgical research, (b) Prospective study in human neonates, at a neo natal intensive care unit of a tertiary care university hospital. Animals and patients: (a) Nineteen tracheostomized ventilated newborn pigle ts (b) Twenty-two spontaneously breathing human newborns nursed either in a n incubator or a cot. Measurements and results: (a) In the piglets nasopharyngeal temperature (T- nasoph) measured at the nose-ear distance, defined as distance from the inn er brim of the nostril to the tragus and inner rim of the meatus accusticus , most closely reflected epidural temperature (T-epidur) at the epidural su rface (r(2) = 0.89), followed by skin temperature at the temple. rectal tem perature (T-rectum) at 2 cm depth, and esophageal temperature (T-esoph) in the middle esophagus, T-nasoph did not significantly differ before and afte r tracheostomy. (b) In the newborns T-nasoph was significantly lower than T -rectum. Measurements of T-nasoph at nose-ear distance within a feeding tub e had a high precision and were unaffected by breathing or head turning A n asopharyngeal probe was imaged by magnetic resonance imaging in four newbor ns of various body weight. its tip when inserted to a depth equal to nose-e ar distance was anatomically closest to the brain base but separated from i t by tissue layer 2.2 cm thick. Conclusions. T-nasoph measured at a position anatomically closest to the br ain reflects epidural brain temperature more closely than T-rectum. When me asured at nose-ear distance it is unaffected by breathing or head turning. Measuring T-nasoph within a feeding tube and standardizing the measuring po sition is crucial for its use as brain temperature analogue.