Optimal Positioning of Nasopharyngeal Temperature Probes: A Prospective Cohort Study

Low body temperature (hypothermia) is often observed in anesthetized patients. Mild
hypothermia increases complications such as surgical blood loss, postanesthesia recovery and
the duration of hospitalization. To assess body temperature and minimize hypothermia-related
complications, it is important to have accurate and reliable methods of measuring
intraoperative core temperature. Common practice is to insert a nasopharyngeal (back of the
throat from the nose) probe through one of the nostrils. However, there is no consensus or
guideline regarding how deep the nasopharyngeal probe needs to be inserted. This study is
being done to determine the insertion depth (or range of depths) that best approximates core
temperature, which is temperature of the vital organs, e.g. heart, liver and lungs.

Participation in the trial will occur on the day of surgery. The subject will be asked to
breathe through one nostril and then the other before receiving anesthesia. The less
congested nostril will be selected for study. If there is no difference, then the
investigator will use the right nostril.

Once under anesthesia, an esophageal temperature probe will be inserted to serve as a
reference core temperature, which is used routinely in surgery. Then the nasopharyngeal
probe will be inserted into the nostril.

Both nasopharyngeal and esophageal temperatures will initially be recorded 45 minutes after
anesthetic induction. The nasopharyngeal probe will then be withdrawn 2 cm and after a
3-minute equilibration period, nasopharyngeal and esophageal temperatures will again be
recorded. The nasopharyngeal probe withdrawal sequence will be repeated, 2 cm at a time,
until only 2 cm remains in the nostril. There will be a total of 10 sets of nasopharyngeal
and esophageal temperatures obtained.