Depression of sublingual temperature by cold saliva

Area of Science:

• Physiology
• Thermometry
• Environmental Health

Background:

• Accurate body temperature measurement is crucial for clinical diagnosis and patient monitoring.
• Sublingual temperature is a commonly used proxy for core body temperature, but its reliability under varying environmental conditions is not fully understood.

Purpose of the Study:

• To compare sublingual and esophageal temperatures across a range of ambient air temperatures.
• To investigate factors influencing the accuracy of sublingual temperature measurements, particularly in cold conditions.

Main Methods:

• 16 healthy subjects were exposed to various air temperatures (5-44°C).
• Sublingual and esophageal temperatures were recorded simultaneously.
• Factors such as facial warmth and breathing route (tracheostomy) were manipulated.
• Parotid saliva temperature and flow rate were measured.

Main Results:

• In warm air (25-44°C), sublingual temperatures closely matched esophageal temperatures (±0.45°C).
• In cold air (5-10°C), sublingual temperatures were significantly lower than esophageal temperatures (up to 4.4°C difference).
• Keeping the face warm reduced the temperature difference in the cold, while tracheostomies did not.
• Low parotid saliva temperature and high flow rate in the cold were identified as primary causes for sublingual temperature depression.

Conclusions:

• Casual use of sublingual temperature measurements carries significant risks, especially in cold environments.
• Cold saliva significantly depresses sublingual temperature readings, leading to inaccurate core body temperature assessment.
• External heat application may be necessary to ensure reliable clinical assessments using sublingual thermometers in challenging conditions.