Cardiopulmonary Bypass Temperature Monitoring Sites

During cardiopulmonary bypass, hypothermia is deliberately employed for cellular protection, particularly of the heart and brain. Temperature is often monitored at several different sites simultaneously. The goal is to measure blood, core, and shell temperature simultaneously.

Blood temperature is typically measured either by a thermistor on the end of a PA catheter, or by the bypass machine itself. This temperature is the quickest to change, as heat is added or removed by the perfusionist directly to the blood.

Core temperature is generally measured at either the tympanic membrane, or more commonly, in the nasopharynx or oropharynx. The core temperature is thought to be that which most closely approximates the vital organs, and is often the “target” temperature for determining adequate rewarming prior to separation from CPB.

Shell temperature is most often measured at the bladder, though occasionally also via the rectum. Bladder temperature measurements can be inaccurate in settings of low urine output, and rectal temperature can be inaccurate if the probe rests in stool. The shell temperature is considered to represent the rest of the body that is not as metabolically active as the vital organs, and acts as a sort of heat sink that lags behind the core in the rewarming process as a result.