The susceptibility of thermistor-based esophageal temperature probes to errors caused by electrically conductive fluids (artificial saliva)

Several brands of esophageal stethoscopes with thermistor-based thermometers were tested to determine the susceptibility of the probe connector to contamination by oral secretions. A solution of half normal saline and 1% carboxy-methyl-cellulose was used to model the conductivity and viscosity of saliva. When 1 ml of test solution was allowed to track down the probe wires to the connector, several brands of thermistors gave erroneously elevated readings. The mean changes in temperature according to brand of thermistor were as follows: Electromedics, 0.1 +/- 0.1 degree C; Mallinckrodt, 1.7 +/- 0.8 degrees C; Respiratory Products, 0.1 +/- 0.2 degrees C; Sheridan, 3.6 +/- 1.9 degrees C; Vital Signs, 4.8 +/- 1.3 degrees C (peak) and 1.4 +/- 1.6 degrees C (final); and Yellow Springs, 0.9 +/- 0.4 degrees C. The manufacturers of the probes susceptible to this type of error should implement the appropriate design modifications. In the meantime, clinicians should be aware of this problem and may choose to prevent these errors by wrapping the connection with waterproof tape.