Internal Temperature of Neonatal Endotracheal Tube Predicted by Infrared Thermography: A Neonatal Bench Study

Neonatal ventilators are managed by monitoring the inspiratory gas temperature with a probe placed outside the incubator, although the temperature decreases as the gases passe through the ventilator circuit extension tube and endotracheal tube (ETT). There are no established methods for measuring the internal temperature of the ETT. This bench study aimed to investigate the feasibility of using infrared thermography (IRT) to predict the internal temperature of the ETT.

A new method for predicting the internal ETT temperature using an IRT camera was established, and its accuracy and reliability were evaluated under various conditions. The external surface temperature of the ETT was measured with IRT, and the internal temperature was measured with thin thermocouples, which has minimal effect on ventilation and served as a true value. Temperature measurements were taken at two points, distal and proximal, respectively, to capture temperature changes during passage of gases through the ETT.

This method allowed prediction of the internal ETT temperature with high accuracy (R² _Adj = 0.946 and 0.974 at the proximal and distal ends, respectively). The internal and external temperatures of the ETT were related to the incubator temperature and ventilator mode. The effects of the size of the ETT, the set temperature of the constant-temperature tank, and the heated humidifier temperature were limited.

This non-contact method of internal temperature prediction allows continuous monitoring without interfering with ventilation, and will help airway management in the neonatal intensive care unit.