The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

VARIATIONS IN INSPIRED GAS TEMPERATURES IN NEONATAL VENTILATION

Stephen G. Staib1



Background: It has been noted that there is a variation in the inspired gas temperature depending on the position of the temperature probe in the neonatal ventilator circuit.

Objective: To determine the actual inspired gas temperature going to the neonatal ventilator patient.

Method: First, bench testing was performed with a neonatal lung, neonatal ventilator,and circuit. Temperature probes were placed in the normal position and at the patient wye for intubated patients and four centimeters from the nasal prongs for the cpap patient. The neonatal lung was placed first in a radiant warmer and then into an isolette, five times each. The temperature was monitored for one hour and the results recorded. There was a drop of three to four degrees (celcius) in the radiant warmer (37°C at the probe located in the normal position and 33.6°C at the patient wye) and one to two degrees in the isolette (37°c vs 35.5°C at the patient wye).
Second, ninety-two patients were tested (31 intubated and 61 on nasal prongs). The circuit was set up as above, the humidifier was set at thirty-seven degrees celcius and the patients were monitored for one hour each. Results; The temperature of the probe located at the normal position read thirty-seven degrees celcius in both the patients in the radiant warmer and the patients in the isolette. The second probe located near the patient wye (or the nasal prongs) showed a drop of 3.4°-5°C for the patients in the radiant warmer (32.0°C-33.6°C), and a drop of 1.7°C-3.5°C for the patients in the isolette (33.5°C-35.3°C).

Conclusion: The temperature drop, shown by the probe at the patient wye (or prongs) shows that there is a heat loss that the neonatal patient would have to make up. It also shows that placing neonatal ventilator patients in isolettes may be the best way to reduce loss of heat in the ventilator circuit. Trying to increase the heat of the of the humidifier to compensate for the heat loss may lead to overheating of the patient and increasing condensation in the circuit. Moving the temperature probe closer to the patient may be the best option to reduce this heat loss.