Inspired gas temperature during mechanical ventilation: effects of environmental temperature and airway temperature probe position.

Abstract

To determine the inspired gas temperature during mechanical ventilation with: (i) five different humidicrib temperatures; (ii) two airway temperature probe (ATP) positions; and (iii) four ATP adaptors. An observational study in the Neonatal Intensive Care Laboratory, Westmead Hospital. The inspired gas temperature was measured at the proximal end of the endotracheal tube (ETT) during conventional mechanical ventilation using a Tele-thermometer. Inspired gas temperature measurements were made with: (i) the humidicrib temperature set at 30.8. 32.9, 35.2, 36.2. or 37.2 degrees C; (ii) the ATP either (A) positioned inside the humidicrib at the distal end of the inspiratory tubing or (B) positioned outside the humidicrib 50 cm proximal to the ETT, with the inspired gas temperatures set at 36.5 and 39.0 degrees C, respectively; and (iii) the measurements repeated with four different ATP adaptors at each humidicrib temperature and each ATP position. With the ATP inside the humidicrib, there were no significant differences between set and actual inspired gas temperature. However, with the ATP outside the humidicrib, there were significant decreases in inspired gas temperature at each humidicrib temperature. For instance, with the ATP outside the humidicrib and set at 39.0 degrees C, the inspired gas temperature decreased to 34.7+/-0.2 degrees C at a humidicrib temperature of 30.8 degrees C and to 37.7+/-0.2 degrees C at a humidicrib temperature of 37.2 degrees C. The type of ATP adaptor also had a significant effect on inspired gas temperature. With the ATP placed outside the humidicrib and with variations of humidicrib temperature, infants are likely to have inspired gas temperatures that are significantly different to the desired temperature. Certain ATP adaptors cause these variations in inspired gas temperature to be more pronounced. Extreme care must be used to avoid suboptimal inspired gas temperatures with these environmental variations and the ATP positioned outside the humidicrib.