Passive or active inspired gas humidification increases thermal steady-state temperatures in anesthetized infants

We tested the hypothesis that active and passive airway humidification minimize hypothermia in infants, but that maintaining normothermia does not decrease the duration of postoperative recovery. A circle system was used to ventilate the lungs of anesthetized, intubated infants who were randomly assigned to active airway humidification and warming with use of an MR450 Servo airway heater and humidifier set at 37 degrees C (n = 10), passive airway humidification with use of the Humid-Vent Mini heat and moisture exchanger placed between the Y-piece of the circle and the endotracheal tube (n = 10), or no airway humidification and heating (control, n = 10). Anesthesia was induced with thiopental and maintained with isoflurane and nitrous oxide in oxygen. The relative humidity of inspired respiratory gases was approximately 35% in the control group and approximately 90% in the group undergoing active airway humidification. Initial inspired humidity in the passive humidification group (45%) increased to approximately 80% after 1 h of anesthesia. Humidity differed significantly across groups at all times (P less than or equal to 0.05). Steady-state rectal temperatures (100-120 min after induction) were 36.2 +/- 0.7 degrees C in patients given active humidification and heating, 35.7 +/- 0.9 degrees C in the passively humidified group, and 35.2 +/- 0.4 degrees C in the control group (P less than or equal to 0.05 between each group). Recovery from general anesthesia was rapid in all patients and did not correlate with central temperature changes or type of humidification (P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)