Humidity in children and adults using the controlled partial rebreathing anesthesia method.

The authors examined inspired humidity using a controlled partial rebreathing anesthesia method (CPRAM) and a circle system in 16 healthy adults and five healthy children. The patients were divided into five study groups (A-E). All patients except those in Group E were anesthetized with fentanyl, pancuronium, nitrous oxide-oxygen, 66-33 per cent, and their lungs were mechanically ventilated; patients in Group E received halothane and nitrous oxide-oxygen, 66-33 per cent, with spontaneous ventilation. Group A (five children) had inspired hummidity measured within a modified coaxial (Bain) anesthesia circuit using CPRAM. Groups B and C (five adults each) had humidity measured within the modified coaxial circuit and at the end of a non-modified coaxial circuit using CPRAM. Groups D and E (three adults each) had humidity measured in the semi-closed and closed circle systems, respectively. Initial, mid-, and end-inspired humidity were measured in all groups for two hours by interrupting the controlled ventilation at 30-min intervals, except in patients of Group E, who had humidity measured at similar intervals for two hours during spontaneous ventilation. No significant difference was found among initial, mid-, or end-inspired humidity, nor was there a significant difference between inspired humidities in children and in adults using CPRAM. The humidity measured in adults within the circuit near the endotracheal tube was not significantly different from that measured distal to the fresh gas flow. The humidities in all CPRAM patients exceeded those of both the semiclosed and closed circle systems, stabilizing within 30 min and remaining constant between 24 and 26 mg H2O/1.