Humidity in Children and Adults Using the Controlled Partial Rebreathing Anesthesia Method

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Abstract
Inspired humidity was examined using a controlled partial rebreathing anesthesia method (CPRAM) and a circle system in 16 healthy adults and 5 healthy children. The patients were divided into 5 study groups (A-E). All patients except those in Group E were anesthetized with fentanyl, pancuronium, nitrous oxide-oxygen, 66-33%, and their lungs were mechanically ventilated; patients in Group E received halothane and N2O-O2, 66-33%, with spontaneous ventilation. Group A (5 children) had inspired humidity measured within a modified coaxial (Bain) anesthesia circuit using CPRAM. Groups B and C (5 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 (3 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 2 h by interrupting the controlled ventilation at 30 min intervals, except in patients of Group E, who had humidity measured at similar intervals for 2 h 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/l.

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