THE EFFECT OF HEATED WIRE CIRCUITS ON HUMIDIFICATION OF INSPIRED GASES

We performed this study to determine the effect of heated wire circuit s on humidity delivered by several humidifiers commonly used during an esthesia. Humidifier bases from three manufacturers with several humid ifying chambers for each base were tested using both heated and unheat ed circuits. Delivered humidity and circuit temperature were measured at the distal end of the circuit. Each chamber was tested under both c ontinuous flow (CF) and intermittent flow (IF) conditions. IF was prov ided by a Servo 900 B ventilator. Adjustments of flow and volume were made for pediatric chambers. At 90 L/m CF, humidifier performance was unsatisfactory with both heated and unheated circuits. At 15 and 45 L/ m CE both distal circuit temperature (DCT) and humidity were within ac ceptable limits; unheated circuits delivered more humidity than heated circuits (P < 0.05). Relative humidity was lower at 45 L/m CF than at 15 L/m (P < 0.05). During IF while all chambers provided satisfactory humidity, humidity was greater when unheated circuits were used. We c onclude that when heated circuits are used, humidifying systems may fa il to deliver 100% humidity to patients.