Effects of ThermH2Osorb carbon dioxide absorber on temperature and humidity in the anesthetic circuit.

Abstract

To the Editor: We studied the efficiency of the ThermH2 Osorb[R] CO2 absorber (Raincoat Corp., Louisville, KY), a product designed to be placed immediately distal to the inspiratory valve of the anesthetic machine to heat and humidify the inspiratory gas mixture (Figure 1).Figure 1: ThermH2 Osorb[R] CO2 absorber and breathing circuit.Eighteen adults, 18-65 yr old, ASA grades I-II, scheduled for elective operations under general endotracheal anesthesia, were recruited. Patients were randomly assigned to a group using a standard CO2 absorber (n = 8) or those using the ThermH2 Osorb[R] CO2 absorber (n = 10). Using a Narkomed 2B[R] anesthesia machine (North American Drager, Telford, PA), anesthesia was induced with thiopental and maintained with isoflurane and 50% nitrous oxide. The total anesthetic gas flow was 4 L/min. The end-tidal CO2 was maintained between 28 and 32 mm Hg. Temperature was measured by scanning thermocouples (Cole-Parmer Instrument Co., Chicago, IL) inserted into the anesthetic circuit at the proximal and distal ends of the inspiratory and expiratory limbs. Humidity was measured at 5 cm from the distal end of the inspiratory limb by a HT-201 Hygro-Thermometer[R] (Elan Technical Corp., Fairfield, CT). Temperature and humidity were measured before induction of anesthesia with oxygen flow at the rate of 4 L/min, and 1, 6, 11, 16, 31, and 61 min after the induction. There were significant differences between groups and over time in temperature (P < 0.01) and humidity (P < 0.05) in the inspiratory limb, as measured using analysis of variance for repeated measures (Table 1). The temperature in the inspiratory proximal limb was significantly higher in the ThermH2 Osorb[R] CO2 absorber circuit than that in the control circuit at 31 and 61 min (P < 0.05), and the humidity was approximately twice as high as that in the control circuit at all measurements (P < 0.001). The body temperature, the room temperature, and the ambient humidity were 36.1 +/- 0.7 degrees C, 20.4 +/- 0.9 degrees C, and 0.39% +/- 0.1%, respectively). The ThermH2 Osorb[R] system was more effective in humidifying the inspiratory gas than was the conventional system.Table 1: Temperature (degrees C) in the Inspiratory and Expiratory Limbs of Breathing Circuit and Humidity (%) in the Distal Portion of the Inspiratory Limb in the Control (n = 8) and ThermH2 Osorb[R] CO2 Absorber (Therm) (n = 10) GroupsPhillip J. Mosca, MD Gary E. Loyd, MD Kentaro Tsueda, MD Department of Anesthesiology; University of Louisville, School of Medicine; Louisville, KY 40292