The Science Journal of the American Association for Respiratory Care

1998 OPEN FORUM Abstracts

COMPARISON OF CONVENTIONAL HEATED HUMIDIFICATION TO A NEW ACTIVE HEAT AND MOISTURE EXCHANGER IN THE ICU.

Richard D. Branson BA RRT, Robert S. Campbell, RRT, Michael Ottaway BS, EMT-P, Jay A. Johannigman. University of Cincinnati, Department of Surgery.

Background: Heated humidification (HH) is commonly used with or without a heated wire circuit (HWC) to humidify inspired gases during mechanical ventilation (MV). We compared HH and HH with a HWC to a new active heat & moisture exchanger (AHME). The AHME (Gibeck, Sweden) consists of a typical HME and a heat and water source delivered between the patient and the HME. The volume of water delivered and heat output are based on a set minute ventilation. A pre-set airway temperature of 37°C is used. Methods: Thirty patients requiring MV for > 72 h were studied. Pts received humidification via a HH, HH + HWC (Fisher & Paykel), and AHME in random sequence for 24 h each. All devices were set to deliver 37°C at the proximal airway. During each period of ventilation, the following were measured; airway temperature, min and max body temperature, # of suctioning attempts, volume of secretions, consistency of secretions, # and volume of saline instilled, water usage, condensate, ventilator settings, minute volume, # of circuit disconnections. Water usage was measured by weighing the water bag before and after 24 h use. Consistency of secretions were judged as thin, moderate, or thick as previously described (Suzukawa, Respir Care 1989;34;976). Condensate was measured by emptying fluid into a graduated container and sputum volume measured by collecting secretions in a Luken's trap. Airway temperature was measured at the ET tube using a rapid response thermistor. Resistance of the AHME was measured before and after use. Results: There were no differences in any of the variables related to humidification efficiency (secretion volume and consistency, # of suctioning attempts, or volume of saline used). Water usage and volume of condensate were significantly different between devices, but delivered airway temperatures were not. Statistical analysis was done with ANOVA. *p < 0.05 See Table.

DEVICE Water Usage Condensate Airway Temp.

(ml) (mL) (°C)

HH 2039 ± 387 930 ± 271 36.3 ± 1.2

HH + HWC 766 ± 281 12 ± 16* 37.1 ± 1.0

AHME 135 ± 53 1 ± 3* 36.4 ± 1.7

Minute volume was similar between groups (11.6 ± 3.3 vs 11.9 ± 3.4 vs 11.8 ± 2.7 L/min) as was bias flow during flow triggering (5.8 ± 2.5 vs 5.4 ± 2.6 vs 5.9 ± 2.3). AHME resistance before and after use was unchanged (1.66 ± 0.11 vs 2.28 ± 0.82 cm H_{2}O/L/s). Conclusions: In a pilot study, the AHME provided equivalent humidification as HH and HH + HWC with a lower water usage. This occurs because the HME portion of the AHME returns [approx equals] 32 mg H_{2}O/L, which only requires the active portion to add [approx equals] 12 mg H_{2}O/L to reach 44 mg H_{2}O/L. Additionally, by placing the AHME between the patient and ventilator circuit, continuous flow from flow triggering systems is not humidified. No other differences were noted. Disadvantages of the AHME include deadspace ([approx equals] 70 mL), weight on the ET tube and the heat source near the patient. Measured external temperature of the AHME did not exceed 38°C. Further long term studies are required to define the role of the AHME.

The 44th International Respiratory Congress Abstracts-On-Disk®, November 7 - 10, 1998, Atlanta, Georgia.

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