The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts

LABORATORY EVALUATION OF FOUR DISPOSABLE CPAP VALVES

Kristy M. Bates* CRTT, Robert S. Campbell RRT, FAARC, Jay A. Johannigman MD, Fred A. Luchette MD, Kenneth Davis Jr. MD, Sandra L. Miller MD, Scott B. Frame MD, Richard D. Branson RRT. Respiratory Care Department*, The University Hospital and Division of Trauma/Critical Care, University of Cincinnati College of Medicine

Introduction: Disposable CPAP valves are fixed or adjustable threshold resistors (TR). An optimal TR will produce a constant pressure in the face of varying flows. We evaluated four commercially available CPAP valves in the laboratory for maintenance of set airway pressure at various constant flow rates.

Methods:
Airway pressure generated with fixed CPAP valves (5, 10 15, 20 cmH2O) from two manufacturers (Caradyne, Vital Signs) were evaluated at constant flow rates of 5, 15, 30, 60, and 90 L/min. Airway pressure generated with adjustable CPAP valves from two manufacturers (Mercury, Intertech) were also tested at the same flow rates. The minimum and maximum pressure generated with each adjustable CPAP valve was measured at 60 L/min. Accuracy of labeled pressure settings for each adjustable CPAP valve was assessed at each flow rate. Effect of varying flow on pressure generated with adjustable CPAP valves was tested by adjusting each to a measured pressure of 10 cmH2O at 60 L/min and measuring the pressure maintained at all other flow rates. Pressure and flow were measured with a calibration analyzer (RT-200).

Results:
Table 1 reveals the pressure (mean ± SD) measured at each flow rate for each CPAP valve set at 10 cmH2O.

Table 1. 5 LPM 15 LPM 30 LPM 60 LPM 90 LPM
Caradyne 10.2 ± 0.1 10.5 ± 0.1 10.6 ± 0.1 10.2 ± 0 9.9 ± 0.1
Vital Signs 9.5 ± 0.1 9.8 ± 0.3 9.8 ± 0.1 9.3 ± 0.1 9.6 ± 0.2
Mercury 5.0 ± 1.2 6.6 ± 1.9 8.1 ± 0.6 10.0 ± 0 11.4 ± 0.9
Intertech 4.1 ± 0.19 5.6 ± 0.14 7.3 ± 0.37 10.0 ± 0 11.8 ± 0.1

Each fixed CPAP valve provided pressure within 10% of the label pressure and were unaffected by varying flow rate. Each adjustable CPAP valve provided significantly higher pressure than indicated by the label. Adjustable valves are poor TRs as evidenced by variability in the pressure as flow is varied. Although adjustable CPAP valves allow adjustment between 0 and 20 cmH2O, the minimum/maximum pressure at 60 L/min was 6.6/31.1 for the Mercury and 5.31/25.9 for the Intertech. Conclusion: The fixed CPAP valves tested are accurate and reliable TRs. The adjustable CPAP valves tested are not accurately labeled and provide inconsistent pressure as flow is varied. Airway pressure should be monitored continuously during clinical use of adjustable CPAP valves.

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