The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts

COMPARISON OF CONTINUOUS FLOW AND A DEMAND CPAP SYSTEM FOR USE IN EMERGENCY CARE OF CONGESTIVE HEART FAILURE

Richard Branson MSc, RRT, Kenneth Davis Jr., MD, Jay A. Johannigman MD. Department of Surgery, University of Cincinnati, Cincinnati, OH 45267-0558

Background: Mask CPAP reduces the need for intubation in patients with cardiogenic pulmonary edema. CPAP use by paramedics has been advocated, but is limited by the high gas consumption.

Method: We evaluated gas consumption, delivered FIO2, and work of breathing (WOB) of a demand CPAP system (CPAP OS, Emergent Respiratory Products, Irvine, CA) and two continuous flow CPAP (Whisperflow fixed and Whisperflow low flow, Respironics, IR) systems using a lung model. All devices were set according to manufacturers instructions. CPAP of 0, 5, 7.5, and 10 cm H2O were studied. Devices were operated from full 2200 psig E-cylinders of oxygen while connected to an active test lung (ASL 5000, Ingmar Medical, Pittsburgh, PA) 'breathing' at a tidal volume of 500 ml and respiratory rate of 20 b/min for determination of gas consumption. A second determination of gas consumption was made with a leak of 5L/min between the circuit and test lung. WOB characteristics were assessed using the ASL 5000 set to create the following 3 conditions: 1) VT - 150 mL, Peak flow - 15 L/min, muscle pressure of 5.0 cm H2O, 2) VT - 350 mL, Peak flow - 40 L/min, muscle pressure of 10 cm H2O, 3) VT - 500 mL, Peak flow - 55 L/min, muscle pressure of 15 cm H2O. At each condition 6 breaths were analyzed and the peak negative pressure (PNP), inspiratory WOB (mj/L) and peak expiratory pressure (PEP) and expiratory WOB (mj/L) were determined.

Results: Data for gas consumption is shown in Table 1 and data for WOB are shown in Table 2 for a CPAP of 10 cm H20. Duration of operation is from a single E cylinder of oxygen at 2200 psig.

Device FIO2 Gas Consumption (L/min) Gas consumption with 5 L/min leak (L/min) Duration of Operation# (mins)
Whisperflow low flow 0.30±.002 10.3 ± 0.6 10.4 ± 0.7 60.6 ± 3.0
Whisperflow fixed 0.30±.002 15.3 ± 0.9 15.6 ± 0.7 39.1 ± 3.3@
CPAP OS 1.0* 10.5 ± 1.6** 16.1 ± 1.5** 58 ± 3.8

* = p< 0.01 vs. fixed flow devices.** p < 0.01 vs. Gray whisperflow, @ p< 0.01 vs. other 2 devices

Table 2 Work of breathing characteristics at 10 CPAP and VT of 500 mL

  PNP (cm H2O) WOBI (j/L) PEP (cm H2O) WOBE (j/L)
Whisperflow low flow 2.3 ± 0.3 1.1 ± 0.2 1.1 ± 0.1 0.21 ± 0.05
Whisperflow fixed 1.6 ± 0.2 0.92 ± 0.1 1.8 ± 0.2 0.28 ± 0.09
CPAP OS 4.9 ± 0.9* 1.4 ± 0.4* 0.4 ± 0.1* 0.13 ± 0.07*

Data are mean ± SD. Comparisons are made using ANOVA. * = p< 0.01 vs. fixed flow devices.

The demand valve system resulted in a higher FIO2 than the fixed devices. Gas consumption was lowest with the demand valve system. The low flow Whisper flow device had a lower gas consumption than the fixed whisperflow system. Duration of operation from an E-cylinder was highest with the Whisperflow fixed compared to the other devices. The demand CPAP OS was associated with significant increases in the inspiratory WOB and the lowest PNP. Expiratory WOB was lowest with the demand CPAP OS and highest with the high flow whisper flow.

Conclusions: CPAP systems vary widely in the FIO2 delivered, duration of operation from an E-cylinder, and WOB characteristics. Clinicians should be aware of these differences when purchasing devices.

1) Kosowsky JM, Prehosp Emerg Care. 2001 Apr-Jun;5(2):190-6.

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