1995 OPEN FORUM Abstracts
ABILITY OF BILEVEL CPAP VENTILATORS TO MEET INSPIRATORY DEMAND: A LUNG MODEL STUDY
Thananchai Bunburaphong, MD, Hideaki Imanaka, MD, Masaji Nishimura, MD, Dean Hess, PhD, RRT, Robert M. Kacmarek, PhD, RRT. Department of Anesthesia and Respiratory Care, Massachusetts General Hospital and Harvard Medical School, Boston MA.
Bilevel CPAP ventilators are being increasingly used to provide noninvasive ventilatory support during acute ventilatory failure. We evaluated the ability of six bilevel CPAP ventilators to meet varying levels of inspiratory demands in a single compartment lung model.
Methods: The lung model was set at a compliance of 50 or 80 mL/cmH_2O and a resistance of 8 cmH_2O/L/s with a rate of 10 /min and an inspiratory time of 1.0 sec. The Respironics BiPAP S/T-D, the Puritan Bennett 320I/E and 335, Sullivan VPAP, Pierre Medical O'NYX, and SEFAM Ventil+ ventilators were compared to the Puritan Bennett 7200ae (Flow-by, base flow of 10 L/min and flow sensitivity of 3 L/min) at lung model peak inspiratory flow of 20, 40, 60, and 80 L/min. Initiation of inspiration and expiration were determined by measurement of pressure in the lung model pleural space. Pressure and flow at airway opening were also measured. All ventilators were set at an IPAP of 15 cmH_2O and EPAP of 5 cmH_2O. The subbaseline inspiratory pressure change (P-I), inspiratory delay time (D-I), suprabaseline expiratory pressure change (P-E), expiratory delay time (D-E), and the area % inspiration (Area%) were determined. The Area% was defined as the percentage of pressure time product of airway opening pressure above EPAP during inspiration to the area of the rectangle created by (IPAP-EPAP) and inspiratory time. Statistical analysis was done by ANOVA with Scheffe test (Pɘ.05).
Results: Differences among ventilators (Pɘ.05) were noted for all variables evaluated. P-I, D-I, and P-E were significantly different among peak flows (Pɘ.05). Compliance settings did not significantly effect any variable. Mean values for 3 breaths at 50 mL/cmH_2O compliance and 40 L/min peak flow are listed below. Negative D-E indicates premature expiratory cycling.
7200ae S/T-DVPAP 320I/EO'NYXVentil+ PB335
P-I (cmH_2O)2.97 1.18 1.08 0.92 1.33 1.69 1.38
D-I (sec)0.15 0.09 0.29 0.09 0.06 0.18 0.11
P-E (cmH_2O)4.15 2.51 3.18 20 1.08 0
D-E (sec)0.11 0.08 0.39 0.06 -0.180.06 -0.1
Area% (%)61.7983.5243.9783.48 75.8266.0875.81
Conclusions: The ability of bilevel CPAP ventilators to meet inspiratory demands equaled or exceeded that of the PB7200ae. However, large differences did exist among the functions of
the bilevel CPAP ventilators.