2009 OPEN FORUM Abstracts
COMPARISON OF TWO DIFFERENT PROPORTIONAL ASSIST VENTILATION ALGORITHMS
Robert L. Chatburn1, Jaimee L. Wear2; 1Respiratory Institute, Cleveland Clinic, Cleveland, OH; 2Medical Intensive Care Unit, Cleveland Clinic, Cleveland, OH
Proportional assist ventilation (PAV) was first described in 1992 (Am Rev Respir Dis 1992;145:114). The first commercial version in the U.S. was Proportional Assist Ventilation Plus (PAV+) in 2008. In 2009 Proportional Pressure Support (PPS) became available. Both versions are based on the equation of motion for the respiratory system to support the patient’s elastic and resistive loads during spontaneous breathing. For PPS the operator sets “volume support” (VS, the supported elastance) and “flow support” (FS, the supported resistance). For PAV+ the operator sets the % work supported and the ventilator selects VS and FS levels. The purpose of this study was to compare the operational characteristics of PAV+ and PPS with different simulated ventilatory patterns. METHODS: Breathing was modeled with an ASL 5000 lung simulator (IngMar Medical Inc.); patient effort set to sinusoidal, insp = 10%, hold = 0%, release = 10%. Modes tested were PAV+ (Puritan Bennett 840) and PPS (DrÃ¤ger Evita XL). PAV+ was set to support 70% of the work of breathing. On the Evita XL, VS was set to 70% of the lung model elastance and FS was set to 70% of the model resistance. For PPS Automatic tube compensation was 100% or 0% for 8.0 ET tube. Experiment 1 (variable effort): Frequency (f ) = 15 breaths/min, patient effort (Pmax) varied from 4 to 10 cm H2O, resistance (R) = 10 cm H2O,L/s, compliance (C) = 33.3 mL/cm H2O. Experiment 2 (variable C): Pmax = 6, R = 10, C varied from 33.3 to 39.3 (elastance = 10 to 25 cm H2O/mL). RESULTS: Experiment 1: Data are shown in the Figure. As Pmax varied from 4 to 10, tidal volume was 206 to 450 for PPS(ATC=0); 314 to 978 for PPS(ATC=100); 214 to 585 for PAV+. Experiment 2: The ratio of ventilator work/L to patient work/L increased with C; 1.0 to 1.4 for PPS(ATC=0); 2.5 to 5.4 for PPS(ATC=100) but remained constant at 1.7 for PAV+. Tidal volume increased with C; 294 to 360 for PPS(ATC=0); 488 to 776 for PPS(ATC=100); 390 to 399 for PAV+. CONCLUSIONS: Although conceptually the same mode, PPS and PAV+ have very different operating characteristics. PAV+ supports a constant proportion of the patient’s work by monitoring and automatically adjusting R and C and includes tube resistance compensation. PPS supports a constant absolute value of R and C, has optional tube resistance compensation (that has a large effect on tidal volume) and must be manually adjusted as the patient’s condition changes. Knowledge of these differences is critical for proper use. Sponsored Research - Draeger loaned us a ventilator for testing. There was no monetary exchange.