The Science Journal of the American Association for Respiratory Care

1999 OPEN FORUM Abstracts

INVASIVE APPLICATION OF PROPORTIONAL ASSIST VENTILATION (PAV) USING SINGLE-LIMB CIRCUIT - NO EVIDENCE OF C02 RETENTION

R Graham RRT#, L Thompson RN PhD(c)*, J Barr MD+#, E Bertaccini MD+#, V Carrieri-Kohlman DNSc*, E Geller MS, MD+# VA Palo Alto HCS#, Stanford U School of Medicine+, UCSF School of Nursing*

Background: Pressure Support Ventilation (PSV) and Proportional Assist Ventilation (PAV) are two modes of partial ventilatory support that assist spontaneously breathing patients. The primary difference between PSV and PAV is in the application of airway pressure once a spontaneous breath has been initiated. With PSV, patient effort and ventilator pressures are independent of each other; in PAV airway pressure is proportional to patient effort. Rebreathing (and retention) of C02 in BiPAPÒ Ventilators with single limb circuit and fixed-resistance exhalation device has been addressed (Ferguson, AJRCCM 151:1126-1135, 1995), yet no studies to date exist investigating C02 retention in the invasive use of PAV in a single limb circuit. This study measured ABG values using PAV delivered by the VisionÒ ventilator (single limb circuit with PlateauÒ exhalation valve, Respironics, Inc, Murrysville, PA) and PSV delivered by the 7200aeÒ ventilator (dual limb circuit with internal exhalation valve, Nellcor Puritan Bennett, Carlsbad, CA). Method: 10 post-operative, intubated patients were studied during weaning from mechanical ventilation. PSV and PAV were randomly applied to all patients at each level, starting at maximal assist and decreasing to 40% assist or onset of dyspnea. PSVmax (100% Assist) was defined as the pressure that produced a Vt of 10ml/kg (mean = 19cmH20±4); PAVmax (80% assist) was defined as 80% of the patient's Resistance (mean = 14.5 ±5) and Elastance (mean = 29.0 ±10) obtained by static measurement while receiving volume ventilation at a Vt of 10ml/kg. Measurements of the following parameters were obtained at the end of each 15 minute study period: Vt (liter), RR (bpm), Ve (liter), pH, PaC02 (mmHg), Pa02 (mmHg), & Sp02 (%).

Results: mean (SD); Repeated ANOVA, p<.05=*

Mode Assist Vt RR Ve pH PaC02 Pa02 Sp02
PAV 80% .493(.18) 20(4) 9.4(3.2) 7.39(.06) 40.9(5.9) 97(30) 97(3)
PAV 40% .436(.14) 22(5) 8.8(1.3) 7.40(.05) 40.2(5.5) 97(29) 97(3)
PSV 100% .716(.14)* 16(5)* 10.8(2.5) 7.40(.04) 38.5(5.5) 91(18) 97(3)
PSV 40% .550(.16) 21(4) 10.4(1.9) 7.38(.06) 41.2(6.7) 96(25) 97(3)

Conclusions: There was no significant difference in PaC02, pH, Ve, or indices of Oxygenation. There was statistical significance between Vt and RR with PAV compared to PSV. These data suggest that PAV may allow stable, post-operative patients more control over their own breathing pattern without evidence of C02 retention with the use of a single limb circuit.

Study made possible by grant from Respironics, Inc.

L Thompson was the recipient of a Fellowship Grant from Respironics, Inc.

OF-99-017

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