Effect of Different Levels of Pressure Support and Proportional Assist Ventilation on Breathing Pattern, Work of Breathing and Gas Exchange in Mechanically Ventilated Hypercapnic COPD Patients with Acute Respiratory Failure

Abstract

Background: Proportional assist ventilation (PAV) has been shown to maintain better patient-ventilator synchrony than pressure support ventilation (PSV); however, its clinical advantage regarding invasive ventilation of COPD patients has not been clarified. Objectives: To compare the effect of PAV and PSV on respiratory parameters of hypercapnic COPD patients with acute respiratory failure (ARF). Methods: Nine intubated hypercapnic COPD patients were placed on the PAV or PSV mode in random sequence. For each mode, four levels (L₁–L₄) of support were applied. At each level, blood gases, flow, tidal volume (V_T), airway pressure (Paw), esophageal pressure (Pes) (n = 7), patient respiratory rate (fp), ventilator rate (fv), missing efforts (ME = fp – fv) were measured. Results: We found increases in ME with increasing levels of PSV but not with PAV. PO₂and V_T increased whereas PCO₂decreased significantly with increasing levels of PSV (p < 0.05). With PAV, PCO₂decreased and V_Tincreased significantly only at L₄ whereas PO₂increased from L₁ to L₄. Runaways were observed at L₃and L₄of PAV. The pressure-time product (PTP) was determined for effective and missing breaths. The mean total PTP per minute (of effective plus missing breaths) was 160 ± 57 cm H₂O/s·min in PSV and 194 ± 60 cm H₂O/s·min in PAV. Conclusion: We conclude that in COPD patients with hypercapnic ARF, with increasing support, PSV causes the appearance of ME whereas PAV develops runaway phenomena, due to the different patient-ventilator interaction; however, these do not limit the improvement of blood gases with the application of both methods.