title: 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.
  
  
  OBJECTIVE
  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 (VT), 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. PO2 and VT increased whereas PCO2 decreased significantly with increasing levels of PSV (p < 0.05). With PAV, PCO2 decreased and VT increased significantly only at L4 whereas PO2 increased from L1 to L4. Runaways were observed at L3 and L4 of 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.
  
  
  CONCLUSIONS
  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.
mesh_terms: D000208:Acute Disease; D000368:Aged; D000403:Airway Resistance; D005260:Female; D006439:Hemodynamics; D006801:Humans; D006935:Hypercapnia / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000379:methods; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications* / Q000503:physiopathology / Q000628:therapy*; D011659:Pulmonary Gas Exchange; D012121:Respiration, Artificial / Q000379:methods*; D012131:Respiratory Insufficiency / Q000209:etiology*; D015656:Respiratory Mechanics; D014939:Work of Breathing