Limited predictability of maximal muscular pressure using the difference between peak airway pressure and positive end-expiratory pressure during proportional assist ventilation (PAV)

作者：Su Po Lan; Kao Pei Shan; Lin Wei Chieh; Su Pei Fang; Chen Chang Wen

来源：Critical Care, 2016, 20(1): 382.

DOI：10.1186/s13054-016-1554-4

• Pressure time product
• Proportional assist ventilation
• Airway pressure

Background: If the proportional assist ventilation (PAV) level is known, muscular effort can be estimated from the difference between peak airway pressure and positive end-expiratory pressure (PEEP) (Delta P) during PAV. We conjectured that deducing muscle pressure from Delta P may be an interesting method to set PAV, and tested this hypothesis using the oesophageal pressure time product calculation.
Methods: Eleven mechanically ventilated patients with oesophageal pressure monitoring under PAV were enrolled. Patients were randomly assigned to seven assist levels (20-80%, PAV20 means 20% PAV gain) for 15 min. Maximal muscular pressure calculated from oesophageal pressure (P-mus,P- oes) and from Delta P (P-mus,P- aw) and inspiratory pressure time product derived from oesophageal pressure (PTPoes) and from Delta P (PTPaw) were determined from the last minute of each level. P-mus,P- oes and PTPoes with consideration of PEEPi were expressed as P-mus,P- oes,P- PEEPi and PTPoes, PEEPi, respectively. Pressure time product was expressed as per minute (PTPoes, PTPoes, PEEPi, PTPaw) and per breath (PTPoes, br, PTPoes, PEEPi, br, PTPaw, br).
Results: PAV significantly reduced the breathing effort of patients with increasing PAV gain (PTPoes 214.3 +/- 80.0 at PAV20 vs. 83.7 +/- 49.3 cmH(2)O.s/min at PAV80, PTPoes, PEEPi 277.3 +/- 96.4 at PAV20 vs. 121.4 +/- 71.6 cm H2O.s/min at PAV80, p < 0.0001). P-mus,P- aw overestimates Pmus, oes for low-gain PAV and underestimates Pmus, oes for moderate-gain to high-gain PAV. An optimal P-mus,P- aw could be achieved in 91% of cases with PAV60. When the PAV gain was adjusted to P-mus,P- aw of 5-10 cmH(2)O, there was a 93% probability of PTPoes < 224 cmH(2)O.s/min and 88% probability of PTPoes, PEEPi < 255 cmH(2)O.s/min.
Conclusion: Deducing maximal muscular pressure from Delta P during PAV has limited accuracy. The extrapolated pressure time product from Delta P is usually less than the pressure time product calculated from oesophageal pressure tracing. However, when the PAV gain was adjusted to P-mus,P- aw of 5-10 cmH(2)O, there was a 90% probability of PTPoes and PTPoes, PEEPi within acceptable ranges. This information should be considered when applying Delta P to set PAV under various gains.

• 出版日期2016-11-27
• 单位长春大学