Accuracy of calculating mechanical power of ventilation by one commonly used equation

Abstract

AbstractGattinoni’s equation, $${\text{MP}}_{{{\text{rs}}}} \, = \,0.098\, \times \,{\text{RR}}\, \times \,\left[ {{\text{V}}_{T} ^{2} \left( {\frac{1}{2}{\text{E}}_{{{\text{rs}}}} \, + \,{\text{RR}}\, \times \,\frac{{1\, + \,I:E}}{{60\, \times \,I:E}}\, \times \,{\text{R}}_{{{\text{aw}}}} } \right)\, + \,{\text{V}}_{{\text{T}}} \, \times \,{\text{PEEP}}} \right]$$ MP rs = 0.098 × RR × V T 2 1 2 E rs + RR × 1 + I : E 60 × I : E × R aw + V T × PEEP , now commonly used to calculate the mechanical power (MP) of ventilation. However, it calculates only inspiratory MP. In addition, the inclusion of PEEP in Gattinoni’s equation raises debate because PEEP does not produce net displacement or contribute to MP. Measuring the area within the pressure–volume loop accurately reflects the MP received in a whole ventilation cycle and the MP thus obtained is not influenced by PEEP. The MP of 25 invasively ventilated patients were calculated by Gattinoni’s equation and measured by integration of the areas within the pressure–volume loops of the ventilation cycles. The MP obtained from both methods were compared. The effects of PEEPs on MP were also evaluated. We found that the MP obtained from both methods were correlated by R2 = 0.75 and 0.66 at PEEP 5 and 10 cmH2O, respectively. The biases of the two methods were 3.13 (2.03 to 4.23) J/min (P < 0.0001) and − 1.23 (− 2.22 to − 0.24) J/min (P = 0.02) at PEEP 5 and 10 cmH2O, respectively. These P values suggested that both methods were significantly incongruent. When the tidal volume used was 6 ml/Kg, the MP by Gattinoni’s equation at PEEP 5 and 10 cmH2O were significantly different (4.51 vs 7.21 J/min, P < 0.001), but the MP by PV loop area was not influenced by PEEPs (6.46 vs 6.47 J/min, P = 0.331). Similar results were observed across all tidal volumes. We conclude that the Gattinoni’s equation is not accurate in calculating the MP of a whole ventilatory cycle and is significantly influenced by PEEP, which theoretically does not contribute to MP.