The effect of inspiratory rise time on mechanical power calculations in pressure control ventilation: dynamic...

Mechanical power may serve as a valuable parameter for predicting ventilation-induced injury in mechanically ventilated patients. Over time, several equations have been developed to calculate power in both volume control ventilation (VCV) and pressure control ventilation (PCV). Among these equations, the linear model mechanical power equation (MP_LM) closely approximates the reference method when applied in PCV. The dynamic mechanical power equation (MP_dyn) computes power by utilizing the ventilatory work of breathing parameter (WOB_v), which is automatically measured by the mechanical ventilator. In our study, conducted in patients with Covid-19 Acute Respiratory Distress Syndrome (C-ARDS), we calculated mechanical power using both the MP_LM and MP_dyn equations, employing different inspiratory rise times (T_slope) at intervals of 5%, ranging from 5 to 20% and compared the obtained results.

In our analysis, we used univariate linear regression at both I:E ratios of 1:2 and 1:1, considering all T_slope values. These analyses revealed that the MP_dyn and MP_LM equations exhibited strong correlations, with R² values exceeding 0.96. Furthermore, our Bland-Altman analysis, which compared the power values derived from the MP_dyn and MP_LM equations for patient averages and all measurements, revealed a mean difference of -0.42 ± 0.41 J/min (equivalent to 2.6% ± 2.3%, p < 0.0001) and -0.39 ± 0.57 J/min (equivalent to 3.6% ± 3.5%, p < 0.0001), respectively. While there was a statistically significant difference between the equations in both absolute value and relative proportion, this difference was not considered clinically relevant. Additionally, we observed that each 5% increase in T_slope time corresponded to a decrease in mechanical power values by approximately 1 J/min.

The differences between mechanical power values calculated using the MP_dyn and MP_LM equations at various T_slope durations were determined to lack clinical significance. Consequently, for practical and continuous mechanical power estimation in Pressure-Controlled Ventilation (PCV) mode, the MP_dyn equation presents itself as a viable option. It is important to note that as T_slope times increased, the calculated mechanical power exhibited a clinically relevant decrease.