Mechanical Power in Pressure-Controlled Ventilation: A Simple and Reliable Bedside Method.

BACKGROUND

Mechanical power (MP) represents the amount of energy applied by the ventilator to the respiratory system over time. There are two main methods to calculate MP in mechanical ventilation. The first is the geometric method, which directly measures the dynamic inspiratory area of the pressure-volume loop during the respiratory cycle. The second involves using various algebraic equations to estimate MP. However, almost all calculations are either complex or not reliable compared with the geometric method, considered the gold standard. This study aimed to develop an easy to use, reliable equation for bedside calculation of MP and to compare its accuracy with other existing equations for calculating MP.

METHODS

In a preliminary study, we measured MP in 56 cases who were mechanically ventilated and without spontaneous breathing efforts. The measurements were done at the ICU of a single university medical center in the Netherlands.

RESULTS

We found that the MP can be accurately calculated using an equation that incorporates the plateau pressure in 56 cases in 42 patients. The MP estimated with our new proposed equation (MP calculated using plateau pressure) correlated well with the reference value of MP with a bias of 0.2 J/min. The 95% limits of agreement (LoAs) were -3.1 to + 3.4 J/min. Other equations give the following bias and LoAs; bias of -0.8, LoA -3.8 to 1.9 J/min (van der Meijden equation), bias of -1.9, LoA -3.7 to -0.0 J/min (comprehensive Becher equation), bias of -2.4, LoA -4.5 to -0.3 J/min (simplified Becher equation), and a bias of -1.9, LoA -3.7 to 0.1 J/min (linear model equation).

CONCLUSIONS

The equation we propose to calculate MP in pressure-controlled ventilation is a reliable, simple, and accurate alternative for the previously published equations. Consequently, this method is highly suitable for routine use in clinical practice.