Effect of Ventilator Settings on Mechanical Power During Simulated Mechanical Ventilation of Patients With ARDS

BACKGROUND:

In recent years, mechanical power (MP) has emerged as an important concept that can significantly impact outcomes from mechanical ventilation. Several individual components of ventilatory support such as tidal volume (V_T), breathing frequency, and PEEP have been shown to contribute to the extent of MP delivered from a mechanical ventilator to patients in respiratory distress/failure. The aim of this study was to identify which common individual setting of mechanical ventilation is more efficient in maintaining safe and protective levels of MP using different modes of ventilation in simulated subjects with ARDS.

METHODS:

We used an interactive mathematical model of ventilator output during volume control ventilation (VCV) with either constant inspiratory flow (VCV-CF) or descending ramp inspiratory flow, as well as pressure control ventilation (PCV). MP values were determined for simulated subjects with mild, moderate, and severe ARDS; and whenever MP > 17 J/min, V_T, breathing frequency, or PEEP was manipulated independently to bring back MP to ≤ 17 J/min. Finally, the optimum V_T-breathing frequency combinations for MP = 17 J/min were determined with all 3 modes of ventilation.

RESULTS:

VCV-CF always resulted in the lowest MPs while PCV resulted in highest MPs. Reductions in V_T were the most efficient for maintaining safer and protective MP. At targeted MPs of 17 J/min and maximized minute ventilation, the optimum V_T-breathing frequency combinations were 250–350 mL for V_T and 32–35 breaths/min for breathing frequency in mild ARDS, 200–350 mL for V_T and 34–40 breaths/min for breathing frequency in moderate ARDS, and 200–300 mL for V_T and 37–45 breaths/min for breathing frequency for severe ARDS.

CONCLUSIONS:

VCV-CF resulted in the lowest MP. V_T was the most efficient for maintaining safe and protective MP in a mathematical simulation of subjects with ARDS. In the context of maintaining low and safe MPs, ventilatory strategies with lower-than-normal V_T and higher-than-normal breathing frequency will need to be implemented in patients with ARDS.