# Adjusting inspiratory rise time alters mechanical power in acute respiratory distress syndrome: opposing effects in pressure-controlled and volume-controlled ventilation modes

## TL;DR

Changing the inspiratory rise time in different ventilation modes has opposite effects on mechanical power in ARDS patients, which could impact lung injury risk.

## Contribution

This study reveals opposing effects of inspiratory rise time on mechanical power in pressure-controlled and volume-controlled ventilation modes in ARDS.

## Key findings

- In volume-controlled ventilation, increasing inspiratory rise time raises mechanical power.
- In pressure-controlled ventilation, increasing inspiratory rise time lowers mechanical power.
- Changing inspiratory-to-expiratory ratios has minimal impact in pressure-controlled mode but reduces mechanical power in volume-controlled mode.

## Abstract

Mechanical power (MP), a predictor of ventilator-induced lung injury (VILI), is influenced by ventilatory parameters such as inspiratory rise time (Tslope). While Tslope affects the flow profile, its impact on MP in acute respiratory distress syndrome (ARDS) has not been thoroughly studied, particularly using the geometric method.

In this prospective observational study, 30 deeply sedated and paralyzed ARDS patients were ventilated in both volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) modes using a Maquet Servo-u ventilator. At inspiratory-to-expiratory (I:E) ratios of 1:2 and 1:1, Tslope was adjusted from 5 to 15%, and pressure–volume (P–V) loop screenshots were captured. Geometric mechanical power (MPtotal) was calculated based on the area enclosed by the P–V loops. A total of 720 images were analyzed.

In VCV mode, increasing Tslope from 5 to 15% led to a statistically significant increase in MPtotal: 0.8 J/min (5%) at I:E 1:2 and 0.1 J/min (1%) at I:E 1:1. Conversely, in PCV mode, Tslope prolongation resulted in a significant decrease in MPtotal: 1.8 J/min (12.5%) at I:E 1:2 and 1 J/min (7%) at I:E 1:1. No intrinsic PEEP was detected.

Modifying Tslope alters MPtotal in opposing directions in PCV and VCV modes. In VCV, prolonging Tslope from 5 to 15% increased MP, whereas increasing the I:E ratio from 1:2 to 1:1 reduced MP. In PCV, prolongation of Tslope from 5 to 15% decreased MP by more than 1 J/min, and changes in the I:E ratio exerted minimal effects on MP.

Diagram displays two sections comparing VCV and PCV ventilator modes, each showing three results for different I:E ratios and Tslope settings. Each result includes a graph, MPtot value, white area pixels, total area, and area ratio, illustrating how increasing I:E ratio or Tslope alters these values.