Measuring patient’s effort on the ventilator

Abstract

Allowing spontaneous breathing with optimal inspiratory effort should be a priority in patients with acute respiratory failure under mechanical ventilation. Low and absent effort promote diaphragmatic dysfunction, creating difficulties in weaning, but also atelectasis and hypoxemia, while intense inspiratory efforts generate negative alveolar pressures and can induce lung (i.e., patient selfinflicted lung injury-P-SILI) and diaphragmatic injury (myotrauma) [1]. Low effort even occurs despite apparently spontaneous "triggered" breaths, because assisted ventilation deliver minimal minute ventilation once triggered. The transition from controlled to assisted ventilation can be associated with vigorous efforts in patients with hypoxemic failure, difficult to control [2]. In addition, lung injury and systemic inflammation are primers for P-SILI and myotrauma with excessive concentric or eccentric loading [1,3]. Mechanisms of P-SILI include excessive global and regional lung stress (due to pendelluft) and increased transvascular pressure, and are directly associated with the magnitude and timing of inspiratory effort [3,4]. There is also evidence of interaction between lung and other organs such as brain and kidneys. Therefore, monitoring respiratory drive and effort to adjust ventilatory settings and sedation seems necessary to achieve lung-and diaphragm-protective targets that should result in better clinical outcomes. This review describes the tools and the different parameters for monitoring respiratory effort, and suggests targets for respiratory drive and effort (Fig. 1).