Implementing a bedside assessment of respiratory mechanics in patients with acute respiratory distress syndrome

Abstract

Background: Despite their potential interest for clinical management, measurements of respiratory mechanics in patients with acute respiratory distress syndrome (ARDS) are seldom performed in routine practice. We introduced a systematic assessment of respiratory mechanics in our clinical practice. After the first year of clinical use, we retrospectively assessed whether these measurements had any influence on clinical management and physiological parameters associated with clinical outcomes by comparing their value before and after performing the test.

Methods: The respiratory mechanics assessment constituted a set of bedside measurements to determine passive lung and chest wall mechanics, response to positive end-expiratory pressure, and alveolar derecruitment. It was obtained early after ARDS diagnosis. The results were provided to the clinical team to be used at their own discretion. We compared ventilator settings and physiological variables before and after the test. The physiological endpoints were oxygenation index, dead space, and plateau and driving pressures.

Results: Sixty-one consecutive patients with ARDS were enrolled. Esophageal pressure was measured in 53 patients (86.9%). In 41 patients (67.2%), ventilator settings were changed after the measurements, often by reducing positive end-expiratory pressure or by switching pressure-targeted mode to volume-targeted mode. Following changes, the oxygenation index, airway plateau, and driving pressures were significantly improved, whereas the dead-space fraction remained unchanged. The oxygenation index continued to improve in the next 48 h.

Conclusions: Implementing a systematic respiratory mechanics test leads to frequent individual adaptations of ventilator settings and allows improvement in oxygenation indexes and reduction of the risk of overdistention at the same time.

Trial registration: The present study involves data from our ongoing registry for respiratory mechanics (ClinicalTrials.gov identifier: NCT02623192 . Registered 30 July 2015).

Keywords: Esophageal pressure; Mechanical ventilation; Pulmonary function test; Quality improvement; Respiratory physiology.

Fig. 1

Illustration of simplified decremental positive end-expiratory pressure (PEEP) maneuver for estimating derecruited lung volume. In this example, respiratory frequency was transiently reduced to 10 breaths per minute to allow a prolonged expiration. Afterward, PEEP was reduced from 15 to 5 cmH₂O. The difference in expiratory tidal volumes (i.e., integral of flow) between the breath while decreasing PEEP (blue area) and the one before changing PEEP (red area) was referred to as the total change in lung volume. Derecruited volume was the difference between the total changes in measured vs. predicted lung volumes (see text for details). Paw Airway pressure

Fig. 2

Panel a shows the clinical adjustments in positive end-expiratory pressure (PEEP) and effects on the oxygenation index (OI) (n = 59). b Patients were classified in three groups according to the change in their PEEP level. Bonferroni adjustment was not used. (Refer to main text for explanations.)

Fig. 3

Individual oxygenation responses to the incremental positive end-expiratory pressure trial. PaO ₂ /FiO ₂ ratio Ratio of partial pressure of arterial oxygen to fraction of inspired oxygen; PEEPtot Total positive end-expiratory pressure