Association Between EIT and CT During PEEP Titration in Patients With Acute Respiratory Failure

This observational study will analyze data already collected by the investigators as part of their routine clinical practice from patients with acute respiratory failure (ARF) treated with mechanical ventilation. The study itself does not require any specific intervention. Mechanical ventilation can save the lives of patients with ARF. However, if used improperly, it can exacerbate lung disease and worsen outcomes (Slutsky et al.). Despite decades of animal and clinical research, it remains unclear how to establish the positive end-expiratory pressure (PEEP) during mechanical ventilation to reduce the risk of lung damage. Several methods have been suggested, but none have consistently proven superior to the others (Sahetya et al.). As part of their routine clinical practice, the investigators study the responses to different PEEP levels of patients with ARF undergoing mechanical ventilation by integrating information from various techniques, each examining different aspects of lung morphology and physiology. The methods the investigators use include lung computed tomography (CT) and electrical impedance tomography (EIT). Lung CT is the reference technique for measuring the morphological response to PEEP (Gattinoni et al.). It quantifies the volume of the hyperinflated and non-aerated lung, both of which are related to the risk of mechanical ventilation causing damage (Slutsky et al.). Lung EIT monitors the functional response to PEEP in terms of changes in regional compliance across different PEEP levels. Allegedly, an increase in compliance when PEEP is decreased reveals overdistention, the functional correlate of (worrisome) hyperinflation, at the higher PEEP. A decrease in compliance when PEEP is decreased signals new collapse, the functional correlate of (worrisome) loss of aeration (Franchineau et al.). In the Unit where the investigators work, patients with ARF treated with mechanical ventilation are routinely studied as follows. First, a lung CT with a PE