Assessing inspiratory drive and effort in critically ill patients at the bedside

Monitoring inspiratory drive and effort may aid proper selection and setting of respiratory support in patients with acute respiratory failure (ARF), whether they are intubated or not. Although diaphragmatic electrical activity (EAdi) and esophageal manometry can be considered the reference methods for assessing respiratory drive and inspiratory effort, respectively, various alternative techniques exist, each with distinct advantages and limitations. This narrative review provides a comprehensive overview of bedside methods to assess respiratory drive and effort, with a primary focus on patients with ARF. First, EAdi and esophageal manometry are described and discussed as reference techniques. Then, alternative methods are categorized along the neuromechanical pathway from inspiratory drive to muscular effort into three groups: (1) techniques assessing the respiratory drive: airway occlusion pressure (P0.1), mean inspiratory flow (Vt/Ti) and respiratory muscle surface electromyography (sEMG); (2) techniques assessing the respiratory muscle effort: whole-breath occlusion pressure (ΔPocc), pressure-muscle index (PMI), nasal pressure swing (ΔPnose), diaphragm ultrasonography (USdi), central venous pressure swing (ΔCVP), breathing effort (BREF) models, and flow index; (3) techniques and clinical parameters assessing the consequences of effort: tidal volume (Vt), electrical impedance tomography (EIT), dyspnea. For each, we summarize the physiological rationale, measurement methodology, interpretation of results, and key limitations.