The invasive and non-invasive monitoring of inspiratory effort and drive during assisted mechanical ventilation

Background: In patients with respiratory failure, assisted mechanical ventilation is often used after the initial acute phase to support patient's respiratory activity, enhance oxygen exchange, and improve lung ventilation and perfusion. In this phase, monitoring inspiratory effort and respiratory drive might reduce the risk of patient self-inflicted lung injury (P-SILI), thus potentially improving the outcome. P-SILI depends on the negative pressure generated by inspiratory muscles and the positive pressure delivered by the ventilator machine. Measuring the amount of inspiratory pressure generated by the patient and assessing work of breathing is therefore essential. For patients without esophageal or gastric catheters, several non-invasive indices have been developed to estimate inspiratory effort, respiratory drive and evaluate diaphragm function. The aim of this clinical review is to summarize current evidence regarding invasive and non-invasive instruments to monitor inspiratory effort and respiratory drive in patients undergoing assisted mechanical ventilation. Main body: Esophageal pressure is the reference measure used to evaluate total work of breathing and patient inspiratory effort. Monitoring esophageal swing may help in preventing both over-assistance and underassistance during mechanical ventilation. The diaphragmatic component of the total work of breathing can be estimated through a gastric catheter, that allows the measurement of transdiaphragmatic pressure. Various non-invasive indices are available in the literature to estimate patients' inspiratory effort, patient's respiratory drive and diaphragm function. During assisted mechanical ventilation, performing an end-inspiratory pause or an end-expiratory pause allows the measurement of pressure muscle index (PMI), airway occlusion pressure at 100 ms (P0.1), and airway occlusion pressure (Delta Pocc). Various cutoffs have been identified in the literature for a low and a high inspiratory effort (PMI, Delta Pocc) and respiratory drive (P0.1) during assisted ventilation. Diaphragmatic function can be quickly assessed using ultrasound. Three indices are extensively described in the literature: diaphragm thickness (DT), diaphragm excursion (DE), and diaphragm thickening fraction (DTf). Conclusion: Monitoring inspiratory effort and respiratory drive is crucial in current clinical practice to reduce P-SILI. At the present time several invasive and non-invasive tools can quantify inspiratory effort and respiratory drive, and they are well correlated to each other and to the reference measures of patient inspiratory effort. Their use should be encouraged to tailor assisted mechanical ventilation to the individual patient and to promote further studies, that are essential for their ultimate validation.