A brief airway occlusion is sufficient to measure the patient’s inspiratory effort/electrical activity of the diaphragm index (PEI)

Abstract

Pressure generated by patient’s inspiratory muscles (Pmus) during assisted mechanical ventilation is of significant relevance. However, Pmus is not commonly measured since an esophageal balloon catheter is required. We have previously shown that Pmus can be estimated by measuring the electrical activity of the diaphragm (EAdi) through the Pmus/EAdi index (PEI). We investigated whether PEI could be reliably measured by a brief end-expiratory occlusion maneuver to propose an automated PEI measurement performed by the ventilator. Pmus, EAdi, airway pressure (Paw), and flow waveforms of 12 critically ill patients undergoing assisted mechanical ventilation were recorded. Repeated end-expiratory occlusion maneuvers were performed. PEI was measured at 100 ms (PEI0.1) and 200 ms (PEI0.2) from the start of the occlusion and compared to the PEI measured at the maximum Paw deflection (PEIoccl, reference). PEI0.1 and PEI0.2 tightly correlated with PEIoccl, (p < 0.001, R2 = 0.843 and 0.847). At a patient-level analysis, the highest percentage error was -64% and 50% for PEI0.1 and PEI0.2, respectively, suggesting that PEI0.2 might be a more reliable measurement. After correcting the error bias, the PEI0.2 percentage error was lower than ± 30% in all but one subjects (range − 39 to + 29%). It is possible to calculate PEI over a brief airway occlusion of 200 ms at inspiratory onset without the need for a full patient's inspiratory effort. Automated and repeated brief airway occlusions performed by the ventilator can provide a real time measurement of PEI; combining the automatically measured PEI with the EAdi trace could be used to continuously display the Pmus waveform at the bedside without the need of an esophageal balloon catheter.