Abstract
BackgroundDiaphragm dysfunction develops frequently in ventilated intensive care unit (ICU) patients. Both disuse atrophy (ventilator over-assist) and high respiratory muscle effort (ventilator under-assist) seem to be involved. A strong rationale exists to monitor diaphragm effort and titrate support to maintain respiratory muscle activity within physiological limits. Diaphragm electromyography is used to quantify breathing effort and has been correlated with transdiaphragmatic pressure and esophageal pressure. The neuromuscular efficiency index (NME) can be used to estimate inspiratory effort, however its repeatability has not been investigated yet. Our goal is to evaluate NME repeatability during an end-expiratory occlusion (NMEoccl) and its use to estimate the pressure generated by the inspiratory muscles (Pmus).MethodsThis is a prospective cohort study, performed in a medical-surgical ICU. A total of 31 adult patients were included, all ventilated in neurally adjusted ventilator assist (NAVA) mode with an electrical activity of the diaphragm (EAdi) catheter in situ. At four time points within 72 h five repeated end-expiratory occlusion maneuvers were performed. NMEoccl was calculated by delta airway pressure (ΔPaw)/ΔEAdi and was used to estimate Pmus. The repeatability coefficient (RC) was calculated to investigate the NMEoccl variability.ResultsA total number of 459 maneuvers were obtained. At time T = 0 mean NMEoccl was 1.22 ± 0.86 cmH2O/μV with a RC of 82.6%. This implies that when NMEoccl is 1.22 cmH2O/μV, it is expected with a probability of 95% that the subsequent measured NMEoccl will be between 2.22 and 0.22 cmH2O/μV. Additional EAdi waveform analysis to correct for non-physiological appearing waveforms, did not improve NMEoccl variability. Selecting three out of five occlusions with the lowest variability reduced the RC to 29.8%.ConclusionsRepeated measurements of NMEoccl exhibit high variability, limiting the ability of a single NMEoccl maneuver to estimate neuromuscular efficiency and therefore the pressure generated by the inspiratory muscles based on EAdi.
Highlights
Diaphragm dysfunction develops frequently in ventilated intensive care unit (ICU) patients
It appears that non-physiological diaphragm activity plays an important role [8], in which both disuse atrophy resulting from ventilator over-assist [3, 9, 10] and high respiratory muscle effort resulting from ventilator under-assist [11,12,13] have been associated with diaphragm dysfunction in ICU patients
Mean neuromuscular efficiency index (NME) repeatability during an end-expiratory occlusion (NMEoccl) was 1.22 ± 0.86 cmH2O/μV, with a repeatability coefficient (RC) of 82.6%. This implies that when NMEoccl is 1.0 cmH2O/ μV, it is expected with a probability of 95% that the subsequent measured NMEoccl will be between 0.17 and 1.83 cmH2O/μV
Summary
Diaphragm dysfunction develops frequently in ventilated intensive care unit (ICU) patients. Diaphragm dysfunction frequently develops in mechanically ventilated intensive care unit (ICU) patients and is associated with adverse clinical outcomes including prolonged mechanical ventilation and mortality [1,2,3,4,5,6,7] It appears that non-physiological diaphragm activity plays an important role [8], in which both disuse atrophy resulting from ventilator over-assist [3, 9, 10] and high respiratory muscle effort resulting from ventilator under-assist [11,12,13] have been associated with diaphragm dysfunction in ICU patients. Limitations of this technique include strict control of balloon inflation volume and complexity of signal interpretation, in particular when expiratory muscles are recruited
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