Rationale In intensive care unit (ICU) patients, diaphragm dysfunction is associated with adverse clinical outcomes. Ultrasound measurements of diaphragm thickness, excursion (EXdi) and thickening fraction (TFdi) are putative estimators of diaphragm function, but have never been compared with phrenic nerve stimulation. Our aim was to describe the relationship between these variables and diaphragm function evaluated using the change in endotracheal pressure after phrenic nerve stimulation (Ptr,stim), and to compare their prognostic value.
Methods Between November 2014 and June 2015, Ptr,stim and ultrasound variables were measured in mechanically ventilated patients <24 hours after intubation (‘initiation of mechanical ventilation (MV)’, under assist-control ventilation, ACV) and at the time of switch to pressure support ventilation (‘switch to PSV’), and compared using Spearman's correlation and receiver operating characteristic curve analysis. Diaphragm dysfunction was defined as Ptr,stim <11 cm H2O.
Results 112 patients were included. At initiation of MV, Ptr,stim was not correlated to diaphragm thickness (p=0.28), EXdi (p=0.66) or TFdi (p=0.80). At switch to PSV, TFdi and EXdi were respectively very strongly and moderately correlated to Ptr,stim, (r=0.87, p<0.001 and 0.45, p=0.001), but diaphragm thickness was not (p=0.45). A TFdi <29% could reliably identify diaphragm dysfunction (sensitivity and specificity of 85% and 88%), but diaphragm thickness and EXdi could not. This value was associated with increased duration of ICU stay and MV, and mortality.
Conclusions Under ACV, diaphragm thickness, EXdi and TFdi were uncorrelated to Ptr,stim. Under PSV, TFdi was strongly correlated to diaphragm strength and both were predictors of remaining length of MV and ICU and hospital death.
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B-PD and MD contributed equally
Contributors B-PD, MD and AD designed the study. MD coordinated the study. MD, B-PD, SD and JM were responsible for patient screening, enrolment and follow-up. MD, B-PD, TS and AD analysed the data. B-PD, MD, TS and AD wrote the manuscript. All authors had full access to all of the study data, contributed to draft the manuscript or revised it critically for important intellectual content, approved the final version of the manuscript, and take responsibility for the integrity of the data and the accuracy of the data analysis.
Funding B-PD was supported by a postgraduate fellowship grant from the Fondation du Centre Hospitalier de l'Université de Montréal (CHUM). MD was supported by The French Intensive Care Society (SRLF bourse de mobilité 2015); The 2015 Short Term Fellowship programme of the European Respiratory Society; The 2015 Bernhard Dräger Award for advanced treatment of ARF of the European Society of Intensive Care Medicine; The Assistance Publique Hôpitaux de Paris; The Fondation pour la Recherche Médicale (FDM 20150734498) and by Mitacs Globalink Sorbonne Universités. The clinical research of ‘Département R3S’ is supported by the programme ‘investissement d'avenir ANR-10-AIHU 06’ of the French Government.
Competing interests B-PD has received honoraria from GlaxoSmithKline, Boehringer Ingelheim, Astra Zeneca and Roche. AD has signed research contracts with Covidien, Maquet and Philips; he has also received personal fees from Covidien and MSD. MD received personal fees from Pulsion Medical System and Astra Zeneca. Relevant to the present study, TS has received personal fees from Lungpacer and is a member of the board of a research association that has received, over the past 10 years, unrestricted research grants from Maquet, Hamilton, Covidien and Philips; he is the head of a research unit (UMRS 1158) that has signed research contracts with Air Liquide Medical Systems, France; he is listed as inventor or co-inventor on several patents, granted or pending, describing a brain-ventilator interface.
Ethics approval Comité de Protection des Personnes Ile de France VI.
Provenance and peer review Not commissioned; externally peer reviewed.
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