Diaphragm ultrasound in patients with prolonged weaning from mechanical ventilation

Abstract

Background: Several publications have examined diaphragmatic ultrasound using two-dimensional (2D) parameters in the context of weaning from mechanical ventilation (MV) and extubation. However, the studied cohorts had rather short duration of ventilation. Examinations on patients with prolonged weaning after long-term ventilation were missing. It was the aim of this study to assess of the diaphragm and peripheral musculature of patients undergoing prolonged weaning creating a chronological sequence of ultrasonic parameters during the course of weaning.

Methods: This study was carried out as a monocentric, prospective observational cross-sectional study. Patients in prolonged weaning who were transferred to a specialized weaning unit were eligible for inclusion if they were ventilated invasively by means of an endotracheal tube or tracheal cannula and if their expected treatment period was at least 5 days. Diaphragmatic function and one representative peripheral muscle were examined in 50 patients between March 2020 and April 2021. The 2D sonographic parameters of diaphragm and diaphragmatic function consisted of diaphragmatic thickness (Tdi) at the end of inspiration and expiration, the fractional thickening (FT) and the diaphragmatic excursion. Additionally, the M. quadriceps femoris was sonographically assessed at two locations. The difference of measurements between the first and the last measuring timepoint were examined using the Wilcoxon signed-rank test. For a longer chronological sequence, the Friedman's rank sum test with subsequent Wilcoxon-Nemenyi-McDonald-Thompson test for multiple comparisons was carried out.

Results: Fifty patients with prolonged weaning were included. The median duration of MV before transfer to the weaning unit was 11.5 [interquartile range (IQR) 10] days. Forty-one patients could be assessed over the full course of weaning, with 38 successfully weaned. Within these 41 patients, the sonographic parameters of the diaphragm slightly increased over the course of weaning indicating an increase in thickness and mobility. Especially parameters which represented an active movement reached statistical significance, i.e., inspiratory Tdi when assessed under spontaneous breathing [begin 3.41 (0.99) vs. end 3.43 (1.31) mm; P=0.01] and diaphragmatic excursion [begin 0.7 (0.8) vs. end 0.9 (0.6) cm; P=0.01]. The presence of positive end-expiratory pressure (PEEP) and pressure support did not influence the sonographic parameters significantly. The M. quadriceps femoris, in contrast, decreased slightly but constantly over the time [lower third: begin 1.36 (0.48) vs. end 1.28 (0.36) cm; P=0.054].

Conclusions: The present study is the first one to longitudinally analyse diaphragmatic ultrasound in patients with prolonged weaning. Sonographic assessment showed that Tdi and excursion increased over the course of prolonged weaning, while the diameter of a representative peripheral muscle decreased. However, the changes are rather small, and data show a wide dispersion. To allow a potential, standardized use of diaphragm ultrasound for diagnostic decision support in prolonged weaning, further studies in this specific patient group are required.

Keywords: Diaphragm; prolonged weaning; ultrasonography; ultrasound; ventilator weaning.

Figure 1

Flow diagram of the exclusion process from screening to final inclusion of patients in the study according to eligibility criteria indicating the reasons to exclude patients and the respective numbers. COVID-19, coronavirus disease 2019.

Figure 2

Sonographic assessment of diaphragm and peripheral musculature at the beginning and at the end of the weaning process. (A) Inspiratory diaphragmatic thickness. (B) Expiratory diaphragmatic thickness. (C) Fractional thickening. (D) Diaphragmatic excursion. (E,F) Diameter of the musculus quadriceps femoris measured on the half (E) as well as between the lower and the two upper thirds (F) of a line between patella and spina iliaca anterior superior. The box indicates the IQR and the median, the whiskers indicate 1.5 times the IQR and the dots indicate outliers. The blue boxes give the data at the beginning of weaning, while the red boxes represent the end of the weaning process. P values were calculated using the Wilcoxon signed rank test. *, P<0.05. IQR, interquartile range.

Figure 3

Sonographic assessment of diaphragm and peripheral musculature over the course of the weaning process. (A) Inspiratory diaphragmatic thickness. (B) Expiratory diaphragmatic thickness. (C) Fractional thickening. (D) Diaphragmatic excursion. (E,F) Diameter of the musculus quadriceps femoris measured on the half (E) as well as between the lower and the two upper thirds (F) of a line between patella and spina iliaca anterior superior. The box indicates the IQR and the median, the whiskers indicate 1.5 times the IQR and the dots indicate outliers. The line within the box indicates the median, while the diamond indicates the mean value. The measurements were derived at the beginning of the weaning process, after 1/3, after 2/3 and immediately before completion of the weaning. P values were calculated using the Friedman’s rank sum test. *, P<0.05. IQR, interquartile range.