Changes in Respiratory Muscle Thickness during Mechanical Ventilation: Focus on Expiratory Muscles

Abstract

Background The lateral abdominal wall muscles are recruited with active expiration, as may occur with high breathing effort, inspiratory muscle weakness, or pulmonary hyperinflation. The effects of critical illness and mechanical ventilation on these muscles are unknown. This study aimed to assess the reproducibility of expiratory muscle (i.e., lateral abdominal wall muscles and rectus abdominis muscle) ultrasound and the impact of tidal volume on expiratory muscle thickness, to evaluate changes in expiratory muscle thickness during mechanical ventilation, and to compare this to changes in diaphragm thickness. Methods Two raters assessed the interrater and intrarater reproducibility of expiratory muscle ultrasound (n = 30) and the effect of delivered tidal volume on expiratory muscle thickness (n = 10). Changes in the thickness of the expiratory muscles and the diaphragm were assessed in 77 patients with at least two serial ultrasound measurements in the first week of mechanical ventilation. Results The reproducibility of the measurements was excellent (interrater intraclass correlation coefficient: 0.994 [95% CI, 0.987 to 0.997]; intrarater intraclass correlation coefficient: 0.992 [95% CI, 0.957 to 0.998]). Expiratory muscle thickness decreased by 3.0 ± 1.7% (mean ± SD) with tidal volumes of 481 ± 64 ml (P < 0.001). The thickness of the expiratory muscles remained stable in 51 of 77 (66%), decreased in 17 of 77 (22%), and increased in 9 of 77 (12%) patients. Reduced thickness resulted from loss of muscular tissue, whereas increased thickness mainly resulted from increased interparietal fasciae thickness. Changes in thickness of the expiratory muscles were not associated with changes in the thickness of the diaphragm (R2 = 0.013; P = 0.332). Conclusions Thickness measurement of the expiratory muscles by ultrasound has excellent reproducibility. Changes in the thickness of the expiratory muscles occurred in 34% of patients and were unrelated to changes in diaphragm thickness. Increased expiratory muscle thickness resulted from increased thickness of the fasciae. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New

High-Intensity Inspiratory Muscle Training Improves Scalene and Sternocleidomastoid Muscle Oxygenation Parameters in Patients With Weaning Difficulties: A Randomized Controlled Trial

“…Importantly, these alternations do not exclusively affect the diaphragm but, although less rapid, may also affect the other Abbreviations: IMT, inspiratory muscle training; PImax, maximal inspiratory pressure; PoB, power of breathing; %StiO 2 , muscle oxygen saturation index; ICU, intensive care unit; EMG, electromyographic; NIRS, near-infrared spectroscopy; COPD, chronic obstructive pulmonary disease; APACHE II, Acute Physiology and Chronic Health Evaluation II Scale; WoB, work of breathing; FVC, forced vital capacity; PIF, peak inspiratory flow; Hb, hemoglobin; Mb, myoglobin; MAP, mean arterial blood pressure. inspiratory and expiratory muscles (Bernard et al, 2003;Capdevila et al, 2003;Shi et al, 2021). Specifically, studies in animal models have found that after 48 h on mechanical ventilation external intercostal muscle of rabbits demonstrated contractile dysfunction and reduction in cross-sectional area of type II fibers (Bernard et al, 2003;Capdevila et al, 2003).…”

“…Diaphragm biopsies of mechanically ventilated patients have demonstrated increased proteolysis and decreased protein synthesis, enhanced number of inflammatory cells and loss of muscle mass as important underlying mechanisms to explain reduced force output of the diaphragm ( Vassilakopoulos and Petrof, 2004 ; Hooijman et al, 2015 ; Berger et al, 2016 ). Importantly, these alternations do not exclusively affect the diaphragm but, although less rapid, may also affect the other inspiratory and expiratory muscles ( Bernard et al, 2003 ; Capdevila et al, 2003 ; Shi et al, 2021 ). Specifically, studies in animal models have found that after 48 h on mechanical ventilation external intercostal muscle of rabbits demonstrated contractile dysfunction and reduction in cross-sectional area of type II fibers ( Bernard et al, 2003 ; Capdevila et al, 2003 ).…”

“…Specifically, studies in animal models have found that after 48 h on mechanical ventilation external intercostal muscle of rabbits demonstrated contractile dysfunction and reduction in cross-sectional area of type II fibers ( Bernard et al, 2003 ; Capdevila et al, 2003 ). A recent study in humans demonstrated time-dependent decreases in abdominal wall muscle thickness due to muscle mass loss in approximately 25% of mechanically ventilated patients ( Shi et al, 2021 ). Furthermore, the increased reliance on the neck inspiratory muscles to overcome the increased respiratory demands has been described in patients with respiratory diseases ( De Troyer and Boriek, 2011 ).…”

Point‐of‐care respiratory muscle ultrasound in a child with medical complexity

“…17,18 In a study of 77 adult patients requiring MV and evaluated with POCUS, 17 (22%) had a decrease of > 15% in expiratory muscle thickness during the first week of MV. 16 In a study of 35 pediatric patients requiring MV, 15 (44%) had a decrease of > 10% in expiratory thickness over the first 4 days of MV. In the latter study, the decrease in expiratory muscle thickness was significantly higher in patients failing extubation compared to those with successful extubation, suggesting that decreases in expiratory muscle thickness may be an early predictor of weaning failure.…”

Point-of-Care Respiratory Muscle Ultrasound in a Child with Medical Complexity

“…[13][14][15] In addition to the adverse effects on the diaphragm attributed to VIDD (longer weaning times, ventilation time and weaning failure), recent investigations of POCUS evaluating the expiratory muscles of the lateral abdominal wall have found similar adverse effects of mechanical ventilation (MV) on these important respiratory muscles resulting in weaning difficulty as well as impaired airway clearance. [16][17][18] Children with medical complexity (CMC) have significant chronic health conditions that may involve multisystem disease (congenital or acquired), high medical fragility, functional and psychosocial impairment, technology dependence (tracheostomies, MV, feeding tubes) and high resource utilization (frequent and/or prolonged hospitalizations). [19][20][21] Advances in obstetric care, neonatal intensive care, pediatric critical care, and medical technology have resulted in a growing population of CMC dependent on long-term MV.…”