Expiratory Muscle Function in Critically Ill Ventilated Patients

Expiratory Muscle Function in Critically Ill Ventilated Patients

Inspiratory muscle weakness develops rapidly in ventilated critically ill patients and is associated with adverse outcome, including prolonged duration of mechanical ventilation and mortality. Surprisingly, the effects of critical illness on expiratory muscle function have not been studied.

The main expiratory muscles are the abdominal wall muscles, including the external oblique (EO), internal oblique (IO) and transversus abdominis muscles (TRA). These muscles are activated when respiratory drive or load increases, which can be during e.g. exercise, diaphragm fatigue, increased airway resistance, or positive airway pressure ventilation. The abdominal wall muscles are also critical for protective reflexes, such as coughing. Reduced abdominal muscles strength may lead to decreased cough function and thus inadequate airway clearance. This will lead to secretion pooling in the lower airways, atelectasis, and ventilator associated pneumonia (VAP). Studies have shown that decreased cough function is a risk for weaning failure and (re)hospitalization for respiratory complications. Further, high mortality was found in patients with low peak expiratory flow.

Considering the importance of a proper expiratory muscle function in critically ill patients, it is surprising that the prevalence, causes, and functional impact of changes in expiratory abdominal muscles thickness during mechanical ventilation (MV) for critically ill patients are still unknown.

Ultrasound is increasingly used in the ICU for the visualization of respiratory muscles. In a recent pilot study the investigators confirmed the feasibility and reliability of using of ultrasound to evaluate both diaphragm and expiratory abdominal muscle thickness in ventilated critically ill patients (manuscript in preparation). Accordingly, the primary aim of the present study is to evaluate the evolution of abdominal expiratory muscle thickness during MV in adult critically ill patients, using ultrasound data.

Inclusion Criteria:

• Age > 18 years
• Invasive mechanical ventilation < 48 hours
• Expected duration of mechanical ventilation > 72 hours

Exclusion Criteria:

• Past medical history of neuromuscular disorders
• Mechanical ventilation > 48 hours within the current hospital admission
• Pregnant women
• Open abdominal wounds at proposed location of the ultrasound probe, due to recent abdominal surgery