Diagnosing Respiratory Muscle Weakness

Abstract

Weakness of the respiratory muscles may be the sole disorder, or an important associated condition in patients admitted to the emergency department or to the intensive care unit (ICU). Thus, acute ventilatory failure is caused by pure respiratory muscle weakness in many neuromuscular disorders, like Duchenne muscular dystrophy, myasthenia gravis, Guillain-Barré syndrome, or amyotrophic lateral sclerosis. In some cases, the disorder is still unrecognized when the patient enters the hospital for acute respiratory failure. Furthermore, respiratory failure due to pulmonary disease, like chronic obstructive pulmonary disease (COPD), may be aggravated by concomittant undernutrition and muscle weakness. After a period of mechanical ventilation, weaning the patient with a neuromuscular disorder from the respirator is critically dependent on respiratory muscle strength. Sometimes, an unrecognized pre-existing neurological disease is detected because of weaning difficulties. Finally, weaning may have to be delayed because of a neuromuscular disorder acquired in the ICU, such as critical illness polyneuropathy, prolonged neuromuscular blockade, or acute necrotizing myopathy [1–3]. Recognizing weakness of the respiratory muscles is, therefore, highly relevant for clinicians working in the emergency department or in the ICU. Focusing on clinically applicable methods, this chapter summarizes the usefulness and limitations of classical tests, and presents recent methodological developments for diagnosing respiratory muscle weakness.