2025 Workshop Handout Bundle-W11RTA Advanced EMG US Respiratory System

W11RTA Advanced EMG US Respiratory System - Boon Litchy

Pdf Summary

This workshop handout by Dr. Andrea Boon and Dr. William Litchy from Mayo Clinic provides an advanced overview of electrodiagnostic and ultrasound techniques for evaluating the respiratory system, focusing primarily on the diaphragm and phrenic nerve.<br /><br />Patients with unexplained dyspnea or difficulty weaning from mechanical ventilation may have pathologies affecting central drive, the phrenic nerve, neuromuscular transmission, or muscle function. Phrenic nerve conduction studies (NCS) and diaphragm needle electromyography (EMG) help differentiate neuropathic, myopathic, and central causes, providing diagnostic and prognostic insights. However, these techniques can be challenging and carry some risk.<br /><br />Ultrasound is now routinely used to evaluate the diaphragm. B-mode ultrasound images the diaphragm thickness and structure, measuring thickness at rest and during inspiration to calculate a thickening ratio, which helps assess muscle function. The right hemidiaphragm is easier to image due to the liver acoustic window. M-mode ultrasound evaluates diaphragm motion/excursion during respiration, aiding in detection of paralysis or dysfunction.<br /><br />The phrenic nerve is stimulated percutaneously at the neck, and responses are recorded from the diaphragm using two electrode montages to ensure accuracy and avoid brachial plexus stimulation. Normal amplitude and latency values are provided. Troubleshooting techniques and safety considerations are discussed, noting the low risk even in patients with cardiac devices.<br /><br />Needle EMG of the diaphragm is performed via an intercostal approach just above the costal margin between the medial clavicular and anterior axillary lines, passing through intercostal muscles to the diaphragm. Ultrasound guidance enhances safety by selecting the safest site, guiding needle depth, and visualizing needle entry, especially in challenging patients such as those obese or with altered anatomy. Complication rates like pneumothorax are low with proper technique.<br /><br />Ultrasound and EMG can also assess other chest wall muscles such as serratus anterior, intercostals, and rhomboids. Ultrasound guidance improves accuracy and lowers pneumothorax risk during needle examination of these muscles.<br /><br />In summary, combining phrenic NCS, diaphragm EMG, and diaphragm ultrasound provides a comprehensive evaluation of respiratory neuromuscular function. Ultrasound is essential for safe and effective diaphragm assessment, improving diagnostic yield and guiding management of respiratory failure.

Keywords

electrodiagnostic techniques

ultrasound evaluation

respiratory system

diaphragm assessment

phrenic nerve conduction studies

diaphragm electromyography

neuromuscular respiratory dysfunction

mechanical ventilation weaning

diaphragm ultrasound imaging

needle EMG safety