From the Guidelines
To assess for phrenic nerve injury, a diaphragmatic ultrasound study is recommended. This non-invasive imaging technique directly evaluates diaphragmatic movement and function, which is controlled by the phrenic nerve. The study involves real-time B-mode ultrasound imaging of the diaphragm during normal breathing and deep inspiration, typically using a 3-5 MHz curvilinear transducer. The sonographer will measure diaphragm thickness, excursion (movement amplitude), and assess for paradoxical motion. Normal diaphragmatic movement shows downward displacement during inspiration, while paradoxical upward movement during inspiration strongly suggests phrenic nerve dysfunction. M-mode ultrasound can also quantify the degree of diaphragmatic movement. The examination should be performed bilaterally to compare the affected side with the normal side.
According to the European Society of Intensive Care Medicine, diaphragmatic ultrasound assessment is a useful and feasible bedside tool that easily identifies diaphragm paralysis and helps in predicting prolonged and/or failure of weaning from mechanical ventilation through examining excursion (DE) or thickening fraction (TF) 1. The panel agreed on the use of DE to assess diaphragmatic dysfunction during the weaning from mechanical ventilation.
Some key points to consider when performing a diaphragmatic ultrasound study include:
- Using a 3-5 MHz curvilinear transducer for optimal imaging
- Measuring diaphragm thickness and excursion (movement amplitude)
- Assessing for paradoxical motion
- Performing the examination bilaterally to compare the affected side with the normal side
- Using M-mode ultrasound to quantify the degree of diaphragmatic movement.
This study is preferred because it's readily available, radiation-free, can be performed at bedside, and provides immediate results. Diaphragmatic ultrasound has high sensitivity and specificity for detecting phrenic nerve injury, making it an excellent first-line diagnostic tool before considering more invasive tests like electromyography.
From the Research
Ultrasound Studies for Phrenic Nerve Injury
To assess for phrenic nerve injury, several ultrasound studies can be utilized:
- Diaphragmatic ultrasound can be used for the early diagnosis of phrenic nerve palsy after shoulder surgery, as it has proven to be a rapid diagnostic tool with high sensitivity and specificity 2.
- Ultrasound-guided transcutaneous phrenic nerve stimulation can be used for the daily bedside assessment of diaphragm function in critically ill patients, as it is a simple and accurate tool 3.
- Phrenic nerve conduction study (NCS) can be used to diagnose unilateral diaphragmatic paralysis, as it is a simple, reproducible, noninvasive method whose results correlate well with transdiaphragmatic pressure measurements 4.
Key Findings
Some key findings from the studies include:
- The use of diaphragmatic ultrasound can anticipate the possible development of immediate complications and act as a guide in choosing the appropriate therapeutic strategy for each case in an early manner 2.
- Phrenic NCS and transdiaphragmatic pressure measurements both had high sensitivity and specificity for diagnosing unilateral diaphragmatic paralysis 4.
- Ultrasound-guided transcutaneous phrenic nerve stimulation had excellent performance for the diagnosis of diaphragm dysfunction and severe diaphragm dysfunction, with areas under the curve of 0.90 and 0.88, respectively 3.
Limitations
It is worth noting that:
- Phrenic nerve conduction study results cannot differentiate success or failure in selection of patients for diaphragm pacing, and direct surgical evaluation of the diaphragm should be performed 5.
- Phrenic NCS are inadequate pre-operative studies, and direct laparoscopic evaluation should be offered for all spinal cord injured patients to receive the benefit of diaphragm pacing 5.