A high cervical spinal cord injury (SCI) is an injury in the upper neck between the first and fourth cervical vertebrae (C1 to C4). SCIs can damage the phrenic nerve that controls the diaphragm (the main muscle used in breathing) and cause chronic respiratory insufficiency. Some people with high cervical SCIs cannot breathe on their own, so they need a mechanical ventilator to help them breathe.
Standard care for managing respiratory insufficiency caused by SCIs includes non-invasive ventilation (such as bi-level positive airway pressure) and invasive mechanical ventilation (such as intubation or tracheostomy). An alternative to ventilatory support is intramuscular diaphragm stimulation for people with intact phrenic nerve function.
This procedure involves directly stimulating the phrenic nerve so that it sends a signal to the diaphragm to contract, which produces the inhalation phase of breathing. It aims to provide ventilatory support for people with intact phrenic nerves and functioning diaphragm muscles.
The procedure is usually done using a thoracic approach (often using a thoracoscopic technique; thoracotomy is rarely used) and under general anaesthesia. Once the phrenic nerve is identified and tested, an electrode is placed around the nerve in the chest, and then stabilised. The electrode is connected to a subcutaneous receiver, usually placed in the chest wall. An external transmitter (powered by batteries) then sends radiofrequency signals to the device through an antenna which is worn over the receiver. The receiver translates radio waves into stimulating electrical pulses that are delivered to the phrenic nerve by the electrode, to achieve diaphragm contraction and support breathing. The device is tested during and after the surgery to ensure that it is working. This procedure is usually done bilaterally but can also be done unilaterally. A cervical approach can also be used and is done under general or local anaesthesia.
After the procedure, the person follows a diaphragm conditioning programme, which involves progressive use of the system for increasing periods of time with gradual weaning from the ventilator.