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    Intramuscular diaphragm stimulation for ventilator-dependent chronic respiratory failure from high spinal cord injuries

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    2 The condition, current treatments and procedure

    The condition

    2.1 High spinal cord injuries can damage the nerves that control breathing and cause chronic respiratory failure.

    Current treatments

    2.2 Current standard care for managing chronic respiratory failure in patients with high spinal cord injuries includes non-invasive forms of ventilation support (such as bi-level positive airway pressure). In advanced stages of respiratory failure, mechanical ventilation is done through a permanent tracheostomy. Phrenic nerve pacing is an alternative treatment for patients who have intact phrenic nerves (the nerves that contract the diaphragm). The diaphragm is stimulated to contract by electrodes placed on the phrenic nerve in the neck or thorax.

    The procedure

    2.3 The aim of intramuscular diaphragm stimulation is to make the diaphragm contract, enabling a full or partial weaning from mechanical ventilation. This procedure needs intact phrenic nerve function. It avoids the need to access the phrenic nerve through the neck or thorax, as well as reducing the risk of phrenic nerve damage.

    2.4 The procedure is done laparoscopically with the patient under general anaesthesia. Areas of the diaphragm where minimal electrical stimulation causes maximal diaphragm contraction (known as the 'motor points') are mapped. Two intramuscular electrodes are implanted on the abdominal surface of each hemi-diaphragm at the motor points. The electrode leads are tunnelled subcutaneously to an exit site in the chest where they are connected to an external battery-powered pulse generator. A reference electrode (anode) is also implanted and the leads tunnelled with the other electrodes. Intraoperative stimulation and voltage calibration tests are done to confirm adequate contraction of the diaphragm. After implantation the patient has a diaphragm conditioning programme, which involves progressive use of the system for increasing periods of time with gradual weaning from the ventilator.