Phrenic Nerve Stimulation for Diaphragm Pacing in a Quadriplegic Patient
A 62-year-old female patient reported severe dyspnea and showed tachypnea. She was diagnosed as a pulmonary thromboembolism and immediate anticoagulation with warfarin was started. In the morning two days after anticoagulation, she felt heaviness in both legs and progressive paraparesis. A neurologist evaluated her and requested a lumbosacral magnetic resonance imaging (MRI) of the lumbar spine. While waiting for the MRI, her paraparesis progressively increased and ascended; eventually she became quadriplegic and respiratory distress developed. After checking whole spine MRI, an emergent endotracheal intubation was performed and neurosurgical consultation was taken. On examination, she was alert and no focal cranial nerve sign was observed. However, grade 0 quadriplegia was noticed and tendon reflex was not elicited. An acute epidural hematoma was noted on the high cervical cord (). After informed consent, an emergent decompression of the cervical cord was performed. Unfortunately, her quadriplegia did not improve after surgery. Moreover, self-respiration was not elicited. Thereafter, she was maintained with artificial ventilation during the following three months in the intensive care unit. During the follow-up, no spontaneous, voluntary respiration was observed and the MRI checked at postoperative 3 months showed a myelomalacia at the C2 level suggesting high cervical cord injury (). A standard apnea test did not elicit voluntary respiratory effort. After 3 months of artificial ventilation, we decided to perform a trial of diaphragm pacing, and informed consent was taken. An electromyographic examination of the diaphragm was performed for the verification of contraction of the diaphragm.\nA stimulation lead implantation was performed in right neck under general anesthesia with the head rotated to the left side. Muscle relaxant was not used to monitor intraoperative contraction of the diaphragm. A linear horizontal skin incision about 4 cm was made at 4 cm rostral to the right clavicle, crossing the posterior border of the sternocleidomastoideus muscle. After dissecting the subcutaneous tissue and retracting the sternocleidomastoideus medially, the anterior scalene muscle and the right phrenic nerve was identified over the scalene muscle with monopolar electrical stimulation (50 Hz, 1 msec, 1.5-2 volts, Eclipse Neurological Workstation, Axon Systems, USA) (). The nerve sheath of the phrenic nerve was carefully dissected about 3 cm in length, but we did not dissect the space between the nerve and the scalene muscle. A quadripolar, cylindrical electrode (Quatrode®, St. Jude Medical, Plano, TX, USA) was placed along the phrenic nerve and fixed with 3 sutures to the surrounding connective tissue (). A great care was taken to avoid injury and entrapment of the phrenic nerve. During intraoperative stimulation, a brisk downward deflection of the diaphragm was noticed under fluoroscopy. The distal end of the electrode was tunneled subcutaneously to the left subclavicular subcutaneous pocket and connected to the implantable pulse generator (IPG) (Eon-Mini Rechargeable®, St. Jude Medical, Plano, TX, USA).\nTwo days after surgery, the IPG was turned on. The second proximal contact of the quadripolar electrode was used as cathode and the third contact was used as positive. The other contacts were set to "off". After turning the IPG on, the carbon dioxide pressure of the exhalation and the arterial oxygen saturation in the fingertip were monitored until the values became stable. The carbon dioxide pressure in the end tidal breath was adjusted to about 400 mm Hg by changing the output strength of the IPG. The parameters of chronic stimulation were 1(-), 2(+), 300 µsec, 30 Hz, 2 seconds on with 4 seconds off in cyclic mode. After confirmation of stable end-tidal PCO2 and SaO2 levels for more than two hours in the patient's bed, the patient was allowed to ambulate in a wheelchair without mechanical ventilation. The ambulation time was gradually increased up to two hours. However, the weaning time of mechanical ventilation could not be increased more than three hours due to fatigue of breathing chest muscles. She was weaned and could ambulate in the wheelchair for two to three hours in daytime, spending time with her family, and she was dependent on the mechanical ventilator for the rest of the time. At an examination twelve months after the operation, she could ambulate with diaphragm pacing in the wheelchair for two to three hours in daytime. Mild neck discomfort around the electrode implantation site was noticed; however, there was no evidence of granulation or infection during the follow-up. She suffered pneumonia two times after diaphragmatic pacing which was easily controlled with antibiotics during the follow-up.