Mapping the phrenic nerve motor point: the key to a successful laparoscopic diaphragm pacing system in the first human series

Abstract

Background: For patients with high spinal cord injury and chronic respiratory insufficiency, electrically induced diaphragm pacing is an alternative to long-term positive pressure ventilation. The goal of this study was to laparoscopically assess the phrenic nerve motor point of the diaphragm and then implant electrodes to produce chronic negative pressure ventilation.

Methods: Patients undergoing elective laparoscopic procedures (volunteer patient group) underwent a series of electrical stimuli (2 to 24 mA at 100-microsecond pulse widths) with a mapping probe to identify the motor point through qualitative visualization of diaphragm motion and quantitative measurement of the abdominal pressure to assess the strength of the contraction. After Food and Drug Administration and Institutional Review Board approval, tetraplegic patients (spinal cord injured patient group) who were ventilator dependent underwent mapping and implantation of electrodes for pacing in both diaphragms.

Results: In the volunteer group, 28 patients underwent 3 to 50 stimulations per diaphragm to identify the motor points. Throughout this series the surgical tools and software were improved to allow rapid motor point location with a grid-mapping algorithm. In the spinal cord injured group, 5 of 6 patients had electrodes successfully implanted at the motor point to produce adequate tidal volumes. The one failure caused a change in our inclusion criteria to include fluoroscopic confirmation of diaphragm movement during surface nerve stimulation. Three patients are completely free of the ventilator, and the other 2 are progressively increasing their time off the ventilator with conditioning.

Conclusions: Mapping and implantation of the electrodes can be done laparoscopically, providing for a low-risk, cost-effective, outpatient, diaphragm pacing system that will support the respiratory needs of patients.