Although phrenic nerve paresis or paralysis is generally believed to have a good prognosis, few studies to date have addressed the rate of phrenic nerve recovery. Chandler et al followed up five patients with bilateral diaphragmatic paralysis after bypass surgery and noted recovery, based on spirometric measurements, in four, partial recovery in three, and complete recovery in one. This recovery was variable occurring over approximately 6 to 12 months after CAB surgery. Abd et al recently reported follow-up data on nine patients with diaphragm dysfunction after bypass surgery. Although serial phrenic nerve studies were not performed, Pimax increased progressively in three patients up to approximately 200 days after surgery, a similar time span to that reported in our study.
Phrenic nerve studies have not commonly been employed to assess phrenic recovery after CAB surgery. Kohorst et al found a reduction in latency and an increase in CDAP in one patient comparing studies at 3 and 10 months. Despite the fact that latencies were within normal limits, persistent diaphragmatic weakness was suggested by a moderate reduction in lung volumes in the latter study. Markand et al performed serial phrenic nerve studies on one patient with left phrenic nerve paralysis after bypass surgery. Phrenic nerve recovery was first noted 28 weeks after CAB surgery; however, marked paresis remained as evidenced by prolonged latency and a reduced CDAP. In this study, we also found a prolonged time course of recovery after bypass surgery. Phrenic nerve integrity was first established between 6 and 12 months, with continued recovery noted thereafter in several patients, up to study termination at a maximum of 20 months.