Phrenic nerve conduction disorder after open heart surgery--electrophysiological study

In 32 consecutive adult patients undergoing heart surgery, the induced diaphragmatic muscle action potential was measured. Phrenic nerve conduction disorder was defined as disappearance of muscle action potential (Edi) and conduction time (CT). Phrenic nerve conduction disorder was observed in 10 patients (31%); 8 patients on the left side and 2 patients on both sides. In non-conduction disorder group (22 patients), Edi and CT were measured. Edi of the right side decreased significantly from preoperative value of 705 +/- 318 microV to 445 +/- 285 microV at 1-3 days after operation (stage I) and to 559 +/- 314 microV at 7-10 days after operation (stage II) (p less than 0.05). CT of the right side prolonged significantly from 7.1 +/- 0.7 msec before operation to 7.44 +/- 0.97 msec at postoperative stage I and to 7.40 +/- 0.21 msec at postoperative stage II (p less than 0.05). For the left phrenic nerve, Edi showed significant (p less than 0.05) decrease from 803 +/- 338 microV before operation to 429 +/- 251 microV at the postoperative stage I and 620 +/- 350 microV at the postoperative stage II. In the conduction disorder group, incidence of atelectasis, diaphragm elevation and pleural effusion as documented by chest roentgenographic findings were higher than those of non-conduction disorder group (p less than 0.01). Moreover, the lowest temperature of the myocardium during operation was significantly (p less than 0.05) lower for conduction disorder group as compared to non-conduction disorder group. We believed that it is necessary to develop a innovative method for preventing the phrenic nerve from cold injury.