Incidence of phrenic nerve block and hypercapnia in patients undergoing carotid endarterectomy under cervical plexus block.

Deep cervical plexus blockade blocks the second, third and fourth cervical nerve roots. The phrenic nerve arises from C3, C4, C5 and should therefore be commonly blocked with cervical plexus blockade. The aim of this study was to report the incidence of phrenic nerve block and to assess the effect of this on arterial carbon dioxide tension (PaCO2) in premedicated and sedated patients. Forty patients were studied, blood gases being taken on the day before surgery, immediately before performing the block and then every 20 minutes until the operation was completed. Fluoroscopy was used to determine ipsilateral hemidiaphragmatic dysfunction due to phrenic nerve block. The patients were then divided into two groups of analysis. Group A patients had evidence of phrenic nerve block, Group B patients had no evidence of phrenic nerve block. Fluoroscopy showed that 22 patients (55%) had evidence of phrenic nerve block (Group A), 18 patients showed no change (Group B). PaCO2 levels increased in both groups following premedication, from 41 +/- 5 mmHg (mean +/- SD) to 46 +/- 5 mmHg in Group A, and 41 +/- 4 mmHg in Group B; twenty minutes after cervical plexus block the PaCO2 rose to 49 +/- 6 mmHg in Group A, and 48 +/- 6 mmHg in Group B. These changes were not statistically significantly different when the two groups were compared.