Purpose: An intermediate cervical plexus block (CPB) targets the posterior cervical space between the sternocleidomastoid muscle and the prevertebral fascia. The phrenic nerve descends obliquely on the surface of the anterior scalene muscle beneath the prevertebral fascia after originating from the C3-C5 ventral rami. Therefore, the phrenic nerve can be affected by a local anesthetic during an intermediate CPB, depending on the permeability characteristics of the prevertebral fascia. This study investigated whether an intermediate CPB affects the phrenic nerve, inducing hemidiaphragmatic paresis.
Methods: In this prospective observational study, 20 patients undergoing single-incision transaxillary robot-assisted right thyroidectomy were enrolled. The intermediate CPB (0.25% ropivacaine 0.2 ml/kg) was performed at the C4-5 intervertebral level carefully, without penetrating the prevertebral fascia, before the patient emerged from general anesthesia. Diaphragmatic motions of the block side were measured by M-mode ultrasonography at three time points: before anesthesia (baseline) and at 30 and 60 min after the intermediate CPB. Hemidiaphragmatic paresis was divided into three grades, depending on the percentage of diaphragm movement compared to the baseline: none (> 75%), partial paresis (25-75%), and complete paresis (< 25%).
Results: No patient showed any partial or complete ipsilateral hemidiaphragmatic paresis within 60 min after the intermediate CPB.
Conclusion: Intermediate CPB using 0.2 ml/kg of 0.25% ropivacaine at the C4-5 intervertebral level did not cause ipsilateral hemidiaphragmatic paresis. This may imply that the effect of the intermediate CPB on the phrenic nerve is not significant.
Keywords: Diaphragm; Intermediate cervical plexus block; Paresis; Phrenic nerve.