The costophrenic recess as the marker of phrenic nerve funct
An interscalene brachial plexus (ISB) nerve block is a commonly utilized modality for shoulder analgesia. However, a side effect of this approach is phrenic nerve blockade which may preclude patients with impaired pulmonary function from the benefit of this nerve block. Previous studies have demonstrated that lower doses of local anesthetics, ultrasound guidance, and a lower cervical approach when performing the block have resulted in a decreased incidence of phrenic nerve blockade. Despite all of this, the side effect of phrenic nerve blockade and pulmonary complications may still occur and there is not a well-established and rapid modality for anesthesia providers to assess for phrenic nerve blockade after completing an ISB. The objective of the study was to determine if the movement of the most caudal lung tissue into the costophrenic recess can be used as a marker of normal diaphragmatic function, aiding in the diagnosis of perioperative respiratory complications.

A prospective, observational pilot study evaluating twenty adult patients (age 18 or older) with ASA classification I-III. Pre block and post block ultrasound scanning of lung tissue was performed to determine the presence or absence of lung tissue in the costophrenic recess, with absence being a marker of phrenic nerve blockade causing paralysis of the ipsilateral diaphragm. A descriptive analysis was performed.
All 20 patients had successful interscalene nerve block and endorsed thumb paresthesia after the block. All patients in the study also had lung tissue present in the costophrenic recess during the pre and post block ultrasounds suggesting no phrenic nerve involvement. None of the patients experienced respiratory complications immediately after the interscalene block, in the post anesthesia care unit, or within 24 hours post-op. The pre and post block scans were all performed in less than three minutes.

Conclusively, study demonstrates that ultrasound scanning of the costophrenic recess is a potential novel, feasible and rapid technique for assessing phrenic nerve function after a low cervical approach interscalene nerve block.

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