Background
Severe shoulder pain occurs frequently after surgery close to the diaphragm, potentially caused by referred pain via the ipsilateral phrenic nerve. We aimed to assess the analgesic effect of an ultrasound-guided phrenic nerve block on moderate to severe right-sided shoulder pain after open partial hepatectomy.

Methods
This was a randomized, double-blind, placebo-controlled, pilot study, comparing ultrasound-guided phrenic nerve block (ropivacaine 0.75 mg/mL) versus placebo (isotonic sodium chloride 0.9 mg/mL) on severe post-hepatectomy shoulder pain (NRS ≥6). Pre- and postoperative spirometry and arterial blood gas analyses were used to assess respiratory function. Subjects with chronic lung disease were excluded. Unfortunately, due to lack of funding, the trial was ended prematurely and therefore presented as a pilot study.

Results
One hundred and one subjects were screened for eligibility; 14 subjects were randomized, and two subjects were later excluded; thus, 12 subjects were analyzed with six in each group. A statistically significant difference in reduction in median pain intensity between groups was observed 15 minutes after phrenic nerve block (“ropivacaine first” ΔNRS: −6.0 [−6.0 to −3.0] vs. “saline first” ΔNRS: 0 [−6.0 to 1.0], P = .026). Spirometry results and arterial blood gas analyses were not clinically impacted by the block.

Conclusions
Postoperative phrenic nerve block significantly reduced severe post-hepatectomy shoulder pain. Larger studies are warranted to confirm the lack of clinically relevant block-related impairment of respiratory function.