Differential lung ventilation assessed by electrical impedance tomography in ultrasound-guided anterior suprascapular nerve block vs. interscalene brachial plexus block

BACKGROUND Ultrasound-guided interscalene brachial plexus block (ISB) is used to control pain after shoulder surgery . Though effective, drawbacks include phrenic nerve block and motor block of the hand. The ultrasound-guided anterior approach to perform suprascapular nerve block (SSNB) may provide a good alternative. OBJECTIVE To compare lung ventilation and diaphragmatic activity on the operated side in ISB and SSNB. DESIGN Randomised, controlled patient-blinded and assessor-blinded trial. SETTING Outpatient surgical clinic with recruitment from June 2017 to January 2018. PATIENTS Fifty-five outpatients scheduled for arthroscopic shoulder surgery were allocated randomly to receive SSNB or ISB. Technical problems with monitoring devices unrelated to the intervention led to exclusion of seven patients. The remaining 48 ( n =24 in each group) were followed up for 24 h without drop-outs. INTERVENTIONS Patients received 10 ml of ropivacaine 1.0% wt/vol for both procedures. OUTCOME MEASURES Percentage lung ventilation on the operated side was the primary endpoint as assessed with electrical impedance tomography (EIT). Secondary endpoints were hemidiaphragmatic motion on the operated side, pain, opioid use, hand strength and numbness, and patient satisfaction. RESULTS Before regional anaesthesia, the lung on the operated side contributed a median [IQR] of 50 [42 to 56]% of the total lung ventilation. Postoperatively, it was 40 [3 to 50]% (SSNB) vs. 3 [1 to 13]% (ISB) for an adjusted difference of 23 (95% CI, 13 to 34)%, ( P < 0.001). Hemidiaphragmatic motion was 1.90 (95% CI, 1.37 to 2.44 cm), ( P < 0.001) lower in the ISB group compared with the SSNB group. Hand strength was 11.2 (95% CI 3.6 to 18.9), ( P = 0.0024) kg greater for SSNB and numbness was observed in 0% (SSNB) vs. 46% (ISB) of patients, P < 0.001. Pain was low in the first 6 h after surgery in both groups with slightly, but not significantly, lower values for ISB. No meaningful or significant differences were found for opioid use or patient satisfaction. CONCLUSION An ultrasound-guided anterior approach to SSNB preserves ipsilateral lung ventilation and phrenic function better than a standard ISB. TRIAL REGISTRATION drks.de identifier: DRKS00011787.