Effect of the Ultrasound-Guided Interscalene and Supraclavicular Blocks on the C4 Dermatome

Yue Qiu,1 Chelsea Cady,1 Bedda L Rosario,2 Steven Orebaugh1 1Department of Anesthesiology and Perioperative Medicine, University of Pittsburgh Medical Center, Pittsburgh, PA, USA; 2Department of Epidemiology, University of Pittsburgh, Pittsburgh, PA, USACorrespondence: Steven Orebaugh, Email [email protected]: The C4 dermatome anesthesia holds significance for arthroscopic shoulder surgery. However, the reliability of achieving C4 dermatome anesthesia with the current low-dose ultrasound-guided interscalene block (ISB) and supraclavicular block (SCB) remains uncertain. This prospective, single-center study examined the effects of ultrasound-guided interscalene block (ISB) and supraclavicular block (SCB) on the C4 sensory dermatome in patients undergoing shoulder, hand, or wrist surgery.Patients and Methods: Patients undergoing outpatient shoulder, hand, or wrist surgeries received ultrasound-guided ISB (for shoulder surgeries) with 12– 15 mL of 0.5% bupivacaine or ultrasound-guided SCB (for hand and wrist surgeries) with 20– 24 mL of 0.5% bupivacaine. The primary objective of the study was to investigate the sensory effect on the C4 dermatome after ISB and SCB. The secondary outcomes included the sensory effect on the C5 dermatome after performing ISB and SCB, pain scores upon arrival at the post-anesthesia care unit (PACU), and the incidence of adverse effects.Results: Sixty-one patients were recruited: 30 for ISB and 31 for SCB. C4 dermatome coverage was achieved in 53% and 29% of patients in the ISB and SCB groups, respectively (p=0.0268). Additionally, C5 dermatome coverage was achieved in 97% and 68% of patients in the ISB and SCB groups, respectively (p=0.0034). A moderate correlation coefficient (r=0.47) was observed between C4 sensory scores and postoperative pain scores.Conclusion: Ultrasound-guided ISB successfully provided C4 coverage in 53% of cases, suggesting that performing an additional C4 block alongside ISB could be advantageous when aiming for complete surgical anesthesia. SCB may not be the primary choice for shoulder surgeries as it often fails to achieve satisfactory sensory blocks at the C4 and C5 levels.Plain language summary: This study examined how the interscalene block and supraclavicular block work for numbing the C4 area in patients undergoing shoulder, hand, or wrist surgery. We found that the interscalene block provided C4 coverage in only 53% of cases, suggesting performing an additional C4 block might help achieve complete surgical anesthesia. The supraclavicular block is not the best option for shoulder surgeries because it often fails to provide adequate anesthesia at the C4 and C5 levels.Keywords: shoulder surgeries, nerve block, ultrasound-guided block, regional anesthesia