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

Purpose: 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.