Background and Objectives Although an increase in skin temperature of the hand implies sympathetic block after stellate ganglion block (SGB), it does not indicate complete sympathetic block unless accompanied by an absence of sweating because skin temperature may increase even with a partial sympathetic block. This study examined the efficacy of the SGB to block sweating in the hand and to determine if the magnitude of temperature change in the hand is predictive of a negative sweat test.

Methods Fifty-nine SGBs were performed in 30 patients (15 women and 15 men) for diagnostic or therapeutic indications. Stellate ganglion block was performed via an anterior paratracheal approach at C6 using 15 mL 0.25% bupivacaine. Skin temperature was measured bilaterally on the index finger. A cobalt blue sweat test was performed bilaterally preand post-SGB on the middle finger. Successful sympathetic block after SGB was considered present when: (a) (change in ipsilateral temperature (postblock-preblock)] (D_i)- [change in contralateral temperature] (D_c) ≥ 1.5°C; (b) Horner's syndrome present; and (c) sweat test changed from positive to negative. Logistical regression was applied to determine what value of D_i - D_c could be used to predict a negative sweat test.

Results Thirty-six percent (21/59) of blocks met all three criteria. Of the blocks where D_i - D_c ≥ 1.5°C, 72% (21/29) had a negative sweat test post-SGB. Of the blocks where D_i - D_c < 1.5°C, 37% (11/30) had a negative sweat test postblock. If D_i - D_c ≥ 2.0°C, a negative sweat test could be predicted with 69 ± 12% sensitivity and 85 ± 10% specificity.

Conclusions Stellate ganglion block often fails to increase skin temperature in the ipsilateral more than the contralateral hand. A value of D_i - D_c ≥ 2.0°C was a good predictor of a sympathetic block, but was not sufficient to guarantee a complete sympathetic block of the hand after SGB in all cases. An apparently successful SGB as measured by “usual” clinical criteria may not result in a complete sympathectomy of the hand as is often assumed. Therefore, if obtaining a sympathectomy is important for diagnostic or therapeutic purposes, performing a sweat test provides important confirmatory evidence of the genuine success of the sympathetic block.