Background and Objectives. When administering stellate ganglion blocks (e.g., to pain patients), it may be essential to know whether the sympathetic block is complete. The aim of the present study was to study the efficacy of stellate ganglion blocks using different concentrations and volumes of local anesthetic and different sites of injection.

Methods. Fifty-four stellate ganglion blocks (cervicothoracic sympathetic blocks) were performed for relief of chronic pain in 30 patients, all with a pre-block palmar skin temperature 32°C or lower. Bupivacaine in random combinations of concentration (high, 5 mg/ml; low, 2.5 mg/ml), volume (high, 15-20 ml; low, 5-10 ml), and site of injection (C6 or C7) was used. The efficacy of these combinations was assessed by registering the following changes in effector organ activity: (1) observed signs (e.g., Horner's syndrome: miosis, ptosis, enophthalmos, and reddening of the sclera) and (2) objective measurements of changes in skin temperature, skin blood flow (laser Doppler flowmetry), skin resistance response, and in skin resistance level.

Results. Only 15 of 54 blocks met four of the five criteria for an effective block: a Horner's syndrome in combination with an increased skin temperature (to ≥34°C), increased skin blood flow (≥50%), and completely abolished skin resistance response on both the radial and the ulnar sides of the blocked hand. Only six of those 54 met all five criteria: they also had an increase (≥13%) in skin resistance level on the radial and ulnar sides. Injection toward C7 instead of injection toward C6, and high concentration instead of low, seemed to be more advantageous, whereas volume seemed to be of less importance. A relationship between pre-block skin temperature and the rise in temperature during the block was found.

Conclusions. It was difficult to achieve a block that met all five established criteria. When assessing the efficacy of a stellate ganglion block, it is essential to evaluate the effects on vasoconstrictor and sudomotor fibers.