Changes in the Skin Conductance Monitor as an End Point for Sympathetic Nerve Blocks

Abstract

Objective: There is a lack of objective methods for determining the achievement of sympathetic block. This study validates the skin conductance monitor (SCM) as an end point indicator of successful sympathetic blockade as compared with traditional monitors.

Methods: This interventional study included 13 patients undergoing 25 lumbar sympathetic blocks to compare time to indication of successful blockade between the SCM indices and traditional measures, clinically visible hyperemia, clinically visible engorgement of veins, subjective skin temperature difference, unilateral thermometry monitoring, bilateral comparative thermometry monitoring, and change in waveform amplitude in pulse oximetry plethysmography, within a 30-minute observation period. Differences in the SCM indices were studied pre- and postblock to validate the SCM.

Results: SCM showed substantially greater odds of indicating achievement of sympathetic block in the next moment (i.e., hazard rate) compared with all traditional measures (clinically visible hyperemia, clinically visible engorgement of veins, subjective temperature difference, unilateral thermometry monitoring, bilateral comparative thermometry monitoring, and change in waveform amplitude in pulse oximetry plethysmography; P ≤ 0.011). SCM indicated successful block for all (100%) procedures, while the traditional measures failed to indicate successful blocks in 16-84% of procedures. The SCM indices were significantly higher in preblock compared with postblock measurements (P < 0.005).

Conclusions: This preliminary study suggests that SCM is a more reliable and rapid response indicator of a successful sympathetic blockade when compared with traditional monitors.

Keywords: Complex Regional Pain Syndrome; Monitor; Skin Conductance; Sympathetic Nerve Block.

© 2017 American Academy of Pain Medicine. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com

Figures

Figure 1

The self-adhesive electrodes, denoted C (current), R (reference), and M (measurement), are attached to plantar skin.

Figure 2

Overview of the skin conductance device.

Figure 3

Left: Detail of recording from the skin conductance monitor (SCM) showing the time period from when the sympathetic nerve block injection was given, start of block (time period 0), until when the block worked. Right: Overview of the skin conductance recording before, at the start of block, and after the block worked. The detail is from the gray area in the overview.

Figure 4

The observational real-time skin conductance monitor (SCM) compared with traditional assessment tools for sympathetic nerve blocks when assessed each minute or each five minutes. All traditional methods of determining the achievement of sympathetic block had substantially smaller odds of indicating successful block in the next moment compared with the observational skin conductance responses tested by the SCM in real time (P < 0.001). When analyzing the skin conductance responses in real time each minute, all patients had successful sympathetic block (defined as the skin conductance responses per second of 0.00 in a real-time 15-second window) within 10 minutes, which was statistically different than the traditional sympathetic block assessment tools (P < 0.001).