Regional Anesthesia: Brief Report
Interscalene block (ISB) is often used to provide anesthesia and analgesia for upper limb surgery (1,2). In a previous study, Takahashi et al. (3) proposed the measurement of brachial artery blood flow as an index of sympathetic function. This prospective study was performed to investigate and quantify the effects of ISB on humeral arterial blood flow (HBF).
After informed consent and institutional approval, 11 ASA physical status I and II patients scheduled for shoulder arthroscopic surgery under ISB were prospectively enrolled. Patients did not receive any premedication. After standard monitoring, an ISB was performed by a single anesthesiologist experienced in the technique using a nerve stimulator with a standard procedure: correct needle position was determined when a stimulating current <0.6 mA produced a characteristic deltoid motor response. Then, 40 mL of an equal volume of lidocaine 1% and ropivacaine 0.75% was injected.
A Doppler ultrasound (Siemens Sonoline Millennium; Siemens Medical Systems, Inc., Issaquah, WA) of the humeral artery was performed before, and 30 min after, the ISB by a single radiologist experienced in this technique. The resistance index (RI) and the HBF were measured using the same Doppler angle and the same vessel size in all patients.
Data analysis was performed using SAS software, version 8.2 (SAS Corp., Cary, NC). We defined two outcomes for the statistical analysis: RI and HBF before and after the block. Because the measurements of RI and HBF were not independent (same patients), these analyses were performed comparing the differences from 0 with the Wilcoxon rank test.
A P value < 0.05 was considered to be statistically significant. Two-sided significance tests were used throughout.
The median RI decreased significantly after the ISB (Table 1). The median HBF increased significantly after the ISB (Table 2). We also noted an inversion of the diastolic curve and a disappearance of the protodiastolic flow (Figs. 1 and 2). Before ISB, the systolic curve was positive whereas the diastolic curve was negative. After ISB, we noted an inversion of the diastolic curve and a disappearance of the protodiastolic flow.
ISB provides effective intraoperative anesthesia and postoperative analgesia for shoulder surgery (4). In our study, the RI was significantly decreased, notably with an inversion of the diastolic curve and a disappearance of the protodiastolic flow attesting to significant vasodilatation. We also noted a significant increase of HBF in all patients. The median HBF was increased from 32 to 88 mL/min. These findings could have important clinical applications, particularly in the management of brachial and digital ischemia (5). In a previous study, Ebert et al. (6) showed that the arterial blood flow after axillary plexus block was 1.9 times greater than before.
Two authors proposed different methods to evaluate the degree of sympathetic blockade after peripheral plexus block. Lehtipalo et al. (7) measured skin blood flow in the finger by laser Doppler technique and regional skin vascular resistance to evaluate the sympathetic block after an ISB. Talke et al. (8) measured finger blood volume by photoplethysmographic determination of light transmitted through a finger. However, all these methods are indirect and do not reflect the sympathetic block directly from measurement of the resistance and blood flow in the humeral artery by Doppler ultrasound. Our results confirm, through direct measurement, the effect of ISB on HBF.
One limitation of our study should be noted. The recording of flow and resistance was limited to 30 minutes after block completion. Nevertheless, the duration of the motor and sensory block suggests that the duration of sympathetic block was prolonged for many hours (9). We did not measure the venous resistance by Doppler. However, the clinical observation shows a significant venous dilation in the blocked limb. In an animal model, Yoshiyuki and Shinsuke (10) showed that stellate ganglion block increased HBF significantly from 10 minutes through 50 minutes after the block.
In conclusion, ISB significantly enhanced HBF and decreased arterial resistance. Additional studies are required to determine the clinical significance and implications of our findings.
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© 2005 International Anesthesia Research Society
10. Yoshiyuki K, Shinsuke H. Addition of clonidine increases duration and magnitude of vasodilative effect induced by sympathetic block with mepivacaine in dogs. Reg Anesth Pain Med 2001;26:329–32.