Clinical trial of nitroglycerin-induced controlled hypotension with or without acupoint electrical stimulation in microscopic middle ear surgery under general anesthesia with halothane.

BACKGROUND

Transcutaneous electrical stimulation (ES) has been shown to produce long-lasting fall of arterial blood pressure in animal or human models. Previous reports have shown that ES of acupuncture points (acupoints) enhances the hypotensive effect of isoflurane anesthesia. This study was designed to investigate the combined effect of acupoint ES and different infusion rates of nitroglycerin on controlled hypotension.

METHODS

Fifty-one adult ASA I patients undergoing elective mastoeidectomy were randomly divided into two groups, to receive either true or sham ES of ST36 (Zusanli) and ST38 (Tiaokou) acupoints. Each group was further subdivided into four groups to receive four different rates of nitroglycerin infusion (1.5, 2, 2.5 and 3 microg/kg/min). Steady state mean arterial blood pressure (MAP) and time to reach it were compared between two groups. The amount of bleeding in microscopic surgical field was quantitatively assessed and compared between two groups.

RESULTS

Steady state MAP was significantly lower in true ES group compared with sham ES group (60 +/- 4 mmHg in true ES vs. 66 +/- 5 mmHg in sham ES, P = 0.000) and the difference was significantly greater in lower dosage of nitroglycerin compared with higher dosage. In addition time to reach steady state MAP was significantly shorter in true ES compared with sham group (10 +/- 3 min in true ES vs. 15.8 +/- 4 min in sham ES, P = 0.000). Heart rate decreased significantly in true ES compared with sham ES group after commencement of ES and nitroglycerin infusion. Quality of operative ischemia was excellent in 20 (83.3%) patients of true ES compared with 6 (25%) patients in sham ES group (P = 0.000).

CONCLUSIONS

The result of this study shows that ES of ST36 combined with nitroglycerin infusion facilitates lowering of blood pressure and produces a bloodless surgical field. The mechanism of blood pressure lowering effect of acupoint ES may be reducing of norepinephrine and other sympathomimetic substances in the blood.