Effects of anesthetic and sedative agents on sympathetic nerve activity

BACKGROUND The effects of sedative and anesthetic agents on sympathetic nerve activity (SNA) are poorly understood. OBJECTIVE The purpose of this study was to determine the effects of commonly used sedative and anesthetic agents on SNA in ambulatory dogs and humans. METHODS We implanted radiotransmitters in 6 dogs to record stellate ganglion nerve activity (SGNA), subcutaneous nerve activity (ScNA), and blood pressure (BP). After recovery, we injected dexmedetomidine (3 mu g/kg), morphine (0.1 mg/kg), hydromorphone (0.05 mg/kg), and midazolam (0.1 mg/kg) on different days. We also studied 12 human patients (10 male; age 68.0 +/- 9.1 years old) undergoing cardioversion for atrial fibrillation with propofol (0.77 +/- 0.18 mg/kg) or methohexital (0.65 mg/kg) anesthesia. Skin sympathetic nerve activity (SKNA) and electrocardiogram were recorded during the study. RESULTS SGNA and ScNA were significantly suppressed immediately after administration of dexmedetomidine (P = .000 and P = .000, respectively), morphine (P = .011 and P = .014, respectively), and hydromorphone (P = .000 and P = .012, respectively), along with decreased BP and heart rate (HR) (P < .001 for each). Midazolam had no significant effect on SGNA and ScNA (P = .248 and P = .149, respectively) but increased HR (P = .015) and decreased BP (P = .004) in ambulatory dogs. In patients undergoing cardioversion, bolus propofol administration significantly suppressed SKNA (from 1.11 +/- 0.25 mu V to 0.77 +/- 0.15 mu V; P = .001), and the effects lasted for at least 10 minutes after the final cardioversion shock. Methohexital decreased chest SKNA from 1.59 +/- 0.45 mu V to 1.22 +/- 0.58 mu V (P = .000) and arm SKNA from 0.76 +/- 0.43 mu V to 0.55 +/- 0.07 mu V (P = .001). The effects lasted for at least 10 minutes after the cardioversion shock. CONCLUSION Propofol, methohexital, dexmedetomidine, morphine, and hydromorphone suppressed, but midazolam had no significant effects on, SNA.