SKIN VASOMOTOR REFLEX PREDICTS CIRCULATORY RESPONSES TO LARYNGOSCOPY AND INTUBATION

Background: An evaluation of autonomic reactivity may help to predict circulatory responses to intubation. The relation between the magnitud e of the skin vasomotor reflex (SVmR) immediately before laryngoscopy and the circulatory responses to intubation was examined. Methods: For ty-four adult patients (classified as American Society of Anesthesiolo gists physical status I or II) were studied. General anesthesia was in duced with fentanyl and thiamylal and maintained with nitrous oxide an d sevoflurane. The SVmR was evoked by an electrostimulus to the ulnar nerve, and decreases in skin blood flow were detected using a laser-Do ppler flowmeter. In study 1, two groups of patients mere studied In th e monitored group (n = 14), laryngoscopy mas performed when the SVmR a mplitude had decreased to less than 0.1. In the control group (n = 15) , intubation was performed regardless of changes in the SVmR amplitude . In study 2, after induction, the end-tidal concentration of sevoflur ane was maintained at 1 MAC (n = 9) or 1.3 MAC (n = 6) for 5 min. The SVmR was tested by changing the electric intensity. Results: In study 1, the blood pressure and heart rate of the control group increased si gnificantly (P < 0.01) after laryngoscopy. The blood pressure of the m onitored group did not increase. The SVmR amplitude and the systolic b lood pressure changes showed a significant linear correlation (P < 0.0 01). In study 2, the relation between the electric intensity and the S VmR amplitude showed a weak but significant correlation (P < 0.01) in the 1 MAC group. Conclusion: The evaluation of the SVmR provides usefu l information for determining the optimal anesthetic depth for laryngo scopy and intubation in individual patients.