SPINAL-ANESTHESIA INCREASES PULMONARY RESPONSIVENESS TO METHACHOLINE IN GUINEA-PIGS

It has been postulated that regional anesthesia, when feasible, is the best anesthetic approach in asthmatic patients. However, there are re ports of severe bronchospasm during regional anesthesia. In the presen t study, we developed an experimental model of spinal (subarachnoid) a nesthesia in guinea pigs and studied respiratory system responsiveness to aerosolized methacholine. The animals received sodium pentobarbita l (50 mg/kg intraperitoneally), a tracheotomy, and mechanical ventilat ion. Four groups of animals were studied: guinea pigs that received sp inal anesthesia with lidocaine (500 mu L of 2% solution) (n = 7); guin ea pigs that received spinal administration of isotonic sodium chlorid e solution (500 mu L) (n = 7); guinea pigs that received an intraperit oneal injection of Lidocaine (500 CLL of 2% solution) (n = 6); and con trol guinea pigs (n = 7). The concentration of methacholine chloride t hat resulted in 50% of the maximal value of respiratory system elastan ce was lower in guinea pigs that received spinal anesthesia compared w ith the other three groups (P < 0.005 for control group, P < 0.01 for spinal saline group, and P < 0.05 for intraperitoneal lidocaine group) . Our results suggest that spinal anesthesia results in an increase in pulmonary responsiveness to bronchoconstrictive stimuli. Implications : Regional anesthesia has been considered the best anesthetic approach in asthmatic patients, although there are reports of severe bronchosp asm. We developed an experimental model of spinal anesthesia with lido caine in guinea pigs and studied respiratory responsiveness to methach oline, a bronchoactive agonist. Spinal anesthesia resulted in an incre ase in respiratory responsiveness.