Spinal anesthesia increases pulmonary responsiveness to methacholine in guinea pigs.

UNLABELLED: It has been postulated that regional anesthesia, when feasible, is the best anesthetic approach in asthmatic patients. However, there are reports of severe bronchospasm during regional anesthesia. In the present study, we developed an experimental model of spinal (subarachnoid) anesthesia in guinea pigs and studied respiratory system responsiveness to aerosolized methacholine. The animals received sodium pentobarbital (50 mg/kg intraperitoneally), a tracheotomy, and mechanical ventilation. Four groups of animals were studied: guinea pigs that received spinal anesthesia with lidocaine (500 microL of 2% solution) (n = 7); guinea pigs that received spinal administration of isotonic sodium chloride solution (500 microL) (n = 7); guinea pigs that received an intraperitoneal injection of lidocaine (500 microL of 2% solution) (n = 6); and control guinea pigs (n = 7). The concentration of methacholine chloride that resulted in 50% of the maximal value of respiratory system elastance was lower in guinea pigs that received spinal anesthesia compared with 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 bronchospasm. We developed an experimental model of spinal anesthesia with lidocaine in guinea pigs and studied respiratory responsiveness to methacholine, a bronchoactive agonist. Spinal anesthesia resulted in an increase in respiratory responsiveness.