RESUMO
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.
Assuntos
Raquianestesia , Broncoconstritores/farmacologia , Cloreto de Metacolina/farmacologia , Mecânica Respiratória/efeitos dos fármacos , Resistência das Vias Respiratórias/efeitos dos fármacos , Animais , Relação Dose-Resposta a Droga , Cobaias , Injeções Intraperitoneais , Lidocaína/administração & dosagem , Medidas de Volume Pulmonar , MasculinoRESUMO
Vasoactive intestinal peptide (VIP) is a potent bronchial smooth muscle relaxant. In the present study we measured the release of VIP-like immunoreactivity (VIP-LI) after tracheal infusion of capsaicin, histamine, and methacholine in isolated guinea pig lungs superfused through the trachea. We also studied if inhibition of VIP enzymatic cleavage using a combination of an inhibitor of neutral endopeptidase [thiorphan (Thio)] and an inhibitor of serine proteases [soybean trypsin inhibitor (STI)] influenced the airway effects of capsaicin. Infusion of capsaicin resulted in a significant increase in VIP-LI in the perfusate (12.32 +/- 4.80 to 33.52 +/- 8.46 fmol/5 min fraction; P < 0.001). There was no increase in VIP-LI after infusion of methacholine or histamine. Maximal changes in airway opening pressure (Pao) observed 0-10 min after tracheal infusion of capsaicin were significantly greater in the Thio group than the control group and the groups of lungs that received STI or STI + Thio (P < 0.005). In addition, recovery of VIP-LI in the superfusate after infusion of capsaicin was significantly greater in the group of lungs that was superfused with Thio + STI compared with STI, Thio, and control groups. Our results suggest that a bronchodilator peptide with the profile of enzymatic cleavage of VIP also modulates capsaicin effects, since the increase in Pao in the presence of Thio + STI was significantly lower than Thio alone.