DESFLURANE INHIBITS HYPOXIC PULMONARY VASOCONSTRICTION IN ISOLATED RABBIT LUNGS

Background: Inhalational anesthetics inhibit hypoxic pulmonary vasocon striction (HPV) in vivo and in vitro with a half-maximum inhibiting ef fect (ED(50)) within concentrations applied for general anesthesia. Be cause it is unknown whether desflurane acts likewise, we studied its e ffect on HPV in isolated blood-perfused rabbit lungs and compared its ED(50) with that of halothane. Methods: Isolated blood-perfused rabbit lungs were randomly allocated to treatment with either desflurane (n = 6) or halothane (n = 6). HPV, defined as an increase in pulmonary ar terial pressure (PAP) at constant flow, was elicited by decreasing ins piratory oxygen concentration from 20% to 3% for 4 min. This effect wa s determined without (control HPV) and with increasing concentrations of the anesthetics (fraction of inspired carbon dioxide kept constant at 4.8 +/- 0.2%, perfusate temperature at 37 degrees C, and blood flow at 100 ml . min(-1)). Results: Before exposure to the anesthetics, PA P increased by 8.6 +/- 1.9 cmH(2)O for all lungs within 4 min of hypox ia (control PAP for all lungs 19.6 +/- 2.5 cmH(2)O). Desflurane decrea sed this effect in a concentration-dependent fashion with an ED(50) of 14.5%, compared with that of halothane, with an ED(50) of 1.7%. Concl usions: Assuming that 1 minimum alveolar concentration (MAC) values of desflurane and halothane for rabbits are 8.9% and 1.39%, respectively , this study yields ED,, values for the inhibition of HPV of approxima tely 1.6 MAC for desflurane and 1.2 MAC for halothane (P not statistic ally significant).