HALOTHRANE AND ISOFLURANE DECREASE ALVEOLAR EPITHELIAL FLUID CLEARANCE IN RATS

Background: Active sodium transport is the primary mechanism that driv es alveolar fluid clearance. In the current study, the effects of expo sure to halothane and isoflurane on alveolar fluid clearance in rats w ere evaluated. Methods: Rats were exposed to either halothane (0.4% fo r 6 h or 2% for 2 h) or isoflurane (0.6% for 6 h or 2.8% for 2 h). Rev ersibility of halothane effects was assessed after 2 h of exposure to 2% halothane. Alveolar and lung liquid clearance were measured by intr atracheal instillation of a 5% albumin solution with 1.5 mu Ci of I-12 5-albumin, during mechanical ventilation with 100% FiO(2) and the halo genated agent, The effect of terbutaline (10(-4) M) added to the album in solution was tested after 2 h of exposure to 2% halothane, The incr ease in protein concentration in the airspaces over 1 h was used to ev aluate alveolar liquid clearance, Lung liquid clearance was calculated gravimetrically.Results: Alveolar liquid clearance rates were decreas ed by 24%, 30% and 40% compared with controls (P < 0.05) after 2 h of exposure to halothane, 6 h of exposure to halothane, and 6 h of exposu re to isoflurane, respectively. After 2 h of exposure to isoflurane, a lveolar liquid clearance did not change. In the 2-h halothane exposure group, alveolar liquid clearance returned to the control value 2 h af ter withdrawal of halothane. Terbutaline increased alveolar liquid cle arance by 50% and 89% in the control and 2-h halothane exposure groups , respectively, In all experiments, the same results were obtained for alveolar and lung liquid clearance. Conclusions: Halothane and isoflu rane caused a reversible decrease in alveolar epithelial fluid clearan ce. Two hours of exposure to halothane did not alter the stimulatory e ffect of terbutaline on alveolar liquid clearance.