Response of the pulmonary microcirculation to fluid loading after hemorrhagic shock and resuscitation

We compared the response of the pulmonary microcirculation to fluid overload before and 24 hours after hemorrhagic shock, resuscitated with either blood or crystalloid, to determine whether vascular permeability was altered, making the lung more susceptable to fluid overload after shock and whether this response differed depending on the type of resuscitation fluid. Fourteen unanesthetized sheep with chronic lung lymph fistula were given a fluid challenge (one half of blood volume) before and 24 hours after hemorrhagic shock. Seven sheep were resuscitated after whock with shed blood and seven sheep were resuscitated with Ringer's lactate alone equal to 2.5 times the amount of shed blood. Pulmonary vascular pressures and lung lymph flow Ql were at baseline in both groups 24 hours after resuscitation except for the decreased plasma oncotic pressure pi p in the crystalloid group. Interstitial oncotic pressure, pi i was also lowered in this group such that the gradient (pi p-pi i) remained at baseline. In the blood group, pulmonary vascular pressures and QL increased transiently after fluid loading before and after shock with the mean time for QL to return to baseline being 5.5 and 5.9 hours for the preshock and postshock periods, respectively. In the crystalloid group, fluid loading after shock produced an increase in pulmonary vascular pressures resulting in a significant increase in QL over the preshock fluid response with the mean time for QL to return to baseline being 10.1 hours. However, changes in the value of (pi p-pi i) were identical to those seen before shock. Therefore we noted that 24 hours after shock, lung permeability was not significantly altered but crystalloid resuscitation did make the lung more susceptible to volume overload.