Prolonged reduction in colloid oncotic pressure does not increase brain edema following cryogenic injury in rabbits

The effects of an 8-h period of reduced colloid oncotic pressure (COP) on cerebral edema formation following cryogenic brain injury were studied in 24 normothermic, normocarbic rabbits. Anesthesia was induced with halothane and catheters inserted to permit the monitoring of arterial, right atrial, and intracranial pressures (MAP, CVP, and ICP, respectively). When surgery was complete, halothane was discontinued, 40 mg/kg of pentobarbital was given iv, and ventilation continued with 66% N2O/balance O2. A left parietal cryogenic injury was then produced using liquid N2, and the animals assigned to one of three groups. In group 1 (Control, n = 8), only maintenance lactated Ringer's solution (LR) was given for the remainder of the study. Beginning 30 min after injury, animals in the other two groups (n = 8 each) underwent 45 min of plasmapheresis (arterial phlebotomy, with packed cells returned). In group 2 (Iso-COP) separated plasma was replaced with 6% hetastarch in LR, while in group 3 (Hypo-COP), plasma was replaced with LR alone. In both groups, the volume of fluid given was adjusted to maintain MAP and CVP at baseline values. After plasmapheresis, animals subsequently received only maintenance LR. Eight and one-half hours after the injury (8 h after the start of plasmapheresis), animals were killed and the brains removed. Regional tissue specific gravities (SpGr) and water contents (%H2O) were measured respectively by microgravimetry and drying. In addition, the %H2O of samples of skeletal muscle and small bowel were determined to assess peripheral edema formation. There were no important intergroup differences in MAP, CVP, ICP, blood gases, or osmolality at any time.(ABSTRACT TRUNCATED AT 250 WORDS)