HEMODYNAMIC-EFFECTS OF ISOVOLEMIC HEMODILUTION DURING DESCENDING THORACIC AORTIC CROSS-CLAMPING AND LOWER TORSO REPERFUSION

Background. Isovolemic hemodilution has been suggested for blood conse rvation and to improve hemodynamic tolerance to abdominal aortic cross clamping. However, hemodynamic effects of hemodilution during descend ing thoracic aortic cross clamping (DAC), have not been established. W e evaluated them in anesthetized swine. Methods. Hemodilution (n = 7) was produced by the isovolemic exchange of blood for 6% hetastarch to a target hematocrit of 20%. Hematocrit in control pigs (n = 7) remaine d at 30%. DAC was performed at the T9 level for 45 minutes. During a 6 0-minute reperfusion period, control pigs were infused with lactated R inger's solution; shed blood was returned to hemodilution pigs, follow ed by lactated Ringer's. If hypotension occurred despite left atrial p ressure of 10 mm Hg or greater, boluses of phenylephrine were given to keep mean arterial pressure above 60 mm Hg. Results. Hemodilution cau sed a marked reduction in hematocrit and in global oxygen delivery (DO 2). DAC produced a significant increase in proximal arterial pressure, cardiac index, and DO2, and oxygen consumption (VO2) was markedly red uced in both groups. A significant increase in systemic vascular resis tance during DAC occurred only in control pigs, requiring a sixfold gr eater dose of phenylephrine avoid hypotension. A lower global DO2 and supply-limited VO2 were also observed in hemodilution pigs. Conclusion s. Isovolemic hemodilution maintains hemodynamic stability during DAC. During lower torso reperfusion, however, hemodilution caused hemodyna mic instability, decreased global DO2, and limited VO2, which may offs et its potential benefits.