Hemodynamic and metabolic consequences of hemodilution with different diluents

Hemodilution was performed with the crystalloid Ringer's lactate (n = 6) and the colloid Haemaccel (n = 5) in dogs during automatically controlled total cardiopulmonary bypass with constant arterial and venous pressures. Single observations were made with Macrodex and Rheomacrodex hemodilution. Hemoglobin concentration and hematocrit were used as parameters for hemodilution. Total plasma protein proved to be unsuitable. The volume needed to induce the same level of hemodilution with lactated Ringer's and Haemaccel was twice the volume needed with Macrodex and Rheomacrodex. The volume shift from intravascular to extravascular was larger during Ringer's lactate hemodilution than during Haemaccel hemodilution. The amount of volume shift was clearly related to changes in colloid osmotic pressure. Lowering of total peripheral vascular resistance, with increased arterial line flow during controlled constant arterial and venous pressures was seen during hemodilution with each of the above materials. Potassium and calcium concentrations in the blood increased significantly during hemodilution with Haemaccel. Base excess was constant during hemodilution with lactated Ringer's but decreased in all other cases. A decrease in oxygen consumption was common, and most pronounced during hemodilution with Haemaccel.