title: Cardiovascular adjustments and gas exchange during extreme hemodilution in humans.
abstract: OBJECTIVE
  To examine the cardiovascular adjustments and pattern of gas exchange that occur during hemodilution.
  
  
  METHODS
  Nonrandomized prospective study.
  
  
  METHODS
  Operating room in a university hospital.
  
  
  METHODS
  Seven patients undergoing elective aortocoronary artery bypass surgery.
  
  
  METHODS
  Before initiating cardiopulmonary bypass, the patients' hematocrit levels were decreased to approximately 15%. This hemodilution was done by removing a sufficient amount of autologous blood from the aortic cannula and replacing it with a sufficient amount of crystalloid solution. After the discontinuation of cardiopulmonary bypass, measurements were made at a hematocrit of approximately 15%. Then, after autologous blood infusion, measurements were made at a hematocrit of 20%, followed by more blood infusion to approximately 25% with repeat measurements.
  
  
  RESULTS
  The following measurements were made before hemodilution and then at all three levels of hemodilution: heart rate, mean arterial pressure (MAP), right atrial pressure, mean pulmonary artery pressure, pulmonary artery occlusion pressure, and cardiac output. From these measurements, the following derived variables were calculated: cardiac index, systemic vascular resistance, and pulmonary vascular resistance. From measurements of arterial oxygen content, mixed venous oxygen content, and cardiac output, intrapulmonary shunt (Qsp/Qt), oxygen uptake (VO2), oxygen extraction ratio, and oxygen delivery (DO2) were derived. The MAP was lowest (57 +/- 3 [SD] vs. 92 +/- 3 mm Hg) at the lowest hematocrit. The cardiac index was highest (4.0 +/- 0.3 vs. 2.3 +/- 0.6 L/min.m2) at the lowest hematocrit. DO2 was lowest at the lowest hematocrit but VO2 remained constant at all levels of hematocrit. The oxygen extraction ratio increased as hematocrit decreased. With progressive increases in hematocrit, DO2 increased and Qsp/Qt decreased.
  
  
  CONCLUSIONS
  The data suggest that, during hemodilution, tissue autoregulation of VO2 and utilization are not impaired, but gas exchange function (Qsp/Qt) is impaired.
authors.affiliation: Loyola University Medical Center, Maywood, IL 60153.
authors.forename: M
authors.initials: M
authors.lastname: Mathru
authors.forename: B
authors.initials: B
authors.lastname: Kleinman
authors.forename: B
authors.initials: B
authors.lastname: Blakeman
authors.forename: D
authors.initials: D
authors.lastname: Dries
authors.forename: A
authors.initials: A
authors.lastname: Zecca
authors.forename: T
authors.initials: T
authors.lastname: Rao
mesh_terms: D001794:Blood Pressure; D001804:Blood Transfusion, Autologous; D002315:Cardiopulmonary Bypass; D006438:Hemodilution; D006439:Hemodynamics; D006801:Humans; D010100:Oxygen / Q000097:blood; D011446:Prospective Studies; D011652:Pulmonary Circulation; D011659:Pulmonary Gas Exchange
chemical_list: D010100:Oxygen