Fluid loading with whole blood or Ringer's lactate solution during CPR in dogs

The influence of fluid loading during CPR on oxygen uptake and blood flow was investigated in 18 dogs (12-26 kg). Blood flows were measured with radioactive microspheres at 5 (control CPR), 13 and 20 min after the initiation of ventricular fibrillation and CPR. After 10 min, 9 dogs received a rapid infusion of whole blood (11 ml/kg, i.v.) and 9 dogs received Ringer's solution (11 ml/kg, i.v.). Oxygen uptake was not significantly altered by fluid loading with either whole blood or Ringer's solution. Fluid loading increased cardiac output 34% over the 5 min control value. However, left ventricular perfusion decreased to 74% and brain flow decreased to 65% of control. At 20 min, cardiac output and brain flow returned to near control values, while left ventricular flow remained low. Changes in organ perfusion can be explained in part by the concurrent changes in blood pressures. Central venous diastolic pressure increased significantly (from 9 to 14 mmHg) after fluid load. However, central arterial diastolic pressure did not rise proportionately (from 32 to 34 mmHg). Hence, the central A-V diastolic pressure difference decreased. Although fluid loading during CPR improved cardiac output, flow to the heart and brain decreased. Further, there was no increase in oxygen consumption, indicating that fluid loading did not improve metabolic status.