OVERESTIMATION OF LOW CARDIAC-OUTPUT MEASURED BY THERMODILUTION

We have investigated the influence of a cold water bolus (CWB) injecti on on overestimation of cardiac output (CO) in low CO states in anaest hetized dogs. CO was measured using three methods: (1) thermodilution (TD), (2) electromagnetic (EM) flow meter placed on the pulmonary arte ry and (3) transoesophageal echo-Doppler (OD) placed on the descending aorta. Measurements of CO were obtained before (steady state) and aft er induction of a low CO state with thiopentone 5 mg kg(-1) i.v. After CWB injection, mean CO measured by EM and OD increased by 26% and 27% , respectively (P<0.05) during steady state, and by 85% and 75% (P<0.0 5) during the low CO state. This transient increase was produced by an increase in stroke volume, while heart rate did not change. Frank Sta rling's law may explain this variation by a sudden increase in preload produced by CWB injection. These results indicate that thermodilution overestimated CO during low CO states when CWB injection was used.