Monitoring of pacemaker induced changes in cardiac output with inspired to endtidal oxygen difference in paediatric cardiac surgery patients

Methods: Fourteen children aged 4-15 months were studied after corrective cardiac surgery. Heart rate was increased by 20% with an external pacemaker. Cardiac output (CO) was measured with thermodilution. Oxygen saturation was measured in systemic artery (SaO(2)), central vein (ScvcO(2)) and pulmonary artery (SvO(2)). Inspiratory to endtidal oxygen difference (FI-ETO2) was measured using a paramagnetic technique. SvO(2) was measured continuously using a spectrophotometric technique. Results: CO increased in three patients and decreased in 11 patients during pacing. Regression between Delta CO and Delta (1/Sa-vO(2)), Delta (FI-ETO2/Sa-vO(2)), Delta (FI-ETO2/Sa-cvcO(2)) showed r = 0.70, r = 0.76 and r = 0.75, respectively. Delta CO exceeded 10% in 17 of 26 interventions. Changes in FI-ETO2 Of equal direction as changes in CO occurred in 12 of these 17 interventions. Conclusions: Estimations of CO changes, based on SvO2, can be enhanced if changes in FI-ETO2 are also measured. ScvcO2 instead of SvO(2) gives equivalent results. Sudden changes in FI-ETO2 after pacemaker initiation or termination can predict the direction of CO changes.