Objective  

To determine whether changes in cardiac output are correlated with changes in other commonly measured covariables (heart rate, respiratory rate, mean arterial pressure, mean pulmonary artery pressure, pulmonary artery occlusion pressure, and temperature).

Design  

Case series.

Setting  

Medical intensive care unit (ICU) in a Veterans Administration Medical Center.

Patients  

Twenty-three patients with Swan-Ganz catheters placed by the primary care team were studied on 25 occasions. Patients were managed by the primary team as clinically indicated.

Interventions  

Thermodilution cardiac output and covariables were determined at baseline and at hourly intervals for the next 5 h. Each cardiac output measurement was calculated by averaging the last four of five individual measurements at each time point.

Results  

The mean cardiac output (9.2l/min), heart rate (107/min), and pulmonary artery occlusion pressure (19 mmHg) were elevated. The hourly mean change in cardiac output was 10.2%. Using least-squares linear regression analysis, we found clinically significant changes in cardiac output (>6.4%) to be most closely correlated with changes in heart rate (R ²=0.29,p<0.001). stepwise="" linear="" regression="" analysis="" showed="" that="" none="" of="" the="" other="" covariables="" added="" significantly="" to="" this="" relationship.="" no="" significant="" relationship="" was="" found="" between="" changes="" in="" cardiac="" output="" and="" changes="" in="" pulmonary="" artery="" occlusion="" pressure.="" despite="" these="" correlations="" clinically="" significant="" changes="" in="" cardiac="" output="" were="" accompanied="" by="" changes="" in="" heart="" rate="" in="" the="" same="" direction="" only="" 62%="" of="" the="">

Conclusion  

Changes in cardiac output were best correlated with changes in heart rate. Changes in pulmonary artery occlusion pressure were not correlated with changes in cardiac output in this population of medical ICU patients. A change in any of the covariables (alone or in combination) cannot be reliably used to indicate a simultaneous change in cardiac output.