Semi-continuous versus injectate cardiac output measurement in intensive care patients after cardiac surgery

Abstract

Objective: Commercially available semi-continuous cardiac output (SCCO) monitoring systems are based on the pulsed warm thermodilution technique. There is evidence that SCCO fails to correlate with standard intermittent bolus cardiac output (ICO) in clinical situations with thermal instability in the pulmonary artery. Furthermore, ventilation may potentially influence thermodilution measurements by enhanced respiratory variations in pulmonary artery blood temperature and by cyclic changes in venous return. Therefore, we evaluated the correlation, accuracy and precision of SCCO versus ICO measurements before and after extubation.

Design: Prospective cohort study.

Setting: Intensive care unit (ICU) of a university hospital.

Patients and participants: 22 cardiac surgical ICU patients.

Interventions: None.

Measurements and results: SCCO and ICO data were obtained at nine postoperative time points while the patients were on controlled mechanical ventilation. Further sets of measurements were taken during the weaning phase 20 min before extubation, and 5 min, 20 min and 1 h after extubation. SCCO and ICO measurements yielded 286 data pairs with a range of 1.8-9.9 l/min for SCCO and 1.9-9.8 l/min for ICO. The correlation between SCCO and ICO was highly significant (r = 0.92; p < 0.01), accompanied by a bias of -0.052 l/min and a precision of 0.56 l/min. Correlation, accuracy and precision were not influenced by the mode of respiration.

Conclusions: Our results demonstrate excellent correlation, accuracy and precision between SCCO and ICO measurements in postoperative cardiac surgical ICU patients. We conclude that SCCO monitoring offers a reliable clinical method of cardiac output monitoring in ICU patients following cardiac surgery.