Objective: The value of different algorithms that estimate cardiac output (CO) by analysis of a peripheral arterial blood pressure (ABP) waveform has not been definitively identified. In this investigation, we developed a testing data set containing a large number of radial ABP waveform segments and contemporaneous reference CO by thermodilution measurements, collected in an intensive care unit (ICU) patient population during routine clinical operations. We employed this data set to evaluate a set of investigational algorithms, and to establish a public resource for the meaningful comparison of alternative CO-from-ABP algorithms.
Design: A retrospective comparative analysis of eight investigational CO-from-ABP algorithms using the Multiparameter Intelligent Monitoring in Intensive Care II database.
Setting: Mixed medical/surgical ICU of a university hospital.
Patients: A total of 120 cases.
Interventions: None.
Measurements: CO estimated by eight investigational CO-from-ABP algorithms, and CO(TD) as a reference.
Main results: All investigational methods were significantly better than mean arterial pressure (MAP) at estimating direction changes in CO(TD). Only the formula proposed by Liljestrand and Zander in 1928 was a significantly better quantitative estimator of CO(TD) compared with MAP (95% limits-of-agreement with CO(TD): -1.76/+1.41 L/min versus -2.20/+1.82 L/min, respectively; p < 0.001, per the Kolmogorov-Smirnov test). The Liljestrand method was even more accurate when applied to the cleanest ABP waveforms. Other investigational algorithms were not significantly superior to MAP as quantitative estimators of CO.
Conclusions: Based on ABP data recorded during routine intensive care unit (ICU) operations, the Liljestrand and Zander method is a better estimator of CO(TD) than MAP alone. Our attempts to fully replicate commercially-available methods were unsuccessful, and these methods could not be evaluated. However, the data set is publicly and freely available, and developers and vendors of CO-from-ABP algorithms are invited to test their methods using these data.