Thermodilution better than estimated Fick for assessing cardiac output

By Will Boggs MD

NEW YORK (Reuters Health) - The thermodilution method is better than the estimated oxygen uptake Fick method for assessing cardiac output in clinical practice, according to a retrospective cohort study.

“The most surprising result was the poor agreement between these two methods to measure cardiac output,” Dr. Alexander R. Opotowsky from Boston Children’s Hospital and Brigham and Women’s Hospital, in Boston, told Reuters Health by email. “While some degree of discrepancy is unavoidable, it is astonishing that the measurements differed by greater than 20% in more than a third of cases. Imagine the implications of similarly imprecise scales or thermometers.”

Thermodilution and Fick are both used to diagnose, manage, and track progress of cardiac output in a variety of settings. There are sparse data to allow a comparison of their performance against clinical endpoints, including mortality.

Dr. Opotowsky and colleagues retrospectively analyzed data from more than 12,000 adults who underwent right-heart catheterization in the Veterans Affairs Clinical Assessment, Reporting, and Tracking (VA CART) program. They assessed the correlation and agreement between thermodilution and Fick, and the association of each method with survival.

The correlation between thermodilution and Fick methods was only modest (r=0.65), and estimates by the two methods differed by more than 20% for 38.1% of the catheterizations examined, according to the September 6 JAMA Cardiology online report.

Fick estimates were higher than thermodilution estimates at the lower (cardiac index <2.2 liters/min/m2) and higher (>4.0 liters/min/m2) ends of the cardiac output range.

Fick estimates tended to be higher than thermodilution estimates for patients older than 75; the converse was true for those age 65 or younger.

When cardiac index was low, thermodilution estimates of cardiac output were significantly better than Fick estimates for predicting all-cause mortality at 90 days and 1 year after catheterization.

The results were validated in a cohort of 3,391 patients from Vanderbilt University.

“While there are surely some providers who take special care and attention to detail, the similar results in two very different settings strongly suggest this finding represents the rule rather than an artifact of a given healthcare system or population,” Dr. Opotowsky said by email.

“We should work diligently to measure cardiac output as precisely as possible whatever technique is being used,” he said. “While it is critical to highlight that the available data did not allow us to analyze whether each technique was applied in the best way possible, it is a plausible source of some of the disagreement between methods.”

“It appears that thermodilution estimates of cardiac output are more strongly related to mortality than are Fick estimates,” Dr. Opotowsky concluded. “This suggests that thermodilution estimates may be more accurate than assumed Fick estimates as performed in practice, and that thermodilution should therefore be favored in most situations.”

SOURCE: http://bit.ly/2y5WkmL

JAMA Cardiol 2017.

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