Comparison of Accuracy of Estimation of Cardiac Output by Thermodilution Versus the Fick Method Using Measured Oxygen Uptake

Impact on Pulmonary Hypertension Hemodynamic Classification Based on the Methodology Used to Measure Pulmonary Artery Wedge Pressure and Cardiac Output

Rationale: Guidelines recommend using end-expiration pulmonary pressure measurements to determine the hemodynamic subgroups in pulmonary hypertension. Pulmonary artery wedge pressure (PAWP) determinations averaged across the respiratory cycle (PAWPav) instead of PAWP at end-expiration (PAWPee) and cardiac output (CO) measured by Fick (COFick) instead of thermodilution (COTD) may affect the hemodynamic classification of pulmonary hypertension. Objectives: To assess the impact on the pulmonary hypertension hemodynamic classification of the use of PAWPee versus PAWPav as well as COFick versus COTD. Methods: This was a single-center retrospective study of consecutive patients (n = 151) who underwent right heart catheterization with COTD, COFick, PAWPee, and PAWPav. A secondary cohort consisted of consecutive patients (n = 71) who had mean pulmonary artery pressure at end-expiration (mPAPee) and mPAP averaged across the respiratory cycle (mPAPav) measured, as well as PAWPee and PAWPav. Results: The PAWPee and PAWPav were 16.8 ± 6.4 and 15.1 ± 6.8 mm Hg, respectively, with a mean difference of 1.7 ± 2.1 mm Hg. The COTD and COFick determinations were 5.0 ± 2.4 and 5.3 ± 2.5 L/min, respectively, with a mean difference of -0.4 ± 1.3 L/min. The hemodynamic group distribution was significantly different when using PAWPee versus PAWPav, when using either COTD or COFick (P < 0.001 for both comparisons), and these results were consistent in our secondary cohort. The pulmonary hypertension hemodynamic group distribution was not significantly different between COTD and COFick when using either PAWPee or PAWPav. Conclusions: The methodology used to measure PAWP, either at end-expiration or averaged across the respiratory cycle, significantly impacts the hemodynamic classification of pulmonary hypertension.

Standardization of the Right Heart Catheterization and the Emerging Role of Advanced Hemodynamics in Heart Failure

The accurate assessment of hemodynamics is paramount to providing timely and efficacious care for patients presenting in cardiogenic shock. Recently, the regular use of the pulmonary artery catheter in cardiogenic shock has had a resurgence with emerging data indicating improved survival in the modern era. Optimal multidisciplinary management of advanced heart failure and cardiogenic shock relies on our ability to effectively communicate and understand the complete hemodynamic assessment. Standardization of data acquisition and a renewed focus on the physiological processes, and thresholds driving disease progression, including the coupling ratio and myocardial reserve, are needed to fully understand and interpret the hemodynamic assessment. This State-of-the-Art review discusses best practices in the cardiac catheterization laboratory as well as emerging data on the prognostic role of emerging advanced hemodynamic parameters.

Beyond Stage C: Considerations in the Management of Patients with Heart Failure Progression and Gaps in Evidence

Despite treatment with contemporary medical therapies for chronic heart failure (HF), there has been an increase in the prevalence of patients progressing to more advanced disease. Patients progressing to and living at the interface of severe Stage C and Stage D HF are underrepresented in clinical trials, and there is a lack of high-quality evidence to guide clinical decision making. For patients with a severe HF phenotype, the medical therapies used for patients with a less advanced stage of illness are often no longer tolerated nor provide adequate clinical stability. The limited data on these patients highlights the need to increase formal research characterizing this high-risk population. This review summarizes existing clinical trial data on and incorporates our considerations for approaches to the medical management of patients advanced "beyond Stage C" HF.

Cardiac output assessment methods in left ventricular assist device patients: A problem of heteroscedasticity

Equipoise remains about how best to measure cardiac output (CO) in patients with left ventricular assist devices (LVAD). In this study, direct Fick CO was compared with thermodilution (TD) and indirect Fick (iFick) CO in 61 LVAD patients. TD and LaFarge iFick showed moderate correlation with direct Fick (R² = 0.49 and R² = 0.38, p < 0.001 for both), while Dehmer and Bergstra iFick showed poor correlation with direct Fick (R² = 0.29 and R² = 0.31, p < 0.001 for both). Absolute bias between all CO estimation techniques and direct Fick CO was lowest for TD compared to iFick methods but significant for all methods. All methods tended to overestimate CO compared to direct Fick, with greatest overestimation present in those with the lowest measured direct Fick CO. Bias and frequency of significant discrepancy were least using TD and Lafarge iFick CO estimation methods in this study, with TD CO demonstrating modestly better correlation and less heteroscedasticity compared to Lafarge.

Does veno-arterial carbon dioxide gradient provide an adequate estimation of cardiac index in pulmonary hypertension?

AIMS

Pulmonary hypertension (PH) management is dependent on cardiac output (CO) assessment. The gold standard Fick method for CO and cardiac index (CI) measurement is not widely available. An accessible and reliable method for CO/CI estimation is needed not only in catheterization labs but also in other environments such as the intensive care unit, where pulmonary artery catheters are less likely to be used. We hypothesized that veno-arterial carbon dioxide gradient (PvaCO2) is a reliable surrogate for Fick CI in patients with PH.

METHODS AND RESULTS

A single-centre retrospective analysis of patients with PH who underwent direct Fick CI (DFCI) measurement during right heart catheterization. The primary outcome was correlation between PvaCO2 and DFCI. To assess the agreement between central and mixed venous CO2 values, a separate prospective cohort of patients was analysed. Data from 186 patients with all haemodynamic types of PH were analysed. PvaCO2 moderately correlated with Fick CI, R = -0.51 [95% confidence interval (CI): -0.61, -0.39]. A higher PvaCO2 was associated with an increased risk of CI < 2.5 L/min/m2 (odds ratio: 1.88, 95% CI: 1.55, 2.35). Low thermodilution CI with normal veno-arterial carbon dioxide gradient values was associated with a thermodilution underestimation of Fick CI. In the prospective analysis of 32 patients, central venous CO2 overestimated mixed venous values (mean difference 3.3, 95% CI: 2.5, 4.0) and there was poor agreement overall (limits of agreement -1.10, 7.59).

CONCLUSION

Veno-arterial carbon dioxide gradient moderately correlates with Fick CI and may be useful to identify patients with low CI. Central and mixed venous CO2 values should not be used interchangeably in PH.