Echo is a good, not perfect, measure of cardiac output in critically ill surgical patients

Abstract

BACKGROUND Compared with a pulmonary artery catheter (PAC), transthoracic echocardiography (TTE) has been shown to have good agreement in cardiac output (CO) measurement in nonsurgical populations. Our hypothesis is that the feasibility and accuracy of CO measured by TTE (CO-TTE), relative to CO measured by PAC thermodilution (CO-PAC), is different in surgical intensive care unit patients (SP) and nonsurgical patients (NSP). METHODS Surgical patients with PAC for hemodynamic monitoring and NSP undergoing right heart catheterization were prospectively enrolled. Cardiac output was measured by CO-PAC and CO-TTE. Pearson coefficients were used to assess correlation. Bland-Altman analysis was used to determine agreement. RESULTS Over 18 months, 84 patients were enrolled (51 SP, 33 NSP). Cardiac output TTE could be measured in 65% (33/51) of SP versus 79% (26/33) of NSP; p = 0.17. Inability to measure the left ventricular outflow tract diameter was the primary reason for failure in both groups; 94% (17/18) in SP versus 86% (6/7) NSP; p = 0.47. Velocity time integral could be measured in all patients. In both groups, correlation between PAC and TTE measurement was strong; SP (r = 0.76; p < 0.0001), NSP (r = 0.86; p < 0.0001). Bland-Altman analysis demonstrated bias of −0.1 L/min, limits of agreement of −2.5 and +2.3 L/min, percentage error (PE) of 40% for SP, and bias of +0.4 L/min, limits of agreement of −1.8 and +2.5 L/min, and PE of 40% for NSP. CONCLUSION There was strong correlation and moderate agreement between TTE and PAC in both SP and NSP. In both patient populations, inability to measure the left ventricular outflow tract diameter was a limiting factor. LEVEL OF EVIDENCE Diagnostic tests or criteria, level III.

A novel method of calculating stroke volume using point-of-care echocardiography

“…While SV cm is superior to BSA based methods it still has a PE of 33%, which is higher than the recommend threshold of 30%. Also, the root mean square error is +/− 13, which could be important in assessing metrics like stroke volume variation, but this is in line with the error reported in multiple studies comparing TTE to PAC in measurement of CO which range from 23 to 40% [7]. This study is describing one step in automating SV assessment with echo, further work is needed evaluate and improve the technique.…”

“…There are several reasons automating LVOTD in the measurement of SV could improve POC-TTE. It would increase the yield of the metric, especially in difficult to image surgical patients [7]. It could also prove to make SV assessment more accurate because LVOTD measurement is difficult, prone to error, and the value is squared (SV = π (LVOT D/2) 2 x LV VTI).…”

“…A significant limitation in the estimation CO and SV by POC-TTE is the inability to measure the LVOTD in about 27.4% of critically ill patients [7,8]. Fortunately, the LVOTD it is a static anatomic measure in adulthood so it is not needed to trend changes in SV or CO.…”

“…Fortunately, LVOT VTI can be measured in greater than 90% of critically ill patients ( Fig. 1) [7]. Therefore, combining the measured and estimated values of LVOTD and LVOT VTI allows calculation of SV at the bedside in most patients, making POC-TTE a viable and reliable alternative to other methods.…”

Point-of-Care Transthoracic Echocardiography: A Growing Body of Evidence, an Educational Need

“…Recently, Olivieri et al demonstrated good correlation and agreement among cardiac output measurements in both medical and surgical patients through the use of PACs and point-of-care TTE. 9 No monitoring device will innately improve patient outcomes, unless used by a clinician able to synthesize the clinical information and coupled with the appropriate treatment. Zarragoikoetxea et al echo this nicely in demonstrating that TTE can aid both in the diagnosis of LCOS and to further assess the response to intervention.…”