Use of minimally invasive hemodynamic monitoring to assess dynamic changes in cardiac output at the bedside

Abstract

I read with dismay the Commentary by Lester Critchley [1] on our recent pulse contour analysis study [2]. We disagree with his statement that, based on our data, one cannot use arterial pulse contour to assess changes in cardiac output (CO). We compared several commercially available arterial pulse contour methods of measuring CO with themselves and pulmonary artery catheter (PAC)-derived bolus thermodilution (COtd) and continuous CO (CCO) modes. We showed that none of these devices trended CO changes well when compared to the others, either separately or compared to a pooled CO value of all the devices. Th us, clinical trials using CO trending data from one device cannot be extrapolated to similar outcomes using other devices. Dr Critchley concluded that none of the pulse contour devices accurately trend CO changes. If that logic were true, then one could also not use PAC CO trending either, as it fared worse than the rest when compared to pooled CO values. Lack of proof of CO trending correlation amongst devices does not equate to lack of ability to trend CO by a device. His argument is based on four lines of reasoning that we dispute. First, he argued that we pooled PAC COtd and CCO measures. However, we also reported separate BlandAltman analyses for COtd and CCO and the relations were unchanged. Second, we then restricted our analysis to low fl ow states and all devices markedly improved their CO estimates, but the concordance remained poor compared to PAC. Furthermore, his study [3] as a reference used COtd as cardiac index (CItd) ‘giving concordance across devices of 90-95% when exclusion criteria of 0.5-1.0 l/min/m 2 are applied.’ We set our exclusion limits at 0.25 l/minute/m 2 , but if we set it at 1 l/minute/m 2 the PiCCO, LiDCO and FloTrac concordance would increase to 83%, 88% and 74% in line with that reported by de Wilde and colleagues [4] using a more accurate PAC COtd reference method. Th ird, the FloTrac algorithm we used would remain the same even in the newer version of their software. Finally, he correctly says that the site of measure may aff ect refl ected arterial pressure waves. But all measures with all devices for a given subject were made from the same site. So this is a non-issue. Accordingly, the conclusion that these devices are inaccurate cannot be made from our study.