The difference between serial measurements of ThD-CO (ΔThD-CO) and serial measurements of MostCare-CO (ΔMostCare-CO) are shown in Figure 2. The correlation coefficient between ΔThD-CO and ΔMostCare-CO was 0.82 (95% CI = 0.76–0.87; P < 0.001) The bias was 0.14 L/min with LoA of −1.31 to 1.59 L/min (lower 95% CI, −1.62 to −1.00; upper 95% CI, 1.28–1.90).
The concordance between ΔThD-CO and ΔMostCare-CO was 89.5% (60 of 67 pairs of ΔCO agreed) and it improved to 95.1% (39 of 41 pairs of ΔCO agreed) when 26 ΔThD-CO <0.5 L/min were excluded from the analysis. A polar plot was used to show the direction of CO changes (i.e., the trending ability) (Fig. 3).
In 1976, Herzlinger24 described a simple method for determining CO on a continuous beat-by-beat basis by the analysis of blood pressure traces in 40 patients with an intraaortic balloon pump. He used a simple mathematical formula that included the pumping volume of the intraaortic balloon pump and changes in the pressure wave generated by ventricular ejection and balloon inflation/deflation). He reported good correlation with indocyanine green dye and thermal dilution CO.24 Høie25 performed a similar study in 13 patients with an intraaortic balloon pump. He found a correlation of r = 0.86 between CO determinations from pulse contour and thermodilution. However, his analyzer failed to give results in 7 patients (60%) because it was not possible to recognize the 3 pressure excursions within the arterial waveform. The author therefore concluded that his algorithm was useless as a method for CO monitoring.25 After this study, the idea of using the arterial trace to calculate CO in patients with an intraaortic balloon pump was rejected for more than 2 decades.
Janda et al.26 studied the impact of an intraaortic balloon pump on measurements of CO made using transpulmonary thermodilution (PiCCO; Pulsion Medical Systems, Irving, TX). These authors demonstrated that the close agreement (r = 0.94) between CO measurements obtained by transpulmonary and pulmonary arterial thermodilution was not affected by an intraaortic balloon pump interposed between the injection and detection site of the indicator over a wide range of pacemaker-induced changes in CO.26 However, continuous CO measurement, a major application of the PiCCO system based on the principle of pulse contour analysis, was not a viable option during the use of an intraaortic balloon pump because of the complete alteration of the arterial pressure curve caused by the inflation and deflation of the intraaortic balloon pump, and this problem could not be circumvented by repeated recalibration of the signal by transpulmonary thermodilution.26 Lorsomradee et al.27 compared CO values obtained by an uncalibrated pulse contour method (Vigileo monitor version 1.07; Edwards Lifesciences) with those from continuous thermodilution (CCO, Vigilance Monitor; Edwards Lifescience) in 52 patients undergoing cardiac surgery. There was poor agreement between the 2 techniques in the subgroup of 12 intraaortic balloon pump patients. In 80% of intraaortic balloon pump patients, the Vigileo monitor displayed the message “unstable signal” or “check arterial waveform” during different periods and failed to show CO values for several minutes.27 Zangrillo et al.10 recently evaluated the accuracy and precision of the MostCare system compared with thermodilution in 32 patients undergoing different cardiac surgical procedures, with two-thirds of patients assisted with an intraaortic balloon pump. They reported good agreement between MostCare-CO and ThD-CO for the whole patient population (r = 0.72, mean bias of 0.072 ± 0.41 L/min/m2). Unfortunately, the agreement between the techniques was not specifically evaluated for the intraaortic balloon pump subgroup.10
Our findings showed close agreement between ThD-CO and MostCare-CO. Several other studies have confirmed the accuracy of MostCare in CO measurement in different clinical scenarios.5–10,28,29 Some interesting findings from the present study should be highlighted. First, the MostCare system identified the dicrotic notch at each cardiac cycle and thus could calculate CO values in all patients. Second, there were no significant differences between the MostCare system and thermodilution (Fig. 1), and the agreement persisted despite changes in the intraaortic balloon pump rate setting. Third, the LoA and the relative errors were within the clinically acceptable limits proposed by Critchley and Critchley16 (Table 3). Fourth, the agreement and the relative errors did not change significantly for all 106 CO measurements considering the repeated-measures design of the data (Table 3, Fig. 4). Finally, the polar plot used to assess trending ability according to Critchley et al.23 showed good concordance between the techniques in the detection of change in CO (ΔCO) (Fig. 3).
Pulse contour methods may have advantages over pulmonary artery catheter–derived thermodilution measurements.30 In particular, the MostCare system is easy to use, has a fast response time (beat-to-beat readout), and may detect abrupt changes in CO more quickly than the thermodilution technique. Moreover, the MostCare system does not require external calibration by thermodilution, and requires no other additional invasive procedure. Because it does not require injection of a thermal solution, a central line is not required, saving time and avoiding potential complications due to the insertion of a central catheter.31
However, there are also some drawbacks and limitations. In particular, various factors may affect the analysis of arterial waveforms. Patient-related conditions can affect the pulsatility and contour of waveforms because of abnormal transmission of the arterial signal; for example, in aortic valve regurgitation and stenosis or vascular pathologies resulting in obstruction to the transmission of the pressure wave (i.e., stenosis along the arterial tree from the aortic valve to the sampling site). Furthermore, over- or underdamped arterial pressure waveforms may affect the precision of the pressure wave analysis by pulse contour methods.32–34 Analysis of the blood pressure wave at 1000 Hz is also dependent on the operator, who needs to maximize the quality of the arterial signal to obtain a reliable pressure wave morphology. In a recent study, Paarmann et al.35 reported a very weak agreement between measurements of CO obtained by MostCare and those obtained using thermodilution in postoperative cardiac surgery patients, in contrast to our findings. However, the authors provided little information regarding the quality of the arterial pressure signal, which, if inadequate, could explain in part the poor agreement observed in their study and the differences between their results and ours.36
Another important limitation of these less-invasive methods in measuring CO is their potential unreliability in patients with cardiac dysrhythmias, especially atrial fibrillation. In such cases, pulse contour methods must compute stroke volume for each heartbeat over a fixed time interval (i.e., 1 minute) and then calculate CO by multiplying stroke volume by the number of heartbeats. This potential drawback was recently demonstrated by Maj et al.37 who studied 41 patients who developed atrial fibrillation and hemodynamic instability after cardiac surgery. The authors compared MostCare with thermodilution and found poor agreement between the techniques.
Finally, the pulmonary artery catheter can provide additional data on pulmonary artery and filling pressures and mixed venous oxygen saturation, which are not available with pulse contour methods and allow accurate interpretation (and therapy) of CO in complex patients. The absence of these measures may be a disadvantage of pulse contour methods, but is perhaps a penalty we have to accept for being less invasive.
Obviously, the range of CO values analyzed in our study was relatively narrow because patients supported with an intraaortic balloon pump do not have a high CO. The studied patients were a homogeneous coronary artery bypass graft group free from ascending aorta disease and aortic valve pathology, which could affect the arterial waveform morphology and its analysis. This may explain why we found a better agreement between ThD-CO and MostCare-CO than did Zangrillo et al.10 in their study that also included intraaortic balloon pump patients with aortic valve and ascending aorta pathologies.
In our patient cohort, we demonstrated that the MostCare device gave results comparable to those obtained by conventional thermodilution during the use of an intraaortic balloon pump, despite alterations in the arterial pressure waveforms.
Name: Sabino Scolletta, MD.
Contribution: Study design, patient inclusion and conduct of the study, data analysis, manuscript preparation.
Conflicts of Interest: Sabino Scolletta has received research grants from Vygon and Vytech.
Name: Federico Franchi, MD.
Contribution: Patient inclusion and conduct of the study, data analysis.
Conflicts of Interest: Federico Franchi reported no conflicts of interest.
Name: Fabio Silvio Taccone, MD.
Contribution: Data analysis, manuscript preparation.
Conflicts of Interest: Fabio Silvio Taccone reported no conflicts of interest.
Name: Katia Donadello, MD.
Contribution: Data analysis, manuscript preparation.
Conflicts of Interest: Katia Donadello reported no conflicts of interest.
Name: Bonizella Biagioli, MD.
Contribution: Data analysis, manuscript preparation.
Conflicts of Interest: Bonizella Biagioli reported no conflicts of interest.
Name: Jean-Louis Vincent, MD, PhD.
Contribution: Data analysis, manuscript preparation.
Conflicts of Interest: Jean-Louis Vincent reported no conflicts of interest.
This manuscript was handled by: Dwayne R. Westenskow, PhD.
We thank Vytech Health (Padua, Italy) for providing us with the MostCare device.
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