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Cardiac output (CO) is a key hemodynamic variable that can be minimally invasively estimated by pulse wave analysis. Multi-beat analysis is a novel pulse wave analysis method. In this prospective observational clinical method comparison study, we compared CO estimations by multi-beat analysis with CO measured by intermittent pulmonary artery thermodilution (PATD) in adult patients treated in the intensive care unit (ICU) after off-pump coronary artery bypass surgery (OPCAB). We included patients after planned admission to the ICU after elective OPCAB who were monitored with a radial arterial catheter and a pulmonary artery catheter. At seven time points, we determined CO using intermittent PATD (PATD-CO; reference method) and simultaneously recorded the radial arterial blood pressure waveform that we later used to estimate CO using multi-beat analysis (MBA-CO; test method) with the Argos monitor (Retia Medical; Valhalla, NY, USA). Blood pressure waveforms impaired by inappropriate damping properties or artifacts were excluded. We compared PATD-CO and MBA-CO using Bland–Altman analysis accounting for repeated measurements, the percentage error, and the concordance rate derived from four-quadrant plot analysis (15% exclusion zone). We analyzed 167 CO values of 31 patients. Mean PATD-CO was 5.30 ± 1.22 L/min and mean MBA-CO was 5.55 ± 1.82 L/min. The mean of the differences between PATD-CO and MBA-CO was 0.08 ± 1.10 L/min (95% limits of agreement: − 2.13 L/min to + 2.29 L/min). The percentage error was 40.7%. The four-quadrant plot-derived concordance rate was 88%. CO estimation by multi-beat analysis of the radial arterial blood pressure waveform (Argos monitor) shows reasonable agreement compared with CO measured by intermittent PATD in adult patients treated in the ICU after OPCAB.

Pulse wave analysis enables stroke volume to be estimated from an arterial blood pressure waveform. Multi-beat analysis is a novel pulse wave analysis method. We aimed to investigate cardiac output (CO) estimations using multi-beat analysis of the radial arterial blood pressure waveform in patients undergoing off-pump coronary artery bypass surgery (OPCAB) using intermittent pulmonary artery thermodilution (PATD) as the reference method. This was a prospective clinical method comparison study. In 58 patients, we measured CO using PATD (PATD-CO; reference method) and simultaneously recorded the radial arterial blood pressure waveform that we used for off-line estimation of CO based on multi-beat analysis (MBA-CO; test method) using the Argos CO monitor (Retia Medical; Valhalla, NY, USA). The final analysis was performed using 572 paired CO measurements. We performed Bland–Altman analysis accounting for multiple observations per patient. To describe the ability of the test method to track changes in CO over time we computed four-quadrant plots using a central exclusion zone of 15% and calculated the concordance rate. Mean PATD-CO was 4.13 ± 1.26 L/min and mean MBA-CO was 4.31 ± 1.25 L/min. The mean of the differences between PATD-CO and MBA-CO was − 0.20 L/min with a standard deviation of ± 1.14 L/min and 95% limits of agreement of − 2.48 to + 2.08 L/min. The concordance rate for CO changes between PATD-CO and MBA-CO was 89%. CO estimations using multi-beat analysis (Argos monitor) show reasonable agreement and trending ability compared with PATD-CO as the reference method in adult patients during OPCAB.

Pulse pressure variation (PPV) and stroke volume variation (SVV) can be used to assess fluid status in the operating room but usually require dedicated advanced hemodynamic monitors. Recently, a smartphone application (Capstesia™), which automatically calculates PPV from a picture of the invasive arterial pressure waveform from any monitor screen (PPVCAP), has been developed. The purpose of this study was to compare PPVCAP with SVV from an uncalibrated pulse wave analysis monitor (SVVPC). In 40 patients undergoing major abdominal surgery, we compared PPVCAP with SVVPC at post-induction, pre-incision, post-incision, end of surgery, and during every hypotensive episode (mean arterial pressure 13%). The agreement between SVVPC and PPVCAP for these three categories was measured by the number of concordant paired measurements divided by the total number of paired measurements and Cohen’s kappa coefficient. In the 549 pairs of PPV–SVV data obtained, the overall agreement of PPVCAP with SVVPC was 79%, and the kappa coefficient was moderate (0.55). The highest agreement and kappa coefficient value were observed after the induction of anesthesia before surgical incision. PPVCAP and SVVPC would have resulted in completely opposite clinical decisions regarding fluid administration in 1% of the cases. In this clinical decision making study in patients undergoing major abdominal surgery, we observed a moderate agreement between PPVCAP and SVVPC with regard to categories used to guide fluid administration. Trial Registration: Clinical Trials.gov (NCT03137901).

The CNAP system allows continuous noninvasive arterial pressure measurement based on the volume clamp method using a finger cuff. We aimed to evaluate the agreement between arterial pressure measurements noninvasively obtained using the CNAP device and arterial catheter-derived arterial pressure measurements in intensive care unit patients. In 55 intensive care unit patients, we simultaneously recorded arterial pressure values obtained by an arterial catheter placed in the abdominal aorta through the femoral artery (criterion standard) and arterial pressure values determined noninvasively using CNAP. We performed Bland–Altman analysis and calculated the percentage error. The mean difference (±standard deviation, 95 % limits of agreement, percentage error) between noninvasive (CNAP) and invasively assessed arterial pressure was for mean arterial pressure +1 mmHg (±9 mmHg, −16 to +19 mmHg, 22 %), for systolic arterial pressure −10 mmHg (±16 mmHg, −42 to +21 mmHg, 27 %), and for diastolic arterial pressure +7 mmHg (±9 mmHg, −10 to +24 mmHg, 28 %). Our results indicate a reasonable accuracy and precision for the determination of mean and diastolic arterial pressure by noninvasive continuous arterial pressure measurements using the volume clamp method compared with the criterion standard (invasive arterial catheter). Systolic arterial pressure is determined less accurately and precisely.

Cardiac output (CO) plays a crucial role in the hemodynamic management of critically ill patients treated in the intensive care unit and in surgical patients undergoing major surgery. In the field of cardiovascular dynamics, innovative techniques for CO determination are increasingly available. Therefore, the number of studies comparing these techniques with a reference, such as pulmonary artery thermodilution, is rapidly growing. There are mainly two outcomes of such method comparison studies: (1) the accuracy of agreement and (2) the precision of agreement. The precision of agreement depends on the precision of each method, i.e., the precision that the studied and the reference technique are able to achieve. We call this “precision of method”. A decomposition of variance shows that method agreement does not only depend on the precision of method but also on another important source of variability, i.e., the method’s general variability about the true values. Ignorance of that fact leads to falsified conclusions about the precision of method of the studied technique. In CO studies, serial measurements are frequently confused with repeated measurements. But as the actual CO of a subject changes from assessment to assessment, there is no real repetition of a measurement. This situation equals a scenario in which single measurements are given for multiple true values per subject. In such a case it is not possible to assess the precision of method.

We aimed to describe and evaluate an autocalibrating algorithm for determination of cardiac output (CO) based on the analysis of an arterial pressure (AP) waveform recorded using radial artery applanation tonometry (AT) in a continuous non-invasive manner. To exemplarily describe and evaluate the CO algorithm, we deliberately selected 22 intensive care unit patients with impeccable AP waveforms from a database including AP data obtained with AT (T-Line system; Tensys Medical Inc.). When recording AP data for this prospectively maintained database, we had simultaneously noted CO measurements obtained from just calibrated pulse contour analysis (PiCCO system; Pulsion Medical Systems) every minute. We applied the autocalibrating CO algorithm to the AT-derived AP waveforms and noted the computed CO values every minute during a total of 15 min of data recording per patient (3 × 5-min intervals). These 330 AT-derived CO (AT-CO) values were then statistically compared to the corresponding pulse contour CO (PC-CO) values. Mean ± standard deviation for PC-CO and AT-CO was 7.0 ± 2.0 and 6.9 ± 2.1 L/min, respectively. The coefficient of variation for PC-CO and AT-CO was 0.280 and 0.299, respectively. Bland-Altman analysis demonstrated a bias of +0.1 L/min (standard deviation 0.8 L/min; 95% limits of agreement -1.5 to 1.7 L/min, percentage error 23%). CO can be computed based on the analysis of the AP waveform recorded with AT. In the selected patients included in this pilot analysis, a percentage error of 23% indicates clinically acceptable agreement between AT-CO and PC-CO.