Continuous noninvasive cardiac output determination using the CNAP system: evaluation of a cardiac output algorithm for the analysis of volume clamp method-derived pulse contour

The CNAP system (CNSystems Medizintechnik AG, Graz, Austria) provides noninvasive continuous arterial pressure measurements by using the volume clamp method. Recently, an algorithm for the determination of cardiac output by pulse contour analysis of the arterial waveform recorded with the CNAP system became available. We evaluated the agreement of the continuous noninvasive cardiac output (CNCO) measurements by CNAP in comparison with cardiac output measurements invasively obtained using transpulmonary thermodilution (TDCO). In this proof-of-concept analysis we studied 38 intensive care unit patients from a previously set up database containing CNAP-derived arterial pressure data and TDCO values obtained with the PiCCO system (Pulsion Medical Systems SE, Feldkirchen, Germany). We applied the new CNCO algorithm retrospectively to the arterial pressure waveforms recorded with CNAP and compared CNCO with the corresponding TDCO values (criterion standard). Analyses were performed separately for (1) CNCO calibrated to the first TDCO (CNCO-cal) and (2) CNCO autocalibrated to biometric patient data (CNCO-auto). We did not perform an analysis of trending capabilities because the patients were hemodynamically stable. The median age and APACHE II score of the 22 male and 16 female patients was 63 years and 18 points, respectively. 18 % were mechanically ventilated and in 29 % vasopressors were administered. Mean ± standard deviation for CNCO-cal, CNCO-auto, and TDCO was 8.1 ± 2.7, 6.4 ± 1.9, and 7.8 ± 2.4 L/min, respectively. For CNCO-cal versus TDCO, Bland–Altman analysis demonstrated a mean difference of +0.2 L/min (standard deviation 1.0 L/min; 95 % limits of agreement ?1.7 to +2.2 L/min, percentage error 25 %). For CNCO-auto versus TDCO, the mean difference was ?1.4 L/min (standard deviation 1.8 L/min; 95 % limits of agreement ?4.9 to +2.1 L/min, percentage error 45 %). This pilot analysis shows that CNCO determination is feasible in critically ill patients. A percentage error of 25 % indicates acceptable agreement between CNCO-cal and TDCO. The mean difference, the standard deviation, and the percentage error between CNCO-auto and TDCO were higher than between CNCO-cal and TDCO. A hyperdynamic cardiocirculatory state in a substantial number of patients and the hemodynamic stability making trending analysis impossible are main limitations of our study.     

A comparison of volume clamp method-based continuous noninvasive cardiac output (CNCO) measurement versus intermittent pulmonary artery thermodilution in postoperative cardiothoracic surgery patients

The CNAP technology (CNSystems Medizintechnik AG, Graz, Austria) allows continuous noninvasive arterial pressure waveform recording based on the volume clamp method and estimation of cardiac output (CO) by pulse contour analysis. We compared CNAP-derived CO measurements (CNCO) with intermittent invasive CO measurements (pulmonary artery catheter; PAC-CO) in postoperative cardiothoracic surgery patients. In 51 intensive care unit patients after cardiothoracic surgery, we measured PAC-CO (criterion standard) and CNCO at three different time points. We conducted two separate comparative analyses: (1) CNCO auto-calibrated to biometric patient data (CNCO_bio) versus PAC-CO and (2) CNCO calibrated to the first simultaneously measured PAC-CO value (CNCO_cal) versus PAC-CO. The agreement between the two methods was statistically assessed by Bland–Altman analysis and the percentage error. In a subgroup of patients, a passive leg raising maneuver was performed for clinical indications and we present the changes in PAC-CO and CNCO in four-quadrant plots (exclusion zone 0.5 L/min) in order to evaluate the trending ability of CNCO. The mean difference between CNCO_bio and PAC-CO was +0.5 L/min (standard deviation?±?1.3 L/min; 95% limits of agreement ?1.9 to +3.0 L/min). The percentage error was 49%. The concordance rate was 100%. For CNCOcal, the mean difference was ?0.3 L/min (±0.5 L/min; ?1.2 to +0.7 L/min) with a percentage error of 19%. In this clinical study in cardiothoracic surgery patients, CNCO_cal showed good agreement when compared with PAC-CO. For CNCO_bio, we observed a higher percentage error and good trending ability (concordance rate 100%).     

Importance of re-calibration time on pulse contour analysis agreement with thermodilution measurements of cardiac output: a retrospective analysis of intensive care unit patients

We assessed the effect of re-calibration time on cardiac output estimation and trending performance in a retrospective analysis of an intensive care unit patient population using error grid analyses. Paired thermodilution and arterial blood pressure waveform measurements (N = 2141) from 222 patient records were extracted from the Multiparameter Intelligent Monitoring in Intensive Care II database. Pulse contour analysis was performed by implementing a previously reported algorithm at calibration times of 1, 2, 8 and 24 h. Cardiac output estimation agreement was assessed using Bland–Altman and error grid analyses. Trending was assessed by concordance and a 4-Quadrant error grid analysis. Error between pulse contour and thermodilution increased with longer calibration times. Limits of agreement were ?1.85 to 1.66 L/min for 1 h maximum calibration time compared to ?2.70 to 2.41 L/min for 24 h. Error grid analysis resulted in 74.2 % of points bounded by 20 % error limits of thermodilution measurements for 1 h calibration time compared to 65 % for 24 h. 4-Quadrant error grid analysis showed <75 % of changes in pulse contour estimates to be within ±80 % of the change in the thermodilution measurement at any calibration time. Shorter calibration times improved the agreement of cardiac output pulse contour estimates with thermodilution. Use of minimally invasive pulse contour methods in intensive care monitoring could benefit from prospective studies evaluating calibration protocols. The applied pulse contour analysis method and thermodilution showed poor agreement to monitor changes in cardiac output.     

Pulse contour analysis of arterial waveform in a high fidelity human patient simulator

The measurement of cardiac output (CO) may be useful to improve the assessment of hemodynamics during simulated scenarios. The purpose of this study was to evaluate the feasibility of introducing an uncalibrated pulse contour device (MostCare, Vytech, Vygon, Padova, Italy) into the simulation environment. MostCare device was plugged to a clinical monitor and connected to the METI human patient simulator (HPS) to obtain a continuous arterial waveform analysis and CO calculation. In six different simulated clinical scenarios (baseline, ventricular failure, vasoplegic shock, hypertensive crisis, hypovolemic shock and aortic stenosis), the HPS-CO and the MostCare-CO were simultaneously recorded. The level of concordance between the two methods was assessed by the Bland and Altman analysis. 150-paired CO values were obtained. The HPS-CO values ranged from 2.3 to 6.6 L min^?1 and the MostCare-CO values from 2.8 to 6.4 L min^?1. The mean difference between HPS-CO and MostCare-CO was ??0.3 L min^?1 and the limits of agreement were ??1.5 and 0.9 L min^?1. The percentage of error was 23%. A good correlation between HPS-CO and MostCare-CO was observed in each scenario of the study (r?=?0.88). Although MostCare-CO tended to underestimate the CO over the study period, good agreements were found between the two methods. Therefore, a pulse contour device can be integrated into the simulation environment, offering the opportunity to create new simulated clinical settings.     

Cross-comparisons of trending accuracies of continuous cardiac-output measurements: pulse contour analysis,bioreactance, and pulmonary-artery catheter

We compared the similarity of cardiac-output (CO) estimates between available bolus thermodilution pulmonary-artery catheters (PAC), arterial pulse-contour analysis (LiDCOplus^?, FloTrac^? and PiCCOplus^?), and bioreactance (NICOM^?). Repetitive simultaneous estimates of CO obtained from the above devices were compared in 21 cardiac-surgery patients during the first 2 h post-surgery. Mean and absolute values for CO across the devices were compared by ANOVA, Bland–Altman, Pearson moment, and linear-regression analyses. Twenty-one simultaneous CO measurements were made before and after therapeutic interventions. Mean PAC CO (5.7?±?1.5 L min) was similar to LiDCO^?, FloTrac^?, PiCCO^?, and NICOM^? CO (6.0?±?1.9, 5.9?±?1.0, 5.7?±?1.8, 5.3?±?1.0 L min, respectively). Mean CO bias between each paired method was ?0.10 (PAC–LiDCO), 0.18 (PAC–PiCCO), ?0.40 (PAC–FloTrac), ?0.71 (PAC–NICOM), 0.28 (LiDCO–PiCCO), 0.39 (LiDCO–FloTrac), ?0.97 (NICOM–LiDCO), 0.61 (PiCCO–FloTrac), ?1.0 (NICOM–FloTrac), ?0.73 (NICOM–PiCCO) L/min, with limits of agreement (1.96 SD, ±95% CI) of ±?2.01, ±2.35, ±2.27, ±2.70, ±1.97, ±2.17, ±3.51, ±2.87, ±2.40, and ±?3.14 L min, respectively, and the percentage error for each of the paired devices was 35, 41, 40, 47, 33, 36, 59, 50, 42, and 55%, respectively. From Pearson moment analysis, dynamic changes in CO, estimated by each device, showed good cross-correlations. Although all devices studied recorded similar mean CO values, which dynamically changed in similar directions, they have markedly different bias and precision values relative to each other. Thus, results from prior studies that have used one device to estimate CO cannot be used to validate others devices.     

Estimated continuous cardiac output based on pulse wave transit time in off-pump coronary artery bypass grafting: a comparison with transpulmonary thermodilution

To evaluate the accuracy of estimated continuous cardiac output (esCCO) based on pulse wave transit time in comparison with cardiac output (CO) assessed by transpulmonary thermodilution (TPTD) in off-pump coronary artery bypass grafting (OPCAB). We calibrated the esCCO system with non-invasive (Part 1) and invasive (Part 2) blood pressure and compared with TPTD measurements. We performed parallel measurements of CO with both techniques and assessed the accuracy and precision of individual CO values and agreement of trends of changes perioperatively (Part 1) and postoperatively (Part 2). A Bland–Altman analysis revealed a bias between non-invasive esCCO and TPTD of 0.9 L/min and limits of agreement of ±2.8 L/min. Intraoperative bias was 1.2 L/min with limits of agreement of ±2.9 L/min and percentage error (PE) of 64 %. Postoperatively, bias was 0.4 L/min, limits of agreement of ±2.3 L/min and PE of 41 %. A Bland–Altman analysis of invasive esCCO and TPTD after OPCAB found bias of 0.3 L/min with limits of agreement of ±2.1 L/min and PE of 40 %. A 4-quadrant plot analysis of non-invasive esCCO versus TPTD revealed overall, intraoperative and postoperative concordance rate of 76, 65, and 89 %, respectively. The analysis of trending ability of invasive esCCO after OPCAB revealed concordance rate of 73 %. During OPCAB, esCCO demonstrated poor accuracy, precision and trending ability compared to TPTD. Postoperatively, non-invasive esCCO showed better agreement with TPTD. However, invasive calibration of esCCO did not improve the accuracy and precision and the trending ability of method.     

The relationship between the area of peripherally-derived pressure volume loops and systemic vascular resistance

Arterial and photoplethysmographic (PPG) waveforms have been utilized to non-invasively estimate stroke volume from the pulse contour. The ability of these pulse contour devices to accurately predict stroke volume is degraded when afterload changes significantly. There is a need for a non-invasive device capable of identifying when vascular tone has changed. Shelley et al. previously described a qualitative relationship between peripheral pressure volume (PV) loops (in which pressure waveforms from an intra-arterial catheter are combined with volume waveforms from the PPG waveform) and changes in vascular tone. The purpose of this study was to quantitatively compare changes in the area of peripheral PV loops with changes in systemic vascular resistance (SVR) in a patient population undergoing major surgery. Physiologic data from ten patients undergoing liver transplantation was extracted from a hemodynamic database. A peak detection algorithm was applied to both the arterial and PPG waveforms, which were manually aligned so that the troughs occurred at identical time points. PV loop area (PVA) for each heartbeat was calculated and median PVA was recorded for each minute. PVA for each patient was indexed to the average value for the first 5 min (because PPG amplitude has no standard and is not comparable between patients) and compared to indexed SVR at all points for which SVR was available. SVR and PVA were plotted as a function of time and outliers (3.1 %) removed. The Pearson correlation coefficient describing the relationship between PVA_i and SVR_i was 0.67 (1,728 min of data, p = 0.0020, sign test over 10 patients) and between MAP and SVR was 0.71. There was no meaningful correlation between ΔSVR and either ΔPVA or ΔMAP (based on minute-to-minute changes). Indexed values of PVA are correlated with indexed values of SVR and may serve as a useful monitor for changes in afterload but in their present form do not offer added value above the measurement of MAP. Incorporation of different (e.g. finger, forehead) and redundant (e.g. bilateral) sites may significantly improve the accuracy of this technique.     

Comparison of electrical velocimetry and cardiac magnetic resonance imaging for the non-invasive determination of cardiac output

A novel algorithm of impedance cardiography referred to as electrical velocimetry (EV) has been introduced for non-invasive determination of cardiac output (CO). Previous validation studies yielded diverging results and no comparison with the non-invasive gold standard cardiac magnetic resonance imaging (CMR) has been performed. We therefore aimed to prospectively assess the accuracy and reproducibility of EV compared to CMR. 152 consecutive stable patients undergoing CMR were enrolled. EV measurements were taken twice before or after CMR in supine position and averaged over 20 s (AESCULON^®, Osypka Medical, Berlin, Germany). Bland–Altman analysis showed insufficient agreement of EV and CMR with a mean bias of 1.2 ± 1.4 l/min (bias 23 ± 26 %, percentage error 51 %). Reproducibility was high with 0.0 ± 0.3 l/min (bias 0 ± 8 %, percentage error 15 %). Outlier analysis revealed gender, height, CO and stroke volume (SV) by CMR as independent predictors for larger variation. Stratification of CO_CMR in quintiles demonstrated a good agreement for low values (<4.4 l/min) with bias increasing significantly with quintile as high as 3.1 ± 1.1 l/min (p < 0.001). Reproducibility was not affected (p = 0.71). Subgroup analysis in patients with arrhythmias (p = 0.19), changes in thoracic fluid content (p = 0.51) or left heart failure (p = 0.47) could not detect significant differences in accuracy. EV showed insufficient agreement with CMR and good reproducibility. Gender, height and increasing CO and SV were associated with increased bias while not affecting reproducibility. Therefore, absolute values should not be used interchangeably in clinical routine. EV yet may find its place for clinical application with further investigation on its trending ability pending.     

Biphasic Waveforms for Ventricular Defibrillation: Optimization of Total Pulse and Second Phase Durations

Waveform parameters may affect the efficacy of ventricular defibrillation. Certain biphasic pulse waveforms are more effective for ventricular defibrillation than monophasic waveforms, but the optimal biphasic waveform parameters have not been identified. The purpose of this study was to investigate the effects of total pulse duration and the duration of the second (negative) phase on voltage and energy defibrillation requirements using biphasic waveforms. Defibrillation efficacy was evaluated in an isolated rabbit heart model using the Langendorff technique. The biphasic waveform was a truncated exponential with the initial voltage of the second phase equal to 50% of the final voltage of the first phase. An up/down protocol was used to determine the 50% probability-of-success levels (E50) for delivered energy and initial voltage. First, using pulse waveforms with equal positive and negative phase durations, test waveforms with total durations of 4 nw (2 ms positive + 2 ms negative), 6 ms (3 + 3 ms), and 16 ms (8 + 8 ms) were compared to the control waveform of 8 ms (4+4 ms) in 30 experiments. Defibrillation voltage requirements with 4 ms (174 ± 56 V) were higher (P = 0.001) compared to 8 ms (127 ± 49 V). Defibrillation voltage requirements for the 6-ms and 16-ms waveforms were similar to the 8-ms control waveform. Delivered energies tended to be higher with the 4-ms waveform. A second series of 40 experiments were performed to compare monophasic (4+0 ms) and three asymmetric biphasic waveforms (4+2 ms, 4 + 8 ms, and 4 + 16 ms) to the symmetric control waveform (4+4 ms). The monophasic (2.15 ± 1.21 J) and the 4 + 16 ms waveform (1.86 ± 1.09 J) required higher energies (P ± 0.05) than the control waveform (1.24 ± 0.41 J and 0.87 ± 0.7 J, respectively). The monophasic waveform also resulted in greater voltage requirements (223 ± 64 V) compared to the control waveform (160 ± 26 V) (P = 0.02). Energy and voltage requirements were similar for the 4+2 ms and 4+8 ms waveforms compared to the control. Defibrillation requirements with biphasic waveforms were affected by total and second phase duration. For waveforms with equal phase durations, total durations between 6–16 ms resulted in the lowest values for defibrillation. For waveforms with variable second (negative) phase durations, durations ranging from 50%-200% of the first phase did not affect defibrillation efficacy.     

Comparison of the ability of two continuous cardiac output monitors to measure trends in cardiac output: estimated continuous cardiac output measured by modified pulse wave transit time and an arterial pulse contour-based cardiac output device

Estimated continuous cardiac output (esCCO), a noninvasive technique for continuously measuring cardiac output (CO), is based on modified pulse wave transit time, which in turn is determined by pulse oximetry and electrocardiography. However, its trending ability has never been evaluated in patients undergoing non-cardiac surgery. Therefore, this study examined esCCO’s ability to detect the exact changes in CO, compared with currently available arterial waveform analysis methods, in patients undergoing kidney transplantation. CO was measured using an esCCO system and arterial pressure-based CO (APCO), and compared with a corresponding intermittent bolus thermodilution CO (ICO) method. Percentage error and statistical methods, including concordance analysis and polar plot analysis, were used to analyze results from 15 adult patients. The difference in the CO values between esCCO and ICO was ?0.39 ± 1.15 L min^?1 (percentage error, 35.6 %). And corrected precision for repeated measures was 1.16 L min^?1 (percentage error for repeated measures, 36.0 %). A concordance analysis showed that the concordance rate was 93.1 %. The mean angular bias was ?1.8° and the radial limits of agreement were ±37.6°. The difference between the APCO and ICO CO values was 0.04 ± 1.37 L min^?1 (percentage error, 42.4 %). And corrected precision for repeated measures was 1.37 L min^?1 (percentage error for repeated measures, 42.5 %). The concordance rate was 89.7 %, with a mean angular bias of ?3.3° and radial limits of agreement of ±42.2°. This study demonstrated that the trending ability of the esCCO system is not clinically acceptable, as judged by polar plots analysis; however, its trending ability is clinically acceptable based on a concordance analysis, and is comparable with currently available arterial waveform analysis methods.     

Pulse-contour derived cardiac output measurements in morbid obesity: influence of actual,ideal and adjusted bodyweight

The non-invasive Nexfin cardiac output (CO) monitor shows a low level of agreement with the gold standard thermodilution method in morbidly obese patients. Here we investigate whether this disagreement is related to excessive bodyweight, and can be improved when bodyweight derivatives are used instead. We performed offline analyses of cardiac output recordings of patient data previously used and partly published in an earlier study by our group. In 30 morbidly obese patients (BMI?>?35 kg/m²) undergoing laparoscopic gastric bypass, cardiac output was simultaneously determined with PiCCO thermodilution and Nexfin pulse-contour method. We investigated if agreement of Nexfin-derived CO with thermodilution CO improved when ideal and adjusted—instead of actual- bodyweight were used as input to the Nexfin. Bodyweight correlated with the difference between Nexfin-derived and thermodilution-derived CO (r?=??0.56; p?=?0.001). Bland Altman analysis of agreement between Nexfin and thermodilution-derived CO revealed a bias of 0.4?±?1.6 with limits of agreement (LOA) from ?2.6 to 3.5 L min when actual bodyweight was used. Bias was ?0.6?±?1.4 and LOA ranged from ?3.4 to 2.3 L min when ideal bodyweight was used. With adjusted bodyweight, bias improved to 0.04?±?1.4 with LOA from ?2.8 to 2.9 L min. Our study shows that agreement of the Nexfin-derived with invasive CO measurements in morbidly obese patients is influenced by body weight, suggesting that Nexfin CO measurements in patients with a BMI above 35 kg/m² should be interpreted with caution. Using adjusted body weight in the Nexfin CO-trek algorithm reduced the bias.     

Cardiac output assessed by non-invasive monitoring is associated with ECG changes in children with critical asthma

The primary aim of this study was to determine changes in CI and SI, if any, in children hospitalized with status asthmatics during the course of treatment as measured by non-invasive EC monitoring. The secondary aim was to determine if there is an association between Abnormal CI (defined as <5 or >95 % tile adjusted for age) and Abnormal ECG (defined as ST waves changes) Non-invasive cardiac output (CO) recordings were obtained daily from admission (Initial) to discharge (Final). Changes in CI and SI measurements were compared using paired t tests or 1-way ANOVA. The association between Abnormal CI on Initial CO recording and Abnormal ECG was analyzed by Fischer’s exact test. Data are presented as mean ± SEM with mean differences reported with 95 % confidence interval; p < 0.05 was considered significant. Thirty-five children with critical asthma were analyzed. CI decreased from 6.2 ± 0.2 to 4.5 ± 0.1 [?1.6 (?0.04 to ?0.37)] L/min/m² during hospitalization. There was no change in SI. There was a significant association between Abnormal Initial CI and Abnormal ECG (p = 0.02). In 11 children requiring prolonged hospitalization CI significantly decreased from 7.2 ± 0.5 to 4.0 ± 0.2 [?3.2 (?4.0 to ?2.3)] L/min/m² and SI decreased from 51.2 ± 3.8 to 40.3 ± 2.0 [?11.0 (?17.6 to ?4.4)] ml/beat/m² There was a significant decrease in CI in all children treated for critical asthma. In children that required a prolonged course of treatment, there was also a significant decrease in SI. Abnormal CI at Initial CO recording was associated with ST waves changes on ECG during hospitalization. Future studies are required to determine whether non-invasive CO monitoring can predict which patients are at risk for developing abnormal ECG.     

Respiratory variations in the photoplethysmographic waveform amplitude depend on type of pulse oximetry device

Respiratory variations in the photoplethysmographic waveform amplitude predict fluid responsiveness under certain conditions. Processing of the photoplethysmographic signal may vary between different devices, and may affect respiratory amplitude variations calculated by the standard formula. The aim of the present analysis was to explore agreement between respiratory amplitude variations calculated using photoplethysmographic waveforms available from two different pulse oximeters. Analysis of registrations before and after fluid loads performed before and after open-heart surgery (aortic valve replacement and/or coronary artery bypass grafting) with patients on controlled mechanical ventilation. Photoplethysmographic (Nellcor and Masimo pulse oximeters) and arterial pressure waveforms were recorded. Amplitude variations induced by ventilation were calculated and averaged over ten respiratory cycles. Agreements for absolute values are presented in scatterplots (with least median square regression through the origin, LMSO) and Bland–Altman plots. Agreement for trending presented in a four-quadrant plot. Agreement between respiratory photoplethysmographic amplitude variations from the two pulse oximeters was poor with LMSO ΔPOP_Nellc = 1.5 × ΔPOP_Mas and bias ± limits of agreement 7.4 ± 23 %. Concordance rate with a fluid load was 91 %. Agreement between respiratory variations in the photoplethysmographic waveform amplitude calculated from the available signals output by two different pulse oximeters was poor, both evaluated by LMSO and Bland–Altman plot. Respiratory amplitude variations from the available signals output by these two pulse oximeters are not interchangeable.     

The effect of head up tilting on bioreactance cardiac output and stroke volume readings using suprasternal transcutaneous Doppler as a control in healthy young adults

To compare the performance of a bioreactance cardiac output (CO) monitor (NICOM) and transcutaneous Doppler (USCOM) during head up tilting (HUT). Healthy young adult subjects, age 22 ± 1 years, 7 male and 7 female, were tilted over 3–5 s from supine to 70° HUT, 30° HUT and back to supine. Positions were held for 3 min. Simultaneous readings of NICOM and USCOM were performed 30 s into each new position. Mean blood pressure (MBP), heart rate (HR), CO and stroke volume (SV), and thoracic fluid content (TFC) were recorded. Bland–Altman, percentage changes and analysis of variance for repeated measures were used for statistical analysis. Pre-tilt NICOM CO and SV readings (6.1 ± 1.0 L/min and 113 ± 25 ml) were higher than those from USCOM (4.1 ± 0.6 L/min and 77 ± 9 ml) (P < 0.001). Bland–Altman limits of agreement for CO were wide with a percentage error of 38 %. HUT increased MBP and HR (P < 0.001). CO and SV readings decreased with HUT. However, the percentage changes in USCOM and NICOM readings did not concur (P < 0.001). Whereas USCOM provided gravitational effect proportional changes in SV readings of 23 ± 15 % (30° half tilt) and 44 ± 11 % (70° near full tilt), NICOM changes did not being 28 ± 10 and 33 ± 11 %. TFC decreased linearly with HUT. The NICOM does not provide linear changes in SV as predicted by physiology when patients are tilted. Furthermore there is a lack of agreement with USCOM measurements at baseline and during tilting.     

The ability of a new continuous cardiac output monitor to measure trends in cardiac output following implementation of a patient information calibration and an automated exclusion algorithm

A new non-invasive continuous cardiac output (esCCO) monitoring system solely utilizing a routine cardiovascular monitor was developed, even though a reference cardiac output (CO) is consistently required. Subsequently, a non-invasive patient information CO calibration together with a new automated exclusion algorithm was implemented in the esCCO system. We evaluated the accuracy and trending ability of the new esCCO system. Either operative or postoperative data of a multicenter study in Japan for evaluation of the accuracy of the original version of esCCO system were used to develop the new esCCO system. A total of 207 patients, mostly cardiac surgical patients, were enrolled in the study. Data were manually reviewed to formulate a new automated exclusion algorithm with enhanced accuracy. Then, a new esCCO system based on a patient information calibration together with the automated exclusion algorithm was developed. CO measured with a new esCCO system was compared with the corresponding intermittent bolus thermodilution CO (ICO) utilizing statistical methods including polar plots analysis. A total of 465 sets of CO data obtained using the new esCCO system were evaluated. The difference in the CO value between the new esCCO and ICO was 0.34?±?1.50 (SD) L/min (95?% confidence limits of ?2.60 to 3.28?L/min). The percentage error was 69.6?%. Polar plots analysis showed that the mean polar angle was ?1.6° and radial limits of agreement were ±53.3°. This study demonstrates that the patient information calibration is clinically useful as ICO, but trending ability of the new esCCO system is not clinically acceptable as judged by percentage error and polar plots analysis, even though it’s trending ability is comparable with currently available arterial waveform analysis methods.     

Evaluation of the use of the fourth version FloTrac system in cardiac output measurement before and after cardiopulmonary bypass

The FloTrac system is a system for cardiac output (CO) measurement that is less invasive than the pulmonary artery catheter (PAC). The purposes of this study were to (1) compare the level of agreement and trending abilities of CO values measured using the fourth version of the FloTrac system (CCO-FloTrac) and PAC-originated continuous thermodilution (CCO-PAC) and (2) analyze the inadequate CO-discriminating ability of the FloTrac system before and after cardiopulmonary bypass (CPB). Fifty patients were included. After exclusion, 32 patients undergoing cardiac surgery with CPB were analyzed. All patients were monitored with a PAC and radial artery catheter connected to the FloTrac system. CO was assessed at 10 timing points during the surgery. In the Bland–Altman analysis, the percentage errors (bias, the limits of agreement) of the CCO-FloTrac were 61.82% (0.16, ??2.15 to 2.47 L min) and 51.80% (0.48, ??1.97 to 2.94 L min) before and after CPB, respectively, compared with CCO-PAC. The concordance rates in the four-quadrant plot were 64.10 and 62.16% and the angular concordance rates (angular mean bias, the radial limits of agreement) in the polar-plot analysis were 30.00% (17.62°, ??70.69° to 105.93°) and 38.63% (??10.04°, ??96.73° to 76.30°) before and after CPB, respectively. The area under the receiver operating characteristic curve for CCO-FloTrac was 0.56, 0.52, 0.52, and 0.72 for all, ≥?±?5, ≥?±?10, and ≥?±?15% CO changes (ΔCO) of CCO-PAC before CPB, respectively, and 0.59, 0.55, 0.49, and 0.46 for all, ≥?±?5, ≥?±?10, and ≥?±?15% ΔCO of CCO-PAC after CPB, respectively. When CO <?4 L/min was considered inadequate, the Cohen κ coefficient was 0.355 and 0.373 before and after CPB, respectively. The accuracy, trending ability, and inadequate CO-discriminating ability of the fourth version of the FloTrac system in CO monitoring are not statistically acceptable in cardiac surgery.     

Reliability of Continuous Pulse Contour Cardiac Output Measurement during Hemodynamic Instability

Objective Arterial pulse contour analysis is gaining widespread acceptance as a monitor of continuous cardiac output (CO). While this type of CO measurement is thought to provide acceptable continuous measurements, only a few studies have tested its accuracy and repeatability under unstable hemodynamic conditions. We compared continuous CO measurement using the pulse contour method (PCCO) before and after calibration with intermittent transpulmonary thermodilution cardiac output (TpCO). Method We compared the two methods of CO measurements in 15 Landrace pigs weighing 20–25 kg in an experimental model of sepsis. Nine pigs were given an infusion of E. coli lipopolysacchride (LPS), and six pigs acted as controls. PCCO values before and after calibration (PCCO₁ and PCCO₂ respectively) were registered, and their errors relative to TpCO measurements were compared. Results The mean coefficient of variation for repeated PCCO measurements was 6.85% for the control group, and 13.99% for the endotoxin group. The range of TpCO was 1.01–3.15 L/min. In the control group the bias ±2SD was 0.11 ± 0.53 L/min (TpCO vs PCCO₁) and −0.02 ± 0.38 L/min (TpCO vs PCCO₂). In the endotoxin group, the agreement was poor between TpCO and PCCO₁, 0.08 ± 1.02 L/min. This improved after calibration (TpCO vs PCCO₂) to 0.01 ± 0.31 L/min. Conclusions In hemodynamically stable pigs, both pre- and post-calibration PCCO measurements agreed well with the intermittent transpulmonary thermodilution technique. However, during hemodynamic instability, and pre-calibration PCCO values had wide limits of agreement compared with TpCO. This was reflected by larger coefficients of variation for PCCO in hemodynamic instability. The error of PCCO measurement improved markedly after calibration, with bias and limits of agreement within clinically acceptable limits. Johansson A, Chew M. Reliability of continuous pulse contour cardiac output measurement during hemodynamic instability.     

A pilot study quantifying the shape of tidal breathing waveforms using centroids in health and COPD

During resting tidal breathing the shape of the expiratory airflow waveform differs with age and respiratory disease. While most studies quantifying these changes report time or volume specific metrics, few have concentrated on waveform shape or area parameters. The aim of this study was to derive and compare the centroid co-ordinates (the geometric centre) of inspiratory and expiratory flow–time and flow–volume waveforms collected from participants with or without COPD. The study does not aim to test the diagnostic potential of these metrics as an age matched control group would be required. Twenty-four participants with COPD and thirteen healthy participants who underwent spirometry had their resting tidal breathing recorded. The flow–time data was analysed using a Monte Carlo simulation to derive the inspiratory and expiratory flow–time and flow–volume centroid for each breath. A comparison of airflow waveforms show that in COPD, the breathing rate is faster (17 ± 4 vs 14 ± 3 min^?1) and the time to reach peak expiratory flow shorter (0.6 ± 0.2 and 1.0 ± 0.4 s). The expiratory flow–time and flow–volume centroid is left-shifted with the increasing asymmetry of the expired airflow pattern induced by airway obstruction. This study shows that the degree of skew in expiratory airflow waveforms can be quantified using centroids.     

Isocapnic hyperpnea with a portable device in Cystic Fibrosis: an agreement study between two different set-up modalities

To evaluate the bias and precision of the respiratory muscle training device formulas to predict respiratory minute volume (RMV) and volume of the reservoir bag (BV) on a cohort of subjects with Cystic Fibrosis (CF). CF patients with available pulmonary function tests and maximal voluntary manoeuvres were included in the study. Vital capacity and maximal voluntary ventilation were extracted from subjects’ records and then inserted to the manufacturer’s formulas to obtain RMV and BV (measured setting). RMV and BV were compared according to standard and measured formulas in males and females. Sample was described and then processed using Bland–Altman analysis. Bland–Altman analysis for RMV revealed a bias and precision of 8.8 ± 29 L/min in males and 28.8 ± 16 L/min in females; 0.4 ± 0.5 L in males and 0.7 ± 0.4 L in females for BV. Concordance correlation coefficients for RMV were ?0.03 in males and 0.02 in females; 0.22 in males and 0.03 in females for BV, reinforcing an unsatisfactory concordance between measured and manufacturer setting. This study shows considerable discrepancies between the two methods, making the degree of agreement not clinically acceptable. This might cause inappropriate setting and disservice to patients with CF.     

Continuous cardiac output measurement by un-calibrated pulse wave analysis and pulmonary artery catheter in patients with septic shock

Septic shock is a serious medical condition. With increased concerns about invasive techniques, a number of non-invasive and semi-invasive devices measuring cardiac output (CO) have become commercially available. The aim of the present study was to determine the accuracy, precision and trending abilities of the FloTrac and the continuous pulmonary artery catheter thermodilution technique determining CO in septic shock patients. Consecutive septic shock patients were included in two centres and CO was measured every 4 h up to 48 h by FloTrac (APCO) and by pulmonary artery catheter (PAC) using the continuous (CCO) and intermittent (ICO) technique. Forty-seven septic shock patients with 326 matched sets of APCO, CCO and ICO data were available for analysis. Bland and Altman analysis revealed a mean bias ±2 SD of 0.0 ± 2.14 L min^?1 for APCO–ICO (%error = 34.5 %) and 0.23 ± 2.55 L min^?1 for CCO–ICO (%error = 40.4 %). Trend analysis showed a concordance of 85 and 81 % for APCO and CCO, respectively. In contrast to CCO, APCO was influenced by systemic vascular resistance and by mean arterial pressure. In septic shock patients, APCO measurements assessed by FloTrac but also the established CCO measurements using the PAC did not meet the currently accepted statistical criteria indicating acceptable clinical performance.