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Background: Changes in central venous pressure (CVP) rather than absolute values may be used to guide fluid therapy in critically ill patients undergoing mechanical ventilation. We conducted a study comparing the changes in the CVP produced by an increase in PEEP and stroke volume variation (SVV) as indicators of fluid responsiveness. Fluid responsiveness was assessed by the changes in cardiac output (CO) produced by passive leg raising (PLR)., Methods: In 20 fully mechanically ventilated patients after cardiac surgery, PEEP was increased +10 cm H2O for 5 min followed by PLR. CVP, SVV, and thermodilution CO were measured before, during, and directly after the PEEP challenge and 30° PLR. The CO increase >7% upon PLR was used to define responders., Results: Twenty patients were included; of whom, 10 responded to PLR. The increase in CO by PLR directly related (r=0.77, P<0.001) to the increase in CVP by PEEP. PLR responsiveness was predicted by the PEEP-induced increase in CVP [area under receiver-operating characteristic (AUROC) curve 0.99, P<0.001] and by baseline SVV (AUROC 0.90, P=0.003). The AUROC's for dCVP and SVV did not differ significantly (P=0.299)., Conclusions: Our data in mechanically ventilated, cardiac surgery patients suggest that the newly defined parameter, PEEP-induced CVP changes, like SVV, appears to be a good parameter to predict fluid responsiveness.

We evaluated cardiac output (CO) using three new methods - the auto-calibrated FloTrac-Vigileo (CO(ed)), the non-calibrated Modelflow (CO(mf) ) pulse contour method and the ultra-sound HemoSonic system (CO(hs)) - with thermodilution (CO(td)) as the reference. In 13 postoperative cardiac surgical patients, 104 paired CO values were assessed before, during and after four interventions: (i) an increase of tidal volume by 50%; (ii) a 10 cm H(2)O increase in positive end-expiratory pressure; (iii) passive leg raising and (iv) head up position. With the pooled data the difference (bias (2SD)) between CO(ed) and CO(td), CO(mf) and CO(td) and CO(hs) and CO(td) was 0.33 (0.90), 0.30 (0.69) and -0.41 (1.11) l.min(-1), respectively. Thus, Modelflow had the lowest mean squared error, suggesting that it had the best performance. CO(ed) significantly overestimates changes in cardiac output while CO(mf) and CO(hs) values are not significantly different from those of CO(td). Directional changes in cardiac output by thermodilution were detected with a high score by all three methods.

The bias, precision and tracking ability of five different pulse contour methods were evaluated by simultaneous comparison of cardiac output values from the conventional thermodilution technique (COtd). The five different pulse contour methods included in this study were: Wesseling's method (cZ); the Modelflow method; the LiDCO system; the PiCCO system and a recently developed Hemac method. We studied 24 cardiac surgery patients undergoing uncomplicated coronary artery bypass grafting. In each patient, the first series of COtd was used to calibrate the five pulse contour methods. In all, 199 series of measurements were accepted by all methods and included in the study. COtd ranged from 2.14 to 7.55 l.min(-1), with a mean of 4.81 l.min(-1). Bland-Altman analysis showed the following bias and limits of agreement: cZ, 0.23 and - 0.80 to 1.26 l.min(-1); Modelflow, 0.00 and - 0.74 to 0.74 l.min(-1); LiDCO, - 0.17 and - 1.55 to 1.20 l.min(-1); PiCCO, 0.14 and - 1.60 to 1.89 l.min(-1); and Hemac, 0.06 and - 0.81 to 0.93 l.min(-1). Changes in cardiac output larger than 0.5 l.min(-1) (10%) were correctly followed by the Modelflow and the Hemac method in 96% of cases. In this group of subjects, without congestive heart failure, with normal heart rhythm and reasonable peripheral circulation, the best results in absolute values as well as in tracking changes in cardiac output were measured using the Modelflow and Hemac pulse contour methods, based on non-linear three-element Windkessel models.

This study was performed to determine the interchangeability of femoral artery pressure and radial artery pressure measurements as the input for the PiCCO system (Pulsion Medical Systems, Munich, Germany). We studied 15 intensive care patients following cardiac surgery. Five-second averages of the cardiac output derived from the femoral artery pressure (COfem) were compared to 5-s averages derived from the radial artery pressure (COrad). One patient was excluded due to problems in the pattern recognition of the arterial pressure signal. In the remaining 14 patients, 14 734 comparative cardiac output values were analysed. The mean sample time was 88 min, range [30-119 min]. Mean (SD) COfem was 6.24 (1.1) l.min(-1) and mean COrad 6.23 (1.1) l.min(-1). Bland-Altman analysis showed an excellent agreement with a bias of - 0.01 l.min(-1), and limits of agreement from 0.60 to - 0.62 l.min(-1). If changes in CO were > 0.5 l.min(-1), the direction of changes in COfem and COrad were equal in 97% of instances. We conclude that femoral artery pressure and radial artery pressure are interchangeable as inputs for the PiCCO device.

Background: Cardiac output by modelflow pulse contour method can be monitored quantitatively and continuously only after an initial calibration, to adapt the model to an individual patient. The modelflow method computes beat-to-beat cardiac output (COmf) from the radial artery pressure, by simulating a three-element model of aortic impedance with post-mortem data from human aortas., Methods: In our improved version of modelflow (COmfc) we adapted this model to a real time measure of the aortic cross-sectional area (CSA) of the descending aorta just above the diaphragm, measured by a new transoesophageal echo device (HemoSonic 100). COmf and COmfc were compared with thermodilution cardiac output (COtd) in 24 patients in the intensive care unit. Each thermodilution value was the mean of four measurements equally spread over the ventilatory cycle., Results: Least squares regression of COtd vs COmf gave y=1.09x[95% confidence interval (CI) 0.96-1.22], R2=0.15, and of COtd vs COmfc resulted in y=1.02x(95% CI 0.96-1.08), R2=0.69. The limits of agreement of the un-calibrated COmf were -3.53 to 2.79, bias=0.37 litre min(-1) and of the diameter-calibrated method COmfc, -1.48 to 1.32, bias=-0.08 litre min(-1). The coefficient of variation for the difference between methods decreased from 28 (un-calibrated) to 12% after diameter-calibration., Conclusions: After diameter-calibration, the improved modelflow pulse contour method reliably estimates cardiac output without the need of a calibration with thermodilution, leading to a less invasive cardiac output monitoring method.

In two adult patients, one with a severe hemorrhage and one with a partial anomalous pulmonary vein, cardiac output (CO) measurements were performed simultaneously by means of the bolus transpulmonary thermodilution technique (COao) and continuous pulmonary artery thermodilution method (CCOpa). In both cases, the methods revealed clinically significant different cardiac output values based upon the site of measurement and the underlying pathology. The assessment of cardiac output (CO) is considered an important part of cardiovascular monitoring of the critically ill patient. Cardiac output is most commonly determined intermittently by the bolus thermodilution technique with a pulmonary artery catheter (COpa). As continuous monitoring of CO is preferable to this intermittent technique, two major techniques have been proposed. Firstly, a nearly continuous thermodilution method (CCOpa) using a heating filament mounted on a pulmonary artery catheter (Baxter Edwards Laboratories, Irvine, CA), with a clinically acceptable accuracy compared with the intermittent bolus technique. Based on these results we assumed CCOpa equivalent to real CO during hemodynamically stable conditions, and secondly, a continuous cardiac output system based on pulse contour analysis (PCCO), such as the PiCCO system (Pulsion Medical System, Munchen, Germany). To calibrate this device, which uses a derivation of the algorithm of Wesseling and colleagues, an independently obtained value of CO by the transpulmonary thermodilution method (COao) is used. Clinical validation studies in patients without underlying intrathoracic pathology, comparing transpulmonary COao with the pulmonary technique (COpa), mostly yielded good agreement.

Background: We recently demonstrated the feasibility of computer controlled infusion of vasoactive drugs for the control of systemic hypertension during cardiac surgery. The objective of the current study was to investigate the effects of computer controlled blood pressures on hemodynamic stability when compared to conventional manual control.Method: Systemic artery blood pressures were managed either by computer (80 patients) or by a well-trained anesthesiologist (80 patients). The vasodilator drugs sodium nitroprusside and nitroglycerin were used. Hemodynamic stability was determined from the standard deviation of the mean arterial pressure samples and from the percentages of time that arterial pressure was hypertensive or hypotensive.Results: The average standard deviation of the mean arterial pressure samples was smaller for the computer controlled than for the manually controlled group: 7.5+/-2.2 (mean+/-SD) versus 8.9+/-2.3 mmHg (P<0.0001). The systemic artery pressure was less hypertensive and less hypotensive in the computer controlled than in the manually controlled group: 9.4+/-5.7 versus 13.1+/-6.0% (P<0.0001) and 8.0+/-5.9 versus 11.8+/-7.4% (P<0.0001), respectively.Conclusion: We conclude that, compared with manual control, computer control of systemic hypertension significantly improved hemodynamic stability during cardiac surgery. [ABSTRACT FROM AUTHOR]

Objective The sonographic technique of automated cardiac output measurement (ACM) is a promising new method to measure cardiac output and could be of use in a high-risk obstetric unit in the treatment of pre-eclamptic patients. The aim was to determine the accuracy of the ACM method. Design Comparative study of the sonographic technique of ACM versus cardiac output measured by thermodilution (TD). Methods The study included 39 intensive care patients, 21 men, 13 non-pregnant women and five severely pre-eclamptic pregnant patients, with a wide range of cardiac outputs, in whom TD catheters had been inserted for clinical reasons. Two separate experienced observers, blinded to the results obtained with the other method, performed four successive measurements in each patient with either the ACM or TD technique. The averaged cardiac output value per patient and method was used for comparison. Results Cardiac output was successfully measured with ACM and TD in 85 and 100% of patients, respectively. Mean cardiac output measured by ACM (6.77 ± 1.90 L/min) was significantly lower than that measured by TD (9.12 ± 3.06 L/min). Although cardiac output values obtained with ACM were significantly correlated with those measured by TD, the ACM values were consistently lower than TD values in the higher cardiac output range; the relationship was represented by ACM = 0.35 TD + 3.55 L/min (r = 0.57, P < 0.001). The (ACM - TD) difference increased significantly with cardiac output, through a difference in stroke volume, not in heart rate. Conclusion The ACM is not an accurate tool to measure cardiac output in patients with a high cardiac output, including treated pre-eclamptic women. [ABSTRACT FROM AUTHOR]