Non-invasive continuous arterial pressure and pulse pressure variation measured with Nexfin(®) in patients following major upper abdominal surgery: a comparative study.

We compared the accuracy and precision of the non-invasive Nexfin(®) device for determining systolic, diastolic, mean arterial pressure and pulse pressure variation, with arterial blood pressure values measured from a radial artery catheter in 19 patients following upper abdominal surgery. Measurements were taken at baseline and following fluid loading. Pooled data results of the arterial blood pressures showed no difference between the two measurement modalities. Bland-Altman analysis of pulse pressure variation showed significant differences between values obtained from the radial artery catheter and Nexfin finger cuff technology (mean (SD) 1.49 (2.09)%, p < 0.001, coefficient of variation 24%, limits of agreement -2.71% to 5.69%). The effect of volume expansion on pulse pressure variation was identical between methods (concordance correlation coefficient 0.848). We consider the Nexfin monitor system to be acceptable for use in patients after major upper abdominal surgery without major cardiovascular compromise or haemodynamic support.

Predicting cardiac output responses to passive leg raising by a PEEP-induced increase in central venous pressure, in cardiac surgery patients.

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.

A comparison of stroke volume variation measured by the LiDCOplus and FloTrac-Vigileo system.

The aim of this study was to compare the accuracy of stroke volume variation (SVV) as measured by the LiDCOplus system (SVVli) and by the FloTrac-Vigileo system (SVVed). We measured SVVli and SVVed in 15 postoperative cardiac surgical patients following five study interventions; a 50% increase in tidal volume, an increase of PEEP by 10 cm H2O, passive leg raising, a head-up tilt procedure and fluid loading. Between each intervention, baseline measurements were performed. 136 data pairs were obtained. SVVli ranged from 1.4% to 26.8% (mean (SD) 8.7 (4.6)%); SVVed from 2.0% to 26.0% (10.2 (4.7)%). The bias was found to be significantly different from zero at 1.5 (2.5)%, p < 0.001, (95% confidence interval 1.1-1.9). The upper and lower limits of agreement were found to be 6.4 and -3.5% respectively. The coefficient of variation for the differences between SVVli and SVVed was 26%. This results in a relative large range for the percentage limits of agreement of 52%. Analysis in repeated measures showed coefficients of variation of 21% for SVVli and 22% for SVVed. The LiDCOplus and FloTrac-Vigileo system are not interchangeable. Furthermore, the determination of SVVli and SVVed are too ambiguous, as can be concluded from the high values of the coefficient of variation for repeated measures. These findings underline Pinsky's warning of caution in the clinical use of SVV by pulse contour techniques.

Performance of three minimally invasive cardiac output monitoring systems.

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.

An evaluation of cardiac output by five arterial pulse contour techniques during cardiac surgery.

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.

Monitoring cardiac output using the femoral and radial arterial pressure waveform.

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.

Less invasive determination of cardiac output from the arterial pressure by aortic diameter-calibrated pulse contour.

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.

Pulmonary artery thermodilution cardiac output vs. transpulmonary thermodilution cardiac output in two patients with intrathoracic pathology.

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.