Using Heart-Lung Interactions for Functional Hemodynamic Monitoring: Important Factors beyond Preload
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Preload
Pulse pressure
Cardiac index
Cardiac function was studied with Scintiview in 107 cases, 24 normal and 83 affected cases, and the following results were obtained. 1. Better data were obtained with converging collimeter than with parallel collimeter in cardiac study. (2) Red blood cells were sufficiently labeled with 99mTc using stannous chloride as reductant, and it was proven to be applicable to measurement of circulation blood volume. (3) Pulmonary circulation time and the systemic circulation time calculated from time activity curve, greater than 9.0 seconds and greater than 25 seconds, respectively, were considered abnormal prolongation. (4) Cardiac output index (cardiac output/circulation blood volume), less than 1.10 was considered decreased cardiac output. (5) Stroke volume index ((stroke volume/circulation blood volume)x 100, less than 1.70 was considered decreased stroke volume. (6) Ejection fraction, less than 60% was considered decreased left ventricular wall motion. (7) Cardiac function index (cardiac output index X ejection fraction), less than 80 was considered decreased cardiac performance.
Cardiac index
Circulation (fluid dynamics)
Blood circulation
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Central venous pressure (CVP) and pulmonary capillary wedge pressure (PCWP) are insensitive preload markers and sometimes misleading. The introduction of the pulse contour method for monitoring of continuous cardiac output enabled the real-time quantification of stroke volume variation (SVV). Studies evaluating the accuracy of this parameter as a measure of preload responsiveness are still limited and conflicting results have been published in cardiac surgical patients. The aim of this study was to reevaluate the predictive value of SVV regarding cardiac responsiveness to fluid therapy and to compare it with the standard preload variables in a clinical setting in the ICU after cardiac surgery.The assessment of cardiac responsiveness to fluid therapy (HAES-steril 6% 10 mL * Body Mass Index) was performed in 92 ventilated coronary artery surgical patients after arrival in the ICU. After the fluid load, detailed hemodynamic measurements were performed. A 'responder' was defined as a patient with a gain in stroke volume index (SVI) of 5% or more from baseline value to the volume challenge.Post hoc analysis showed that there were 47 responders to the fluid challenge and 45 non-responders. Hemodynamic data before the fluid therapy show that stroke volume variation in the responders group was significantly higher than in the non-responders groups (9.7 +/- 4.3% versus 7.6 +/- 3.0%, P = 0.01). The receiver operating characteristic curves for the baseline values of CVP, PCWP and SVV were constructed for illustrative purposes. The area under the curve for baseline values of SVV was significantly higher than random guess (area = 0.65, p < 0.05), indicative for the value of SVV as a marker of cardiac responsiveness to fluid therapy. The static preload parameters CVP and PCWP had no predictive value.SVV as measured with the LiDCO system is a better functional marker of cardiac responsiveness to fluid therapy than the static parameters CVP and PCWP.
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Pulmonary wedge pressure
Cardiac index
Pulse pressure
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This study investigated whether a small volume of 7.2% hypertonic saline solution (HSS) could affect M-mode echocardiographic indices in dogs. HSS induced significant increase in heart rate, stroke volume and cardiac index, when the fluid infusion was completed (P<0.05). In the HSS group, the left ventricular end-diastolic volume index, as an index of preload, significantly increased (P<0.05), whereas left ventricular end-systolic volume index were not altered. HSS induced slight increases in ejection fraction at end of infusion despite significantly differences were not observed. In conclusion, HSS did not induce a demonstrable effect on M-mode echocardiographic indices of systolic function-enhance cardiac contractility, but it caused preload augmentation that may contribute to an abrupt and transient increase in cardiac output just after HSS infusion.
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Contractility
Cardiac index
Hypertonic saline
End-diastolic volume
End-systolic volume
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To the Editor: We read with interest the recent article by Wiesenack et al. (1) suggesting, in contrast to other recent studies (2–4), that stroke volume variation (SVV) derived from pulse contour analysis could not serve as an indicator of fluid responsiveness in cardiac surgical patients. This conclusion was based on the lack of correlation between SVV at baseline and the percentage changes in stroke volume index (ΔSVI) after volume loading. The validity of this conclusion relies thus on the assumption that changes in preload were the only determinants of ΔSVI in all patients. However, achieving fluid challenge and measurements in an otherwise hemodynamic steady-state in every patient may be uncertain after induction of anesthesia and introduction of isoflurane. The large changes in SVI and in systemic vascular resistance observed following fluid loading were relatively unexpected in patients scheduled for elective surgery and may suggest that such steady-state was not obtained in all patients. In addition, it was not clearly stated in the article how SVI was measured. This is important because the validity of the pulse contour technique for the accurate quantification of changes in SVI in individual patients remains poorly established, especially when arterial compliance may have changed. In fact, we believe that much data in this study actually suggested that SVV is useful to the assessment of preload, and probably, preload responsiveness. The high correlation between SVV at baseline and its changes after volume replacement (ΔSVV) is apparently consistent with this hypothesis but was not reported in other studies on fluid responsiveness. We thus retrospectively calculated these correlations from a study where the ‘delta down‘ component of the systolic pressure variation was shown to be a reliable indicator of fluid responsiveness in patients with septic shock (5). Interestingly, the correlation was highly significant for ‘delta down‘ (r = 0.85; P < 0.001), but not for either PCWP (r = 0.01; P = 0.98) or the left ventricular end-diastolic area (r = 0.13; P = 0.66). It is also notable in the Wiesenack et al. (1) study that the change in mean SVV associated with volume replacement was much larger than that observed with either CVP or PCWP. Thus, at the ‘group level,‘ results suggest a close relationship between the increase in intravascular volume (due to volume loading), the large ΔSVV, and the large ΔSVI. Moreover, because profound functional hypovolemia would be very unlikely at this stage of surgery, it can be assumed that a second fluid challenge would have been associated with small, if any, ΔSVI. Thus, as compared with baseline measurements, the smaller values of SVV observed at the end of the study would have been associated with smaller ΔSVI, reinforcing the hypothesis of a preload responsiveness assessment by SVV. Nicolas Bouteau, MD Benoît Tavernier, MD, PhD
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Summary The prone position can reduce cardiac output by up to 25% due to reduced preload. We hypothesised that preload optimisation targeted to stroke volume variation before turning prone might alleviate this. A supine threshold stroke volume variation of 14% in a preliminary study identified patients whose cardiac outputs would decline when turned prone. In 45 patients, cardiac output declined only in the group whose supine stroke volume variation was high (mean (SD) 5.1 (2.0) to 3.9 (1.9) l.min −1 ; p < 0.001), but not in patients in whom it was low, or in those in whom stroke volume variation was high, but who received volume preload (p = 0.525 and 0.941, respectively). We conclude that targeted preload optimisation using a supine stroke volume variation value < 14% is effective in preventing falls in cardiac output induced by the prone position.
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Supine position
Prone position
Stroke
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Method This was a prospective observational study of 15 elective cardiac patients. In all patients, there was simultaneous haemodynamic recording using the three test devices and thermodilution with a pulmonary artery catheter. Measurements were taken before and after the administration of a fluid which was defined as 250mls of a colloid or crystalloid given rapidly over 5-10mins. The cardiac index (CI) was compared using Bland Altman analysis. A fluid responder was defined as a patient in whom the CI as measure by thermodilution increased by >10%. The ability of the devices to predict fluid responsiveness was assessed using the area under receiver operating curves(ROC) 4 for these parameters: Stroke Volume Variation Flotrac (SVV-FT), Stroke Volume Variation LiDCO (SVV-LI), Flow corrected time Oesophageal Doppler (FTc-ODM). Results
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Hemodynamic indices were determined in 13 anesthetized dogs. In 7 of them,iv injection of endotoxin(E coli 12*10(10)/mL/kg) followed by iv infusion of saline(0.05/ mL/kg/min) increased the vascular resistance, and decreased the mean arterial pressure, the stroke volume, cardiac output and cardiac index. In the other 6 dogs, iv jinfusion of higenamine (dl-demethylcoclaurine) 1 microg/kg/min after iv endotoxin caused no significant changes in blood pressure, decreased the vascular resistance and icreased the stroke volume, cardiac output and cardiac index as compared with those of the control dogs. These results suggest that higenamine improves the circulation of the endotoxin shock dogs.
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Mean arterial pressure
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The evolution of different hemodynamic parameters with ponderal growth has been studied in conscious Wistar rats. The thermodilution method has been used to determine cardiac output and related variables. The results suggest that, between animal weight and the different hemodynamic parameters, there is a direct proportional relationship to blood volume, mean arterial pressure, cardiac output, stroke volume and total peripheral resistance, and an indirect proportional relationship to heart rate, cardiac index and stroke volume index. Body weight, therefore, plays a major role in hemodynamic determination, this having to be kept in mind when designing the experiment.
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Mean arterial pressure
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Central venous pressure, intrathoracic blood volume, and left ventricular end-diastolic area are reliable measures of cardiac preload under stable clinical conditions. The purpose of this study was to compare different preload parameters over 24 h under conditions of multiple, frequently changing treatments in early septic shock.In 28 mechanically ventilated patients within 6 h of the onset of septic shock, left ventricular end-diastolic area was measured using transoesophageal echocardiography. Intrathoracic blood volume, stroke volume variation, and central venous pressure were analysed as preload parameters. The relation between parameter changes and changes in therapy was examined with respect to cardiac index and stroke volume index.Regarding preload variables, linear regression analyses revealed a significant correlation between left ventricular end-diastolic area and stroke volume index (r=0.59, P<0.001) and cardiac index (r=0.41, P<0.001), respectively. Changes in left ventricular end-diastolic index and intrathoracic blood volume index reflected changes in the stroke volume index, whereas central venous pressure did not. Myocardial responsiveness also failed to predict changes in the stroke volume index.Only the left ventricular end-diastolic area index may help predict preload in ventilated patients with early septic shock.
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Venous return curve
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