Influence of vascular enhancement, age and gender on pulmonary perfused blood volume quantified by dual-energy-CTPA.

OBJECTIVES: To determine the influence of technical and demographic parameters on quantification of pulmonary perfused blood volume (PBV) in dual energy computed tomography pulmonary angiography (DE-CTPA). MATERIALS AND METHODS: Pulmonary PBV was quantified in 142 patients who underwent DE-CTPA for suspected pulmonary embolism but in whom no thoracic pathologies were detected. Multivariate linear regression analysis was performed to calculate the influence of age, gender, enhancement of pulmonary trunk and enhancement difference between pulmonary trunk and left atrium (as a measure of timing) on PBV values. The resulting regression coefficients were used to calculate age-specific ranges of normal for PBV values adjusted for vascular enhancement and timing. RESULTS: Enhancement of the pulmonary trunk (ß=-0.29, p=0.001) and enhancement difference between pulmonary trunk and left atrium (ß=-0.24, p=0.003) were found to significantly influence PBV values. Age (ß=-0.33, p<0.001) but not gender (ß=0.14, p=0.05) had a significant negative influence on pulmonary PBV values. There was a 20% relative decrease of pulmonary PBV from patients aged <30 to patients over 80 years of age. CONCLUSIONS: DE-CTPA derived PBV values need to be corrected for age, vascular enhancement and timing but not for gender. The age-specific ranges of normal derived from this study can be used as a reference in future studies of PBV in pulmonary pathologies.

Sensitivity of blood volume monitoring for fluid status assessment in hemodialysis patients.

BACKGROUND/AIMS: This study investigates the use of blood volume monitoring (BVM) markers for the assessment of fluid status. METHODS: Predialysis fluid overload (FO) and BVM data were collected in 55 chronic hemodialysis patients in 317 treatments. Predialysis FO was measured using bioimpedance spectroscopy. The slope of the intravascular volume decrease over time normalized by ultrafiltration rate (Slope4h) was used as the primary BVM marker and compared against FO. RESULTS: Average relative blood volume curves were well separated in different FO groups between 0 and 5 liters. Receiver-operating characteristics analysis revealed that the sensitivity of BVM was moderate in median FO ranges between 1 and 3 liters (AUC 0.60-0.65), slightly higher for volume depletion of FO <1 liter (AUC 0.7) and highest for excess fluid of FO >3 liters (AUC 0.85). CONCLUSION: Devices that monitor blood volume are well suited to detect high FO, but are not as sensitive at moderate or low levels of fluid status.

Absolute blood volume in hemodialysis patients: why is it relevant, and how to measure it?.

Intradialytic hypotension (IDH) is the most common complication during hemodialysis and is associated with significant morbidity. It occurs as a consequence of a reduction in blood volume during ultrafiltration. Today, devices for monitoring relative blood volume (i.e. the intradialytic blood volume as a fraction of the blood volume at the start of the dialysis treatment) are routinely available and have been used to analyze the relationship between changes in relative blood volume and the occurrence of IDH in an attempt to derive critical thresholds that, when observed, would help avoid hypotensive episodes during the treatment. However, the results have been unsatisfactory in many patients. Here we illustrate the importance of absolute blood volume in hemodialysis patients, summarize the acute physiologic mechanisms involved in the preservation of adequate circulation during ultrafiltration, and outline why hemodialysis patients are often particularly vulnerable to reductions in blood volume. We then discuss the shortcomings of relative blood volume measurements, make a case for the superiority of absolute blood volume measurements, and introduce the reader to a mathematical concept that allows relative blood volume devices to be used for the estimation of absolute blood volume. Finally, we discuss the implications of absolute blood volume beyond IDH and propose a paradigm shift in the approach to dry weight attainment.

Association of intradialytic hypotension and convective volume in hemodiafiltration: results from a retrospective cohort study.

BACKGROUND: Hemodiafiltration (HDF), as a convective blood purification technique, has been associated with favorable outcomes improved phosphate control, removal of middle-molecules such as Beta2-microglobulin and the occurrence of intradialytic hypotension (IDH) as compared to diffusive techniques. The aim of this retrospective cohort study in dialysis patients receiving HDF in one urban dialysis facility in Mexico City was to investigate the occurrence of IDH during HDF treatments with varying convective volume prescriptions. METHODS: Subjects were stratified into equal groups of percentiles of convective volume prescription: Group 1 of 0 to 7.53 liters, group 2 of 7.54 to 14.8 liters, group 3 of 14.9 to 16.96 liters, group 4 of 16.97 to 18.9 liters, group 5 of 21 to 19.9 liters and group 6 of 21.1 to 30 liters. Logistic Regression with and without adjustment for confounding factors was used to evaluate factors associated with the occurrence of IDH. RESULTS: 2276 treatments of 154 patients were analyzed. IDH occurred during 239 HDF treatments (10.5% of all treatments). Group 1 showed 31 treatments (8.2%) with IDH whereas group 6 showed IDH in only 15 sessions (4% of all treatments). Odds Ratio of IDH for Group 6 was 0.47 (95% CI 0.25 to 0.88) as compared to Group 1 after adjustment. CONCLUSIONS: In summary the data of this retrospective cohort study shows an inverse correlation between the occurrence of IDH and convective volume prescription. Further research in prospective settings is needed to confirm these findings.

Blood volume monitoring a crucial step in reducing mortality.

Weir articulates it best in his editorial commentary in Hypertension: "Ultimately, the main goal of treatment of blood pressure is to prevent cardiac events. Perhaps the most important strategy in the dialysis patient is to achieve an appropriate dry weight, minimize volume overload, and use blood pressure-lowering medications only in the setting of 'hypertension' when dry weight is truly probed and demonstrated. It is possible that if more patients achieved dry weight, then less antihypertensive medication would be required, as is observed in patients on longer-session nocturnal hemodialysis. I suspect that long-term volume/pressure overload of the left ventricle, because of inadequate achievement of dry weight, may be one of the most important cardiovascular concerns in the hemodialysis patient." I do believe euvolemia is possible. In the Grass Valley study (Rodriguez et al), we evaluated post-dialytic vascular compartment refill. After deciding that refill could be evaluated after 10 minutes of ultrafiltration in minimum (200 mL/ hour), we used the following steps. Step 1. Note hematocrit Step 2. Place UF in minimum Step 3. Wait 10 minutes Step 4. Note hematocrit If hematocrit declines by 0.5 or more in 10 minutes, patient has refill, and is "not dry:' If hematocrit declines by 0.4 or less in 10 minutes, patient is "vascularly dry" If additional fluid is available, and willing to shift from the extracellular compartment to the intravascular compartment, it will decrease the hematocrit by hemodilution, hence the "not dry" patient has a decline in hematocrit in the absence of ultrafiltration (see Table 1).

Quantitative helical dynamic contrast enhanced computed tomography assessment of the spatial variation in whole tumour blood volume with radiotherapy in lung cancer.

We aim to assess the spatial distribution of blood volume (BV) in whole lung tumours in patients undergoing radiotherapy using helical dynamic contrast enhanced computed tomography (DCE-CT), and to determine whether conventional single level, or whole tumour measurements is more representative of the vascular effects of radiotherapy. Following ethical approval and informed consent, 15 patients with histologically proven non-small cell lung cancer underwent paired helical DCE-CT studies at baseline to assess repeatability, and after two fractions of radiotherapy (9 Gy total dose). Tumour BV was calculated for individual contiguous 10mm axial slices, and for the entire tumour volume on a pixel-per-pixel basis. Baseline tumour BV was heterogeneous varying by 15.33%+/-17.11 between adjacent 10mm axial slices. Within subject coefficient of variation was 36.72% with conventional single tumour level evaluation, and 13.62% with whole tumour measurements. Following radiotherapy, one patient had an increase in BV greater than baseline variation (derived from the 95% limits of change) using single level evaluation; in contrast, seven patients had an increase in BV when the whole tumour was assessed. As a group, following radiotherapy, mean BV increased by 17.27% (paired t-test, p=0.20) with single level evaluation and 19.26% (p=0.049) with whole tumour assessment. Tumour BV measured using DCE-CT is spatially heterogeneous. Given the slice-by-slice variation in blood volume, our results demonstrate that whole tumour DCE-CT measurements are more repeatable, and may be a better predictor of vascular changes following therapy, compared to conventional single tumour level evaluations.

Relative cerebral blood volume measurements of low-grade gliomas predict patient outcome in a multi-institution setting.

BACKGROUND/PURPOSE: The prognostic value of defining subcategories of gliomas is still controversial. This study aims to determine the utility of relative cerebral blood volume (rCBV) in predicting clinical response in patients with low-grade glioma at multiple institutions. MATERIALS AND METHODS: Sixty-nine patients were studied with dynamic susceptibility contrast-enhanced perfusion MRI at two institutions. The pathologic diagnoses of the low-grade gliomas were 34 astrocytomas, 20 oligodendroglioma, 9 oligoastrocytomas, 1 ganglioglioma and 5 with indeterminate histology. Wilcoxon tests were used to compare patients in different response categories with respect to baseline rCBV. Kaplan-Meier curve and log-rank tests were used to predict the association of rCBV with time to progression. RESULTS: At both institutions, patients with an adverse event (progressive disease or death) had a significantly higher baseline rCBV than those without (complete response or stable disease) (p value=0.0138). The odds ratio for detecting an adverse event when using rCBV was 1.87 (95% confidence interval: 1.14-3.08). rCBV was significantly negatively associated with time to progression (p=0.005). The median time to progression among subjects with rCBV>1.75 was 365 days, while there was 95% confidence that the median time to progression was at least 889 days among subjects with rCBV<1.75. CONCLUSION: Our study suggests not only that rCBV measurements correlate well with time to progression or death, but also that the findings can be replicated across institutions, which supports the application of rCBV as an adjunct to pathology in predicting glioma biology.

Native arteriovenous fistula blood flow and resistance during hemodialysis.

BACKGROUND: Measurement of vascular access flow (Qa) has been proposed as the ideal method for surveillance of native fistulae. However, debate exists about the influence of blood pressure (mean arterial pressure [MAP]) on Qa during dialysis. METHODS: During three consecutive dialysis treatments, 10 patients had paired measurements of Qa and MAP performed at 30, 60, 120, 180, 210, and 240 minutes. Access resistance (AR; in peripheral resistance units, PRUs) was calculated from MAP and Qa values. RESULTS: Overall pooled coefficients of variation (CVs) for MAP, Qa, and AR were 8.4%, 12.3%, and 12.9%, respectively. A significant reduction in Qa and MAP occurred throughout the dialysis treatment (Qa, 104 mL/min; P = 0.008; MAP, 10.4 mm Hg; P = 0.007). Mean percentages of change in Qa for the first third compared with the middle and last thirds of the session were -4.6% +/- 11.15% (SD) and -9.6% +/- 10.5%, respectively. Thus, Qa varied between 11.4% and -30.6% from baseline during the last hour of dialysis treatments. A stronger correlation between MAP and Qa was seen in radiocephalic (r2 = 0.55; P < 0.0001) compared with brachiocephalic fistulae (r2 = 0.06; P = 0.023). Mean AR was unchanged during the dialysis session (0.23 PRU; P = 0.358). AR for radiocephalic fistulae was significantly greater compared with brachiocephalic fistulae (6.03 +/- 3.90 versus 3.00 +/- 1.11 PRU; P < 0.0001). CONCLUSION: Qa could decrease up to 30% from baseline, potentially impairing the ability of Qa to predict impending vascular access failure. AR remained stable during the treatment and may be a more useful measure of vascular access performance as part of an access surveillance program.

Quantitative estimation of errors in the indicator dilution measurement of extravascular lung water.

OBJECTIVE: To assess the accuracy of the diffusible indicators heavy water and thermal indicator in the measurement of extravascular lung water (EVLW). DESIGN: Cardiac output (CO), mean transit time and EVLW for the two diffusible indicators were measured. CO for indocyanine green, gravimetric EVLW and the calculated mean transit time for a diffusible indicator were used as independent reference variables. CO, mean transit time and EVLW for the two diffusible indicators were compared to the reference variables and the percentage error for each measured variable was calculated for each bolus injection. SETTING: 6 sheep with healthy lungs and 6 with pulmonary oedema in a research laboratory. INTERVENTIONS: CO was altered with positive end-expiratory pressure and dobutamine. MEASUREMENTS: All indicators were given together in a bolus through a central venous line. Indicators were detected simultaneously in the aorta, and CO, mean transit time and EVLW were measured. EVLW was measured gravimetrically (EVLWgrav) postmortem. RESULTS: In the combination of a low CO and a large distribution volume, heavy water and thermal indicator produced a large number of slow wash-out curves. These curves were abolished from further analysis. The mean errors in CO and mean transit time for heavy water were close to zero and independent of the distribution volume; the product EVLW was close to EVLWgrav. The mean error in thermodilution CO measured in the aorta was close to zero but dependent on the distribution volume. The mean error in mean transit time for the thermal indicator was 36% and dependent on the distribution volume. Their product EVLW overestimated EVLWgrav by 70%. CONCLUSIONS: The results obtained for heavy water confirmed the theoretical basis of the indicator dilution method. The mean transit time for the thermal indicator was not proportionate to its distribution volume. The magnitude of this error prevents the calculation of an anatomically defined EVLW using a catheter-mounted thermistor in the aorta.