Do alterations in pulmonary vascular tone result in changes in central blood volumes? An experimental study

Background The effects of selective pulmonary vascular tone alterations on cardiac preload have not been previously examined. Therefore, we evaluated whether changing pulmonary vascular tone either by hypoxia or the inhalation of aerosolized prostacyclin (PGI2) altered intrathoracic or pulmonary blood volume (ITBV, PBV, respectively), both as surrogate for left ventricular preload. Additionally, the mean systemic filling pressure analogue (Pmsa) and pressure for venous return (Pvr) were calculated as surrogate of right ventricular preload. Methods In a randomized controlled animal study in 6 spontaneously breathing dogs, pulmonary vascular tone was increased by controlled moderate hypoxia (FiO2 about 0.10) and decreased by aerosolized PGI2. Also, inhalation of PGI2 was instituted to induce pulmonary vasodilation during normoxia and hypoxia. PBV, ITBV and circulating blood volume (Vdcirc) were measured using transpulmonary thermo-dye dilution. Pmsa and Pvr were calculated post hoc. Either the Wilcoxon-signed rank test or Friedman ANOVA test was performed. Results During hypoxia, mean pulmonary artery pressure (PAP) increased from median [IQR] 12 [8–15] to 19 [17–25] mmHg (p < 0.05). ITBV, PBV and their ratio with Vdcirc remained unaltered, which was also true for Pmsa, Pvr and cardiac output. PGI2 co-inhalation during hypoxia normalized mean PAP to 13 (12–16) mmHg (p < 0.05), but left cardiac preload surrogates unaltered. PGI2 inhalation during normoxia further decreased mean PAP to 10 (9–13) mmHg (p < 0.05) without changing any of the other investigated hemodynamic variables. Conclusions In spontaneously breathing dogs, changes in pulmonary vascular tone altered PAP but had no effect on cardiac output, central blood volumes or their relation to circulating blood volume, nor on Pmsa and Pvr. These observations suggest that cardiac preload is preserved despite substantial alterations in right ventricular afterload.

Effect of Intra- and Post-Operative Fluid and Blood Volume on Postoperative Pulmonary Edema in Patients with Intraoperative Massive Bleeding

In patients with intraoperative massive bleeding, the effects of fluid and blood volume on postoperative pulmonary edema are uncertain. Patients with intraoperative massive bleeding who had undergone a non-cardiac surgery in five hospitals were enrolled in this study. We evaluated the association of postoperative pulmonary edema risk and intra- and post-operatively administered fluid and blood volumes in patients with intraoperative massive bleeding. In total, 2090 patients were included in the postoperative pulmonary edema analysis, and 300 patients developed pulmonary edema within 72 h of the surgery. The postoperative pulmonary edema with hypoxemia analysis included 1660 patients, and the condition occurred in 161 patients. An increase in the amount of red blood cells transfused per hour after surgery increased the risk of pulmonary edema (hazard ratio: 1.03; 95% confidence interval: 1.01–1.05) p = 0.013) and the risk of pulmonary edema with hypoxemia (hazard ratio: 1.04; 95% confidence interval: 1.01–1.07; p = 0.024). An increase in the red blood cells transfused per hour after surgery increased the risk of developing pulmonary edema. This increase can be considered as a risk factor for pulmonary edema.

Abstract P193: Effect Of Nitroglycerin And Sympathetic Withdrawal On Splanchnic Capacitance And Cardiac Blood Volumes

The splanchnic vasculature is the largest blood volume reservoir in the human body. Reduced capacitance of this vascular bed, in part due to sympathetic venoconstriction, is proposed to play a role in hypertension and heart failure. Thus, interventions that increase splanchnic capacitance or decrease sympathetic activity may be beneficial in these conditions. In a proof-of-concept study in healthy and hypertensive subjects, we evaluated whether venodilation with nitroglycerin (NTG; Study 1) or sympathetic withdrawal with trimethaphan (Study 2) increase splanchnic capacitance and reduce cardiac and stroke volumes. In Study 1 (n=10, 36±4 yrs, BMI 26.1±1.7, 4 men), abdominal and chest scintigrams, to measure regional blood volumes, were obtained before and after 0.6 mg sublingual NTG. Splanchnic capacitance (volume-pressure relationships, VPR) and compliance (VPR slope) were estimated by recording abdominal scintigrams during progressive escalation of intrathoracic pressure using continuous positive airway pressure (CPAP) at 0, 4, 8, 12, and 16 cm H 2 O, each for ≤2 min. We found that NTG increased splanchnic blood volume at rest (4%, IQR 1.81-9.95; P<0.01) resulting in a rightward parallel shift in splanchnic VPR (P slope =0.46 and P intercept =0.01), indicating an increase in splanchnic capacitance. This was associated with a decrease in cardiac blood volume (-9%, IQR 2.2-10.3; P<0.01). In Study 2, we measured blood pressure (BP) and stroke volume, used as a surrogate of venous return, during the same CPAP protocol before and during autonomic blockade with trimethaphan in 12 hypertensive subjects (49±2 yrs, BMI 29.9±1.7, 5 men). Sympathetic withdrawal decreased systolic BP (-27±14 mmHg) and produced a leftward parallel shift in VPR (i.e. reduced stroke volume; P slope =0.12 and P intercept <0.01), indicating a reduction in venous return likely due to an increase in splanchnic capacitance. In conclusion, venodilation with NTG increased splanchnic capacitance and decreased cardiac volume. Sympathetic withdrawal had similar hemodynamic effects. These findings highlight the importance of splanchnic capacitance in cardiovascular regulation.

Lithium heparin interference in the Abbott enzymatic creatinine assay: the significance of under-filled tubes

Background Spuriously high results using the Abbott Architect enzymatic creatinine assay were noted to be particularly associated with very small sample volumes. This led us to query the effect of under-filling lithium heparin tubes on the measured enzymatic creatinine result. Methods Blood was provided by 5 laboratory personnel and then decanted into 5 x1.2 mL Sarstedt S-Monovette tubes, giving final blood volumes of 200, 400, 600, 800 and 1200 μL. Plasma was analysed using Abbott Architect Jaffe, enzymatic creatinine, Beckman Coulter (AU500) enzymatic creatinine and Roche (Cobas c702) enzymatic creatinine assays. Saline was also added to Sarstedt 1.2 mL and Teklab 2 mL tubes and analysed using the Abbott Jaffe and enzymatic creatinine methods. Results Increasing degrees of under-fill were associated with greater over-estimation of creatinine using the Abbott enzymatic assay, but no difference was noted using Jaffe methodology on the same platform or enzymatic assays provided by Roche or Beckman. On average, creatinine was 40.6% (+27.7 μmol/L) higher when only 200 μL of blood was present in the tube. Small volumes of saline added to lithium heparin tubes measured significant creatinine concentrations using the Abbott enzymatic method. Conclusions Lithium heparin directly interferes in the Abbott Architect enzymatic creatinine assay. Under-filling lithium heparin tubes can lead to clinically significant over-estimation of creatinine results by this assay. Users of this assay should be aware of the potential for spurious results in small sample volumes collected into lithium heparin tubes and implement robust procedures for identifying and reporting results on these samples.

Comparison of microorganism detection and time-to-positivity in pediatric and standard media from three major commercial continuously monitored blood culture systems

New blood culture instrumentation and media formulations have led to improved time-to-positivity (TTP) for positive blood cultures. Data regarding the necessity of pediatric blood culture bottles with contemporary blood culture systems are sparse. We compared performance of three commercial blood culture systems, evaluating impact of blood volumes in standard and pediatric blood culture media across systems. Simulated blood cultures with packed red blood cells and three Gram-positive, four Gram-negative, and one anaerobic organism (final concentrations ranging from 0.5-19 CFU/mL blood) on the VIRTUO, VersaTREK, and Bactec FX were evaluated with FAN Plus, REDOX, and BACTEC Plus media, respectively. For each media/instrument/organism combination 1, 3, 5, and 10 mL blood volumes were evaluated in triplicate. Detection rate was not affected by blood volume. Aerobic organisms that demonstrated variable detection were Kingella kingae, Haemophilus influenzae and Neisseria meningitidis. Bacteroides fragilis was detected in 83%, 100%, and 100% of VIRTUO, VersaTREK, and Bactec anaerobic bottles. Average TTP of standard media for aerobic organisms detected on VIRTUO was decreased compared to VersaTREK (-2.3 h) and Bactec (-4.9 h). Compared to standard media, detection rate and TTP was unchanged on VIRTUO, while TTP was reduced with pediatric media for 2/8 organisms tested on Bactec and 7/8 organisms on VersaTREK, illustrating the potential benefit of pediatric media on VersaTREK or BACTEC when low blood volumes (<5 mL) are collected. These results demonstrate that TTP is decreased on the VIRTUO compared to VersaTREK and Bactec for many microorganisms associated with BSI but may have species-specific limitations.

Education of medical personnel optimizes filling volume of blood culture bottles without negatively affecting microbiology testing

Background Anemia is a risk factor for adverse outcomes, which can be aggravated by unnecessary phlebotomies. In blood culture testing, up to 30 ml of blood can be withdrawn per sample, even though most manufacturers recommend blood volumes of 10 ml or less. After assessing the filling volume of blood culture bottles at our institution, we investigated whether an educational intervention could optimize filling volume of blood culture bottles without negatively affecting microbiology testing. Methods We weighed 10,147 blood cultures before and 11,806 blood cultures after a six-month educational intervention, during which employees were trained regarding correct filling volume via lectures, handouts, emails, and posters placed at strategic places. Results Before the educational intervention, only 31% of aerobic and 34% of anaerobic blood cultures were filled correctly with 5–10 ml of blood. The educational intervention increased the percentage of correctly filled bottles to 43% (P < 0.001) for both aerobic and anaerobic samples without negatively affecting results of microbiologic testing. In addition, sample volume was reduced from 11.0 ± 6.5 to 9.4 ± 5.1 ml (P < 0.001) in aerobic bottles and from 10.1 ± 5.6 to 8.8 ± 4.8 ml (P < 0.001) in anaerobic bottles. Conclusion Education of medical personnel is a simple and effective way to reduce iatrogenic blood loss and possibly moderate the extent of phlebotomy-induced anemia.

Technical validation of a new microfluidic device for enrichment of CTCs from large volumes of blood by using buffy coats to mimic diagnostic leukapheresis products

Diagnostic leukapheresis (DLA) enables to sample larger blood volumes and increases the detection of circulating tumor cells (CTC) significantly. Nevertheless, the high excess of white blood cells (WBC) of DLA products remains a major challenge for further downstream CTC enrichment and detection. To address this problem, we tested the performance of two label-free CTC technologies for processing DLA products. For the testing purposes, we established ficollized buffy coats (BC) with a WBC composition similar to patient-derived DLA products. The mimicking-DLA samples (with up to 400 × 106 WBCs) were spiked with three different tumor cell lines and processed with two versions of a spiral microfluidic chip for label-free CTC enrichment: the commercially available ClearCell FR1 biochip and a customized DLA biochip based on a similar enrichment principle, but designed for higher throughput of cells. While the samples processed with FR1 chip displayed with increasing cell load significantly higher WBC backgrounds and decreasing cell recovery, the recovery rates of the customized DLA chip were stable, even if challenged with up to 400 × 106 WBCs (corresponding to around 120 mL peripheral blood or 10% of a DLA product). These results indicate that the further up-scalable DLA biochip has potential to process complete DLA products from 2.5 L of peripheral blood in an affordable way to enable high-volume CTC-based liquid biopsies.

Flow Cytometric Assessment of AKT Signaling in Platelet Activation: An Alternative Diagnostic Tool for Small Volumes of Blood

Introduction The diagnosis of platelet function disorder in children is challenging. Light transmission aggregometry is the gold standard for platelet function disorders. However, large blood volumes are required. Currently, there are no existing tools for the diagnosis of platelet function disorders that use small blood volumes. AKT signaling plays a central role in platelet activation during hemostasis and might be visualized by flow cytometry. Methods Platelet-rich plasma obtained by centrifugation of citrated blood from healthy volunteers was activated with arachidonic acid, thrombin receptor activating peptide-6 (TRAP-6), collagen, adenosine diphosphate ADP, collagen-related peptide (CRP), and epinephrine. After platelet activation, the phosphorylation of AKT was assessed by flow cytometer using a Navios cytometer. Results Healthy volunteers showed a reproducible phosphorylation of AKT upon activation. In comparison to nonactivated platelets, we documented an increase in pAKT expression with all agonists. Especially TRAP-6 and CRP caused considerable increase in percentage of pAKT expression throughout all the tested healthy volunteers. Conclusion An activation of the AKT-signal pathway by different agonists can clearly be detected on the flow cytometer, indicating that the visualization of signaling in platelets by flow cytometry might be an efficient alternative for light transmission aggregometry to test platelet function in children.

Effects of exercise on thoracic blood volumes, lung fluid accumulation, and pulmonary diffusing capacity in heart failure with preserved ejection fraction

Patients with heart failure with preserved ejection fraction (HFpEF) experience symptoms of exertional dyspnea that may be related to lung fluid accumulation during exercise. A computed tomography (CT)-based method was used to measure exercise-induced changes in extravascular lung fluid content and thoracic blood volumes and to determine the effect of lung fluid on lung diffusing capacity for carbon monoxide (DLCO) in stable subjects with HFpEF and healthy controls. Nine subjects with HFpEF (age = 68 ± 8 yr; body mass index = 32.1 ± 2.6 kg/m2) and eight healthy controls (62 ± 9 yr, 23.8 ± 2.4 kg/m2) performed triplicate rebreathe DLCO/DLNO (lung diffusing capacity for nitric oxide) tests in a supine position at rest and duplicate measurements during two 5-min submaximal exercise stages (15W and 35W) and recovery. Subjects subsequently performed a 5-min exercise bout (35W) inside a CT scanner, and extravascular lung fluid content and thoracic blood volumes were quantified at rest and immediately following exercise from thoracic and contrast perfusion scans, respectively. Subjects with HFpEF had a higher lung fluid content at rest compared with controls (means ± SD, HFpEF: 14.4 ± 1.7%, control: 12.8 ± 1.7%, P = 0.043) and a higher lung fluid content following exercise (15.2 ± 2.0% vs. 12.6 ± 1.5%, P = 0.009). Higher lung fluid content was associated with a lower DLCO and alveolar-capillary membrane conductance (Dm) in subjects with HFpEF (DLCO: R = −0.57, P = 0.022, Dm: R = −0.61, P = 0.012) but not in controls. Pulmonary blood volume was not altered by exercise and was similar between groups. Submaximal exercise elicited a greater accumulation of lung fluid in subjects with HFpEF compared with in controls, and lung fluid content was negatively correlated with lung diffusing capacity and alveolar-capillary membrane conductance in subjects with HFpEF.