Microfluidic devices for continuous blood plasma separation and analysis during pediatric cardiopulmonary bypass procedures

As an extension of previous work, a microfluidic device, which can separate blood plasma in a continuous, real-time fashion from a whole blood, is successfully integrated with a mock cardiopulmonary bypass circuit. The functionality of the device is demonstrated with the use of freshly harvested bovine blood. The plasma selectivities were 100% and 99.4% and the plasma separation volume percents were 18.7% and 24.5% for 26% and 37% inlet hematocrit levels, respectively. As an advanced stage of this research, a microfluidic device, which can measure the concentration of clinically relevant blood plasma protein in a continuous fashion, is being developed on the basis of fluid handling circuits coupled to fluorescent cytometric bead assays. The functionality of the device is demonstrated with the use of a biotinylated FITC solution and a streptavidin-coated, 8-mum-diameter bead. The binding event between biotinylated FITC and the streptavidin bead is continuously detected within a detection window at the outlet of the device. For a known concentration (1 microg/ml) of biotinylated FITC solution, the measured fluorescent intensity is fairly constant and shows a stable gaussian distribution of the bead fluorescence intensity. It is expected that the proposed device can be used for continuous measurement of clinically relevant proteins during cardiac surgery with the cardiopulmonary bypass procedure.     

体外循环管理中的感染监测

体外循环（cardiopulmonary bypass,CPB）是心脏外科手术中的一个重要环节。体外循环管理工作均在手术室中进行,而手术室是感染的高危科室之一,从事体外循环工作的医务人员除了做好体外循环灌注管理外,还应做好体外循环期感染监控的工作[1]。我科长期以来规范无菌物品监管制度,     

Blood gas strategies and management during pediatric cardiopulmonary bypass

Blood gas management during hypothermic cardiopulmonary bypass may be corrected by pH stat or alpha stat strategy. The pH stat philosophy is to maintain the blood pH constant at any temperature. Carbon dioxide must be introduced to the oxygenator in order to maintain the pH and pCO2 during hypothermic cardiopulmonary bypass. Conversely, during alpha stat blood gas management pH is maintained according to 37 degrees C despite the patient temperature. Alpha stat management preserves intracellular pH and autoregulation of cerebral vasculature by following the natural shift of the oxyhemoglobin dissociation curve. In-line blood gas analysis is a practical tool in assessing adequate blood gas management, because this technology provides immediate detection for modification of air/oxygen/carbon dioxide parameters. Results from several studies favor the pH stat strategy during neonatal cardiopulmonary bypass. This strategy increases tissue oxygenation and cerebral blood flow while cooling. Data also suggest that pH stat management results in better outcomes with shorter ventilation times and intensive care unit stays after pediatric cardiac surgery.     

Patterns of blood response during cardiopulmonary bypass.

Monitoring of cardiopulmonary bypass (CPB) in terms of alterations to the concentrations of selected blood constituents leads to contrasting patterns of response. This has been verified by determining the influence of CPB on the activation of fibrinolysis, complement, leucocytes and the contact phase of coagulation. Fibrinolytic activity was determined by fibrin degradation products (X-FDP's), complement activation by C3a and C5a, leucocyte activation by granulocyte elastase and contact activation by factor XII-like activity (FXIIA). Five patients undergoing elective coronary artery surgery using a bubble oxygenator and pulsatile perfusion were studied. X-FDP's rose gradually during CPB and remained elevated. Similar patterns were observed for elastase and FXIIA. In contrast, C3a rose sharply with peak values at 1 1/2-2h of bypass while C5a did not show significant changes during bypass. The data obtained have enabled the establishment of response patterns for parameters in CPB which will provide information relevant to the clinical application of biomaterials.     

The influence of neurophysiologic monitoring on the management of pediatric cardiopulmonary bypass

We describe a process by which we sought to determine how the addition of intraoperative neurophysiologic monitoring (IONM) impacted the management of cardiopulmonary bypass (CPB) during pediatric cardiac surgery. While maintaining a consistent team of surgeons, anesthesiologists, nurses, and perfusionists, a multi-modal, IONM program was established consisting of Near Infrared Spectroscopy, Transcranial Doppler, and eight channel electroencephalography. A retrospective review of cases from 1 year before the institution of the IONM program was compared with data obtained from cases performed after neurophysiologic monitoring was established as a standard of care for pediatric patients on CPB. This comparative analysis of CPB management revealed a significant increase in the use of donor blood added to the CPB circuit prime as well as in the maintenance of a higher hematocrit during the bypass period after the implementation of IONM. These changes in the management of pediatric CPB correlated with recommendations of previous studies that examined postoperative neurophysiologic outcomes, suggesting that these changes were not only consistent with best practices, but that the presence of IONM data facilitated a transition to evidence-based practice.     

Effect of hypothermic cardiopulmonary bypass on blood viscoelasticity in pediatric cardiac patients

The objective of this study was to determine the changes in blood viscoelasticity during and after pediatric cardiopulmonary bypass (CPB) procedures. Twelve pediatric cardiac patients, subjected to hypothermic (22-28 degrees C) CPB procedures were enrolled in this study. Viscosity and elasticity were measured at strains of 0.2, 1.0, and 5.0 using a Vilastic-3 Viscoelasticity Analyzer. Arterial blood samples (1 ml each) were taken before CPB, on normothermic CPB, hypothermic CPB, and 1 and 24 hours after CPB. Compared with the pre-CPB levels (0.0464 +/- 0.007 Poise), viscosity at a strain of 1.0 was significantly lower during normothermic CPB (0.0305 +/- 0.006 Poise, p < 0.01), hypothermic CPB (0.03 +/- 0.0007 Poise, p < 0.01), and 1 hour after CPB (0.0334 +/- 0.006 Poise, p < 0.01). Viscosity at a strain of 1.0 24 hours after CPB (0.0525 +/- 0.01 Poise, p = NS) was slightly higher than pre-CPB levels. Elasticity at a strain of 1.0 was significantly altered during normothermic CPB (0.0016 +/- 0.0007 Poise, p < 0.01), hypothermic CPB (0.0015 +/- 0.0007 Poise, p < 0.01), and 1 hour after CPB (0.0017 +/- 0.0005 Poise, p < 0.01) compared to the pre-CPB levels (0.0048 +/- 0.0001 Poise). Elasticity at a strain of 1.0 24 hours after CPB (0.0068 +/- 0.003 Poise, p = 0.06) was significantly higher compared to the pre-CPB level (0.0048 +/- 0.0001 Poise). Viscoelasticity at strains of 0.2 and 5.0 had patterns similar to those seen with a strain of 1.0. Viscosity and elasticity at strains of 0.2, 1.0, and 5.0 were significantly altered during normothermic and hypothermic CPB and 1 hour after CPB. Viscoelasticity of blood was slightly higher 24 hours after CPB at all strains. Further investigation of the effects of hypothermic CPB on blood viscoelasticity and the outcomes of pediatric cardiac patients are warranted.     

Accuracy of portable blood glucose monitoring. Effect of glucose level and prandial state

Glucose was determined on capillary and venous blood samples from 274 adult diabetics by three different methodologies: the Glucoscan 2000 and Accu-Check II portable glucose meters (capillary) and the Kodak Ektachem 700 analyzer (venous). Both glucose meters correlated significantly with the Ektachem results. A significant positive bias was found for the Glucoscan compared with Ektachem, not found with the Accu-Check II. The Accu-Check performed better than the Glucoscan at venous plasma glucose levels less than 1 g/L. The mean error of Glucoscan determinations was significantly greater and biased positive when the measurement was performed within 4 hours of eating, whereas no such effect was seen with Accu-Check error. Multiple regression analysis revealed that the Glucoscan measurement was independently influenced by both venous plasma glucose and prandial state, whereas the Accu-Check II measurement was not dependent on either variable. The within-run precision for both glucose meters were comparable.     

Microdialysis based device for continuous extravascular monitoring of blood glucose

Glycemic control of intensive care patients can be beneficial for this patient group but the continuous determination of their glucose concentration is challenging. Current continuous glucose monitoring systems based on the measurement of interstitial fluid glucose concentration struggle with sensitivity losses, resulting from biofouling or inflammation reactions. Their use as decision support systems for the therapeutic treatment is moreover hampered by physiological time delays as well as gradients in glucose concentration between plasma and interstitial fluid. To overcome these drawbacks, we developed and clinically evaluated a system based on microdialysis of whole blood. Venous blood is heparinised at the tip of a double lumen catheter and pumped through a membrane based micro-fluidic device where protein-free microdialysate samples are extracted. Glucose recovery as an indicator of long term stability was studied in vitro with heparinised bovine blood and remained highly stable for 72 h. Clinical performance was tested in a clinical trial in eight healthy volunteers undergoing an oral glucose tolerance test. Glucose concentrations of the new system and the reference method correlated at a level of 0.96 and their mean relative difference was 1.9 ± 11.2%. Clinical evaluation using Clark’s Error Grid analysis revealed that the obtained glucose concentrations were accurate and clinically acceptable in 99.6% of all cases. In conclusion, results of the technical and clinical evaluation suggest that the presented device delivers microdialysate samples suitable for accurate and long term stable continuous glucose monitoring in blood.     

Multicenter evaluation of the reliability of five blood glucose monitoring systems

As part of a tender AP-HP Paris Hospitals, an assessment of the reliability record of five blood glucose monitoring systems (BGMSs) (Optium Xceed (Abbott), Contour TS (Bayer), One Touch Ultra (Lifescan), Stat Strip Xpress (Nova) and Accu Check (Roche) and an evaluation of their sensitivity to changes in hematocrit were conducted in 4 hospitals of Paris. In terms of inaccuracy, all BGMSs have submitted CV repetability under the limits of acceptability. One BGMS (Lifescan) presented a CV of reproducibility outside limit of acceptability (13.1%). The inaccuracy was measured by a comparison method on multiparameter analyser relative to the hexokinase method for two sites, the glucose oxidase for the two others. The coefficients of correlation varied from 0.8405 to 0.9303. However, according to both defined acceptability criteria (absolute value difference between the result acquired on analyzer and those determined with the BGMS), the percentage of results outside acceptability was above 20% for two BGMSs (Abbott and Lifescan). Similarly, a net effect of changes in hematocrit was observed on the results of those two BGMSs. BGMS Nova was the most reliable, because of the correction device for hematocrit and blank substractions owed to interferences. In terms of expertise, BGMSs Nova and Roche have been selected with the best analytical performance and practicability satisfactory. In the future, accreditation with standard NF/EN 22870 requested for point of care testing, will require a close collaboration between biologists and clinicians to establish a system of strict quality control to detect deviations of these BGMSs.     

Usefulness of continuous air tonometry for evaluation of splanchnic perfusion during cardiopulmonary bypass

Although gastric mucosal tonometry has been reported as a useful method to assess splanchnic perfusion during cardiovascular surgery, the conventional discontinuous method of tonometry (saline tonometry) was cumbersome and prone to systematic errors. A new automated system of air tonometry (Tonocap; Datex Ohmeda, Helsinki, Finland) allows for frequent (every 10 minutes) measurement of gastric regional CO2 (PrCO2) and may be more suitable as a monitoring system in cardiac patients. We evaluated the usefulness of continuous air tonometry as a marker of splanchnic perfusion during cardiopulmonary bypass (CPB). In 19 patients (53-79 years, mean 63 years) who underwent cardiovascular surgery under standard CPB with mild hypothermia (32 degrees C) from January 2001 to May 2002, the PrCO2 and calculated intramucosal pH (pHi) of gastric tonometry was monitored using Tonocap, and their relation to postoperative visceral organ function was evaluated. The pHi significantly increased after initiation of CPB from 7.32 +/- 0.07 to 7.43 +/- 0.10 (p < 0.05) and then consistently decreased in all patients to 7.39 +/- 0.09 at the end of CPB. The value of PrCO2 significantly (p < 0.01) correlated with the value of pHi. The lowest value of pHi during CPB was significantly related to blood urea nitrogen (r = -0.75, p < 0.05), serum creatinine (r = -0.78, p < 0.05), creatinine clearance (r = 0.68, p < 0.05) on postoperative day 1, and blood urea nitrogen (r = -0.84, p < 0.01) on day 3. In contrast, arterial blood lactate level, venous oxygen saturation, and routinely measured hemodynamics (e.g., pump flow, arterial pressure) during CPB were unrelated to the postoperative visceral organ function. These results suggest that continuous monitoring of gastric regional CO2 and pHi by air tonometry system is useful for the evaluation of splanchnic perfusion during CPB and may contribute to improve CPB technique by allowing the early detection of visceral malperfusion.     

A novel method for indirectly monitoring arterial pO2 during cardiopulmonary bypass

Arterial blood oxygen tension (P_aO₂) is a vital variable that has to be monitored during cardiopulmonary bypass (CPB). The aim of this study was to develop an alternative method for continuously P_aO₂ monitoring during CPB, based on measurements of exhaust-gas from an oxygenator. A total of 15 adult patients undergoing CPB (n = 81 samples) were included in a study in order to develop an appropriate algorithm for P_aO₂ estimation based on exhaust gas monitoring of the oxygen tension (P_exO₂). The acquired data was used as a basis for developing a statistical prediction algorithm designed for continuously estimating the P_aO₂-level based on exhaust gas data in combination with data from the surrounding medical equipment. A new instrument was developed in order to implement this P_aO₂ prediction algorithm and was tested on five patients (n = 39 samples). When the first sample was used for calibrating the instrument, the mean (SD) error was 8.7% (7.3%) with a 95% CI of 6.1–11.3%. Our results indicate that a pO₂-exhaust monitoring device with adequate precision is obtainable, but further studies are required.     

Evaluation of artificial pancreas technology for continuous blood glucose monitoring in dogs

Artificial pancreas technology, involving “closed-loop??controls with real-time blood glucose monitoring, has been increasing in reliability as its potential for clinical use and application grows. One such device, based on this technology, is the STG-22 (Nikkiso Co., Ltd., Tokyo, Japan) artificial pancreas apparatus. In order to assess the reliability and accuracy of the device for measuring blood glucose, it is important to compare its readings to those obtained using a ‘gold standard??method, such as the hexokinase method. Therefore, in the present study, canine blood [glucose] measurements using the STG-22 were compared to those obtained using a previously established commercial reagent, Quickauto-Neo GLU-HK. Furthermore, two different sample types (whole blood versus plasma constituent) were compared to determine which sample type results in more accurate and optimal readings with the STG-22. Given that the STG-22 was not primarily designed for canine blood samples, results for canine blood samples were not accurate. Measurements performed by the STG-22 with whole blood were significantly lower than reference [glucose] counterparts. Alternatively, an opposite trend was observed with plasma measurements that were significantly higher. A conversion format using the following formula, Hexokinase [glucose]?=?STG-22 [glucose]?×?1.407?+?1.532, was observed with canine samples in our study.     

Fluid distribution kinetics during cardiopulmonary bypass

OBJECTIVE:

The purpose of this study was to examine the isovolumetric distribution kinetics of crystalloid fluid during cardiopulmonary bypass.

METHODS:

Ten patients undergoing coronary artery bypass grafting participated in this prospective observational study. The blood hemoglobin and the serum albumin and sodium concentrations were measured repeatedly during the distribution of priming solution (Ringer''s acetate 1470 ml and mannitol 15% 200 ml) and initial cardioplegia. The rate of crystalloid fluid distribution was calculated based on 3-min Hb changes. The preoperative blood volume was extrapolated from the marked hemodilution occurring during the onset of cardiopulmonary bypass. Clinicaltrials.gov: {"type":"clinical-trial","attrs":{"text":"NCT01115166","term_id":"NCT01115166"}}NCT01115166.

RESULTS:

The distribution half-time of Ringer''s acetate averaged 8 minutes, corresponding to a transcapillary escape rate of 0.38 ml/kg/min. The intravascular albumin mass increased by 5.4% according to mass balance calculations. The preoperative blood volume, as extrapolated from the drop in hemoglobin concentration by 32% (mean) at the beginning of cardiopulmonary bypass, was 0.6-1.2 L less than that estimated by anthropometric methods (p<0.02). The mass balance of sodium indicated a translocation from the intracellular to the extracellular fluid space in 8 of the 10 patients, with a median volume of 236 ml.

CONCLUSIONS:

The distribution half-time of Ringer''s solution during isovolumetric cardiopulmonary bypass was 8 minutes, which is the same as for crystalloid fluid infusions in healthy subjects. The intravascular albumin mass increased. Most patients were hypovolemic prior to the start of anesthesia. Intracellular edema did not occur.     

Altered lymphocyte subsets during cardiopulmonary bypass

Peripheral blood lymphocyte subsets were quantified by immunofluorescence in nine patients undergoing open heart surgery for coronary artery, valvular, and congenital heart disease. Compared with normal preoperative values, all patients developed an absolute lymphopenia, a reduction in T4 (helper) lymphocytes, and a statistically significant reversal of the T4/T8 ratio two hours after cardiopulmonary bypass (CPB). These changes could be caused by mechanical or immunogenic injury. A return to normal of the T4 subset and T4/T8 proportion occurred 24 hours after surgery. Whereas transient inactivation of immunoreactive lymphocyte clones may prevent unwanted immunization to blood products received during surgery, such temporary immune dysfunction could make certain patients liable to infectious sequelae. Viral-induced postperfusion syndromes, transmission of human T lymphotropic virus (HTLV) III by blood products, and reports of acquired immune deficiency syndrome after CPB foster a concern regarding postoperative infections under these circumstances.     

深低温体外循环与降温期不同血气管理方法的脑电图监测

目的:在对深低温体外循环与降温期实行不同的血气管理状态下进行脑电图(EEG)监测,探讨利于脑保护的体外循环方法。方法:24头上海种白猪,年龄3～5周,体重5～7 kg。随机分为四组,即A组:深低温停循环,降温期alpha稳态血气管理;B组:深低温停循环,降温期pH稳态血气管理;C组:深低温低流量,降温期alpha稳态血气管理;D组:深低温低流量、降温期pH稳态血气管理。术中及降温期连续监测EEG并观察其变化。结果:EEG监测示B组、D组降温期EEG平坦波出现早。C组、D组复温期EEG恢复早于A组、B组。结论:深低温体外循环低流量灌注和降温期pH稳态血气管理,两种方法配合应用具有较好的脑保护协同作用。     

Use of ecarin clotting time in whole blood for monitoring recombinant hirudine treatment during cardiopulmonary bypass in patients with heparin-induced thrombocytopenia

Lepirudin (Refludan is a recombinant hirudin, approved for anticoagulation treatment of heparin-induced thrombocytopenia patients with thrombosis. We report here our method for laboratory monitoring with ecarin clotting time (ECT) of hirudin therapy as anticoagulation for cardiac surgery. Ecarin is extracted from the Echis carinatus snake venom and directly converts prothrombin to its intermediate, meizothrombin. This one binds in a stoechiometric way to hirudin to be proportioned in whole blood. The activation of coagulation starts up only when the totality of the hirudin is bound to the meizothrombin. To minimize the effect of dilution related to the CEC on the prothrombin and fibrinogen levels, thus lengthening the ECT, the specimen to be tested is diluted with normal whole blood. In 1997, when we have performed our first surgery with cardiopulmonary bypass, only one team (P?tzsch et al., 1997) had described the use of the ECT in whole blood. We describe in this work our assay to dose hirudin with ECT after dilution in whole blood. This assay was used during 8 CEC among 7 patients affected with HIT (n = 6) or potentially sensitized with heparin (n = 1). Experimental conditions and interpretation of the assay are reported here. This test is fast enough to provide useful information for adjusting the dose during cardiopulmonary bypass.     

Vasoactive pressure hormones during and after cardiopulmonary bypass

The differences in the pattern of the vasoactive hormone release in response to the stress of surgery and cardiopulmonary bypass (CPB) (pulsatile n = 15 and non pulsatile n = 23) were studied in the adult patients with mitral valve disease (MVD), aortic valve disease (AVD), and the coronary artery disease (CAD). A differential stimulation of the osmoreceptors, baroceptors, renin-angiotensin and the sympathetico-adrenal systems in these patients, resulted in the variations in the pattern of hormone release. Patients with MVD showed a greater stimulation of osmoreceptors, baroceptors and release of Arginine vasopressin (AVP). Renin-angiotensin system was more easily triggered in patients with AVD or CAD; and sympathetico-adrenal system in patients with CAD. The renin-angiotensin-aldosterone axis was better preserved in patients with CAD (r = 0.49, p less than 0.001) than in the patients with MVD (r = 0.38, p less than 0.02). Plasma renin release showed a significant correlation with noradrenaline release in the patients with MVD (r = 0.47, p less than 0.01); but this relationship was lost in the patients with the CAD, due to an excessive noradrenaline release. Pulsatile bypass reduced but did not abolish this response. Under unfavourable conditions, the stress response may persist in the early post-operative period.     

浅低温体外循环围术期血清炎症介质的变化

目的 探讨浅低温体外循环围术期炎症介质的释放规律。方法 按入选标准筛选先天性心脏病患者24例，均采用浅低温体外循环心脏直视术，用酶联免疫吸附法测定患者术前（T1）、CPB30min（T2）、CPB结束后2h（T3）、12h（T4）、24h（T5）各时间点血清IL-6、IL-8、IL-10的浓度。结果 所有患者血清IL-6、IL-8、IL-10浓度在CPB开始后均升高（P〈0，01），于术后2h（T3）逐渐达高峰，术后12h（T4）逐渐下降，术后24h（T5）虽仍高于术前（T1）水平，但较高峰时（T3）已明显下降。结论 浅低温CPB术后患者血清IL-6、IL-8、IL-10浓度逐渐升高．术后2h达高峰．并于24h内恢复接近正常水平。