Ultrasound Dilution Research Articles

Flow-Regulated Extracorporeal Arteriovenous Tubing Loop for Cardiac Output Measurements by Ultrasound Velocity Dilution: Validation in Post-Cardiac Surgery Intensive Care Unit Patients

Assessment of cardiac output (CO) is crucial in the management of the critically ill, especially in post cardiac surgery intensive care unit (ICU) patients. In this study, we validated CO measured by the novel ultrasound dilution (COUD) with those measured by pulmonary artery (PA) thermodilution (COTD) in 26 adult post cardiac surgery patients. For COUD, blood was circulated through an extracorporeal arteriovenous (AV) loop from the radial artery catheter to the introducer of PA catheter for 5-8 minutes. Three to four injections of 25 ml body temperature isotonic saline were performed into the venous limb of the AV loop. For COTD, five injections of 10 ml ice cold saline were performed. A total of 77 COUD and COTD measurement sets were compared. Cardiac output measured by thermodilution ranged from 3.28 to 9.4 L/min, whereas COUD ranged from 2.85 to 10.1 L/min. The correlation between the methods was found to be r = 0.91, COUD = 0.93(COTD) + 0.42 L/min. Bias and precision (mean difference ± 2SDs) was -0.004 ± 1.34 L/min between the two methods. The percentage error (2SD/mean) was 22.2%, which is below the clinically acceptable limit (<30%). Cardiac output measured by ultrasound dilution and thermodilution methods agreed well in post cardiac surgery ICU patients and hence can be interchangeably used.

220 Assessing Cardiac Output and Derived Blood Volumes in a Neonatal Lamb Model with a Left-To-Right Shunt

Aims: To assess cardiac output and derived blood volumes in lambs with a left-to-right shunt using the ultrasound dilution technique (UDCO).Methods: In 8 lambs (mean weight 6.4 kg) arterial and central venous catheters were inserted and connected to the UDCO-monitor (COstatus™). A Gore-Tex® shunt was placed between the left pulmonary artery and the descending aorta. This shunt was intermittently opened and closed while cardiac output was changed by creating hemorrhagic hypotension followed by fluid administration (closed shunt only). Measurements of cardiac output (QUDCO), central blood volume index (CBVI), active circulating volume index (ACVI) and total enddiastolic volume index (TEDVI) were performed using the UDCO.Results: 342 measurements were performed. Mean cardiac output was 160 mL/kg/min. Mean Qp/Qs ratio during open shunt was 1.7. Mean total hemorrhage was 17.8 mL/kg and mean total fluid administration 28.5 mL/kg. Figure 1 shows mean values of QUDCO, CBVI, ACVI and TEDVI during the entire experiment. During shunt opening, only changes in TEDVI were significant (p=0.038). During hemorrhage, CBVI and TEDVI decreased significantly with closed and open shunt (CBVI: p< 0.001 respectively p< 0.001 and TEDVI: p< 0.001 respectively p=0.027), while QUDCO only decreased significantly with closed shunt (p= 0.03). There were no significant ACVI changes, probably due to redistribution. During fluid administration, QUDCO and all volumes increased significantly.[cardiac output and derived volumes]Conclusion: The expected changes in cardiac output and derived blood volumes can be detected with UDCO technology, even in the presense of left-to-right shunts.

226 Accuracy and Precision of a New Method for Hemodynamic Assessment in Children Undergoing Cardiac Surgery Based on Ultrasound Dilution Methodology

Background and aims: This novel monitor (COstatus, Transonic Systems Inc., Ithaca, NY) uses existent intravascular lines for injections of isotonic saline to measure CO and BV (blood volume) by ultrasound dilution methodology. It can also identify the presence of cardiac shunts. We investigated the accuracy and precision of the method during pediatric congenital heart surgery (CHS).Methods: 9 pts scheduled for CHS [age 8 (0-39) months; weight 7.6 (3.2 - 14.1) kg] were included. Measurements (2-4 injections of saline 0.5-1 mL/kg/session) started in the OR, before/immediately after CPB and then repeated in PICU at 2, 3, 4, 5, 6, 12 and 24 h after weaning. Accuracy was tested in the OR using transit time technology (TT).Results: 56 measurement-sessions were performed. In 5 pts, during stable hemodynamic conditions, TT was simultaneously obtained (Fig 1). We identified left-to-right shunts in 12 sessions. The coefficient of variation (CV= SD/mean) was calculated for CO, central BV index (CBVI), total end-diastolic volume index (TEDVI), and active circulation volume index (ACVI) in each session.[Accuracy] Table Table Full size table Conclusions: COStatus offers reproducible measurements in pediatric patients. It does not require insertion of dedicated catheters. In the absence of shunts, two injections are typically adequate for data collection; in the presence of shunts, more injections may be required.

224 Novel Ultrasound Dilution Technique Detects Left-To-Right Shunts with High Accuracy in Children

Objectives: Recently introduced paediatric cardiac output monitor (COstatus, Transonic Systems Inc. Ithaca, NY) also measures blood volumes and detects cardiac shunts. The current study assessed its ability to identify left-to-right shunts and measured associated blood volumes during cardiac catheterisation in children. Patients and Methods: Cardiac catheterisation was performed in 20 children and adolescents (3.5 kg- 102 kg). Shunts and pulmonary (Qp) versus systemic blood flow (Qs) ratio were determined by routine oximetry. Subsequently three measurements with COstatus were performed while the monitor software announces the recognition of left-to-right shunt. Dilutions curves were recorded and validated. Results: Left-to-right shunts due to various types of cardiac defects were detected in 6 patients by oximetry. Applying COstatus diagnostic accuracy was very convincing, with a sensitivity of 100% (6/6) and a specificity of 92.8% (13/14). The threshold for determination a left-to-right shunt was an Qp/Qs ratio of 1.3. In one case of a hypertrophic obstructive cardiomyopathy the distortion of the dilution curve led to a false positive result. A significant difference was detected for means of central blood volume index between patients with left-to-right shunts and controls with no cardiac shunts (95% CI; 24.9 versus 18.2 ml/kg; P< 0.05). Conclusion: Novel ultrasound dilution technique identifies left-to-right shunts in children with a high sensitivity and detects even small shunts with an Qp/Qs ratio of 1.3. Raised central blood volume index corresponds well with clinical features in patients with left-to-right shunts and may become helpful a diagnostic parameter in the future.

Application of ultrasound dilution technology for cardiac output measurement: Cerebral and systemic hemodynamic consequences in a juvenile animal model

Analysis of cerebral and systemic hemodynamic consequences of ultrasound dilution cardiac output measurements. : Prospective, experimental piglet study. Animal laboratory. Nine piglets. Ultrasound dilution cardiac output measurements were performed in ventilated, anesthetized piglets. Interventions that are required for ultrasound dilution cardiac output measurement were evaluated for its effect on cerebral and systemic circulation and oxygenation. DeltacHbD and DeltactHb, representing changes in cerebral blood flow and cerebral blood volume, respectively, were measured with near infrared spectrophotometry. Pulmonary artery (Q) and left carotid artery (Q) blood flow were assessed with transit time flow probes. Starting and/or stopping blood flowing through the arteriovenous loop did not cause relevant hemodynamic changes. Fast injection of isotonic saline caused a biphasic change in DeltacHbD and DeltactHb. After injection of 0.5 mL/kg, the mean (sd) increase in DeltacHbD and DeltactHb was 0.175 (0.213) micromol/L and 0.122 (0.148) micromol/L, respectively, with a subsequent mean decrease of -0.191 (0.299) micromol/L and -0.312 (0.266) micromol/L. Injection of 1.0 mL/kg caused a mean increase in DeltacHbD and DeltactHb of 0.237 (0.203) micromol/L and 0.179 (0.162) followed by a mean decrease of -0.334 (0.407) micromol/L and -0.523 (0.335) micromol/L, respectively. Q and Q changed shortly with a mean increase of 5.9 (3.0) mL/kg/min and 0.23 (0.10) mL/kg/min after injection of 0.5 mL/kg and with 12.0 (4.2) mL/kg/min and 0.44 (0.18) mL/kg/min after injection of 1.0 mL/kg, respectively. The observed changes were more profound after an injection volume of 1.0 mL/kg compared with 0.5 mL/kg for DeltacHbD (p = .06), DeltactHb (p = .09), Q, and Q (p < .01). No relevant changes in mean arterial blood pressure or heart rate were detected in response to the indicator injection. Cardiac output measurement by ultrasound dilution does not cause clinically relevant changes in cerebral and systemic circulation and oxygenation in a piglet model.

Comparison of cardiac output and blood volumes in intrathoracic compartments measured by ultrasound dilution and transpulmonary thermodilution methods

To compare cardiac output (CO) and blood volumes measured by COstatus(®) (Transonic Systems Inc., NY, USA) versus PiCCO (Philips IntelliVue MP40 with PiCCO-technology module M3012A#10, Netherlands) in adult ICU patients. This was a prospective single-center study. Each of the 30 patients studied received a 5-Fr Pulsiocath femoral arterial and a standard central venous catheter. Twenty ml of iced 5% dextrose solution was injected for PiCCO measurements. For COstatus measurements, an extracorporeal arteriovenous loop, with two sensors placed on it, was connected between the Pulsiocath femoral arterial and central venous catheters. Blood was circulated through this loop at 12 ml/min for 5-8 min using a pump. Twenty ml of warm saline was injected into the venous side for measurements. For each method, three injections were averaged for comparison. A good agreement for measured CO (range 3.65-16.3 l/min) with a percentage error of 20% was observed, with r = 0.95, bias = -0.037 l/min. PiCCO's global end-diastolic volume (GEDV) was 2.5 times larger than the analogous COstatus's total end-diastolic volume (TEDV) [TEDV = 0.28 × GEDV + 176 ml]. PiCCO's intrathoracic blood volume (ITBV) was larger than the analogous COstatus's central blood volume (CBV) [CBV = 0.73 × (ITBV) +78 ml]. CO measured by COstatus was found to be equivalent and hence interchangeable with PiCCO in this study population. COstatus blood volumes were found to be within the expected physiological range whilst PiCCO blood volumes were significantly higher, which was also observed in other studies. Future studies using 3D echo/MRI are required to validate these blood volumes.

The Measurement of Hemodialysis Access Blood Flow by a Conductivity Step Method

Measurement of blood flow rate (Qa) is used to monitor dialysis access, AV fistulas, and grafts. Indicator dilution measurements of the recirculation (R) induced by reversal of hemodialysis blood lines are commonly used. This plus the dialysis circuit flow (Qb) allows calculation of Qa. R also changes the conductivity, which can be measured by a conductivity cell in the spent dialysate. The change in conductivity caused by line reversal should vary with Qa. A methodology for Qa measurement utilizing this conductivity step is proposed. This study compares conductivity step methodology against the reference method of ultrasound dilution (Qa-Trans). This was an open diagnostic test study in a single academic hospital setting involving 15 hemodialysis-dependent patients. Each was studied over four hemodialysis treatments. During each treatment, two pairs of Qa measurements (conductivity step and Trans) were made. Pre- and postdialysis sodium levels were also measured. Average Qa-conductivity step was 1040 ml/min. Average Qa-Trans was 1030 ml/min. The difference was NS. The data pairs showed mean difference of 1.3 +/- 17% (SD). The SD indicates a relatively large variation between data pairs. There was significant linear correlation between the Qa-conductivity step and Qa-Trans results (r = 0.91, P < 0.001). Serum sodium rose slightly but significantly over dialysis (P < 0.001). Qa measurement by conductivity step may be an acceptable alternative to ultrasound dilution methodology. Care must be taken to prevent salt loading when the conductivity step is used.

Arteriovenous Fistula, Blood Flow, Cardiac Output, and Left Ventricle Load in Hemodialysis Patients

The aim of this study was to investigate an association between vascular access blood flow (QVA), cardiac output(CO), and load of left ventricle (LLV) using a simple physical model calculation based on real data, specifically inpatients with high access blood flow arteriovenous fistula(AVF). Vascular access blood flow, CO, and peripheral vascular resistance (PR) were determined by ultrasound dilution technique (HD01; Transonic Systems, Inc., Ithaca, NY). Load of left ventricle was calculated using simplified formula: LLV x PR CO2. This total load was computationally divided into the part spent to run the flow QVA through the AVF (LLVAVF) and that part ensuring the flow (CO-QVA) through the vascular system. The model calculation was first performed in a selected group of 15 patients with high access blood flow (QVA >1,300 ml/min, group 1) and later extended for comparison by another group of 40 unselected patients with access blood flow in lower range (QVA range 200-1,400 ml/min, group 2).Mean LLV in group 1 was 2.10 +/- 0.68 W. LLV(AVF) was 21.8% of total LLV. Mean LLV in group 2 was 1.2 +/- 0.5 W.LLVAVF was 11.1% of total LLV. Our computational results suggest that AVF in typical range of QVA shall not increase heart load significantly.

Effectiveness of Stent-graft Placement for Salvage of Dysfunctional Arteriovenous Hemodialysis Fistulas

To determine the clinical effectiveness of stent-graft placement in dysfunctional autogenous hemodialysis fistulas. Between September 2006 and June 2008, 24 Fluency Plus stent-grafts were inserted in 17 patients with failing autogenous hemodialysis fistulas (two radiocephalic, 12 brachiocephalic, and three brachiobasilic). Six fistulas were thrombosed at presentation. Indications for stent-graft insertion included 10 residual stenoses, six pseudoaneurysms, and one fistuloplasty-induced rupture. Fistula function before and after intervention was assessed with ultrasound dilution technique. The technical success rate was 100%, as were the anatomic and clinical success rates. Via Kaplan-Meier method, the primary access patency rates were 94.1% at 3 months (95% CI, 0.461-0.995) and 88.2% at 6 and 12 months (95% CI, 0.468-0.980). The primary lesion patency rate was 94.1% (95% CI, 0.650-0.992) at 3, 6, and 12 months. The secondary access patency rate had a point estimate of 100% at 3 months, and was 93.8% (95% CI, 0.632-0.991) at 6 and 12 months. Univariate analysis suggested that male sex and left-sided accesses were associated with a longer primary access patency rate (P = .02). The binary restenosis rate at 6 months was 5.9%. Mean transonic flow rates were 667.5 mL/min before intervention and 2,076.0 mL/min after intervention (P = .03, Wilcoxon signed-rank test). No patients were lost to follow-up. Stent-graft placement in dysfunctional autogenous hemodialysis fistulas is technically feasible and effective in preserving function and preventing access abandonment, with patency rates that exceed historical patency rates with angioplasty and/or uncovered stents.

Validation of QB stress test as a useful tool in the detection of native arteriovenous fistula stenosis: results after 22 months of follow-up

Access flow (QA) surveillance is the best method recommended for early stenosis detection, but in native arteriovenous fistula (AVF), the literature is conflicting about the real need for monthly monitoring of QA, as suggested by the K-DOQI Guidelines. From 1 January 2006 to 31 October 2007 (mean 18.0 +/- 4.9 months), we prospectively followed up 224 patients with monthly AVF monitoring by means of clinical examination and QB stress test (QBST). Suspected malfunctioning AVFs were referred to ultrasound dilution technique (UDT) and imaging techniques (Doppler ultrasonography, angiography), with eventually further percutaneous angioplasty (PTA) or surgical revision. We observed a good correlation between QBST and QA measurement obtained by the UDT. Patients with positive QBST had a lower QA than negative QBST subjects (433 +/- 203 vs 1168 +/- 681 ml/min, P < 0.0001). Fifty-four out of 224 (24%) patients were selected for possibly malfunctioning AVF. We found no stenosis in 13 out of 54 (24%) patients, inflow stenosis in 29 out of 54 (54%) patients and outflow stenosis in 12 out of 54 (22%) patients. The QBST positive predictive value for inflow stenosis was 76.3%. The interventional radiologist performed 38 PTA procedures in 33 patients (11 PTA per 100 patient-years) and we surgically created 13 new AVF (3.7 per 100 patient-years). Only five thrombosis episodes occurred in five patients during the follow-up (1.5 thromboses per 100 patient-years). QBST is a simple, low-cost, not time-consuming test, able to select, together with clinical evaluation, malfunctioning AVF with stenosis located specifically in the inflow tract. Our follow-up data demonstrated that it is possible to achieve a low AVF thrombosis rate by adding QBST in an AVF monitoring program, thus reducing the surveillance burden.

Cardiac output measurement using an ultrasound dilution method: A validation study in ventilated piglets

To assess agreement between a new method of cardiac output monitoring, using ultrasound dilution technology and ultrasound transit time-based measurement of pulmonary blood flow in a piglet model. Prospective, experimental juvenile animal study. Animal laboratory of a university hospital. Nine random-bred piglets. After the animals received general anesthesia, we placed intravascular arterial and central venous catheters with the tip positioned in the abdominal aorta and the right atrium, respectively. The catheters were connected to the ultrasound dilution cardiac output monitor. An ultrasound transit time perivascular flow probe was positioned around the common pulmonary artery and served as the standard reference measurement. Cardiac output was manipulated during the experiment by creating hemorrhagic hypotension. Ultrasound dilution cardiac output was measured intermittently with injection volumes of 0.5 mL/kg and 1.0 mL/kg of isotonic saline at body temperature. Ultrasound dilution cardiac output (Q) measurement was compared with pulmonary blood flow (Q). Bias, defined as Q minus Q, was calculated for each measurement. Mean bias with standard deviation was calculated for measurements with volumes of injected saline, 0.5 mL/kg and 1.0 mL/kg, and compared using the Mann-Whitney U test. Mean bias (sd) between Q and Q was 0.040 (0.132) and 0.058 (0.136) L/min for measurement with 0.5 mL/kg and 1.0 mL/kg of isotonic saline, respectively (no statistically significant difference). Ultrasound dilution cardiac output measurement is reliable in piglets with the use of a small volume of a nontoxic indicator (isotonic saline).

Early Vascular Access Blood Flow as a Predictor of Long-term Vascular Access Patency in Incident Hemodialysis Patients

The long-term clinical benefits of vascular access blood flow (VABF) measurements in hemodialysis (HD) patients have been controversial. We evaluated whether early VABF may predict long-term vascular access (VA) patency in incident HD patients. We enrolled 57 patients, of whom 27 were starting HD with arteriovenous fistulas (AVFs) and 30 with arteriovenous grafts (AVGs). The patients' VABF was measured monthly with the ultrasound dilution technique over the course of the first six months after the VA operation. During the 20.4-month observational period, a total of 40 VA events in 23 patients were documented. The new VA events included 13 cases of stenosis and 10 thrombotic events. The lowest quartile of average early VABF was related to the new VA events. After adjusting for covariates such as gender, age, hypertension, diabetes, VA type, hemoglobin levels, body mass index, parathyroid hormone, and calcium-phosphorus product levels, the hazard ratio of VABF (defined as <853 mL/min in AVF or <830 mL/min in AVG) to incident VA was 3.077 (95% confidence interval, 1.127-8.395; P=0.028). There were no significant relationships between early VABF parameters and VA thrombosis. It is concluded that early VABF may predict long-term VA patency, particularly VA stenosis.

Cardiac output measurement is feasible in the presence of left-to-right shunt with ultrasound dilution method: a validation study in lambs

It remains a great challenge to measure systemic blood flow in critically ill newborns, especially during the transitional period with intracardiac and extracardiac shunts. Due to technical restraints, size limitations, the necessity for a relatively large amount of blood withdrawn and possible indicator toxicity, many methods of cardiac output monitoring are not feasible, hence cardiac output is generally estimated from indirect parameters of systemic blood flow. In a former study we assessed the agreement for cardiac output using the ultrasound dilution method (UDCO) and ultrasound transit time-based measurement of main pulmonary blood flow in a juvenile piglet model without shunts [1]. In the present study we analyzed the influence of a left-to-right shunt on the agreement between UDCO and ultrasonic transit time pulmonary blood flow in a juvenile lamb model.

Evolution of Hemodialysis Access Resistance: A Longitudinal 5-Year Model using Functional Principal Components Analysis

Arteriovenous fistulae (AVF) and grafts (AVG) are the preferred accesses in hemodialysis (HD). By monitoring access resistance (AR) one can potentially identify problems with an established HD access, but little is known about how these changes in AR occur, or the variations between the two access types as they mature longitudinally. We postulated that AR evolves differentially between AVF and AVG, a critical aspect to further understanding of the natural history of HD accesses. To describe these changes, we applied a novel statistical methodology of functional principal component (FPC) analysis. Using ultrasound dilution flow studies, we retrospectively studied 479 functional HD accesses in which a total of 4573 assessments were made. Accounting for patient factors of age, race, gender and diabetes mellitus (DM) status, we employed a multivariate, mixed-effects model. Using the mean effects of those covariates, we then applied FPC analyses to assess the longitudinal, timedependent changes between AVFs and AVGs over a 5-year period. Both types of upper-arm access were associated with a lower initial AR. Older age and DM were associated with a higher AR. Longitudinal AR varied significantly for both AVF and AVG, between the upper arm and lower arm. As a function of time, AVG was associated with an increasing AR. Conversely, AVF, especially upper-arm ones, demonstrated a longitudinal drop in AR. Evolutionally, AR can be predicted not only by the type of access, but also by the location along the arm of that access and by clinical patient factors. Longitudinal change in AR does differ between AVG and AVF. Our report provides the foundation of observed changes over time and provides insight as to how these variations are affected. We endorse ongoing surveillance to screen for clinical sequelae, even years from initial placement.

Calculating mixed venous saturation during veno-venous extracorporeal membrane oxygenation

Recirculation (R), the shunting of arterial blood back into to the venous lumen, commonly occurs during veno-venous extracorporeal membrane oxygenation (VV-ECMO) and renders the monitoring of the venous line oxygen saturation no longer reflective of patient mixed venous oxygen saturation (S(V)O(2)). Previously, we failed to prove the hypothesis that, once R is known, it is possible to calculate the S(V)O(2) of a patient on VV-ECMO. We hypothesize that we can calculate S(V)O(2) during VV-ECMO if we account for and add an additional correction factor to our model for dissolved oxygen content. Therefore, the purpose of this study is to derive a more accurate model that will allow clinicians to determine S(V)O(2) during VV-ECMO when ultrasound dilution is being used to quantify R. Using an extracorporeal circuit primed with fresh porcine blood, two stocks of blood were produced; (1) arterial blood (AB), and (2) venous blood (VB). To mimic recirculation, the AB and VB were mixed together in precise ratios using syringes and a stopcock manifold. Six paired stock AB/VB sets were prepared. Two sets were mixed at 20% R increments and 4 sets were mixed at 10% R increments. The partial pressure of oxygen (pO(2) ) and oxygen (O(2)) saturation of the stock blood and resultant mixed blood was determined. The original model was modified by modeling the residual errors with linear regression. When using the original model, as the partial pressure of arterial oxygen (P(a)O( 2)) of the stock AB increased, the calculated S(V)O(2) was higher than actual, especially at higher R levels. An iteration of the original model incorporating the P(a)O(2) level (low, medium, high) and R was derived to fit the data. The original model using R and circuit saturations for the calculation of S(V)O( 2) in VV-ECMO patients is an oversimplification that fails to consider the influence of the high pO(2) of arterial blood during therapy. In the future, further improvements in this model will allow clinicians accurately to calculate S(V)O(2) in conjunction with recirculation measurements.

Comparison of a New Cardiac Output Ultrasound Dilution Method With Thermodilution Technique in Adult Patients Under General Anesthesia

The purpose of this study was to investigate the reliability of cardiac output (CO) measured by a new ultrasound dilution method (COud) in comparison with CO by pulmonary artery thermodilution (COtd) in adult patients undergoing surgery. A prospective study. A university hospital, single institutional. Twenty-nine adult patients undergoing abdominal surgery. After approval of the institutional ethics review board, 29 adult patients were evaluated. After induction, radial and pulmonary artery catheters were inserted. A disposable extracorporeal AV loop was connected between existing arterial and central venous catheters. Reusable ultrasound sensors that measure changes in blood ultrasound velocity after dilution by isotonic saline were clamped onto the arterial and venous limbs of the loop. Ultrasound dilution (UD) measurements (COstatus; Transonic Systems, Inc, Ithaca, NY) were obtained by injecting 30 mL of body-temperature isotonic saline into the venous limb of the AV loop. An average of 3 COud and 5 COtd was obtained for comparison. Bland-Altman plot and correlation analysis were used for statistical comparison. A total of 142 comparison measurements were obtained. The correlation coefficient between the 2 techniques was r = 0.91. Bland-Altman analysis did not produce any significant bias (bias = 0.02, standard deviation = 0.56). The percentage error of these data was 23.53%. COud measurements agreed well with COtd. The results of this study indicated that COud might be interchangeable with conventional COtd in perioperative adult patients.

Measurements of Recirculation during Neonatal Veno-Venous Extracorporeal Membrane Oxygenation: Clinical Application of the Ultrasound Dilution Technique

Recirculation during dual lumen veno-venous (DLVV) extracorporeal membrane oxygenation (ECMO) is a dynamic event that results in a fraction of the oxygenated blood exiting the arterial lumen and immediately shunting back into the venous lumen. Excessive recirculation will result in suboptimal oxygen delivery to the patient. Ultrasound dilution is a technology that has been shown to rapidly quantify recirculation in veno-venous (VV) ECMO animal models. This manuscript reports the first clinical application of ultrasound dilution in quantifying recirculation during neonatal VV ECMO. A 2.8-kg neonate with congenital diaphragmatic hernia was placed on VV ECMO using a single DLVV cannula inserted into the right atrium through the internal jugular vein. Ultrasound sensors were clamped to the arterial and venous lines near the dual lumen cannula and 3- to 5-mL bolus injections of isotonic saline were used proximal to the circuit heat exchanger to make the recirculation measurements. Recirculation measurements were made after initiation and periodically thereafter. During the 12-day ECMO period, 86 recirculation measurements were performed. The average recirculation was 34.3% (range, 15–57%). Reproducibility of paired measurements was 5.6%. Changes in patient positioning resulted in significant changes in recirculation. Measurements using platelet injections were compared with those made with saline. The two were found to closely correlate (mean difference, .25% ± 2.8%). Ultrasound dilution measurements of recirculation provided rapid monitoring data during a clinical VV ECMO procedure. Application of this technique could provide early data that will assist the clinician in guiding interventions to minimize recirculation.

Theory and in vitro validation of a new extracorporeal arteriovenous loop approach for hemodynamic assessment in pediatric and neonatal intensive care unit patients*

No simple method exists for repeatedly measuring cardiac output in intensive care pediatric and neonatal patients. The purpose of this study is to present the theory and examine the in vitro accuracy of a new ultrasound dilution cardiac output measurement technology in which an extracorporeal arteriovenous tubing loop is inserted between existing arterial and venous catheters. Laboratory experiments. Research laboratory. None. None. In vitro validations of cardiac output, central blood volume, total end-diastolic volume, and active circulation volume were performed in a model mimicking pediatric (children 2-10 kg) and neonatal (0.5-3 kg) flows and volumes against flows and volumes measured volumetrically. Reusable sensors were clamped onto the arterial and venous limbs of the arteriovenous loop. A peristaltic pump was used to circulate liquid at 6-12 mL/min from the artery to the vein through the arteriovenous loop. Body temperature injections of isotonic saline (0.3-10 mL) were performed. In the pediatric setting, the absolute difference between cardiac output measured by dilution and cardiac output measured volumetrically was 3.97% +/- 2.97% (range 212-1200 mL/min); for central blood volume the difference was 4.59% +/- 3.14% (range 59-315 mL); for total end-diastolic volume the difference was 4.10% +/- 3.08% (range 24-211 mL); and for active circulation volume the difference was 3.30% +/- 3.07% (range 247-645 mL). In the neonatal setting the difference for cardiac output was 4.40% +/- 4.09% (range 106-370 mL/min); for central blood volume the difference was 4.90% +/- 3.69% (range 50-62 mL); and for active circulation volume the difference was 5.39% +/- 4.42% (range 104-247 mL). In vitro validation confirmed the ability of the ultrasound dilution technology to accurately measure small flows and volumes required for hemodynamic assessments in small pediatric and neonatal patients. Clinical studies are in progress to assess the reliability of this technology under different clinical situations.

Is Basilic Vein Transposition a Real Alternative to an Arteriovenous Bypass Graft? A Prospective Study

Basilic vein transpositions (BVTs) are considered to be superior to arteriovenous bypass grafts (AVGs). However, for the most part studies comparing BVTs to AVGs have been retrospective in design and without a set follow-up protocol. In this analysis, data were prospectively collected from patients with either a BVT or a brachio-axillary AVG. When all other native options were exhausted a BVT was performed if the vein had a diameter of 3 mm. All patients had bimonthly measurements of access inflow and recirculation using ultrasound dilution and were followed up for 2 years. Of 76 patients, 34 had a BVT and 42 an AVG (p > 0.05). BVT group: 12 were male, 22 female, the mean age was 62 and 26% were diabetic. AVG group: 22 were male, 20 female, the mean age was 57 and 56% were diabetic. The maturation delay was higher in the BVT group (6 weeks vs. 2 weeks). For the BVT and AVG groups, at 6, 12 and 24 months, respectively, primary patency was 90% vs. 76% (p < 0.05), 73% vs. 61% and 69% vs. 54% (p > 0.05). Assisted primary patency was 100% vs. 90% (p = 0.1201), 96% vs. 56% and 74% vs. 40% (p < 0.001). Secondary patency was 100% vs. 83%, 93% vs. 70% (p < 0.025) and 85% vs. 62% (p < 0.01). In the BVT group, 18 patients had 32 interventions for a total cost of $127,800, while in the AVG group, 27 patients had 54 interventions for a total cost of $227,300. This is the first prospective study to confirm that BVTs were cost effective and associated with better outcomes when compared with AVGs.

A novel simple hemoglobin dilution technique to measure hemodialysis vascular access flow

Measurement of the vascular access flow rate (Q(a)) is a widely accepted method for surveillance and predicting access failure. Among current practical methods, the ultrasound dilution technique is standard, but this requires a costly device available in few hemodialysis (HD) centers. Here, we devised a simple hemoglobin dilution technique to accurately measure Q(a) without the need for any special machines. Before HD, values of Q(a) were determined in each of 30 patients by hemoglobin dilution and then, in the same session, by ultrasound dilution. There was a significant correlation between the two techniques using automated hemoglobin and hematocrit or centrifuge-measured hematocrit levels to calculate HD fluid-derived Q(a) values. Our study shows that the HD dilution technique, using no special device, is economical, highly accurate, and easy to perform, and can be used as an alternative to standard ultrasound dilution for vascular access surveillance.