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The theory shows that access flow can be measured by the dilution technique by reversal of the blood dialysis lines with the venous outlet facing the access stream: (1.) with one dilution sensor in arterial line and two injections Equation (6); (2.) with two matched dilution sensors on the venous line and on the arterial line and one injection Equation (8); (3.) with blood sampling as for recirculation measurement using BUN or other methods in Equation (12). In all cases, accurate measurement of hemodialysis blood flow is required. The results of this bench validation demonstrate that dialysis blood flows, in the clinical range of 200 to 350 ml/min or more, create good mixing conditions in a vascular access model. Accurate measurements are provided for all clinically significant ranges of access flows, needle positions, and vascular access inner diameters. This simple, non-invasive, and inexpensive technique shows great promise for routine diagnosis of vascular access failure in hemodialysis patients.

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Objectives-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. Design-Laboratory experiments.Setting-Research laboratory. Subjects-None. Interventions-None.Measurements and Main Results-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). No routine method exists for repetitive measurements of cardiac output (CO) in pediatric and neonatal intensive care unit (ICU) patients. The small size of blood vessels, the amount of blood involved, and the need to use toxic indicators limit the routine use of existing methods (1,2). Ul-trasound dilution (UD) technology, used in extracorporeal circuits (mostly in hemodialysis), uses isotonic saline as an indicator to measure hemodynamic variables (3,4). The purpose of this study is to present the theory and examine the in vitro accuracy of a novel application for UD technology. In this application, an extracorporeal arteriovenous (AV) tubing loop is inserted between existing arterial and venous catheters to measure hemodynamic variables in ICU patients. Conclusions-In MATERIALS AND METHODS Cardiac OutputBlood ultrasound velocity (1560-1585 m/sec) is a function of total blood protein concentration (sum of proteins in plasma and in red blood cells), temperature, and average ion concentration in plasma (3,4). Injection of body temperature isotonic saline (ultrasound velocity of saline is 1533 m/sec) into the AV loop ( Fig. 1) decreases blood ultrasound velocity, producing dilution curves (Fig. 2). The CO calculation is based on the Stuart-Hamilton principle:where Vinj...