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

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). Conclusions: 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.