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

Abstract

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...

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

“…The first factor is that COstatus uses a non-diffusible indicator (saline) that travels only through the intravascular space [9,10,13], whilst PiCCO uses a diffusible indicator (thermal) that travels through both intravascular and extravascular space, during the first pass [5]. Since it is the time taken by the indicator to travel only through intravascular space that is used to estimate blood volumes [14], special assumptions and adjustments will have to be made when using a diffusible indicator [5]. The second factor is the difference in the assumptions and mathematical models for the calculation of blood volumes which lead to using different formulae by the two methods (see ''Theory'' section in the ''Electronic supplementary material'').…”

“…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 Introduction Assessment of cardiac output (CO) and blood volumes is fundamental to the management of critically ill patients [1][2][3][4] as CO without blood volumes or cardiac filling pressures may not indicate the complete hemodynamic state of the critically ill. Transpulmonary thermodilution (TT) technology (Philips IntelliVue MP40 monitor with PiCCO-technology module M3012A#10) has been explored to measure CO (COTT) and preload parameters such as global end-diastolic volume (GEDV, sum of all end-diastolic volumes of the atria and ventricles) and intrathoracic blood volume (ITBV, sum of GEDV and pulmonary blood volume) [5].…”

Comparison of Transpulmonary Thermodilution and Ultrasound Dilution Technique: Novel Insights into Volumetric Parameters from an Animal Model

“…Today this technique is limited by existing catheter sizes [24] and the risk of thrombotic occlusion after insertion of the femoral artery thermodilution catheter [12], particularly in small children weighing \15 kg. Recently introduced minimally invasive ultrasound dilution technology (UDT) offers a promising alternative because it can be used in patients of any age and weight with already existing peripheral arterial and central venous catheters [6,8,13,16]. Body-temperature isotonic saline is used as the indicator, and changes of blood ultrasound velocity caused by isotonic saline are measured [16].…”

“…Body-temperature isotonic saline is used as the indicator, and changes of blood ultrasound velocity caused by isotonic saline are measured [16]. Similar to the thermodilution technique, after central venous injection and passage through the cardiopulmonary system, a dilution curve is detected on the arterial side, and CO is calculated based on the Stewart-Hamilton equation [16]. Analogous to PiCCO, the UDT monitor obtains the following volumetric parameters: central blood volume (CBV) corresponding to ITBV and total end-diastolic volume (TEDV), which is comparable with GEDV.…”

“…Recently introduced minimally invasive ultrasound dilution technology (UDT) offers a promising alternative because it can be used in patients of any age and weight with already existing peripheral arterial and central venous catheters [6,8,13,16]. Body-temperature isotonic saline is used as the indicator, and changes of blood ultrasound velocity caused by isotonic saline are measured [16]. Similar to the thermodilution technique, after central venous injection and passage through the cardiopulmonary system, a dilution curve is detected on the arterial side, and CO is calculated based on the Stewart-Hamilton equation [16].…”