Seattle Children’s describes modified blood priming in 26 patients weighing 2.0–6.5 kg. Calculated red-cell priming combined with autologous priming reduced crystalloid exposure; mean PRBC use was 52 mL in the prime and 96 mL across bypass. The comparison was with the center’s standard prime, not a controlled patient cohort. Variable hematocrit results and limited clinical outcome reporting mean this technical series supports feasibility rather than proven safety or superiority.
A Middle Ground Between Clear and Standard Blood Priming
Kailey Fuegmann and colleagues at Seattle Children’s Heart Center describe modified blood priming (MBP), an approach intended for neonates and infants whose predicted hematocrit after circuit dilution is too low for a clear prime. The method combines a calculated quantity of donor packed red blood cells with retrograde and venous autologous priming. Its aim is to limit unnecessary donor-blood volume while supporting oxygen-carrying capacity during the transition to cardiopulmonary bypass.
The report builds on a blood-conservation program begun in May 2021. The center previously blood-primed most circuits for patients weighing 12 kg or less. Its subsequent approach considered patients of any weight for a clear prime when predicted post-dilutional hematocrit was adequate. MBP was developed for the intermediate group who still needed red cells but might not require the institution’s standard blood-prime volume.
Circuit Volume and Predicted Hematocrit
Reducing circuit prime volume preceded the introduction of MBP. The authors report neonatal and infant circuit prime volumes of 126 and 142 mL, respectively, down from earlier volumes of 165 and 200 mL. These reductions matter because circuit-related dilution is proportionally large in very small patients.
The team estimated post-dilutional hematocrit using patient blood volume, baseline hematocrit, and the anticipated dilutional contribution of the circuit. For these calculations, they used effective dilutional volumes of 70 mL for the neonatal circuit and 90 mL for the infant circuit to account for crystalloid expected to be removed by autologous priming. Those values are specific to the described circuit and technique; they are not interchangeable with the full physical prime volumes.
Patients predicted to have inadequate hematocrit with a clear prime received a calculated red-cell volume. The report discusses a minimum on-bypass hematocrit around 24%, but the target prediction varied early in the series. Midway through the cohort, the center standardized the target predicted hematocrit at 27% to provide a buffer for uncertainty. This small series does not establish a universal transfusion threshold for neonatal or infant bypass.
What the Modified Technique Changes
At a conceptual level, MBP concentrates donor red cells within the core of the circuit—the reservoir, arterial pump segment, and oxygenator—while replacing crystalloid in the arterial and venous lines with the patient’s own blood through retrograde and venous autologous priming. After bypass begins, crystalloid in the ultrafiltration and cardioplegia circuits is displaced to reduce further dilution. This is a coordinated perfusion technique rather than simply adding a smaller blood volume to an otherwise unchanged prime.
The center used leukocyte-reduced, irradiated red cells and did not wash them with a cell saver before administration. Fresh frozen plasma was not added to the modified prime. Hemoconcentration was available during bypass, and modified ultrafiltration was performed afterward. The authors also describe incremental volume or red-cell supplementation when reservoir volume, hematocrit, and physiologic observations indicated a need.
The detailed technical sequence involves circuit isolation, crystalloid displacement, and temporary changes to reservoir-level monitoring. It requires an institutionally validated procedure and coordinated surgical, anesthesia, and perfusion practice. This summary explains the strategy without presenting the report as a stand-alone operating protocol.
Monitoring and Conditions for Abandoning Autologous Priming
The authors describe continuous bubble detection, arterial-pressure monitoring, and restoration of reservoir-level protection before initiating bypass. An additional arterial-pressure transducer alarms for negative pressure during retrograde priming. Venous cannulation is completed before retrograde priming so that bypass can be initiated promptly if the patient becomes unstable.
During autologous priming, the team monitored filling pressures, mean arterial pressure, and near-infrared spectroscopy. In the reported protocol, inability to maintain pressure or a greater than 20% fall in NIRS prompted immediate initiation of bypass. On-bypass assessment incorporated hematocrit, venous oxygen saturation, NIRS, pressure support requirements, and lactate. These criteria describe the center’s practice and were not independently validated by the 26-patient series.
Reported Blood Use and Hematocrit Results
MBP was used in 26 patients beginning in November 2023. Body weight ranged from 2.0 to 6.5 kg, with baseline hematocrits of 21%–31%. Total red-cell administration during bypass, including the prime, ranged from 33 to 160 mL.
| Reported measure | Result |
|---|---|
| Patients | 26 |
| Weight range | 2.0–6.5 kg |
| Mean baseline hematocrit | 26.4% |
| Mean PRBC volume in modified prime | 52 mL |
| Mean total PRBC during CPB, including prime | 96 mL |
| Mean measured post-dilutional hematocrit on CPB | 24.5% |
| Mean post-MUF hematocrit | 29.8% |
No patient received fresh frozen plasma during bypass. The authors also report that platelets and cryoprecipitate were not administered in the operating room. These findings describe product use during the reported periods; they do not demonstrate an absence of postoperative transfusion or establish that patients avoided donor exposure.
The center’s standard blood prime contained 180 mL of packed red cells and 100 mL of fresh frozen plasma. Against that reference, the mean 96 mL of red cells administered throughout an MBP bypass run was approximately half the red-cell volume in the standard prime alone. This is a comparison with a standard recipe, not a randomized or matched comparison of total perioperative transfusion between patient groups. It should not be described as proof of a 50% reduction in overall transfusion requirements.
Predicted Targets Were Not Always Achieved
The patient-level table provides an important qualification to the favorable overall averages. Measured post-dilutional hematocrits ranged from 20% to 29%, with five of 26 patients below 24%. Post-MUF hematocrit ranged from 20% to 39%. The report therefore does not demonstrate that all patients remained at or above the proposed hematocrit threshold.
The authors acknowledge uncertainty in estimated patient blood volume, donor-cell hematocrit, anesthesia-related fluid administration, and mixing at the interface between crystalloid and blood. Early target values also varied with surgeon preference and baseline hematocrit. Standardizing the prediction target at 27% was an attempt to accommodate these factors, but the series does not establish which calculation or buffer is optimal.
Evidence Limitations and Perfusion Relevance
This is an uncontrolled technical series from one experienced institution. It offers practical information about circuit preparation and donor red-cell volume, but does not provide a controlled assessment of mortality, neurologic outcomes, kidney injury, ventilation duration, or intensive-care stay. The authors’ favorable description of feasibility should not be interpreted as proof of comparative safety or improved clinical outcomes.
For perfusion teams, the central contribution is the integration of smaller circuits, patient-specific dilution estimates, autologous priming, and measured donor red-cell supplementation. The work supports evaluating how circuit volume and priming decisions affect transfusion exposure. Broader adoption would require local validation, clear monitoring and rescue criteria, and prospective outcome assessment that captures both transfusion reduction and the consequences of lower hematocrit.
Attribution: © 2026 The Authors, published by EDP Sciences. The original article is available under CC BY 4.0. This independently written IPA summary accompanies the source article. Cover artwork is conceptual.
Original Article
Fuegmann K, Charette K, Falconer A, Sharma N, Perfette B, Phillips M, Bohuta L. Introduction of modified blood priming technique in the neonatal and infant populations undergoing congenital heart surgery. J Extra Corpor Technol. 2026;58:313–317. Read the original article.
