An assessor-blinded randomized trial of 80 children compared SBUF-SMUF with conventional ultrafiltration during cardiac surgery. The combined technique achieved a more negative crystalloid fluid balance, higher post-bypass hematocrit, lower reported red-cell transfusion volumes and earlier extubation. Potassium and urine-output findings were similar. The small single-center trial, limited CUF comparator, and inconsistent reporting support further clinical research rather than universal adoption.
Why ultrafiltration matters in pediatric bypass
Cardiopulmonary bypass can impose a substantial fluid burden on a small child. Circuit prime and cardioplegia add volume relative to the patient’s circulating blood volume, contributing to hemodilution and potentially complicating postoperative recovery. Ultrafiltration provides a way to manage that burden, but techniques differ in when filtration occurs, how replacement fluid is handled, and whether concentration continues after bypass. This study examines a combined approach: subzero-balance ultrafiltration followed by simple modified ultrafiltration, abbreviated SBUF-SMUF. Its central question is whether this two-phase strategy improves selected clinical outcomes compared with the conventional ultrafiltration practice used at the investigators’ hospital.
Trial design and patient population
Shadmehr and colleagues conducted a prospective, parallel-group randomized trial at Shahid Fagihi Hospital in Shiraz, Iran, between July 2023 and September 2024. Of 91 patients screened, 80 were randomized equally to CUF or SBUF-SMUF. Outcome assessors and ICU nurses were blinded; perfusionists and the operating-room team could not be blinded to the circuit strategy. Eligible patients were between one month and 18 years old, weighed 4–40 kg, had a pre-bypass hematocrit below 45%, and underwent at least 45 minutes of bypass. Patients with transposition of the great arteries or a history of premature birth were excluded.
The actual study population was much narrower than those broad age limits suggest. Mean ages were approximately three years, and mean weights were 10.81 kg in the CUF group and 12.08 kg in the intervention group. Ventricular septal defect and tetralogy of Fallot repairs were common. Reported baseline characteristics and the distribution of procedures were not statistically different between groups. Bypass and cross-clamp times were numerically longer with SBUF-SMUF but did not differ significantly. These findings provide context for the comparison, although nonsignificant baseline tests do not guarantee equivalence in a small trial.
What the two strategies compared
In the control group, CUF was used during bypass to remove prime volume and cardioplegia-related fluid, without modified ultrafiltration after separation from bypass. The intervention combined continuous SBUF during bypass with SMUF afterward. During SBUF, filtered blood returned to the venous reservoir while replacement-fluid administration and effluent removal were coordinated to produce net fluid removal. After bypass, the circuit transitioned to a veno-arterial filtration configuration for additional hemoconcentration. The study used conventional perfusion equipment, including roller pumps and a pediatric hemoconcentrator.
The distinction between treatment strategies is essential to interpreting the results. This was not a comparison of two otherwise identical ultrafiltration protocols, nor did it test SBUF-SMUF against CUF combined with standard MUF. The intervention added both a continuous net-negative fluid strategy and post-bypass filtration. The authors acknowledge that their CUF practice was relatively limited and that a more aggressive CUF strategy, particularly one followed by MUF, might yield similar benefits. The results therefore describe the performance of these specific institutional approaches rather than proving that SBUF-SMUF is the best technique across all pediatric programs.
Fluid balance and hematocrit findings
Reported mean crystalloid fluid balance was +192.1 ± 178.81 mL with CUF and −105.0 ± 78.90 mL with SBUF-SMUF, with p < 0.001. The negative sign for the intervention is visible in the PDF’s clinical-characteristics table and is also stated in the abstract and results. Importantly, the discussion says this balance concerns crystalloid fluid and treats transfused blood separately. It should not be interpreted as a complete accounting of all perioperative fluid inputs and outputs or as a directly interchangeable measure of postoperative fluid overload.
Post-bypass hematocrit was also higher with SBUF-SMUF: 31.2% compared with 27.3% for CUF, with p = 0.001. This supports a hemoconcentration effect in the studied setting. A higher hematocrit, however, is an intermediate outcome rather than proof of improved oxygen delivery or organ protection. The trial did not establish a universally appropriate hematocrit target or show that all patients would benefit from the same degree of fluid removal. Individual physiology, preload, hemodynamics, and institutional practice remain relevant to clinical interpretation.
Blood-product utilization and reporting caveats
The paper reports lower packed red-cell transfusion volumes in the intervention group: approximately 141.66 ± 70.17 mL compared with 261.00 ± 68.80 mL, with p < 0.001. Those same means appear for the intraoperative and ICU red-cell outcomes in Table 2. The discussion also describes fewer intraoperative recipients, 12 versus 30, and fewer ICU recipients, 34 versus 40, for SBUF-SMUF and CUF, respectively. Because the presentation does not clearly reconcile the identical volume estimates with these different recipient counts, the exact denominators and independence of these transfusion outcomes need clarification.
Immediate post-bypass fresh frozen plasma reporting is similarly inconsistent. The abstract and table present values labeled as percentages, whereas the discussion identifies two intervention patients and ten control patients. The direction of the reported difference favors SBUF-SMUF, but the publication should not be summarized uncritically as showing 2% versus 10% exposure. ICU FFP use was reported in nine intervention patients and 17 CUF patients; that difference did not reach the stated significance threshold, with p = 0.056. These inconsistencies temper confidence in the precise magnitude of the blood-conservation benefit.
Extubation, ICU stay, and safety
Mean time to extubation was 1.05 ± 1.03 days with SBUF-SMUF and 2.27 ± 2.37 days with CUF, with p = 0.006. This is a clinically relevant signal of earlier respiratory recovery in the intervention group. It does not establish the mechanism. Inflammatory mediators were not directly measured, so claims that cytokine removal caused the difference remain speculative. Chest drainage over the first three ICU days was not significantly different, and ICU length of stay was approximately five days in both groups, without a significant difference.
Potassium measurements and urine-output comparisons did not show significant between-group differences. These observations are reassuring within the limits of this sample, but they do not prove equivalent renal safety or exclude uncommon adverse events. Although the abstract refers to acute kidney injury, the detailed reporting emphasizes urine output and does not present a clearly specified, standardized AKI endpoint with comprehensive event data. Sodium and calcium were not systematically analyzed despite use of bicarbonate-containing replacement fluid. The trial therefore offers incomplete electrolyte and kidney-safety assessment rather than definitive evidence that the combined technique adds no risk.
Implications for perfusion practice
The study provides a useful rationale for further evaluation of coordinated intra-bypass fluid management and post-bypass hemoconcentration. Randomization and blinded postoperative assessment strengthen the findings compared with an uncontrolled technical report. Nevertheless, the single-center sample, incompletely described allocation methods and power assumptions, multiple tested outcomes, limited comparator, and reporting inconsistencies constrain the conclusions. Applicability to premature infants, neonates, transposition repairs, markedly different circuits, or programs already using CUF-MUF is uncertain.
For perfusion departments, the most defensible takeaway is that SBUF-SMUF showed promising fluid-management, hematocrit, transfusion, and extubation signals in this particular trial. The evidence supports a larger, well-reported comparison against contemporary CUF-MUF, with standardized transfusion criteria, complete fluid accounting, clearly defined renal outcomes, and systematic electrolyte monitoring. It does not establish universal superiority or justify treating the authors’ protocol as a new standard of care. Reviewing the complete paper and local multidisciplinary practices is necessary before translating these findings into an institutional technique.
Keywords: Pediatric Perfusion, Cardiopulmonary Bypass, Ultrafiltration, SBUF-SMUF, Conventional Ultrafiltration, Modified Ultrafiltration, Congenital Heart Surgery, Fluid Balance, Blood Conservation, Hemoconcentration, Randomized Clinical Trial.
Source: Shadmehr M, Ali B, Abdollahzadeh R, Zarrabi K, Gerami H, Butt SP. SBUF-SMUF: On the path to the optimum hemofiltration technique in pediatric cardiopulmonary bypass: A randomized clinical trial. Journal of ExtraCorporeal Technology. 2026;58:228–236. doi:10.1051/ject/2026020. Open access under CC BY 4.0.
