Heart Surgery Wrecks the Infant Gut Microbiome, and Butyrate May Be Why Recovery Stalls

Congenital heart defects affect roughly one in every hundred births, and many require surgical repair in the first months of life. Cardiopulmonary bypass (CPB), the machine that takes over heart and lung function during the procedure, has long been known to trigger systemic inflammation. Now, preliminary research published in June 2026 in the journal Clinical and Experimental Gastroenterology suggests the gut pays a steep and measurable price: beneficial bacteria collapse, short-chain fatty acids drop, and the risk of feeding intolerance more than doubles. The findings are early, drawn from a small cohort, and should be interpreted with caution, but they point toward a biological mechanism that could explain why so many of these children struggle to eat and gain weight after surgery.

Butyrate and Propionate Collapse After Cardiopulmonary Bypass

The study enrolled 20 children aged 0 to 3 years undergoing cardiac surgery with CPB at a center in Uzbekistan, collecting stool samples before and within one to five days after the procedure. Eight additional children with congenital heart disease who had not yet undergone surgery served as a comparison group. The core finding is stark: fecal butyrate and propionate levels fell significantly in postoperative children, while populations of Bifidobacterium, Lactobacillus, and Bacteroides, the main SCFA-producing taxa in the infant gut, were sharply reduced. In their place, opportunistic microorganisms including Enterobacteriaceae and Clostridium species expanded. Acetic acid concentrations moved in the opposite direction, rising postoperatively and increasing further with the child's age.

Short-chain fatty acids are not a niche biochemical detail. Butyrate, propionate, and acetate are produced when beneficial gut bacteria ferment dietary fiber; they fuel the cells lining the intestine, reinforce the gut barrier, and help regulate immune responses. When butyrate runs low, enterocytes, the cells that absorb nutrients, lose a primary energy source. Research on gut microbiota disruption in infants with congenital heart disease shows that CPB can exacerbate this intestinal inflammation, compounding a dysbiosis that may actually predate the operating room. A separate trajectory analysis of pediatric CPB surgery found gut dysbiosis present before the procedure and worsened by it, lending context to the new study's postoperative snapshots.

Feeding Intolerance and Growth Setbacks in Postoperative Children

The downstream consequences documented in this study are clinically concrete. Postoperative feeding intolerance was significantly more common in children with severe dysbiosis (p = 0.022). Children with depleted fecal SCFAs had a relative risk of feeding intolerance of 2.1 (95% CI: 1.1 to 4.0), meaning they were roughly twice as likely to struggle with feeds compared to children without that depletion. Reduced butyrate correlated moderately with slower weight gain velocity (Spearman's rho = 0.39, p = 0.044) and lower serum albumin, a marker of protein status (rho = 0.41, p = 0.036).

These growth setbacks matter beyond the immediate hospitalization. Disruptions to the gut microbiota in the first thousand days of life carry downstream risks including inflammatory disorders, immune dysregulation, and obesity, making the period right after cardiac surgery a potentially sensitive window. The infant microbiome influences immunological, endocrine, and neural pathways that extend far beyond digestion, raising the stakes for any prolonged disruption during recovery.

Markers of intestinal barrier dysfunction reinforced the picture. Circulating levels of claudin-2, claudin-3, and intestinal fatty acid-binding protein (I-FABP), proteins that leak into the bloodstream when gut wall integrity breaks down, were all significantly elevated postoperatively. Fecal calprotectin, a standard marker of intestinal inflammation, was also raised, suggesting that the barrier disruption was accompanied by active mucosal inflammation.

How the Researchers Measured Dysbiosis and SCFA Levels

The microbiome was assessed using culture-based microbiological methods rather than modern sequencing approaches. That is an important methodological note: culture-based techniques offer limited taxonomic resolution and may miss many species, particularly obligate anaerobes that are difficult to grow in the laboratory. SCFA concentrations in fecal samples were measured by gas chromatography, a well-established analytical method. Accurate SCFA quantification using gas chromatography methods is considered reliable for fecal microbiome research, which lends confidence to those specific measurements even if the microbial taxonomy data is coarser than sequencing would provide.

Dysbiosis severity was quantified using an intestinal dysbiosis index, calculated from deviations in microbial counts relative to age-specific reference values. That index correlated positively with CPB duration (rho = 0.42, p = 0.038), suggesting that longer time on the bypass machine is associated with greater microbial disruption. Reduced butyrate and propionate were moderately associated with higher dysbiosis index scores (rho = 0.38 to 0.42, p less than 0.05).

Significant Limitations That Shape What Can Be Concluded

This study is preliminary in almost every methodological dimension. Twenty patients is a very small sample, limiting statistical power and making it impossible to generalize the findings with confidence. The comparison group, children with the same heart defects who had not yet had surgery, may not represent a truly healthy gut baseline, since congenital heart disease itself is associated with altered microbial communities even before intervention. The observational design means that all reported relationships are associations; the study cannot establish whether dysbiosis causes poor feeding outcomes or whether both are driven by a third factor, such as antibiotic exposure or perioperative feeding regimens, that the authors acknowledge were not fully controlled. The one-to-five-day follow-up window provides no information about whether the microbiome rebounds over subsequent weeks or months.

Probiotic and Microbiome Monitoring Strategies Worth Exploring

Despite those limits, the authors suggest that targeted monitoring of the gut microbiome in children undergoing CPB could help clinicians identify high-risk patients earlier. Beyond monitoring, the question of whether active microbiome support, such as probiotic supplementation before or after surgery, could blunt the dysbiosis is a natural next step. A recent systematic review found that probiotic supplementation significantly reduced postoperative infections and improved Bifidobacterium abundance in children undergoing gastrointestinal surgery, suggesting that a similar approach in cardiac surgery populations could be worth testing in adequately powered randomized trials. For now, the study's contribution is to give this under-researched complication a measurable shape: CPB disrupts the infant gut microbiome, SCFA levels drop in tandem, and the clinical cost appears in the feeding charts and growth curves of children who are already vulnerable.

Evidence rating

INVESTIGATIONAL — 75/100

Caveats:

• Very small sample size (n=20) severely limits statistical power and generalizability.
• Microbiome assessment relied on culture-based methods rather than modern sequencing, providing limited taxonomic resolution.
• Observational design: reported relationships are associations only, not causal effects.
• Short follow-up window (1–5 days post-surgery) prevents conclusions about longer-term outcomes.
• Potential confounders including antibiotic exposure and feeding regimens were not fully controlled.
• Funding was not disclosed.

Prospective observational study of 20 children (0–3 years) undergoing cardiac surgery with cardiopulmonary bypass. Reports associations between postoperative dysbiosis, reduced fecal butyrate and propionate, and feeding intolerance, but the very small sample size, culture-based microbiome methodology, and short follow-up period (1–5 days) substantially limit the strength of these findings. The observational design establishes association only, not causation, and the study has not been independently replicated.