Healthy adults harbor a dense, anaerobe-dominated community in which Firmicutes (notably Clostridium clusters IV and XIVa) and Bacteroidetes predominate (15,41). These taxa express a broad repertoire of butyrogenic genes that convert dietary fiber into millimolar concentrations of butyrate, propionate and acetate (26,42). Butyrate fulfils three homeostatic tasks: It i) fuels colonocytes via β-oxidation, thereby maintaining tight-junction integrity; ii) acts as a histone-deacetylase inhibitor that expands peripheral regulatory T cells; and iii) triggers enteric neuronal 5-hydroxytryptamine release that coordinates segmental motility (43–45). A recent multi-center metagenomic survey of 167 healthy volunteers showed that individuals in the highest quartile of fecal butyrate (≥12 mmol/kg) displayed lower systemic interleukin-6 (IL-6) and higher zonula-occludens-1 expression in rectal biopsies, underscoring the anti-inflammatory and barrier-stabilizing properties of the metabolite (26).

Within 24–48 h of critical illness, the symbiotic architecture collapses. In three independent ICU cohorts (n=34-115 patients), a ≥30% reduction in observed species richness and a ≥10-fold drop in butyrate concentration during the first week of admission were documented (15,41,46). Proteobacteria (Escherichia, Klebsiella, Enterococcus) expand from <5 to 30–50% of total reads, whereas in the study by Ravi et al (15), butyrate producers such as Faecalibacterium prausnitzii and Roseburia spp. fell below the limit of detection in 60% of subjects. Both prospective (41) and retrospective (46) studies identified identical predictors of this shift: Broad-spectrum β-lactams, PPIs and vasopressor infusion. Notably, Lamarche et al (41) demonstrated that every additional day of meropenem correlated with a 2.3% loss in Shannon diversity per day (P<0.001) and a 0.15 mmol/l decline in serum butyrate.

Antibiotics exert class-dependent collateral damage on the gut ecosystem. Metagenomic analysis of 21 critically ill adults revealed that meropenem selectively depletes Firmicutes carrying the butyryl-CoA:acetate CoA-transferase gene, while vancomycin eradicates commensal Gram-positive taxa without compensatory butyrate recovery (47). PPIs amplify the effect by raising gastric pH >4, permitting oral Streptococci and Candida spp. to reach the colon and out-compete anaerobic fiber degraders (48,49). In a double-blind randomized controlled trial involving 48 healthy volunteers, 7-day pantoprazole decreased fecal butyrate by 38% and increased fungal internal transcribed spacer 1 copies 5-fold; these changes were reversed within 4 weeks of drug cessation, indicating a transient yet quantifiable perturbation (49).

The metabolic vacuum left by fiber-fermenting bacteria is filled by opportunistic pathogens that exploit ethanolamine and mucin-derived sugars. Elevated proteolytic metabolites (p-cresol, indoxyl sulfate) and reduced SCFA synergize to impair epithelial oxygen consumption, resulting in a ‘leaky’ phenotype (46,50). Using ex-vivo Using chambers, Chernevskaya et al (46) showed that serosal-to-mucosal permeability doubled in biopsy samples collected from septic patients with low butyrate (<2 mmol/kg) compared with ICU controls with preserved levels. Consistently, animal data confirm that antibiotic-induced dysbiosis decreases claudin-1 and occludin expression via HDAC3-mediated transcriptional repression, a defect rescued by oral butyrate supplementation (45,51).

A total of three observational studies have linked the magnitude of dysbiosis to subsequent gastrointestinal complications. In 115 mechanically ventilated adults, the relative abundance of butyrate producers on ICU day 3 predicted FI (GRV >250 ml) with an area under the receiver operating characteristic curve (AUROC) of 0.81 (95% CI 0.73–0.89) (15). Similarly, a pediatric critical-care cohort study found that loss of microbial diversity preceded the first episode of emesis by a median of 2 days, suggesting that microbiota disruption is not merely associative but temporally antecedent (26). Importantly, the same datasets revealed that patients in the lowest quartile of butyrate synthesis capacity had a 2.4-fold higher hazard of 28-day mortality, implicating gut-derived metabolite deficiency as a contributor to systemic decompensation (15,41).

Despite converging evidence, important inconsistencies persist. Geographic origin, baseline diet and ethnicity moderate the resilience of the microbiome; Asian populations appear to retain higher levels of butyrate producers under comparable antibiotic pressure (3). Furthermore, most reports are limited to 16S rRNA surveys; only two studies to date have integrated metagenomic and metabolomic layers to assign functional gene loss to specific taxa (47,52). Finally, inter-individual variation in host toll-like receptor signaling and bile-acid composition may confound the speed and extent of dysbiosis, underscoring the need for personalized profiling before implementing microbiota-targeted interventions (52,53).

Collectively, these iatrogenic and physiological stressors orchestrate a shift from homeostasis to a maladaptive dysbiotic state, creating a vicious cycle of metabolite depletion and epithelial dysfunction. Fig. 1 illustrates this cumulative pathophysiological trajectory from ICU admission to the manifestation of FI, depicting the stepwise transition from a healthy butyrate-producing microbiota through the collapse of microbial ecology and butyrate deficit to clinical feeding intolerance and a self-perpetuating vicious cycle.

Butyrate is generated almost exclusively by anaerobic fermentation of dietary fibers and resistant starch. Metagenomic analyses of healthy adults consistently map >80% of fecal butyrogenic potential to three Firmicutes lineages: Faecalibacterium prausnitzii, Roseburia spp. and Eubacterium rectale (54–56). These taxa express either the butyryl-CoA:acetate-CoA-transferase or the butyrate-kinase pathway; both routes converge on butyryl-CoA, which is then converted to butyrate via phosphate butyryl-transferase (56). In a case-control study comparing 58 patients with Graves' disease and 63 healthy controls, Su et al (55) observed that the relative abundance of butyrate-producing genera, including Faecalibacterium and Roseburia, was significantly reduced in the patient group and positively associated with fecal short-chain fatty acid (including butyrate) concentrations. This correlation reinforces the quantitative link between the density of these microbial clusters and their metabolic output in the human gut, as a loss of producer taxa directly paralleled a decline in metabolite levels.

Once released into the colonic lumen, butyrate is rapidly taken up by colonocytes through MCT-1 and sodium-coupled MCT. Inside the cell it undergoes β-oxidation, supplying ≥70% of basal oxygen consumption and maintaining hypoxic niche conditions that suppress pathogen expansion (57,58). Mechanistic work in Caco-2 monolayers demonstrated that 2 mmol/l butyrate increases transepithelial electrical resistance by 35% within 6 h, an effect mediated by AMP-activated protein kinase-dependent phosphorylation of tight-junction proteins occludin and claudin-1 (58). Consistently, a randomized trial in antibiotic-induced dysbiosis revealed that 4-week oral sodium butyrate (1 g/day) restored the urinary lactulose-to-mannitol ratio to baseline values while raising colonic zonula occludens-1 mRNA 2.3-fold (59). These observations position butyrate as the principal metabolic fuel for epithelial renewal and paracellular sealing.

Beyond energetics, butyrate functions as a potent epigenetic regulator. Its inhibition of HDAC1/2/3 promotes acetylation of promoter regions for forkhead box P3 (FOXP3) and IL-10, thereby expanding peripheral regulatory T cells (Treg) and dampening type 17 T-helper cell polarization (54,60,61). In a gnotobiotic mouse model colonized with butyrate-producing Roseburia hominis, lamina propria FOXP3+ cells increased from 8 to 22% and IL-17+ cells fell by 40% relative to germ-free controls (62). Translationally, with the caveat that these data derive from inflammatory bowel disease rather than critical illness, a double-blind study in ulcerative colitis showed that enema-delivered butyrate (100 mmol/l, 14 days) raised mucosal IL-10 concentration 3-fold and decreased tumor necrosis factor α and IL-6 by 50%, paralleling clinical remission in 65% of recipients (63). Collectively, these data indicate that butyrate orchestrates a tolerogenic milieu through HDAC inhibition and subsequent Treg expansion.

Butyrate also interacts with the enteric nervous system to regulate motility. Electrophysiological recordings from murine colonic segments revealed that 5 mmol/l butyrate depolarizes cholinergic interneurons via G protein-coupled receptor 109A signaling, increasing acetylcholine release and promoting high-amplitude propagating contractions (60). Clinically, a pilot trial in critically ill adults demonstrated that enteral infusion of sodium butyrate (4 g/day for 7 days) shortened gastric emptying time (T½) from 180 to 120 min (P=0.02) and reduced GRV >250 ml episodes by 45% (64). While these motility benefits are encouraging, heterogeneity in dose (0.5–4 g), route (oral vs. rectal) and patient phenotype precludes firm dosing recommendations; nevertheless, the consistency across mechanistic and early-phase studies supports a causal role for butyrate in accelerating gut transit.

Despite converging evidence, several caveats should be noted. First, most mechanistic insights derive from supra-physiological concentrations (2–10 mmol/l) that exceed portal levels recorded in healthy humans (0.2–1 mmol/l) (55,56). Second, host genetics and diet modify responsiveness: Individuals carrying MCT-1 loss-of-function variants achieve lower intracellular butyrate and derive weaker barrier protection (65). Third, comparative studies reveal that propionate and acetate share certain immunomodulatory properties, raising the possibility that synergistic SCFA mixtures, not butyrate alone, mediate observed benefits (66). Future dose-response trials integrating metagenomics, metabolomics and transcriptomics are warranted to define minimal effective concentrations and to identify responders most likely to benefit from butyrate-centric therapeutics.

Recent microbiome analyses have consistently revealed a significant reduction in butyrate-producing bacteria in critically ill patients, particularly those developing FI. Wijeyesekera et al (26) conducted a multi-compartment metabolomic and microbiomic study in pediatric ICU patients and found that the depletion of Firmicutes, particularly Clostridium clusters IV and XIVa (e.g., Faecalibacterium prausnitzii, Roseburia spp.), was strongly associated with intestinal dysbiosis and systemic metabolic disturbances. These taxa are known to harbor butyryl-CoA:acetate CoA-transferase and butyrate kinase pathways, which are essential for butyrate biosynthesis. Their reduction was temporally linked with the onset of gastrointestinal dysfunction, suggesting a potential causal relationship rather than mere association.

Although COVID-19 pathophysiology differs from general critical illness in its specific inflammatory and immunological features, it provides proof-of-principle that butyrate loss can persist beyond the acute phase; similarly, Zhang et al (67) reported that COVID-19 patients exhibited prolonged impairment in SCFA biosynthesis, particularly butyrate, due to a persistent decline in butyrogenic bacteria. This dysbiosis was not transient and persisted beyond the acute phase of illness, implying that microbiota disruption may have long-term consequences on gut function and immunity. These findings align with earlier observations in sepsis patients, where a significant reduction in butyrate producers was associated with increased mucosal inflammation and impaired gastrointestinal motility (68).

Metabolomic profiling has provided direct evidence of butyrate depletion in critically ill populations. Valdés-Duque et al (69) quantified stool SCFAs in septic ICU patients and found significantly lower levels of butyrate compared to healthy controls. This reduction was inversely correlated with markers of intestinal permeability and systemic inflammation, reinforcing the role of butyrate in maintaining mucosal integrity and immune homeostasis.

In a murine model of Klebsiella pneumoniae-induced pneumosepsis, Wu et al (27) observed a marked decrease in cecal butyrate levels, coinciding with an overgrowth of pathogenic taxa and a reduction in beneficial fiber-fermenting bacteria. Importantly, this study also demonstrated that butyrate depletion was closely associated with the onset of systemic inflammatory responses, suggesting that microbial metabolite deficiency may be an early driver rather than a consequence of critical illness. However, the original study did not report a specific time interval between these events (27). These findings are consistent with human studies showing that fecal butyrate levels are significantly reduced in patients with EN intolerance and are predictive of worse clinical outcomes (26).

Beyond taxonomic shifts, metagenomic analyses have revealed a functional collapse in butyrate synthesis pathways during critical illness. Haak et al (70) performed an integrative transkingdom analysis in ICU patients and identified a significant reduction in genes encoding butyryl-CoA:acetate CoA-transferase and butyrate kinase, key enzymes in butyrate biosynthesis. This functional gene loss was most pronounced in patients exposed to broad-spectrum antibiotics and those with prolonged ICU stays, indicating that iatrogenic factors may exacerbate microbiota dysfunction.

Furthermore, Zhou et al (32) demonstrated that the gut-lung axis disruption in mechanically ventilated patients was associated with a reduction in microbial genes involved in SCFA metabolism, including butyrate production. This metagenomic dysfunction was predictive of 28-day mortality, underscoring the clinical relevance of microbial metabolic capacity beyond taxonomic composition. These data collectively support the hypothesis that the loss of butyrogenic function, rather than simply the absence of specific taxa, is a critical determinant of gastrointestinal dysmotility and FI.

The convergence of microbiomic, metabolomic and metagenomic evidence points to a coherent pathway wherein critical illness-induced dysbiosis leads to butyrate depletion, which in turn compromises intestinal barrier integrity, immune regulation and motility, culminating in FI. However, some inconsistencies merit discussion. For instance, geographic and dietary factors may modulate microbiota resilience, with certain populations (e.g., Asian cohorts) retaining higher levels of butyrate producers despite antibiotic exposure (3). Additionally, host genetics, such as MCT-1 polymorphisms affecting butyrate uptake, may influence individual susceptibility to FI (65).

Furthermore, while most studies report a consistent decline in butyrate and its producers, a small number of studies have noted partial recovery of SCFA levels following probiotic or synbiotic interventions, albeit with variable clinical efficacy (71,72). This suggests that microbiota-targeted therapies may hold promise, but their success likely depends on the timing, baseline microbiota composition and host metabolic context.

Before detailing the intervention components, the operational scope of the term ‘nurse-driven’ must be clarified. A nurse-driven model does not imply independent nursing performance of interventions that legally or institutionally require physician orders [such as fecal microbiota transplantation (FMT) prescription, antibiotic de-escalation, probiotic selection, diagnostic gastric ultrasound]. Rather, nurses function as protocol initiators, continuous monitors and care coordinators operating within validated institutional protocols and multidisciplinary team structures. Final clinical decisions, including prescribing, ordering of diagnostic tests and invasive procedures, remain with physicians or pharmacists where required by law, hospital policy or scope of practice. This distinction aligns with published nurse-driven protocol models in critical care, including nurse-driven sedation monitoring and early mobility protocols (73,74).

Critical care nurses are uniquely positioned to operationalize microbiota-targeted therapies. Compared with physicians, pharmacists and dietitians, nurses offer the distinct advantage of continuous bedside presence for real-time dynamic monitoring, direct administration of EN and probiotics with immediate adverse event detection and integration of gut health assessment with overall patient status (hemodynamics, sedation, infection). Continuous bedside presence, responsibility for EN delivery and participation in infection-control bundles confer a pivotal role in modulating antibiotic exposure, feeding substrates and probiotic/synbiotic logistics. Recent meta-analyses demonstrate that bundles coordinated by nurses reduce ventilator-associated pneumonia (VAP) and antibiotic consumption, both of which indirectly preserve butyrate-producing taxa (75,76). Furthermore, nurse-driven withdrawal of routine gastric residual aspiration increases EN volume delivered without increasing infectious complications, thereby augmenting fermentable substrate influx to the colon (34,77). Collectively, these observations justify framing microbiota support as an integral component of nursing quality indicators.

Pharmacovigilance studies reveal that every additional day of broad-spectrum β-lactam therapy correlates with a 2.3% daily loss in gut microbial Shannon diversity and a quantifiable decline in fecal butyrate (78). Nurse-initiated daily ‘antibiotic time-outs’ (i.e., a brief, structured daily review of antibiotic necessity, indication, spectrum and duration, typically performed at the bedside as part of routine care) embedded in the ICU bundle do not grant nurses prescribing authority. Instead, nurses trigger a multidisciplinary review by flagging patients who meet predefined duration criteria (e.g., ≥72 h of broad-spectrum therapy). The final decision to de-escalate, change or discontinue antibiotics rests with the attending physician or infectious disease pharmacist as per institutional antimicrobial stewardship policies. This nurse-triggered mechanism has been shown to shorten median antibiotic duration by 1.8 days and to lower the incidence of subsequent multidrug-resistant gram-negative bacteremia (75). Likewise, restricting proton-pump inhibitors to patients with overt upper gastrointestinal bleeding reduces gastric pH-driven colonization of oral Streptococci and Candida spp., taxa that out-compete fiber-fermenting anaerobes (79,80). Although comparative trials specifically measuring butyrate rebound after PPI restriction are lacking, observational data report a 38% increase in fecal butyrate within four weeks of drug cessation, supporting the biological plausibility of this intervention (80).

Randomized work by Freedberg et al (81) demonstrated that a fiber-enriched enteral formula (15 g mixed fermentable substrate/day) attenuated antibiotic-associated diarrhea and doubled the abundance of butyrate producers in ICU patients receiving broad-spectrum agents. Of note, the benefit was restricted to individuals whose baseline microbiota retained ≥5% relative abundance of Firmicutes. This threshold was derived from the exploratory analysis of the pilot trial by Freedberg et al (81). Notably, the benefit was restricted to individuals whose baseline microbiota retained ≥5% relative abundance of Firmicutes; complete ecological collapse precluded fiber conversion, underscoring the need for early intervention. When fiber alone is insufficient, synbiotics offer a pragmatic escalation. In a double-blind trial, Shimizu et al (71) administered Lactobacillus casei plus galacto-oligosaccharides to septic adults, achieving a 27% reduction in enteritis and VAP incidence alongside restoration of fecal butyrate to control levels. Consistent with these observations, a randomized trial in enterally fed critically ill patients showed that synbiotic supplementation significantly improved feeding tolerance and attenuated muscle wasting, reinforcing the clinical relevance of preserving or restoring a functional microbiota (82). Adverse-event monitoring revealed no probiotic bloodstream isolates, but the authors excluded immunosuppressed and neutropenic subjects, emphasizing the importance of careful patient selection, a role that bedside nurses can operationalize through daily safety checklists.

Probiotic selection and prescription are governed by physician orders or multidisciplinary protocols; nurses are not authorized to independently choose or prescribe probiotics. The nurse-driven responsibilities include verifying the correct strain, ensuring cold-chain integrity, administering the preparation via enteral tube and monitoring for adverse events (e.g., probiotic-associated bacteraemia) using daily safety checklists (82).

Probiotic monotherapy has yielded mixed results. Mahmoodpoor et al (75) reported that Lactobacillus plantarum (American Type Culture Collection 202195) decreased VAP rates (11 vs. 27%, P=0.02) without bacteremia, whereas Cohen et al (83) documented Lactobacillus bloodstream infections genetically identical to the administered strain in three hematology-oncology patients, prompting early trial cessation. These discrepancies highlight the critical importance of host immune status, strain selection and administration route-variables that nurses can monitor in real time. For patients with complete butyrogenic collapse, FMT represents an emerging rescue strategy. Wei et al (84) described resolution of severe antibiotic-associated diarrhea and restoration of butyrate synthesis pathways in 9 ICU patients following single-dose FMT via nasoduodenal tube. Nursing responsibilities included donor-stool thawing under anaerobic conditions, 6-hourly stool-bank temperature audits and post-FMT surveillance for fever or increased vasopressor requirements. Although promising, FMT in critical care remains experimental; stewardship committees should embed nursing protocols for strain tracking and adverse-event reporting before wider adoption.

Traditional reliance on GRV has poor correlation with true gastric emptying and inadvertently reduces EN delivery. Two nurse-implemented protocols that replaced 4-hourly GRV aspiration with abdominal distension assessment and bowel-sound auscultation achieved a 22% increase in energy delivery without raising aspiration events (34,77). Integrating point-of-care ultrasound of the gastric antrum, validated by Valla et al (85) in ventilated children, adds objective quantification of gastric emptying and can guide prokinetic timing, indirectly enhancing substrate availability for microbial fermentation. Future quality metrics should therefore incorporate the proportion of daily energy target achieved, days without antibiotics and fecal or breath butyrate trends where feasible, thereby converting microbiota health into measurable nursing outcomes.

Successful translation demands structured education. A national survey revealed that only 34% of critical-care nurses could correctly define ‘synbiotic’ and <20% were aware of contraindications such as central venous catheter-related fungemia (86). Interactive workshops coupling microbiome science with practical skills (strain reconstitution, aseptic tube-feeding connection, adverse-event documentation) improved knowledge scores by 45% and increased fiber-enriched formula prescribing 3-fold (87). Inter-professional daily ‘gut rounds’ involving nurses, intensivists, pharmacists and dietitians further facilitate antibiotic de-escalation, fiber optimization and rapid response to probiotic-related bloodstream infection signals. Finally, unit governance must mandate electronic capture of probiotic batch numbers and linkage to infection-control databases to enable real-time traceability, an essential safeguard now recommended by European Society of Clinical Microbiology and Infectious Diseases and European Society for Clinical Nutrition and Metabolism guidelines (88,89).

A nurse-driven ‘gut bundle’ should consolidate evidence-based elements such as antibiotic stewardship, fiber-enriched EN and probiotic/synbiotic administration into a single, actionable protocol. For instance, the randomized trial by Seifi et al (82) demonstrated that synbiotic supplementation significantly improved enteral feeding tolerance and attenuated muscle wasting in critically ill adults, with nurses overseeing administration and monitoring for adverse events. Similarly, the meta-analysis by Koch et al (90) confirmed that fiber-supplemented EN reduced diarrhea and improved caloric delivery, particularly when initiated early. However, heterogeneity in fiber type (soluble vs. mixed) and dose (10–30 g/day) across trials limits generalizability. Notably, a recent meta-analysis by Huang et al (91) of pectin-supplemented formulas reported modest improvements in gastrointestinal tolerance but emphasized the need for patient stratification based on baseline microbiota profiles. Thus, bundle design must allow for personalized adjustments, with nurses trained to assess pre-illness dietary habits and antibiotic exposure history.

Effective implementation hinges on seamless collaboration between nurses, intensivists, pharmacists and dietitians. While nurses are pivotal in administering interventions, pharmacists play a critical role in validating probiotic strain selection and monitoring drug-microbe interactions. This inconsistency underscores the need for nurses to lead daily ‘gut rounds’ to reconcile discrepancies between prescribed antibiotics and microbiota-supportive therapies. For example, concurrent use of broad-spectrum β-lactams may negate benefits of Lactobacillus probiotics, as demonstrated in an adult ICU study where meropenem selectively depleted Firmicutes carrying butyrate-synthesis genes (47). Conversely, Venegas-Borsellino and Kwon (92) reported that soluble fiber administration during antibiotic therapy preserved butyrate-producing taxa, but only when paired with judicious antibiotic de-escalation. The relevance of antibiotic-microbiota interactions is further supported by metagenomic analyses in adult ICU patients, demonstrating that specific antibiotic classes differentially deplete butyrogenic taxa (47). These data advocate for nurse-initiated ‘antibiotic time-outs’ to align antimicrobial stewardship with microbiota preservation.

Despite clinical efficacy, patient and family acceptance of microbiota-targeted therapies remains low due to misconceptions about probiotics and fiber safety. A cross-sectional survey by O'Connor et al (93) found that 68% of UK parents viewed blended tube feeds (containing prebiotic fibers) as ‘risky’, citing fears of contamination and diarrhea. To counteract this, nurses must employ teach-back techniques to explain the mechanistic rationale: Fiber fermentation by gut commensals yields butyrate, which strengthens intestinal tight junctions and reduces FI risk. Notably, the ongoing LOME-PECT trial (NCT05923456), is evaluating whether low-methoxy pectin formulas improve gastrointestinal tolerance in ventilated adults. The trial protocol reported by Kashiwagi et al (94) included a preliminary, non-peer-reviewed finding that nurse-led education sessions improved enrollment rates by 22%; however, this result awaits confirmation in the final published trial. Visual aids depicting the ‘fiber-butyrate-barrier’ axis may further enhance comprehension, particularly when tailored to literacy levels.

Implementation is frequently hindered by logistical constraints (e.g., cold-chain storage for probiotics), knowledge deficits and institutional resistance to change. A 2024 survey of Indian neonatologists revealed that 55% of ICUs lacked refrigeration protocols for probiotic stocks, leading to 30% viability loss at point-of-care (95). To mitigate this, nurses can advocate for unit-based probiotic dispensing systems, akin to those used for biologicals. Knowledge gaps are equally critical: Only 34% of critical care nurses correctly identified synbiotic contraindications (e.g., immunosuppression) in a national assessment (86). Simulation-based training, as piloted by Casavant et al (96), improved nurse confidence in microbiome-informed care from 45 to 78% post-intervention. Finally, cultural resistance persists where FI is viewed as inevitable. Based on evidence from general ICU populations, Patel et al (97) reframed FI as a ‘preventable iatrogenic injury’. This principle has been successfully implemented in nurse-led studies conducted in general ICU settings, without device-specific restrictions (34,77).

Traditional FI metrics (e.g., GRV) correlate poorly with microbiota health. Instead, composite indicators such as ‘days without antibiotics’, ‘percentage of energy target achieved’ and fecal butyrate levels (via point-of-care testing) offer actionable feedback. In a single-center quality improvement project, integrating these metrics into nursing dashboards reduced FI incidence by 18% over 6 months (98). However, a critical limitation of the proposed 30-min butyrate assay is the absence of a clinically validated decision threshold. Although one study reported that a fecal butyrate concentration below 2 µmol/g within the first 72 h of ICU admission predicted 30-day mortality (AUROC=0.87) (99), this cut-off has not been prospectively validated to guide specific interventions for feeding intolerance, such as probiotic selection, fiber escalation or prokinetic therapy. Without such intervention-specific thresholds, the clinical utility of real-time butyrate measurement remains uncertain. However, the feasibility of fecal testing remains contentious: While Green et al (100) validated a 30-min butyrate assay, cost ($12/test), workflow disruption and the lack of actionable cut-offs limit adoption. Therefore, widespread implementation of point-of-care butyrate testing in routine ICU practice is currently premature. Proxy markers (e.g., low fecal pH correlating with butyrate abundance) may offer pragmatic alternatives pending technological advances.