Induction of peritoneal adhesions with small intestinal ischaemia and distention in the foal.

This study tested whether two types of surgical injury—intestinal distension and temporary loss of blood supply—cause peritoneal adhesions in foals, and described the tissue changes that follow. Both methods reliably produced adhesions and rapid damage to the intestinal surface lining, with inflammation, fibrosis, and partial re-lining by new mesothelial-like cells over 10 days.

What question did the study ask and why does it matter?

• Whether controlled small-intestinal distension or transient ischaemia can reproducibly induce peritoneal adhesions in foals.
• Why it matters: Peritoneal adhesions are a major postoperative and post-colic complication in equine patients, leading to recurrent colic, obstruction, and need for repeat surgery. Reliable models and a clearer timeline of injury and repair are essential for testing preventive strategies.

Study design and methods

• Animals: 22 foals assigned to experimental groups (intestinal distension or intestinal ischaemia) plus a control group with no bowel occlusions.
• Injury models:
  • Distension: A distal small-intestinal segment was occluded intraluminally (without compromising mesenteric vessels) and distended in situ with lactated Ringer’s solution to a constant pressure of 25 cm H2O for 2 hours.
  • Ischaemia: Total vascular occlusion of an identical bowel segment for 70 minutes, followed by reperfusion.
• Sampling timeline:
  • Serosal (outer intestinal surface) biopsies before the procedure (baseline).
  • Immediately after the occlusion/distension period.
  • After 60 minutes of reperfusion (for both groups; distension segments also experienced reperfusion once occlusion was released).
  • Terminal collection: All foals euthanized 10 days post-surgery for histological and ultrastructural (electron microscopy) evaluation.
• Comparators: Similar serosal biopsies were obtained from control foals; control segments were isolated/manipulated but not occluded, allowing assessment of effects of surgical handling alone.

Key findings

• Immediate surface injury:
  • Mesothelial denudation (loss of the protective peritoneal lining) was present histologically immediately after the occlusion procedures in the experimental segments.
  • Some degree of serosal fibrosis also developed in most control segments by 10 days, implying that surgical isolation/manipulation can be injurious on its own.
• Inflammation and oedema:
  • Ischaemia group: Serosal oedema and cellular infiltration became evident after reperfusion (i.e., a reperfusion-associated inflammatory surge).
  • Distension group: Oedema and inflammatory cell infiltration were already present immediately after the 2-hour distension period.
• Adhesion formation:
  • All experimentally injured foals developed bowel-to-bowel and bowel-to-mesentery adhesions involving the treated segments by day 10.
• Tissue remodeling and repair:
  • Fibrous tissue formed on the outer aspect of the original serosa (serosal fibrosis), consistent with maturation of provisional fibrin into collagenous adhesions.
  • New mesothelial-like cells were present on the surface of this fibrous tissue in some areas, indicating partial re-mesothelialization.
• Age-related control differences:
  • Control foals under 30 days old showed mesenteric contraction and thickening of the isolated segment.
  • Control foals older than 30 days showed minimal to no mesenteric thickening or contraction.

Interpretation and mechanisms

• Either mechanical distension or transient ischaemia that denudes the mesothelium is sufficient to trigger adhesions in foals.
• Distension alone (at 25 cm H2O for 2 hours) produced immediate serosal inflammation and oedema, showing that luminal overpressure and stretch can injure the peritoneal surface without primary vascular compromise.
• Ischaemia-reperfusion injury likely amplified inflammation through oxidative stress and leukocyte recruitment, explaining the post-reperfusion surge in oedema and cellular infiltration.
• The sequence observed—mesothelial loss ➝ fibrin deposition ➝ cellular infiltration and oedema ➝ collagenous fibrosis ➝ partial re-mesothelialization—is characteristic of adhesion pathophysiology.
• Serosal fibrosis seen even in controls underscores the contribution of surgical handling and tissue isolation to peritoneal injury in foals.

Age-related observations in controls

• Stronger mesenteric reactive changes in foals under 30 days suggest developmental differences in peritoneal and mesenteric responsiveness, healing, or baseline extracellular matrix turnover.
• Older foals (>30 days) exhibited less mesenteric reactivity under similar manipulation, hinting that very young foals may be at higher inherent risk for adhesion-promoting responses.

Clinical implications for foal surgery and colic

• Intestinal distension encountered during obstructive colic can itself be a potent driver of peritoneal injury and adhesions, even without overt vascular compromise.
• Surgical strategies should prioritize:
  • Minimizing intestinal overdistension (gentle decompression; avoiding high intraluminal pressures).
  • Limiting duration of vascular occlusion and handling time.
  • Meticulous, atraumatic tissue handling to preserve mesothelium.
  • Considering anti-adhesion measures immediately after recognized mesothelial injury and at reperfusion.
• Awareness that very young foals may react more vigorously to manipulation should guide perioperative planning and prophylaxis.

Strengths and limitations

• Strengths:
  • In vivo foal model directly relevant to equine practice.
  • Standardized injuries with defined pressure and ischaemia durations.
  • Serial biopsies capturing immediate and early reperfusion changes, plus 10-day outcomes with histology and ultrastructure.
• Limitations:
  • Small sample with unspecified allocation per group limits statistical inference.
  • 10-day endpoint may not reflect long-term adhesion remodeling or clinical sequelae.
  • Adhesion severity/extent not quantified with a standardized scoring system in the abstract.
  • Evidence of serosal fibrosis in controls indicates potential confounding from surgical manipulation.

Future directions

• Define pressure and time thresholds for “safe” distension and the kinetics of mesothelial repair in foals.
• Test barrier agents, fibrinolytics, anti-inflammatory or antioxidant strategies timed to mesothelial denudation and reperfusion.
• Investigate age-dependent differences in peritoneal healing biology and tailor prophylaxis for neonates vs older foals.
• Extend follow-up to assess adhesion maturation, breakdown, and long-term clinical outcomes.

Key takeaways

• Both 2 hours of controlled intestinal distension and 70 minutes of total ischaemia reliably produced adhesions in foals.
• Mesothelial denudation occurs rapidly and appears central to adhesion formation; distension causes immediate serosal inflammation, while ischaemia triggers a strong post-reperfusion response.
• Even surgical manipulation without occlusion can induce serosal fibrosis, emphasizing the need for gentle handling.
• Very young foals may be more reactive to manipulation, potentially increasing adhesion risk.