Necrotizing Enterocolitis (nec)

Introduction

NEC is a syndrome of acute intestinal necrosis. The etiology is unknown and pathogenesis is complex and multifactorial. It is the most common serious surgical disorder among infants in the NICU & a significant cause of neonatal morbidity and mortality. It is seen in 2.5% of all NICU admissions and has an overall mortality rate of 30-40% with mortality increasing to more than 80% in neonates less than 1 kg.

Pathology: Common sites are the terminal ileum and ascending colon.

Predisposing Factors

• Prematurity: Seen commonly at a mean gestational age of 30-32 wks. (AGA). It is the single greatest risk factor. Incidence of NEC increases as gestational age decreases.
• In Term infants & near terms: Conditions predisposing to decreased gastrointestinal oxygen delivery
• Perinatal asphyxia (lower 1 minute apgar score)
• Lower cord PH (acidosis)
• Polycythemia
• RDS/apnea
• Shock
• Umbilical artery catheterization
• Early or large volume nasogastric feeding
• Congenital heart disease

Pathogenesis

• Role of immature Gastrointestinal host defenses
• Role of infectious agents & bacterial toxins
• Role of inflammatory mediators
• Role of oxygen radicals & ischemia reperfusion injury

Clinical Staging Of NEC

Clinical Features

• Symptoms may appear within 96 hrs after initiation of feeds
• Majority of cases occur within first 10 days of life
• Onset may be insidious/explosive/delayed
• Earliest signs: abdominal distension, retention of milk in a sick-looking LBW infant.
• Clinical triad: Abdominal. Distension + GI bleeding + Pneumatosis intestinalis
• Signs of functional Intestinal obstruction: Abdominal distension, progressive decreased peristalsis, bilious vomiting, hematemesis and blood in stools
• Signs of peritonitis & perforation: Ascites, erythema & edema of abdominal wall, localized mass or rigidity
• Systemic signs respiratory distress, apnea, bradycardia, lethargy, thermal instability, irritability, poor feeding, hypotension (shock), oliguria, bleeding diathesis, sclerema

Investigations

• Serial X-rays of abdomen: Fixed bowel loop, appearance of mass, pneumatosis intestinalis, portal or hepatic venous air, pneumoperitoneum
• Stool examination: Occult blood, reducing substances for unabsorbed lactose, culture for aerobic/anaerobic bacteria
• Blood: Electrolytes, hematocrit, coagulation status, culture, ABG. Watch for triad of thrombocytopenia, severe refractory hyponatremia and acidosis.
• USG: Micro bubbles of gas in portal vein
• Hydrogen breath test

Management

Differential Diagnosis

• Pneumonia & sepsis

• Surgical abdominal catastrophes
  • Malrotation with obstruction
  • Malrotation with midgut volvulus
  • Intusussception
  • Ulcer
  • Gastric perforation
  • Mesenteric vessel thrombosis

• Infections enterocolitis with diarrhea
• Inherited metabolic disease
• Feeding intolerance
• Systemic candidiasis

Prevention

Corticosteroids - Prenatal/Postnatal

• Lower incidence of NEC in mothers of preterm who received dexamethasone antenatally.

Feeding regimen

• Breast feeding
• Acidified feeds
• Small iso-osmolar feeds with gradual increase in feeds

Oral Immunoglobulins (IgA & IgG)

• Enhances intestinal immune defenses

Reduce incidence of:

• Preterm delivery
• Prevent predisposing factors

Prognosis

Recurrent NEC is 4%

Sequelae

• Strictures (20%) most common in large bowel
• Enteric fistulas
• Short bowel syndrome (following surgery)
• Malabsorption & chronic diarrhea
• Dumping syndromes: loss of terminal ileum
• Fluids electrolyte losses (with ileostomy)
• Parenteral nutrition associated hepatic disease
• Developmental delay