Meconium Retention

Meconium consists of digested amniotic fluid, glandular secretions, mucus, bile and epithelial cells, is greenish black to light brown, has little odor and has a tarry consistency. It is usually first seen to be evacuated from the foal within 3 hours after birth.

Etiology

• High prevalence in males suggests a narrowed pelvis plays a role.
• Meconium is retained in the large colon (high retention) or in the rectum - near the pelvic inlet (low retention).
• Time of passage is not the determinate of the condition but rather the difficulty or discomfort associated with attempts at passage.

Clinical Signs

• Develops 6-24 hours following birth.
• Restlessness, attempts to defecate, swishing or ‘flagging’ of the tail, walking around the stall, tail elevation and straining.
• Advanced signs are colic pain, lying down and getting up, rolling, and lying upside down. These signs are usually associated with a high retention.
• May appear to be attempting to urinate frequently.

Diagnosis

Diagnosis is based on clinical signs and, with a low impaction, by manual palpation of a firm mass via a well lubricated finger in the rectum of an adequately restrained foal.

Persistent signs of recurrent pain with lack of passage of the lighter color milk stool in a less than 36 hour foal are suggestive.

• Persistent, unrelenting pain should be investigated with an abdominal ultrasound, abdominal paracentesis, hemogram and abdominal radiography. (See Chapter 50 - Colic in the Neonatal Foal)
• Differentials include colon torsion, intussusception, volvulus of the small intestine, enteritis, atresia coli, lethal white syndrome, diaphragmatic hernias with bowel strangulation, enteritis, ruptured bladder and cystitis.

Treatment

Meconium retention

• Responds to one or two pints of warm soapy water administered per rectum through a soft, flexible tube by gravity flow.
  • Use caution to avoid mucosal trauma with a tube in the rectum.
  • Forceps or firm metal instruments to grasp the meconium is not recommended by the authors due to risk of trauma and mucosal penetration.
  • Repeated enemas of 3 or more are often not rewarding.
• 4% Acetyl-cysteine^1-3
  • The acetyl-cysteine breaks down the mucoid component of meconium. Works best at pH 7-8.
  • Medical treatment for refractory meconium retention has been very successful in our hands.¹
  • Can use the sterile MucomystTM (Bristol Laboratories, Evansville, IN 47721) or powdered N-Acetyl-L-Cysteine if available.
  • Solution preparation from powder: add 1.5 level tablespoons (20 gm) of baking soda (NaCO3) powder to 200 ml of water and then add 8 gms of acetyl-cysteine (1 packed tablespoon). It makes a pH 7.6 solution. Editorial Comment - watch out for hypernatremia with the baking soda in some sick foals (Thanks Jon P)
  • Solution preparation from MucomystTM - add 40 ml of the 20% solution (10 ml vials) to 160 ml of water to make the 4% solution. ​​​​​
    ​​Editorial Comment -  I prefer this over making out of powdered acetyl cysteine.
    • This costs approximately $30.00.
    • Solution is pH balanced.
• Administration
  • Restrain foal; ± sedation.
  • Insert a size 30 French FoleyTM catheter with 30cc balloon (Argyle-Division of Sherwood Medical, St. Louis, MO 63103), into the rectum approximately 1-2 inches.
  • Inflate balloon on end of catheter - slowly. iv. 
  • Administer 4-8 oz (120-240 ml) of 4% acetyl-cysteine slowly.
  • The FoleyTM catheter allows retention of the enema - keep in for up to 45 minutes, then deflate balloon, remove catheter.
  • May repeat enema in 1 hour.
  • May require 1-3 hours to soften meconium and pass stool.
• Still a problem, the two acetyl-cysteine enemas have not worked now what? 
  Use a plastic ‘weed wacker’ (strimmer) line (smooth, not serrated) the kind used to cut weeds on a machine (Figure 1). Cut the ‘plastic line’ about 14 inches in length. Bend it to form a loop at one end. Insert the bent part of the loop into the rectum and pass so it goes through the pelvic inlet and then the loop expands around the meconium. Pull it back and a big wad of meconium will be on the end within the loop (Figure 2). Repeat as needed. Use lube. If the foal’s rectum becomes very swollen may need one dose (2 mg) dexamethasone and use antibiotics because bacteria may translocate across the inflamed gut. Use flunixin for pain.

High meconium retentions

Others have suggested administration, via nasogastric tube, of either mineral oil (8 oz; 240 ml), milk of magnesia (4 oz; 120 ml) or castor oil (2 oz; 60 ml). Editorial Comment - see low retention therapy

• Intravenous fluid therapy for hydration or to increase fluid in the colonic lumen can be beneficial. 1-2 liters of warmed lactated Ringer's IV.
• Pain control can be attempted with butorphanol or, if necessary, flunixin (Banamine®, Schering) at 1.1 mg/kg once daily.

Foals with persistent low grade pain and lack of improvement with medical treatment may require surgery in a low percentage of cases.

Prevention

• Early post birth administration of a small enema such as Fleet® (C.B. Fleet) will often soften the first passed stool but have no effect on a high meconium retention or subsequent accumulation of meconium in the pelvic inlet.
• Allow early exercise
• CAUTION -
  • Large volumes of any solution used as an enema can produce severe electrolyte imbalance.
  • Water intoxication with severe hyponatremia and neurologic signs has been observed with large volume water enemas.
  • Fatal hyperphosphatemia has occurred in human infants with phosphate retention enemas.