Pediatrics [CONSTIPATION + FTPM]
Introduction
“Slow gut” is a general term we’re using to describe a category of diseases
that involve the bowel. Stratify this general concept into failure to pass
meconium (FTPM) seen in the first days of life and infrequent hard stools
in toddlers or older children.
For FTPM, anything that prevents stool from getting from the stomach to
the anus should be considered. Specifically, the obstructive diseases in
bilious emesis in the Emesis lecture should be considered. But the diseases
you should commit to memory are the three below. Usually 48 hours is the
cutoff for this. However, almost 99% of term kids pass stool by 24 hours
and 100% pass by 48 hours. The timing is delayed in premature infants. In
general, once you’ve hit 24 hours the odds are there’s something wrong
FTPM
Imperforate Anus
Meconium Ileus
Constipation
Voluntary Holding
Hirschsprung's
Hirschsprung's
Bilious emesis
Mom’s Mg, K
Medications,
Baby’s Mg, K
1) Imperforate Anus
The earliest and most obvious of causes of FTPM. Just look at it - there’s
no hole. This is why we NEVER take a baby’s first temp rectally. But
there’s a continuum of disease. Do a cross table X-ray on the prone child
with radiopaque perineal marking. This will give a relationship between gas
bubble and anus. Low lesions (closer to the anus) can be corrected via
dilation or a minor surgical procedure. There’s also a higher chance of
maintaining continence. High lesions (away from the anus) need a
colostomy with future correction. All patients need evaluation for
VACTERL and should undergo sacral ultrasound and X-ray, VCUG, NG
tube passage, and echocardiogram.
2) Meconium Ileus
Usually seen in patients with cystic fibrosis, it’s a collection of meconium
that too thick and viscous to pass as a result of pancreatic insufficiency.
Typical location is in the ileum - hence its placement in the “small bowel”
section. This can cause any combination of bilious vomiting or failure to
pass meconium. X-ray can show an area of obstruction (air-fluid levels)
with a gas-filled plug. Perform water-soluble contrast enema (like
gastrografin) to help breakdown the obstruction. Sometimes surgical
intervention is required. Complications include perforation which can lead
to meconium peritonitis (which is an emergency).
3) Hirschsprung’s
This is caused by absent ganglion migration to the Meissner and Auerbach
plexuses in the colon. This means no motility – the muscles are unable to
relax and contribute to peristalsis. It just so happens that it’s a migratory
issue, which means only the proximal colon (area with ganglions) is
effective. Regardless, the x-ray is the first step; it will show a dilated
proximal colon (normal) and a normal looking distal colon (abnormal).
There are two presentations; they drive the diagnostic step. The first is
failure to pass meconium, occurring in 90% of cases. It’s diagnosed with a
contrast enema, which shows a transition zone and is followed up by a
biopsy. The second, occurring in 10% of cases, presents with overflow
incontinence in the older child or a stool eruption after doing a digital
examination in the nursery. Anorectal manometry is done which shows
increased tone, followed by biopsy. Resect the affected area and connect
(pull-through procedure). Severe cases (perforation, full colon
involvement) require colostomy.
© OnlineMedEd. http://www.onlinemeded.org
Pediatrics [CONSTIPATION + FTPM]
4) Voluntary Constipation
The most common cause of constipation is voluntary holding. Whether to
avoid pain or simply due to embarrassment, kids may hold it in. The
longer they hold it the more water gets taken out of it - the harder it gets.
Because the colon is working, stool may sneak around and cause
intermittent diarrhea or encopresis. To get the kid unplugged (voluntary
may convert to involuntary) there may have to be a disimpaction in the
OR. Make sure to teach the child that holding it in is dangerous!
5) Additional Causes
Other Causes
There are other causes of small bowel obstruction leading to failure to pass
meconium that are covered under the Vomiting review as the presentation
can include any combination of failure to pass meconium and bilious
vomiting. These causes include duodenal atresia, malrotation/volvulus, and
distal intestinal atresia. See Vomiting for more information.
Medication-induced
Sometimes we do things that cause other issues. Failure to pass meconium
is no exception. Medications given to both mother and infant can affect stool
transit. Think of the mother with pre-eclampsia that received magnesium.
Think of the infant born with neonatal abstinence syndrome (narcotic
withdrawal) who is receiving opiates.
Metabolic-induced
Electrolyte derangements can contribute to decreased gut motility. Keep in
mind two “high” ones (hypercalcemia, hypermagnesemia) and two “low”
ones (hypoglycemia, hypokalemia). Also consider additional endocrine
causes such as hypothyroidism and adrenal insufficiency.
CONSTIPATION IN GENERAL
Overview
There are a multitude of criteria that can be used to define constipation
(Rome III is one). They’re not worth remembering as nobody agrees on a
unified definition anyway. Just remember that essentially you’re looking for
bowel movements associated with pain, straining, decreased frequency,
or incontinence. Constipation can be broken down into two etiological
categories: organic (underlying pathology) and functional (no underlying
medical pathology). A thorough history and physical will be the best way
to obtain a diagnosis. Ask about initial bowel movements as a history of
delayed meconium passage could points towards organic cause. Also ask
about stressors and history of previous continence as these could point
towards a functional cause.
Red flags include: fever, blood per
rectum, complete obstruction, failure to
thrive, and weight loss
© OnlineMedEd. http://www.onlinemeded.org