Infantile Hypertrophic Pyloric Stenosis (IHPS)

• Infantile hypertrophic pyloric stenosis (IHPS) is the most common cause of gastrointestinal obstruction in newborns and infants.
• Classic presentation includes nonbilious repeated emesis, progressing to projectile vomiting.
• IHPS occurs in 2 to 3 per 1000 live births, more common among white males.
• IHPS is most common among first-born males, with a male to female ratio of 4:1.
• Typical age of diagnosis is 3 to 6 weeks but can manifest as late as 12 weeks of age.
• Over 90% of infants with pyloric stenosis do not have associated pathologic conditions.
• Initial therapy focuses on optimizing fluid volume and electrolyte status.
• Surgery is not performed on an emergency basis.
• Preoperative management of fluid, electrolyte, and acid-base imbalances is imperative for patient stability.

Pathophysiology

• Pyloric stenosis is due to thickening of the smooth muscle of the pyloric valve, located at the junction between the stomach and small intestine.
• The pathologic process is associated with a cleft palate and gastroesophageal reflux.
• Depending on the degree of gastric outlet obstruction, digestive contents are unable to move normally into the duodenum.
• Increased intragastric pressure results in vomiting immediately after feeding.
• Newborns are predisposed to rapidly developing hypovolemia, gastric aspiration, and electrolyte abnormalities, most commonly hypokalemic, hypochloremic, and metabolic alkalosis.
• Vomiting leads to a decrease in fluid volume intake.
• High concentrations of hydrogen and chloride are present in gastric fluid that is lost.
• A possible relationship links thickening of the muscle of the pylorus to a deficiency in nitric oxide synthetase production, though the etiology of pyloric stenosis is unknown.
• Pyloric stenosis may be a medical emergency due to fluid loss, electrolyte, and acid-base imbalances caused by repeated emesis over several days.

Preoperative Strategy

• An initial fluid bolus with crystalloids between 10 and 20 mL/kg, depending on the severity of dehydration and the patient's preoperative medical condition.
• Fluids 1.5 to 2 times maintenance with 5% dextrose and 0.25% normal saline with potassium chloride 2 to 4 mEq/100 mL only if UOP is greater than 1 mL/kg/hr.
• Repeat blood gas measurements to ensure improved metabolic alkalosis with pH between 7.30 and 7.50 and sodium bicarbonate less than 30 mmol/l.
• Repeat electrolytes to ensure stable sodium and potassium levels.
• Check urine dipstick to assess specific gravity to be less than 1.02.
• Ensure weighing of diapers for UOP greater than 1 mL/kg/hr.
• Discuss antibiotic administration with surgeon; cefazolin 25 mg/kg.

Surgical Procedure

• Pyloromyotomy can be performed laparoscopically, endoscopically, or open via a periumbilical or right upper quadrant incision.
• The laparoscopic technique utilizes a periumbilical telescope and two incision sites.
• Surgeons may make the incision in the duodenum that extends toward the stomach or from the stomach toward the duodenum to adequately spread the pyloric muscle.
• The open technique uses a small incision in the skin on the anterior abdominal wall.
• The layer of thickened muscle is separated.
• The avascular part of the pylorus is identified, and a longitudinal incision is made to expose the mucosa.
• The separated muscle is brought up to the serous membrane, at which point closure of the area is initiated.
• The laparoscopic method allows quicker return to full feedings and has been associated with a more rapid hospital discharge compared with the open technique.

Intraoperative Period

• Rapid sequence induction (RSI) with cricoid pressure is the most suitable induction technique.
• These patients have a gastric outlet obstruction and are at increased risk for aspiration.
• Stomach decompression with an orogastric tube is recommended to minimize the risk for aspiration.
• Atropine 0.02 mg/kg (0.1 mg minimum) is administered before the induction of anesthesia to inhibit parasympathetic predominance resulting in bradycardia.
• Preoxygenation for several minutes followed by IV induction with propofol and rocuronium is indicated.
• Fentanyl may also be used to attenuate the response to laryngoscopy.
• If a difficult intubation is anticipated, an awake intubation should be planned.
• Surgical time for pyloromyotomy, regardless of technique, is between 30 and 60 minutes.
• If the surgical time is greater than 30 minutes, muscle relaxation may be maintained.
• An inhalation agent such as sevoflurane and air/O2, is an appropriate option for maintenance.
• Small amounts of opiates are considered to minimize the risk for postoperative apnea.
• Communication with the surgeon in relation to wound infiltration with local anesthetic should be discussed to guide the plan for pain management.
• The abdominal contents are suctioned before awakening.
• Ondansetron is administered to decrease the potential for postoperative nausea and vomiting.
• Neostigmine and atropine are administered on a per kilogram weight basis for reversal of the muscle relaxant.
• The patient should be extubated when fully awake and meeting accepted extubation criteria.
• Increased risk for aspiration exists due to full stomach precautions.
• Preoperative medication to decrease gastric contents, gastric decompression, and placement of an endotracheal tube may decrease the risk, but do not prevent aspiration.
• Active inspiration and emesis may allow the passage of contents around the endotracheal tube, especially because uncuffed tubes are commonly used in this population.
• Initiation of the celiac reflex results from mesenteric traction stimulating afferent vagal nerve endings.
• Parasympathetic nervous system predominance will lead to bradycardia, apnea, and hypotension.
• Because neonates are dependent on a rapid heart rate to establish cardiac output, bradycardia results in decreased tissue perfusion and, potentially, cardiac arrest.
• The response from the celiac reflex usually resolves when the surgeon is asked to release tension on the mesentery or pressure on the intraabdominal organs or peritoneal cavity.
• Atropine can also be administered to help extinguish the celiac reflex response or treat recurring episodes of bradycardia.
• Duodenal perforation occurs in less than 5% of cases performed by pediatric surgeons.
• If the procedure is performed laparoscopically, the surgeon may decide to convert the case to open for repair.

Postoperative Period

• Potential postoperative complications include respiratory distress, hypoxemia, hypercarbia, hypoglycemia, hypothermia, pain, recurrent vomiting, electrolyte abnormality, and inadvertent bowel perforation resulting in septicemia.
• Two potential reasons exist for postoperative respiratory depression.
• Hypothermia is common among neonates and infants due to their increased body surface area and small amount of subcutaneous fat tissue.
• Maintain a warm environment, cover the head, and utilize forced-air warming blankets intraoperatively and postoperatively.
• This patient population does not possess the concentration of muscle needed to shiver to increase heat production.
• If hypothermia exists in neonates and young infants, nonshivering thermogenesis occurs as blood is shunted to anatomic areas where brown fat exists.
• The triglycerides that comprise the brown fat will be metabolized, and this process liberates heat.
• Metabolic acidosis can rapidly occur due to the formation of acetone, B-hydroxybutyric acid, and acetoacetic acid.
• The presence of hypoglycemia should be ruled out if apnea is noted in the postoperative period.
• Patients should receive IV fluids with dextrose until they are advanced to full feedings.
• Restarting feedings 8 hours after surgery is common.
• The estimated pain score that is associated with pyloromyotomy is 4 to 5 on a 10-point scale.
• Acetaminophen 10 to 15 mg/kg every 4 to 6 hours either by mouth or per rectum is a common treatment for postoperative pain management.
• A caudal block can also be performed.