Saturday, December 19, 2009

65 - Hypertrophic Pyloric stenosis

The majority of infants vomit. Because infant vomiting is so common, it is important to differentiate between normal vomiting—as occurs in almost all infants, to some degree—and abnormal vomiting, which may be indicative of a potentially serious underlying disorder. The color of the emesis and the child's overall condition must be assessed. Vomit that looks like feeds and comes up immediately after a feeding is almost always gastroesophageal reflux. This may or may not be of concern, as described earlier. Vomiting that occurs a short while after feeding, or indeed vomiting that projects out of the baby's mouth, may be indicative of pyloric stenosis. By contrast, vomit that has any green color in it is always worrisome. This may be reflective of intestinal volvulus, an underlying infection, or some other cause of intestinal obstruction.

Clinical Manifestations :

The ability to provide timely diagnosis and treatment of infants with hypertrophic pyloric stenosis (HPS) is another milestone in the history of pediatric surgery. HPS occurs in approximately 1 in 300 live births and originally was believed to occur in first-born males between 3 and 6 weeks of age. Subsequent studies determined that this was a statistical error; investigators did not account for the incidence of first-born males as a group. However, children with HPS outside of this age range are commonly seen, and the cause of HPS has not been determined. Studies have shown that HPS is found in several generations of the same family, which suggests a familial link. Administration of erythromycin in early infancy was also thought to be linked to the subsequent development of HPS, but rates of HPS have not decreased with the decline in the use of erythromycin, so this may also have been an erroneous conclusion.

Infants with HPS present with nonbilious vomiting that becomes increasingly projectile over the course of several days to weeks. Eventually, the infant develops almost complete gastric outlet obstruction and is no longer able to tolerate even clear liquids. Despite the recurrent emesis, the child normally has a voracious appetite, which leads to a cycle of feeding and vomiting that invariably results in severe dehydration if the condition is untreated. Jaundice may occur in association with HPS, although the reason for this is unclear. Particularly perceptive caregivers will mention that the infant is passing less flatus, which provides a further clue that gastric outlet obstruction is complete.

Infants with HPS develop a hypochloremic, hypokalemic metabolic alkalosis. The urine pH is high initially but eventually drops because hydrogen ions are preferentially exchanged for sodium ions in the distal tubule of the kidney as the hypochloremia becomes severe. The diagnosis of pyloric stenosis usually can be made on physical examination by palpation of the typical "olive" in the right upper quadrant and the presence of visible gastric waves on the abdomen. When the olive cannot be palpated, ultrasonography can diagnose the condition accurately in 95% of patients. Criteria for ultrasonographic diagnosis include a channel length of greater than 16 mm and pyloric thickness of greater than 4 mm.

Treatment :

Pyloric stenosis is never a surgical emergency, although the dehydration and electrolyte abnormalities may present a medical emergency. Fluid resuscitation with correction of electrolyte abnormalities and metabolic alkalosis is essential before induction of general anesthesia for operation. For most infants, administration of fluid containing 5% dextrose and 0.45% saline with 2 to 4 mEq/kg of added potassium at a rate of approximately 150 to 175 mL/kg for 24 hours will correct the underlying deficit. It is important to ensure that the child has an adequate urine output (greater than 1 mL/kg per hour) as further evidence that rehydration has occurred. After resuscitation, a Fredet-Ramstedt pyloromyotomy is performed. The procedure may be performed using an open or laparoscopic approach. Open pyloromyotomy is performed through either an umbilical or a right upper quadrant transverse abdominal incision. The former route is cosmetically more appealing, although the transverse incision provides easier access to the antrum and pylorus. In recent years, the laparoscopic approach has gained great popularity. Two randomized trials have demonstrated that both the open and laparoscopic approaches may be performed safely with equal incidence of postoperative complications, although the cosmetic result is definitely superior after the laparoscopic approach. Whether performed using an open or laparoscopic approach, surgical treatment of pyloric stenosis involves splitting the pyloric muscle until the submucosa bulges upward. The incision begins at the pyloric vein of Mayo and extends onto the gastric antrum; it typically measures between 1 and 2 cm in length. Postoperatively, IV fluids are continued for several hours, after which an oral electrolyte solution (Pedialyte) is offered, followed by formula or breast milk, which is gradually increased to 60 mL every 3 hours. Most infants can be discharged home within 24 to 48 hours after surgery. Recently, several authors have shown that ad lib feedings are safely tolerated by the neonate and result in a shorter hospital stay.

The complications of pyloromyotomy include perforation of the mucosa (1 to 3%), bleeding, wound infection, and recurrent symptoms due to inadequate myotomy. When perforation occurs, the mucosa is repaired with a stitch that is placed to tack the mucosa down and reapproximate the serosa in the region of the tear. A nasogastric tube is left in place for 24 hours and taped securely to prevent it from reinjuring the repaired mucosa. The outcome is generally very good.

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