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Chapter 29

Pediatric Surgery

Eric Strauch

Charles W. Wagner

I Introduction

Pediatric surgery has evolved as a subspecialty for several reasons. First, infants and children differ from adults physiologically as well as anatomically. For example, the nutritional needs and fluid and electrolyte management for infants and children are not the same as those required for adults. Therefore, specialized knowledge is required for the care of pediatric surgical patients. Second, infants and children also differ to some extent with regard to the types of disorders that require surgical management. In infants, congenital malformations require prompt correction, and specialized knowledge is needed. The full discussion of specialized pediatric considerations is much too extensive to be covered in this chapter; therefore, only certain topics are discussed. For more complete information, the reader can consult standard textbooks on pediatric surgery.

II Congenital Hernias (see Chapter 2, III)

A Inguinal hernia

Repair of an inguinal hernia remains the most common general surgical procedure in the case of the child. The defect is caused by nonfusion of the processus vaginalis and not by a breakdown of the floor of the inguinal canal.

Incidence

Inguinal hernia occurs in 1%–3% of all children.

The hernia is on the right approximately 60% of the time, on the left approximately 30% of the time, and bilateral between 10% and 15% of the time.

The male:female ratio is 6:1.

In premature infants, the incidence is 1½ to 2 times greater.

The incidence of hernias is increased in patients with hydrocephalus who are treated with ventriculoperitoneal (VP) shunts, in patients with connective tissue disorders, and in infants and children on peritoneal dialysis.

Clinical presentation

An inguinal hernia is diagnosed in infancy, and approximately 35% of patients present before 6 months of age.

The classic history and clinical presentation are those of a mass or bulge in the groin, scrotum, or labia, which usually occurs during times of abdominal pain. The mass usually disappears after the straining or crying has been resolved, but it is for the most part easily reducible.

If no mass is present, the physician can feel the thickened spermatic cord, which represents the nondistended hernia sac. This cord has been described as the “silk glove” sign.

If no hernia is identified but the patient's history is both classic and reliable, most surgeons believe that surgery is indicated.

Incarceration

In boys , the risk associated with a hernia is the chance of incarceration of the intestine.

Intestinal ischemia and obstruction can occur.

With time, the entrapped bowel becomes edematous enough to compress the spermatic vessels and cause testicular ischemia with resultant damage or necrosis.

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The risk of incarceration in a premature infant is 2–5 times higher than in the older child.

In girls , incarceration of the ovary is more common than incarceration of the intestine. Although ischemia of the ovary may result, it does not usually occur.

Treatment includes reduction of the incarcerated hernia, hydration of the patient, and herniorrhaphy.

These steps should all be taken within 48–72 hours.

Reduction is performed with or without sedation by gentle, continuous pressure on the incarcerated intestine.

Most hernias in children will reduce, but if the hernia cannot be reduced, emergent repair, evaluation of the intestine, and resection of necrotic intestine needs to be performed. The chance of reducing necrotic intestine is very low.

Herniorrhaphy. A hernia should be repaired soon after it is diagnosed, unless a major medical reason prohibits the use of anesthesia. In most children, the hernia can be repaired with outpatient surgery. Premature infants may have apnea and bradycardia after surgery and require overnight admission for monitoring for these conditions. Small infants with lung disease can have their hernias repaired under spinal anesthesia.

Procedure. Herniorrhaphy in the child consists of identifying the sac, dissecting the spermatic structures free, and ligating the sac high at the internal ring of the inguinal canal. Floor repair is rarely needed.

Complications of the procedure include damage to the vas deferens, vascular injury to the testes, recurrence of the hernia, and iatrogenic cryptorchidism.

The recurrence rate is reported to be approximately 1%, and the highest frequency occurs in patients with incarcerated hernias, connective tissue disorders (e.g., Ehler -Danlos or Hunter's syndrome), or increased intra -abdominal pressure (VP shunts or peritoneal dialysis [PD] catheters).

Iatrogenic cryptorchidism occurs when the testicle has been mobilized from the scrotum but has not been properly replaced. Unlike regular cryptorchidism, in which the testes may later descend, the testes remain in the abnormally high position with iatrogenic cryptorchidism.

B

Diaphragmatic hernias are communications through the diaphragm that allow abdominal contents to migrate into the thoracic cavity.

Incidence. The incidence of this defect is 1 in 4,000 live births.

Etiology. Two underlying anatomic defects are common; both result from the failure of the surrounding tissues to fuse in utero.

The foramen of Bochdalek is a posterolateral diaphragmatic defect.

This hernia is the most common congenital hernia (Fig. 29 -1).

It occurs most often in the left hemidiaphragm and is bilateral in fewer than 10% of infants.

The foramen of Morgagni is an anterior diaphragmatic defect. It is much less common and generally results in less severe problems.

Diagnosis of herniation of abdominal contents into the thorax is based primarily on impaired ventilatory capacity. The earlier that respiratory distress is noted in the infant (especially if it occurs during the first 24 hours), the more severe will be the impairment and the worse the prognosis.

The physical examination reveals the following:

Tachypnea, dyspnea, use of accessory muscles for ventilation, cyanosis, and nasal flaring are evident.

Breath sounds are decreased or absent on the affected side.

Heart sounds are shifted away from the affected side.

Bowel sounds are heard in the affected hemithorax.

A scaphoid abdomen is caused by the migration of abdominal contents into the chest.

A chest radiograph shows signs typical of herniation.

A loculated gas pattern is found in the affected hemithorax.

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FIGURE 29-1 Bochdalek's hernia.

A mediastinal shift occurs away from the hernia.

Atelectasis occurs in the unaffected lung.

The nasogastric tube is found in the affected hemithorax after passage of the tube through the nose or mouth.

Preoperative management

Gastrointestinal decompression should be performed via a nasogastric or orogastric tube.

A pneumothorax in the unaffected hemithorax should be sought and, if present, treated with a chest tube.

Preoperative management is aimed at both respiratory insufficiency and pulmonary vascular hypertension.

Hypoxemia due to hypoplastic lung(s) causes acidosis.

Acidosis causes pulmonary vasculature to constrict, which decreases blood flow to the lung and increases the right -to -left shunt.

If hypoxemia and hypercarbia can be improved with routine ventilator methods, surgical repair should then proceed.

If acidosis with hypoxemia persists, preoperative use of extracorporeal membrane oxygenation (ECMO) should be considered.

The hernia can be repaired while using ECMO.

The use of nitric oxide (NO) is increasing as a step to improve hypoxemia. This agent is a potent pulmonary vasodilator and is mixed with the gases used in the ventilator. By dilating the pulmonary vasculature, the right -to -left shunt decreases.

Operative management is based on the following principles:

The herniated contents are reduced surgically back into the abdomen (through an abdominal incision), which can immediately relieve the distress.

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The hernia defect is repaired.

An exploratory laparotomy is carried out to diagnose associated congenital anomalies (intestinal malrotation is often associated with this hernia).

A chest tube can be inserted into the affected hemithorax but should not be placed on suction.

The infant's acid -base balance and respiratory function are monitored carefully.

A nasogastric tube is left to decompress the gastrointestinal tract.

Postoperative management is aimed primarily at maintaining adequate ventilation and perfusion and includes the following:

Respiratory support on a ventilator is given as needed, and arterial blood gases are monitored.

Atelectasis of either lung is treated, and the retained secretions are prevented.

Chest tube suction is used on the affected side to stabilize the mediastinum in the midline.

The patient is observed for contralateral pneumothorax and is treated rapidly if it occurs.

Adequate gastrointestinal compression is provided.

The abdomen is small and may not be able to hold all of the contents after reduction.

The loss of the “right of domain” of the abdominal contents greatly distends the abdomen and raises intra -abdominal pressures.

Abdominal distention significantly impairs both thoracic excursion and venous return from the lower body.

ECMO can also be initiated during postoperative care.

The oxygenator allows correction of hypoxemia and acidosis, thus decreasing the pulmonary vascular hypertension.

The patient is slowly weaned from ECMO so that normal pulmonary physiology can occur.

If NO is used, levels of methemoglobulin are monitored. If greater than 5, one must decrease the concentration of NO in the ventilator gas mix.

The use of diuretics to aid in fluid management is now being recognized as an important part of care in congenital diaphragmatic hernias.

The prognosis for the infant with a diaphragmatic hernia is a function of the preoperative severity and time of presentation of this hernia.

The immediate mortality rate is approximately 35%–40%.

The resolution of respiratory insufficiency in the postoperative period depends on the maturity of the contralateral lung and the control of pulmonary hypertension.

The ipsilateral lung is almost always hypoplastic when a diaphragmatic hernia is present and, therefore, does not aid in respiratory function during the immediate postoperative period.

If the infant survives, the lung eventually develops.

No permanent respiratory difficulties have been noted in later life once the acute pulmonary insufficiency has resolved.

Patients who have been treated with ECMO have a survival rate of 65%. Associated risks (e.g., bleeding, cerebral infarction, recurrent hernias) keep this modality from being used routinely.

Other therapeutic interventions being investigated are high-frequency ventilation (which prevents barotrauma to the already hypoplastic lung). NO acts as a potent pulmonary vasodilator.

III Abdominal Wall Defects

A Types

The two types of abdominal wall defects are gastroschisis and omphalocele. Although the abdominal contents are located outside of the peritoneal cavity in each type, the similarities (both developmental and therapeutic) end at that point.

Gastroschisis is an opening in the abdominal wall, immediately adjacent to the right of the umbilicus, which is located in the normal position.

During fetal development, the abdominal wall is completely formed, but the peritoneal cavity does not enlarge enough to hold the abdominal contents.

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The protruding viscera, which consist of the midportion of the small intestine, the spleen, the stomach, the colon, and occasionally the liver, has no protective covering.

The intestine is edematous, semirigid, leathery, and matted together as a result of chemical peritonitis.

Associated anomalies and syndromes are rare, and intestinal atresia is the most frequent (10% of cases) anomaly.

Omphalocele is an opening in the abdominal wall at the umbilicus.

It is caused by incomplete closure of the somatic folds of the anterior abdominal wall in the fetus.

Unless ruptured, a sac covers the extruded visceral contents, and no signs of chemical peritonitis appear.

The liver and small bowel are the organs that most commonly protrude through the defect.

The omphalocele may be a part of the pentalogy of Cantrell, which also includes:

Diaphragmatic hernia

Cleft sternum

Absent pericardium

Intracardiac defects

If the caudal folds are involved, exstrophy of the bladder or cloacal exstrophy is present.

Associated anomalies. Approximately 50% of these infants have one or more associated anomalies, including trisomies 13 and 18; Beckwith's syndrome; and cardiac, neurologic, and genitourinary malformations.

B

Prenatal diagnosis may be made by the use of ultrasonography. This visualization of deep structures aids in the diagnosis of associated anomalies and in prenatal counseling as well as in early post delivery management.

C

Preoperative management is similar in both disorders.

Gastrointestinal decompression, intravenous fluids, and antibiotics are instituted.

Protection of the abdominal contents is imperative, especially because the escape of moisture and heat is considerable in these patients.

The unruptured omphalocele is left intact and protected with a sterile dressing to prevent it from drying out.

Gastroschisis or a ruptured omphalocele is protected under a plastic covering (intestinal bag).

When the patient with gastroschisis has a small defect and a swollen intestine, kinking of the vascular supply may occur at the edge of the defect. This vascular compromise may be prevented by placing the infant on his or her side. Occasionally, emergent enlargement of the defect may be necessary to protect the blood supply to the intestine.

The outcome of gastroschisis is related to the condition of the intestines at the time of surgery.

D

Operative management differs slightly for the two disorders. However, the goal in both conditions is to cover the abdominal viscera either with prosthetic material or with the abdominal wall itself.

Gastroschisis. Closure is emergent, as there is no covering over the gastrointestinal tract to prevent heat and fluid losses. Primary closure involves decompressing the gastrointestinal tract and stretching the abdominal wall over the defect.

If the closure is too tight, the blood supply to the intestine, abdominal wall, or lower extremities is compromised. To avoid this complication, it is better to cover the exposed organs temporarily with prosthetic materials.

Preconstructed silicon ventral wall defect silo bags are now available for staged closure. They eliminate suture lines that leak, and they also have a spring anchoring device for ease of application.

Reduction can now usually be completed by days 5–7, thus minimizing the risk of infection.

A nasogastric tube is placed for decompression with either method of treatment.

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Omphalocele. A ruptured omphalocele, like a gastroschisis must be covered emergently. If the sac is intact, workup for associated defects such as a cardiac anomaly can be performed. The choice of procedures includes primary closure; staged repair; or, for an unruptured omphalocele, nonoperative management. The important factor is the size of the defect.

The greater the size of the defect, the less the peritoneal cavity has enlarged with adequate musculature of the abdominal wall; with a large defect, primary closure may involve too much tension.

An alternative method of treatment is to cover the defect with skin flaps, leaving the resultant

ventral hernia to be repaired later on.

Silastic sheeting or preconstructed silo bags can be used to stage the repair; by keeping tension on the prosthetic sac, the Silastic sheet stretches the abdominal wall enough to accommodate the herniated viscera.

As with a staged repair of gastroschisis, closure is usually accomplished within 10 days.

A prosthetic material such as Alloderm can be used to close the defect.

Nonoperative management is an alternative in patients with associated anomalies.

The sac is coated with silver sulfadiazine (Silvadene).

An eschar forms with subsequent coverage by granulation tissue.

The resultant ventral hernia can be repaired later on.

The risks associated with this method are rupture of the sac, requiring subsequent repair in an infected area; sepsis; undiagnosed intestinal atresia; and prolonged hospitalization.

As with gastroschisis, a nasogastric tube is placed for decompression.

E Postoperative management

With primary closure, respiration may be inhibited if the reduced abdominal contents compress the diaphragm. Patients may require muscular paralysis and mechanical ventilation until the abdomen stretches enough to accommodate the viscera.

Venous return may be compromised owing to compression of the inferior vena cava.

For vascular access, upper extremity veins should be used.

The legs may show signs of venous obstruction and resultant edema.

With staged repair, the patient needs to be observed after each daily reduction for both respiratory compromise and decreased venous return due to increased abdominal pressure.

Patients require hyperalimentation with both primary and staged repairs, because intestinal motility and absorption are slow to return.

After an unruptured omphalocele has been repaired, intestinal function is not as delayed as gastroschisis; however, hyperalimentation may still be needed.

F Prognosis

Gastroschisis , although more difficult to manage initially, has very few long-term problems.

Intestinal strictures may occur at the site of evisceration and will require resection later on.

The mortality rate , approximately 30% in the past, has improved greatly with the use of hyperalimentation and is now approximately 5%. Mortality is related to sepsis and the viability of the gastrointestinal tract at the time of surgery.