Abdominal wall defects

A 2-day-old, 3-kg neonate, born at 36 weeks’ gestation, was brought to the operating room for surgical repair of an abdominal wall defect. The defect was at the base of the umbilicus and had a membranous covering.

What are the differences between gastroschisis and omphalocele?

Gastroschisis and omphalocele differ in their embryologic origin, location, and associated congenital anomalies. Fetal ultrasonography during the first trimester can distinguish the two defects from each other. Specificity for identifying gastroschisis and omphalocele by ultrasound is 95%, but sensitivity is only 60%–75%. Maternal alpha fetoprotein (AFP) levels may suggest a diagnosis of omphalocele or gastroschisis. High levels of AFP obtained during amniocentesis are associated not only with neural tube defects but also with abdominal wall defects.

At 5–10 weeks of gestational age, the midgut is extruded into the extraembryonic coelom. By 10 weeks of gestational age, the midgut normally returns to the abdominal cavity. Omphalocele results from failure of intestinal contents to migrate from the yolk sac into the abdominal cavity. Amnion covers the omphalocele and protects the abdominal contents from infection and loss of intracellular fluid. The bowel is morphologically and usually functionally normal. Omphalocele is located at the base of the umbilical cord and includes not only the intestines but also often parts of the liver and other organs. Omphalocele has a high association with congenital anomalies such as cardiac, craniofacial, and urologic defects and chromosomal abnormalities. Omphalocele associated with macroglossia, organomegaly, hypoglycemia, and mental retardation is known as Beckwith-Wiedemann syndrome. Omphalocele is also associated with advanced maternal age. Most mothers of infants with omphalocele are >30 years of age.

In contrast to omphalocele, gastroschisis develops later in fetal life, after the intestines have returned to the abdominal cavity, and has a higher incidence of prematurity. Gastroschisis develops from occlusion of the omphalomesenteric artery, resulting in ischemia and atrophy of abdominal wall layers. The abdominal wall defect, which is commonly located to the right of the umbilicus, permits abdominal viscera to herniate. The degree of herniation outside the peritoneal cavity varies from slight to major. There is no membranous covering of the intestines in gastroschisis resulting in loss of extracellular fluid and risk of infection. The intestines are edematous, dilated, inflamed, and functionally abnormal. Gut malrotation and volvulus are associated with gastroschisis. Gastroschisis is a neonatal emergency that requires immediate or urgent surgical intervention. Risk factors for gastroschisis include maternal age <20 years, maternal cigarette smoking, maternal illicit drug use, and maternal use of over-the-counter vasoactive drugs. Although no congenital anomalies are associated with gastroschisis, intestinal abnormalities such as malrotation, volvulus, and atresia can occur ( Table 59-1 ).

TABLE 59-1

Comparison of Omphalocele and Gastroschisis

Omphalocele Gastroschisis
Etiology Failure of gut migration from yolk sac to abdominal cavity Occlusion of omphalomesenteric artery
Incidence 1:3000–1:10,000 1:15,000–1:30,000
Epidemiology Advanced maternal age Young maternal age
Associated with maternal smoking and illicit drug use
Gender Male > Female Male = Female
Location Base of umbilical cord Periumbilical (usually to the right of umbilical cord)
Peritoneal covering No peritoneal covering
Anomalies High association with congenital anomalies Malrotation
Beckwith-Wiedemann syndrome Volvulus
Chromosomal abnormalities Atresia

What are the preoperative concerns for these two defects?

Management of neonates with these defects preoperatively focuses on reducing fluid losses and preventing infection, hypothermia, and trauma to the viscera. A warm moistened sterile dressing should be applied to the exposed viscera, and a sterile clear plastic bag should envelope the lower body of the infant to minimize temperature and fluid losses.

Neonates with abdominal wall defects are assessed for associated congenital anomalies, particularly cardiac and urologic problems. For preterm infants, respiratory abnormalities should be ascertained. Adequate intravenous access is established for fluid resuscitation. An arterial catheter may be necessary for frequent blood sampling, and a central venous catheter may be used to aid in fluid management. Significant electrolyte imbalances and fluid deficits should be corrected preoperatively. Neonates with gastroschisis may require multiple boluses of 20 mL/kg of balanced salt solution to replace evaporative and third space losses. Albumin is occasionally required for intravascular volume expansion.

How would you manage this neonate intraoperatively?

The operating room should be warmed, and a forced air warming blanket should be placed on the operating room table. Standard American Society of Anesthesiologists monitors should be placed, and gastric decompression should be performed to prevent distention and aspiration. A rapid-sequence induction with cricoid pressure followed by intubation or an awake intubation should be performed. The choice of intravenous induction agent depends on the medical condition and volume status of the neonate. Muscle relaxation can be achieved with either succinylcholine or a double dose of rocuronium (1.2 mg/kg). When succinylcholine is administered, many anesthesiologists precede it with an anticholinergic (e.g., atropine) because neonates have an immature sympathetic nervous system putting them at risk of developing bradycardia during suctioning, induction, and laryngoscopy and after succinylcholine administration. Rocuronium provides adequate intubating conditions within 60–90 seconds, although significant desaturation may occur requiring positive pressure breaths before intubation. Laryngoscopy is performed with either a Miller No. 0 or 1 laryngoscope blade, and a 3.0–3.5 uncuffed tracheal tube or a 3.0 cuffed tube is placed. An air leak of 20–30 cm H 2 O is desirable.

Nitrous oxide should be avoided because it diffuses into intestines (closed space) faster than nitrogen escapes into the circulation, resulting in intestinal distention. A mixture of air and oxygen should be used to maintain oxygen saturation between 95%–100% and arterial oxygen tension (PaO 2 ) <100 mm Hg.

Intraoperative fluid management should consist of maintenance fluid, replacement of third space loss, and blood to match losses as needed. Maintenance fluid volume is determined based on the patient’s weight ( Table 59-2 ).

TABLE 59-2

Maintenance Fluid Requirement

Patient’s Weight (kg) Hourly Fluid Requirement
<10 4 mL/kg per hour
11–20 40 mL + 2 mL/kg per hour for each kg between 11 and 20 kg
>20 60 mL + 1 mL/kg per hour for each kg >20 kg

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Jul 14, 2019 | Posted by in ANESTHESIA | Comments Off on Abdominal wall defects

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