Surgical Care Of Major Newborn Malformations

Stephen E Dolgin, Chad E Hamner

• Publisher: WSPC
• Year: 2012
• ISBN:
  9789814434607
• Topic: Medicine
• Subtopic: Surgery & Surgical Medicine

This volume addresses the major “index cases” involving neonates that are taught in pediatric surgical training programs. The discussion emphasizes practical features of the diagnosis and management of these malformations. The intention is to help clinicians sculpt a creative adaptable approach that can be individualized for each child. The current approach is situated in its historical context to encourage ongoing advancement in the care of these patients.

Contents:

• Perioperative Management of the Neonatal Patient (Matias Bruzoni and Craig T Albanese)
• Malrotation (Jeremy Aidlen)
• Congenital Duodenal Obstruction (Chad E Hamner)
• Jejunoileal Atresia and Stenosis (Stephen E Dolgin)
• Hirschsprung's Disease (Meade Barlow, Nelson Rosen and Stephen E Dolgin)
• Meconium Syndromes (Ankur Rana and Stephen Dolgin)
• Anorectal Malformations (Meade Barlow, Nelson Rosen and Stephen E Dolgin)
• Necrotizing Enterocolitis (Loren Berman and R Lawrence Moss)
• Esophageal Atresia (Frederick Alexander)
• Abdominal Wall Defects (Benedict C Nwomeh)
• Malformations of the Lung (David H Rothstein)
• Congenital Diaphragmatic Hernia (Samuel Z Soffer)
• Extra Hepatic Biliary Atresia (Rebecka L Meyers and Erik G Pearson)
• Ovarian Cysts (Stephen E Dolgin)
• Vascular and Lymphatic Anomalies (Ann M Kulungowski and Steven J Fishman)
• Sacrococcygeal Teratoma (Richard D Glick)

Readership: Surgical residents and fellows training in pediatric surgery, pediatric surgeons, neonatologists, pediatricians and nurses involved in the care of newborns with surgical problems.

CHAPTER 1

PERIOPERATIVE MANAGEMENT OF THE NEONATAL PATIENT

Matias Bruzoni, M.D. and Craig T. Albanese, M.D., M.B.A.^*

Lucile Packard Children's Hospital, Stanford California

INTRODUCTION

Over the past several decades, advances in prenatal evaluation, neonatal care, diagnostic techniques, anesthesia, and clinical management have enhanced care of pediatric surgical patients. Neonates have their own physiologic characteristics that must govern their care. The most distinctive and rapidly changing functions occur during the neonatal period. This is due to the newborn infant's adaptation from complete placental support to the extrauterine environment, differences in physiologic maturity of individual neonates, small size of these patients, and demands of growth and development.¹ Advances in neonatal care have resulted in survival of increasing numbers of extremely low birth weight infants. However, pediatric surgeons and neonatologists are now faced with more complex diseases due to extreme prematurity. Derangements in temperature regulation, fluid and electrolyte homeostasis, glucose metabolism, hematologic indices, and immune function are magnified in this setting. Preterm infants are more vulnerable to specific problems such as intraventricular hemorrhage, hyaline membrane disease, and hyperbilirubinemia. This chapter will focus on principle considerations that distinguish the perioperative care of neonates.

GENERAL CONSIDERATIONS

Fetal Circulation and Implications of the Ductus Arteriosus

Fetal growth and development occur in a “hypoxic” environment and the placenta, rather than the lung, is the source of oxygen. Oxygen saturation of blood that flows through the umbilical vein is only 65%, corresponding to a partial pressure of oxygen of 35 mmHg. In the fetal right atrium, this blood mixes with even lower oxygen saturated blood that comes from the fetal liver, inferior and superior vena cava, and coronary sinus. This hypoxic environment is compensated by different mechanisms that help provide adequate oxygen to fetal tissues. First, in contrast to adult hemoglobin, fetal hemoglobin has a lower p50 which allows more efficient oxygen extraction from the placenta. Second, there are three physiologic shunts that allow preferential circulation of more saturated umbilical vein blood into the systemic circulation. These include the ductus venosus, which helps bypass unsaturated portal flow, foramen ovale, which allows flow into the left heart avoiding mixture with the superior vena cava and coronary sinus, and ductus arteriosus, which shunts blood from the pulmonary artery into the aorta for systemic oxygen delivery. Finally, fetal cardiac output is about three times greater than that of adults. This, coupled with low systemic resistance, allows better oxygen delivery. The two umbilical arteries that originate from the internal iliac arteries return blood with lower oxygen content from the systemic circulation back to the placenta.

Pulmonary vascular resistance in fetal life is suprasystemic and therefore the right ventricle performs twice the work as the left ventricle. Ninety-percent of right ventricular output goes into the aorta via the ductus arteriosus. Within hours to days after birth, there is physiologic closure of the ductus arteriosus as pulmonary vascular resistance decreases and systemic vascular resistance increases. These hemodynamic changes, together with an increase in arterial oxygen saturation, cause constriction of the ductus' vascular smooth muscle, which shortens and narrows its lumen. This functional closure is followed by an anatomical closure several weeks later, resulting in the fibrotic ligamentum arteriosus.² Postnatal failure of the ductus to close can result in a left-to-right shunt into the pulmonary artery with resultant pulmonary hypertension and high output congestive heart failure. If this problem persists, pulmonary hypertension can get so severe that the shunt reverses, resulting in systemic hypoxemia.

In preterm infants, clinical evidence of a patent ductus include a continuous murmur, bounding pulses with widened pulse pressure (greater than 20 mmHg), and respiratory failure. Diagnosis is confirmed by echocardiography. Initial treatment consists of relative fluid restriction and indomethacin, which inhibits cyclooxygenase activity and reduces local ductal tissue synthesis of prostaglandin E₂, the most potent dilator of the ductus arteriosus. Side effects of indomethacin include inhibition of platelet function and reduction of renal and splanchnic blood flow. Treatment of asymptomatic patent ductus arteriosus remains controversial due to these side effects. Surgical occlusion is reserved for patients who are refractory to medical treatment, have a contraindication to indomethacin therapy (e.g. intraventricular hemorrhage, established necrotizing enterocolitis), or have developed a complication of indomethacin treatment (e.g. ileal perforation).

Low Birth Weight Infants

Neonates may be classified (Tables 1 and 2) according to their level of maturation (gestational age) and development (weight). This classification is important because the physiology of neonates may vary significantly depending on these parameters.

Under this classification system, a term, appropriate for gestational age infant is born between 37- and 42-week gestation with a birth weight greater than

Table 1. Newborn classification by maturation (gestational age).

Classification	Age at birth
Preterm	Birth before 37-week gestation period
Term	Birth between 37- and 42-week gestation period
Post-term	Birth after 42-week gestation period

Table 2. Newborn classification by development (weight).

Classification	Birth weight
Small for gestational age	Birth weight below 10th percentile
Appropriate for gestational age	Birth weight between 10th and 98th percentile
Large for gestational age	Birth weight greater than 98th percentile

Table 3. Alternative newborn classification by weight.

Classification	Birth weight	% of preterm births	Mortality rate vs.term infants
• Moderately low birth weight	Birth weight between 2500 g and 1501 g	82%	40 times higher
• Very low birth weight	Birth weight between 1500 g and 1001 g	12%	200 times higher
• Extremely low birth weight	Birth weight < 1000 g	6%	600 times higher

2500 g. In the United States, approximately 7% of all babies do not meet these criteria. This may be due to prematurity or intrauterine growth retardation. From a clinical standpoint, neonates born under 2500 g are broadly classified as low birthweight (LBW) infants. Further subclassification into moderately low birth weight, very low birth weight, and extremely low birth weight infants have been used for epidemiologic and prognostic purposes (Table 3). Using this terminology, low birth weight infants may be preterm and appropriate for gestational age, term but small for gestational age, or both preterm and small for gestational age. This distinction is important in that overall prognosis and potential risks may be significantly different for the different populations.

Preterm infant

By definition, preterm infants are born before 37 weeks of gestation. They generally have body weights appropriate for their age, though they may also be small for gestational age. The rate of premature birth is the major contributor to infant mortality and has not changed significantly. The United States ranks between 20th and 30th among countries around the world in infant mortality and premature delivery rates.³ If gestational age is not accurately known, the prematurity of an infant can be estimated by physical examination. Principle features of preterm infants are head circumference below 50th percentile, thin, semi-transparent skin with absence of plantar creases, soft and malleable ears with poorly developed cartilage, absence of breast tissue, undescended testes (testicular descent from the inguinal canal towards the scrotum begins in the 26th week of gestation) with a flat scrotum in boys, and relatively enlarged labia minora and small labia majora in girls.

In addition to these physical characteristics, several physiologic abnormalities exist in preterm infants. These abnormalities are often a result of unfinished fetal developmental tasks that normally enable an infant to successfully transition from intrauterine to extrauterine life. These tasks, which include renal, skin, pulmonary, and vascular maturation, are usually completed during final weeks of gestation. The more premature the infant, the more fetal tasks are left unfinished and the more vulnerable the infant.

This physiologic and anatomic vulnerability sets the preterm infant up for several specific and clinically significant problems:

(1) Central nervous system immaturity leading to episodes of apnea and bradycardia, and a weak suck reflex;

(2) Pulmonary immaturity leading to surfactant deficiency which can result in hyaline membrane disease and respiratory distress at birth;

(3) Cerebrovascular immaturity leading to fragile cerebral vessels which lack the ability to autoregulate. This predisposes preterm infants to intraventricular hemorrhage, the most common acute brain injury of neonates;

(4) Skin immaturity leading to underdeveloped stratum corneum with significant transepithelial water loss. This complicates thermal regulation and fluid status management of infants;

(5) Gastrointestinal underdevelopment causing inadequate absorption and risk of necrotizing enterocolitis;

(6) Impaired bilirubin metabolism causing predominantly indirect hyperbilirubinemia;

(7) Cardiovascular immaturity leading to patent ductus arteriosus or patent foramen ovale. These retained elements of fetal circulation can cause persistent left-to-right shunting and cardiac failure;

(8) Fragile retinal vessels leading to retinopathy of prematurity.

From a practical standpoint, care of preterm infants must therefore be directed at preventing and/or treating these specific problems. Episodes of apnea and bradycardia are common and may occur spontaneously or as nonspecific signs of problems such as sepsis or hypothermia. Prolonged apnea with significant hypoxemia leads to bradycardia and ultimately to cardiac arrest. All preterm infants should therefore undergo apnea monitoring and electrocardiographic pulse monitoring, with the alarm set at a minimum pulse rate of 90 beats per minute. In neonates with respiratory difficulties, chest radiography will help detect hyaline membrane disease and cardiac failure. The lungs and retinas of preterm infants are very susceptible to high oxygen levels, and even relatively brief exposures may result in various degrees of pulmonary insult and retinopathy of prematurity. Infants receiving supplemental oxygen therefore require continuous pulse oximetry monitoring, with the alarm set to trigger below 85% and above 92%. Preterm infants may also be unable to tolerate oral feeding because they have a weak suck reflex, necessitating intragastric tube feeding or total parenteral nutrition. Finally, impaired bilirubin metabolism may necessitate serum bilirubin monitoring for rising levels of unconjugated bilirubin; this may require phototherapy or exchange transfusion in order to prevent brain damage (i.e. kernicterus).

Small for gestational age infant

Infants whose birth weight is below the 10th percentile are considered to be small for gestational age (SGA). SGA newborns are thought to be a product of restricted intrauterine growth due to placental, maternal, and fetal abnormalities. Table 4 lists several conditions which may lead to intrauterine growth retardation. It should be noted that not all infants in this group are truly growth retarded. Some infants are simply born small as a result of a variety of factors including race, ethnicity, sex, and geography. It is important to differentiate these infants from those whose relatively low birth weight is a result of genetic or intrauterine abnormality.

SGA infants can be divided into two broad categories; symmetric SGA infants and asymmetric SGA infants. This distinction is primarily based on when in the gestational period fetal growth was actually restricted. If fetal growth is restricted during the first half of pregnancy, when cellular hyperplasia and differentiation lead to tissue and organ formation, the neonate is generally a symmetric SGA

Table 4. Common conditions associated with ...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Contents
• Contributors
• Introduction
• Chapter 1 The Fundamentals
• Chapter 2 MALROTATION
• Chapter 3 A Minimum of Mathematics
• Chapter 4 JEJUNOILEAL ATRESIA AND STENOSIS
• Chapter 5 HIRSCHSPRUNG's DISEASE
• Chapter 6 MECONIUM SYNDROMES
• CHAPTER 7 ANORECTAL MALFORMATIONS
• CHAPTER 8 NECROTIZING ENTEROCOLITIS
• CHAPTER 9 ESOPHAGEAL ATRESIA
• CHAPTER 10 ABDOMINAL WALL DEFECTS
• CHAPTER 11 MALFORMATIONS OF THE LUNG
• Chapter 12 CONGENITAL DIAPHRAGMATIC HERNIA
• CHAPTER 13 EXTRA HEPATIC BILIARY ATRESIA
• CHAPTER 14 OVARIAN CYSTS
• CHAPTER 15 VASCULAR AND LYMPHATIC ANOMALIES
• CHAPTER 16 SACROCOCCYGEAL TERATOMA
• Index