Growth and Development Robert M. Insoft and I. David Todres CHAPTER 2 Normal and Abnormal Growth Gas Exchange Gestational Age Assessment Regulation of Breathing Weight and Length Normal Respiratory Parameters Head Circumference Cardiovascular System Face Heart Rate Teeth Blood Pressure Body Composition Cardiac Output Development of Organ Systems Normal Electrocardiographic Findings from Infancy to Development of Airways and Lungs Adolescence Transition to Air Breathing Renal System Mechanics of Breathing Hepatic System Chest Wall and Respiratory Muscles Physiologic Jaundice Elastic Properties of the Lung Gastrointestinal Tract Static Lung Volumes Swallowing Total Lung Capacity Gastroesophageal Refl ux Functional Residual Capacity Meconium Closing Capacity Pancreas Airway Dynamics Hematopoietic System Resistance and Conductance Coagulation in the Infant Distribution of Resistance Neurologic Development Inspiratory and Expiratory Flow Limitation Developmental Issues AS AN INFANT GROWS and matures, vital changes occur that aff ect 2-1); deviations from this relationship may be associated with the child’s response to disease, drugs, and the environment. (1) inadequate maternal nutrition (malnutrition or placental Growth is an increase in physical size, and development is an insuffi ciency); (2) signifi cant maternal disease (pregnancy- increase in complexity and function. An overview of the subject induced hypertension, diabetes, collagen disorders); (3) mater- is presented so that anesthesiologists can appreciate the unique- nal toxins (tobacco, alcohol, drugs); (4) fetal infections ness of developing children from both physical and psychologi- (toxoplasmosis, rubella, cytomegalovirus, syphilis); (5) genetic cal perspectives. We discuss the respiratory organ system in abnormalities (trisomy 21, 18, 13); and (6) fetal congenital depth because of its primary considerations for anesthesiolo- malformations. gists; however, it is necessary to integrate all organ systems so Th e term prematurity has conventionally been applied to that a child is treated appropriately. infants weighing less than 2500 g at birth, but the designation preterm infant is more appropriate and is defi ned as one born before 37 completed weeks of gestation. A term infant is one Normal and Abnormal Growth born after 37 and before 42 completed weeks of gestation. Post- Prenatal growth is the most important phase in development, term infant refers to an infant born after 42 completed weeks of comprising organogenesis in the fi rst 8 weeks (embryonic gestation. growth), followed by the functional development of organ Preterm infants are further classifi ed according to their actual systems and maturation of the fetus to full term (fetal growth). birth weight. A low birth weight infant (LBW) is one weighing Rapid growth occurs particularly in the second trimester; a less than 2500 g regardless of the duration of the pregnancy. A major increase in weight from subcutaneous tissue and muscle very low birth weight (VLBW) infant weighs less than 1500 g, mass occurs in the third trimester. Th e duration of gestation and and an extremely low birth weight infant weighs less than the weight of an infant have an important relationship (Table 1000 g. In addition, infants weighing less than 750 g are now 7 A Practice of Anesthesia for Infants and Children Table 2-1. The Relationship of Gestational Age to Weight Table 2-2. Common Neonatal Problems with Respect to Gestation (weeks) Mean Weight (grams) Weight and Gestation 28 1165 ± 109 Relative Neonatal Problems at 32 1760 ± 128 Gestation Weight Increased Incidence < 36 2621 ± 274 Preterm ( 37 wk) SGA Respiratory distress syndrome 40 (full term) 3351 ± 448 Apnea Perinatal depression Data from Naeye RL, Dixon JB: Distortions in fetal growth. Pediatr Res Hypoglycemia 12:987, 1978 Polycythemia Hypocalcemia being called “micropremies”; there is very little published infor- Hypomagnesemia mation regarding the anesthetic management of this vulnerable Hyperbilirubinemia subpopulation of neonates (see Chapter 35). Viral infection An infant may also be classifi ed as small for gestational age Thrombocytopenia (SGA), large for gestational age (LGA), or appropriate for ges- Congenital anomalies tational age (AGA) depending on where the infant’s birth weight Maternal drug addiction plots out on a fetal growth curve. SGA infants (those whose Fetal alcohol syndrome weight is below the 10th percentile at any gestational age) have AGA Respiratory distress syndrome usually been aff ected by intrapartum factors that have led to Apnea intrauterine malnutrition, such as toxemia and placental insuf- Hypoglycemia fi ciency. Other known causes include intrauterine infections, Hypocalcemia 1 chromosomal abnormalities, and congenital malformations. Hypomagnesemia SGA infants are particularly prone to hypoglycemia, hypocalce- Hyperbilirubinemia mia, polycythemia, hypothermia, and, potentially, mental and LGA Respiratory distress syndrome physical handicaps. Problems associated with length of gesta- Hypoglycemia: infant of a tion and body weight are summarized in Table 2-2. diabetic mother Infants classifi ed as LGA (those whose weight is above the Apnea 90th percentile at any gestational age) are usually born to Hypocalcemia mothers whose pregnancy has been complicated by diabetes. Hypomagnesemia Th e increased weight is the result of organomegaly and excessive Hyperbilirubinemia deposition of subcutaneous fat secondary to increased fetal Normal (37-42 wk) SGA Congenital anomalies insulin produced in response to maternal hyperglycemia. With Viral infection improved control of maternal diabetes with home blood glucose Thrombocytopenia monitoring, these infants are less likely to be LGA and therefore are at less risk for hypoglycemia, polycythemia, birth trauma, Maternal drug addiction hyaline membrane disease, and congenital malformations.2 Perinatal depression Hypoglycemia Gestational Age Assessment AGA – Th e gestational age of an infant may be assessed in one of three LGA Birth trauma ways. Th e most accurate means of assessing gestational age Hyperbilirubinemia is by measuring the crown-rump length of the fetus during a Hypoglycemia: infant of a fi rst-trimester ultrasonographic examination. Another method diabetic mother involves calculating gestational age from the fi rst day of the Postmature (>42 wk) SGA Meconium aspiration mother’s last menstrual period, but this is commonly inaccurate, syndrome leading to errors in estimation. Finally, the Dubowitz scoring Congenital anomalies system is a well-accepted method combining neurologic and Viral infection physical criteria of the infant to provide an accurate assessment Thrombocytopenia 3,4 of gestational age. A summary of the more signifi cant neuro- Maternal drug addiction logic and physical signs of maturity is presented in Table 2-3. Perinatal depression Aspiration pneumonia Weight and Length Hypoglycemia Assessment of growth is measured by changes in weight, length, AGA – and head circumference. Percentile charts are valuable for moni- LGA Birth trauma toring the child’s growth and development. Deviation from Hyperbilirubinemia growth within the same percentile for a child of any age is of greater signifi cance than any single measurement (Figs. 2-1 and Hypoglycemia: infant of a 2-2). Weight is a more sensitive index of well-being, illness, or diabetic mother poor nutrition than length or head circumference and is the AGA, appropriate for gestational age; LGA, large for gestational age; most commonly used measurement of growth. Change in weight SGA, small for gestational age. refl ects changes in muscle mass, adipose tissue, skeleton, and 8 Growth and Develoment 2 Table 2-3. Neurologic and External Physical Criteria to Assess Head Circumference Gestational Age Head size refl ects growth of the brain and correlates with intra- cranial volume and brain weight. Changing head circumference Physical refl ects head growth and is a part of the total body growth Examination Preterm (<37 wk) Term (≥37 wk) process; it may or may not indicate underlying involvement of Ear Shapeless, pliable Firm, well formed the brain. Th e mean expected head circumference for preterm Skin Edematous, thin skin Thick skin and full-term newborns is presented in Table 2-7. An abnor- Sole of foot Creases on anterior Whole foot creased mally large or small head may indicate abnormal brain develop- third ment, which must alert the anesthesiologist to possible Breast tissue Less than 1 mm More than 5 mm underlying neurologic problems. A large head may indicate a diameter diameter normal variation, familial feature, or pathologic condition (e.g., Genitalia hydrocephalus or increased intracranial pressure), whereas a Male Scrotum poorly Scrotum rugated small head may indicate a normal variant, a familial feature, or developed pathologic condition such as craniosynostosis or abnormal Testes undescended Testes descended brain development. During the fi rst year of life, head circumference normally Female Large clitoris, gaping Labia majora developed increases 10 cm, and it increases 2.5 cm in the second year. By labia majora 9 months of age, head circumference reaches 50% of adult size, Limbs Hypotonic Tonic (fl exed) and by 2 years it is 75%. For the fi rst 6 months of life, the cir- Grasp refl ex Weak grasp Can be lifted by refl ex cumference of the head is greater than that of the thorax. After grasp 2 years of age, the head circumference increases much less Moro refl ex Complete but Complete exhaustible (>32 wk) Sucking refl ex Weak Strong, synchronous