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Powered by TCPDF (www.tcpdf.org) Powered by TCPDF (www.tcpdf.org) Chapter_01.qxd 11/10/08 10:29 PM Page 1 ONE General Considerations Part 1: Medical Considerations Anne R.Hansen, MD, MPH Full-term human gestation is 37 to 42 weeks. Currently, the bor- derline of viability is approximately 23 to 25 weeks of gestation. High-Risk Infants PREMATURITY Infants born at < 37 weeks of gestation are considered premature. Preterm delivery can be either induced or spontaneous, starting as contractions or premature rupture of membranes. Induced deliv- eries, whether vaginal or cesarean section, can be for either maternal indications (eg, progressive pregnancy-induced hypertension or cervical incompetence) or fetal indications (eg, distress, infection, poor growth or oligohydramnios). The etiology of spontaneous preterm labor is infection in some cases, but often it is not known. Risk factors include low socio- economic status, black race, younger (< 16) or older (> 35 years) maternal age, maternal illness (acute or chronic), multiple gestations, and previous preterm delivery. Anticipated Complications Risk is in direct proportion to the degree of prematurity, including the following: • Neurologic: Intraventricular hemorrhage (IVH), periventricu- lar leukomalacia, retinopathy of prematurity, hearing deficit 1 Chapter_01.qxd 11/10/08 10:29 PM Page 2 2 Manual of Neonatal Surgical Intensive Care • Respiratory: Surfactant deficiency/hyaline membrane disease/respiratory distress syndrome, pneumothorax and other air-leak conditions, pulmonary interstitial emphysema, inadequate respiratory effort or apnea/bradycardia of prematurity, chronic lung disease (CLD) • Cardiac: Patent ductus arteriosus (PDA), hypotension (second- ary to intravascular volume depletion; poor myocardial function and vascular tone; and/or component of adrenal insufficiency) • Renal/fluid and electrolyte balance: Initially, low glomerular fil- tration rate (GFR); poor concentrating ability with wasting of free water, electrolytes, and bicarbonates; large insensible losses, result is needed for monitoring of fluids and electrolytes, large total fluid requirement, high level of electrolyte supplementation, sometimes HCO therapy, longer half-life for many medications 3 • Gastrointestinal (GI): Suck and swallow dyscoordination with requirement for gavage feedings until suck reflex develops at approximately 34 to 36 weeks of gestation, feeding intoler- ance, necrotizing enterocolitis (NEC), immature hepatic function combined with relative polycythemia resulting in increased risk of hyperbilirubinemia • Hematologic: Exaggerated and delayed physiologic anemia • Temperature regulation: Tendency toward hypothermia and temperature instability, with results needed for monitoring, exter- nal heat source, generally warming lights or incubator (isolette) SMALL FOR GESTATIONAL AGE/INTRAUTERINE GROWTH RESTRICTION Though the terms small for gestational age (SGA) andintrauterine growth restriction (IUGR) are often used interchangeably, they have two distinct meanings. Fetuses are SGA if they are more than 2 SDs below the mean or < 10% for gestational age. In IUGR, fetuses do not reach their growth potential. A constitutionally small infant who grows steadily along the 5% for gestational age is SGA but not IUGR. A fetus that started growing at the 90% and then drops to the 20% due to maternal hypertension is IUGR but not SGA. Poor growth that starts early in gestation tends to result in symmetric IUGR, in which weight, length, and head cir- cumference (HC) are proportionately small. Poor growth that starts later in gestation generally results in asymmetric IUGR in which the weight is affected most profoundly, the height less so, Chapter_01.qxd 11/10/08 10:29 PM Page 3 General Considerations 3 and the HC is relatively spared. SGA/IUGR status can result from maternal, placental, or fetal factors including the following: • Maternal: older maternal age (> 40 years), small constitutional size, race, high altitude, medications and/or drugs, malnutri- tion, chronic disease, any maternal condition resulting in decreased placental blood and oxygen flow (eg, cardiac disease including chronic or gestational hypertension, advanced diabetes, renal disease, hemoglobinopathies including sickle cell, pulmonary disease, collagen vascular disease, antiphospholipid antibodies), uterine anomalies • Placental: insufficiency resulting from abruption, abnormal implantation, maternal vascular disease (eg, infarction), multiple gestations • Fetal: familial and/or constitutional, chromosomal, congenital infection (especially rubella and cytomegalovirus), anomalies, and/or syndromes; multiple gestations; some post-term infants Anticipated Complications The complications depend on the etiology but can include any of the following: fetal distress, perinatal depression, meconium aspi- ration, hypoxia, hypothermia, hypoglycemia, polycythemia, hyponatremia, hypocalcemia, pulmonary hemorrhage, and persistent pulmonary hypertension. LARGE FOR GESTATIONAL AGE Infants are generally considered to be large for gestational age (LGA) if they are > 2 SDs above the mean or > 90% for their gestational age. LGA status can result from maternal or fetal factors including the following: • Maternal: Large constitutional size, diabetes before the devel- opment of vascular disease (gestational and classes A to C) • Fetal: Familial and/or constitutional factors, some postterm infants, Beckwith-Wiedemann syndrome, hydrops fetalis Anticipated Complications The complications depend on the etiology but can include any of the following: increased rate of cesarean delivery, birth injury (eg, brachial plexus injury), hypoglycemia, polycythemia, and delayed pulmonary maturity. Chapter_01.qxd 11/10/08 10:29 PM Page 4 4 Manual of Neonatal Surgical Intensive Care Fluid, Electrolytes, and Nutrition Daily fluid and electrolyte requirements depend on gestational and postbirth age (Table 1). After an initially low GFR in the first few days of birth, renal perfusion improves and total fluid and electrolyte requirements tend to increase. A large daily fluid volume is required by infants who have immature renal function or poor skin integrity or who need to remain under an open warmer (vs. an incubator). Infants typically need 3 to 5 mEq/kg/d of sodium, 2 to 3 mEq/kg/d of potassium, and 200 to 500 mg/kg/d of calcium gluconate; however, this varies considerably, especially for infants receiving diuretic therapy. The initial goal is to achieve a mild degree of dehydration in babies with respiratory disease to minimize risk of pulmonary edema and subsequent CLD. For preterm infants, relative dehydration also decreases the risk of persistent PDA and IVH. In the first week of life, normally term infants lose approximately 5 to 10% of birth weight and preterm infants lose up to 15% of birth weight. Babies should regain their birth weight by 2 weeks of age. Once babies are beyond the acute phase of their illness and are recuperating and growing, they most typically receive total fluids of 150 mL/kg/d. Some infants with CLD or congenital heart disease require fluid restriction to avoid pulmonary edema. Other infants with high caloric needs require additional fluids or high–caloric density milk to achieve optimal growth and nutrition. INTRAVENOUS NUTRITION AND HYDRATION If an infant cannot be started on enteral feedings, nutrition and hydration need to be maintained intravenously. Intravenous (IV) TABLE 1 Approximate Total Fluids (mL/kg/d) Required by Birth Weight and Age Age (hours) Birth Weight (kg) < 24 24–48 > 48 < 1 100–150 120–160 140–190 1–1.5 80–100 100–120 120–160 > 1.5 60–80 80–120 100–150