Abstract
In this chapter, the authors discuss numerous anesthetic considerations related to the care for the premature infant. A host of topics associated with prematurity are reviewed including bronchopulmonary dysplasia, pulmonary hypertension, apnea of prematurity, retinopathy of prematurity, cerebral palsy, neonatal hypoglycemia, hypothermia and acidosis, necrotizing enterocolitis and the performance of neonatal spinal anesthetics.
A 32-week-old baby girl presents for bilateral inguinal hernia repair. She was born at 26 weeks due to premature rupture of membranes. She had a patent ductus arteriosus (PDA) which was closed with indomethacin, as well as intubation for 1 week after birth for respiratory distress. She is currently extubated with a HR of 151, non-invasive blood pressure (NIBP) 51/33, with an O2 sat of 95% on 2L nasal cannula (NC).
What Is a Preterm Infant? What Is a Term Baby?
A preterm infant is born between 20 weeks (viability) and 37 weeks of gestation. A term infant is born after 37 weeks of gestation. Classification is based on birth weight which can be correlated with morbidity and mortality (Table 7.1). Numerous issues are experienced by pre-term neonates affecting nearly every system (Table 7.2).
Table 7.1 Gestational age and weight classifications
| Gestational age | Birth weight | Classification |
|---|---|---|
| 36–37 weeks | <2,500 grams | Low birth weight |
| 31–36 weeks | <1,500 grams | Very low birth weight |
| 24–30 weeks | <1,000 grams | Extremely low birth weight |
Table 7.2 What are the most common problems faced by preterm infants?
| Cardiovascular system | Patent ductus arteriosus, impaired ventricular diastolic filling |
| Respiratory system | Apnea of prematurity, bronchopulmonary dysplasia, pulmonary hypertension, laryngotracheal anomalies |
| Neurological system | Intraventricular hemorrhage, seizures, cerebral palsy |
| Integumentary system | Increased heat loss, decreased brown fat |
| Endocrine system | Hypoglycemia, decreased synthesis of vitamin K dependent factors |
| Hematopoietic system | Relative anemia, thrombocytopenia |
| Genitourinary system | Decreased tubular bicarbonate absorption |
| Gastrointestinal system | Necrotizing enterocolitis (NEC) |
| Ophthalmologic | Retinopathy of prematurity |
What Are the Unique Cardiovascular Issues in Preterm Infants?
Preterm infants generally have a higher total blood volume per kg than a term infant – approximately 110–120 mL/kg. However, their left ventricles are generally stiffer than term infants, and therefore very dependent on diastolic filling for generating cardiac output. As a result, very high heart rates may be deleterious as they impair diastolic filling due to shortening of the diastolic period. As such, they are less able to augment their cardiac output by increases in stroke volume when compared with older children and adults.
Patent ductus arteriosus, a highly prevalent issue in pre-term neonates, will be covered in Chapter 59.
What Is Bronchopulmonary Dysplasia?
Bronchopulmonary dysplasia (BPD) is a chronic lung disease as a result of prolonged mechanical ventilation and high O2 concentration exposure, and is more common in preterm infants (Figure 7.1). With better lung protection strategies in premature infants, specifically surfactant and steroid utilization, the severity of BPD has declined in recent years. These children also have increased airway reactivity throughout childhood.
Figure 7.1 Chest X-ray demonstrating severe bronchopulmonary dysplasia.
How Is Pulmonary Hypertension Related to Prematurity?
Elevated pulmonary artery pressure is a major source of morbidity in the preterm infant. Failure of arborization or development of the pulmonary vasculature leads to elevated pressures. Severity of illness is directly proportional to the degree of prematurity. Vasculature development may improve as the child grows but is often abnormal.
What Is Apnea of Prematurity? Can It Be Prevented?
Apnea of prematurity is a form of centrally mediated apnea which decreases in incidence with rising post-menstrual age. In the NICU, generally physical stimulation or bag mask ventilation is used to resolve the apnea. Intravenous caffeine citrate reduces the incidence of apnea, however it has other side effects which have to weighed against apnea reduction. This is discussed in greater detail in Chapter 18.
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