Prematurity and Associated Pathologies

Prematurity is defined as an infant born prior to 37 weeks gestation. Premature infants can be further subdivided by their birth rate: low birth weight (< 2500 g), very low birth weight (< 1500 g), and extremely low birth weight (< 1000 g). The earlier a baby is born and the lower the birth weight, the higher the risk for morbidity and mortality. There are certain risk factors that increase the likelihood of premature birth related to the fetus, placenta, uterus, and mother. Premature infants have a risk for multiorgan dysfunction due to multiple anatomical pathologies.

The risk factors that increase the risk for preterm birth include:

• Fetus

  • Fetal distress

  • Multiple gestation

• Placenta

  • Abruptio placentae

  • Placenta previa

• Uterus

  • Incompetent cervix

  • Premature rupture of membranes

  • Polyhydramnios

• Mother

  • Pre-eclampsia

  • Heart disease

  • Drug abuse (ie. Cocaine, nicotine)

  • Extremes of age (younger or older)

There are 9 specific complications to be aware of when evaluating a premature newborn. These include:

1. Intraventricular Hemorrhage

2. Temperature instability

3. High risk for infection

4. Retinopathy of Prematurity

5. Respiratory Distress Syndrome

6. Bronchopulmonary Dysplasia

7. Apnea of Prematurity

8. Necrotizing Enterocolitis

9. Patent Ductus Arteriosus

Intraventricular hemorrhage is the most common type of intracranial hemorrhage in preterm infants. It is due to the small, premature capillary beds of the germinal matrix. Prematurity is the highest risk factor for intracranial bleeds. IVH presents during the first days of life but rarely after 10 days old. One complication to look out for post-bleed is posthemorrhage hydrocephalus, which can sometimes require a ventriculoperitoneal shunt. Other factors that can contribute to intracranial hemorrhage include hypertension and hyperosmolality.

Temperature instability is multifactorial:

• Increased surface area to mass ratio

• Limited insulating adipose tissue

• Decrease number of brown fat cell able to generate heat

• Think skin from lack of keratinization

Hypothermia is associated with hypoglycemia, acidosis, respiratory distress, increased O2 consumption, decreased cardiac output, increased peripheral vascular resistance, and sepsis. To maintain a warm body temperature, you can use forced warming air devices, radiant warmers, head coverings, and warming the room. Temperature should be monitored to avoid iatrogenic hyperthermia.

Increased risk for infection comes from reduced cellular and tissue immunity and is a constant threat to life. Because of this immaturity, sepsis can exist without a positive blood culture, increased white blood cell count, or fever. Signs of sepsis can present as apnea, bradycardia, or acidosis. The best way to prevent infection is practicing proper hand hygiene.

Retinopathy of prematurity is inversely related to birth weight, with the highest risk for ROP when infants weight less than 1000 grams. It is thought to be due to abnormal tissue oxygen levels, changing angiogenesis resulting in hypoxic and ischemic changes in the retina. The goal is to minimize inspired oxygen exposure until 44 weeks postmenstrual age once’s the retinal vascularization has been completed. SpO2 goals are typically 90-95%.

Respiratory Distress Syndrome is common in preterm infants and is due to a lack of surfactant in the premature lungs. Surfactant lines alveoli and reduces surface tension within the alveoli, decreasing risk of atelectasis. Atelectasis in a newborn can lead to acidosis, hypoxemia,intrapulmonary and extrapulmonary shunting, and need for mechanical ventilation. Typical treatment is nasal CPAP for spontaneously breathing neonates. Infants who fail noninvasive measures will require intubation and mechanical ventilation.

Bronchopulmonary dysplasia is defined as an infant requiring supplemental oxygen after 28 days of life. It is a chronic disorder and is commonly seen after a history of RDS. Risk factors for BPD include increased inspired FiO2, use of positive pressure ventilation, patent ductus arteriosus, and fluid overload in the first few days of life. With BPD comes increased airway resistance, decreased pulmonary compliance, ventilation/perfusion mismatch, decreased pulmonary compliance, decreased PaO2, tachyons, increased O2 consumption, increased pulmonary infections.

All premature infants have some degree of periodic breath holding. Apnea is defined as a breath hold lasting for at least 15 seconds or a breath hold with hypoxia or bradycardia. Risk factors include anemia, history of apnea spells, neurologic diseases, significant comorbidities. Infants younger than 50-60 weeks gestation age who require surgery are recommended to be observed in the hospital for at least 12 hours after the patient has received anesthesia.

Necrotizing entercolitis is multifactorial but is mostly but to hypoperfusion to the gut. The biggest risk factors are early gestation (< 32 weeks) and low birth weight (< 1500 g). There are three stages of NEC: abdominal distention, feeding intolerance, and hematochezia or Melina. The second stage of NEC is associated with radiologic evidence of air within the wall of the intestines (pneumatosis intestinalis). In the third stage, you see intestinal perforation or necrotic bowel, usually requiring surgical correction. NEC can lead to diffuse intravascular coagulation (DIC) and septic shock.

The ductus arteriosus is a connection between the aorta and the pulmonary artery, present during fetal circulation. Typically at birth, the systemic vascular resistance increased and pulmonary vascular resistance decreased, reversing the blood flow in the DA to L —> R. A persistent PDA can lead to left ventricular hypertrophy, increased pulmonary blood flow, and congestive heart failure. If an infant has significantly elevated PVR from hypoxia or hypercarbia, the PDA shunt can reverse and become R —> L. Treatment of a persistent PDA include supportive care, fluid restriction, COX inhibitors (ie. Indomethacin) to block prostaglandin E2, or surgical ligation via a left posterolateral thoracotomy. Anesthetic considerations for surgical ligation include a pre- and post-ductal pulse-oximetry and blood pressure monitoring to ensure that the right vessel is ligated (close proximity to aorta). Recurrent laryngeal nerve paralysis is a possible complication.