SECTION XII. Neonatal Anesthetic Considerations
A Preoperative Assessment
The perioperative management of any neonate is determined by the nature of the surgical procedure, the gestational age at birth, postconceptual age at surgery, and associated medical conditions.
1. Gestational age and postconceptual age at surgery
a) The gestational age and postconceptual age are critical to the determination of the physiologic development of the neonate. The history of the delivery and the immediate postdelivery course can influence the choice of anesthetic technique and assist in anticipating possible postoperative complications.
b) Preterm neonates are classified as borderline preterm (36 to 37 weeks gestation); moderately preterm (31 to 36 weeks gestation); and severely preterm (24 to 30 weeks gestation).
c) Neonates can be classified according to their weight as well as their gestational age. Full term is considered to be 37 to 42 weeks gestation.
d) However, even full-term neonates that are small for gestational age (SGA) often present with conditions requiring surgical intervention. SGA neonates have different pathophysiologic problems from preterm infants (<37 weeks gestation) of the same weight.
e) Gestational age and neonatal problems are closely related. Maternal health problems also can have significant implications for preterm as well as full-term (even SGA) neonates.
f) Several common maternal problems and the possible associated neonatal sequelae are listed in the following table.
2. Prematurity
a) Due to advances in neonatal medicine, many preterm babies born at exceptionally early gestational age and extremely low birth weights are surviving to be challenged with a plethora of unique diseases and pose many anesthetic challenges.
b) Prematurity presents its own set of complications, which include anemia, intraventricular hemorrhage, periodic apnea accompanied by bradycardia, and chronic respiratory dysfunction.
c) Postconceptual age (gestational age + postnatal age) should be determined at the time of the anesthetic evaluation. Premature infants of less than 60 weeks postconceptual age have the greatest risk of experiencing postanesthetic complications.
d) The manifestations of prematurity are thought to occur as a result of inadequate development of respiratory drive and immature cardiovascular responses to hypoxia and hypercapnia.
e) Premature infants have a significant risk of postoperative apnea and bradycardia during the first 24 hours after general anesthesia.
f) The contributing factors that may influence the occurrence of apnea in premature infants are listed in the following box.
Factors Contributing to the Incidence of Apnea in the Premature Infant
Central Contributors
Inadequate development of respiratory centers
Incomplete myelination of central nervous system
Metabolic Contributors
Hypothermia
Hypoglycemia
Hypocalcemia
Acidosis
Anesthetic Contributors
Residual inhalation anesthesia
Residual opioid plasma concentrations
Residual neuromuscular blockade
3. Apnea in the premature infant
a) The incidence of apnea in the postoperative period is inversely related to postconceptual age and is most frequent in infants of less than 50 weeks postconceptual age.
b) Apnea may still occur when regional anesthetic techniques have been substituted for general anesthesia.
c) Premature infants without a history of apnea or bradycardia may still experience postoperative apnea.
d) Premature infants with histories of respiratory distress, concurrent respiratory disease, and periods of apnea are twice as likely to develop postoperative apnea.
e) Concurrent anemia (hematocrit <30%) places additional risk for the occurrence of postoperative apnea.
f) Outpatient surgical care is usually not an acceptable venue for premature infants. Although the literature supports an increased risk for premature infants up to 60 weeks postconceptual age, debate continues as to when this risk decreases.
g) Perioperative use of caffeine: The standard doses of caffeine and theophylline are 10mg/kg and 6mg/kg, respectively. Both have been shown to reduce the incidence of idiopathic apnea of prematurity and reduce the occurrence of apnea after surgery in the premature baby.
4. Preanesthetic assessment and neonatal anesthetic implications
a) Valuable information is obtained from those caring for the baby in the neonatal intensive care unit. It is often best to alter the infant’s plan of therapy as little as possible (e.g., management of ventilation, acid base status, and glucose). Consultation with the neonatologist will be helpful.
b) A maternal drug history is very important. In presence of illicit drugs, such as heroin and cocaine, the baby could be withdrawing from the drug at the time of surgery. Particularly with cocaine, there is an increased incidence of pulmonary hypertension and bowel perforation.
c) Some mothers take large doses of aspirin or acetaminophen during pregnancy. Their infants could also exhibit pulmonary hypertension and persistent fetal circulation during the first few days of life.
d) All of the information gathered during the assessment will lead to the anesthetic plan based on the implications of all the transitioning body systems. The characteristics of the body system and the anesthetic implications are listed in the following table.
5. System review and examination
a) When performing a physical assessment, one should look carefully for congenital anomalies. A rule of thumb is that if there is one anomaly present, there are probably more, since many occur in clusters, labeled a syndrome.
b) These problems can occur most often in small and large for gestational age neonates and should be analyzed and understood as listed in the following box.
Common Metabolic and Structural Problems in Small- and Large-for-Gestational- Age (SGA and LGA) Infants
SGA
• Congenital anomalies
• Chromosomal abnormalities
• Chronic intrauterine infection
• Heat loss
• Asphyxia
• Metabolic abnormalities (hypoglycemia, hypocalcemia)
• Polycythemia/hyperbilirubinemia
LGA
• Birth injury (brachial, phrenic nerve, fractured clavicle)
• Asphyxia
• Meconium aspiration
• Metabolic abnormalities (hypoglycemia, hypocalcemia)
• Polycythemia/hyperbilirubinemia
6. Head and neck abnormalities
a) Any abnormality of the head and/or neck should raise concerns regarding airway management. The shape and size of the head, with or without the presence of pathology, can make airway management difficult. The small mouth and large tongue can obstruct the airway during mask ventilation.
b) Neonates have very small nares, and when obstructed by an anesthesia facemask they do not convert to mouth breathing, particularly if the mouth is being held closed.
c) A nasogastric tube can obstruct half of the neonate’s airway and should be placed orally. A small and/or receding chin, as seen in Pierre Robin and Treacher Collins syndromes, may make direct laryngoscopy and visualization of the glottis impossible, requiring other types of airway management.
d) Cleft lip, with or without cleft palate, may complicate intubation. Anomalies such as cystic hygroma or hemangioma of the neck can produce upper airway obstruction. In the case of a preterm neonate, it should also be determined if the patient has retinopathy of prematurity (ROP), cataracts, or glaucoma.
e) Atropine administration could result in significant increases in intraocular pressure and further damage to the eye.
7. Respiratory system abnormalities
a) The incidence of respiratory distress syndrome (RDS) and bronchopulmonary dysplasia (BPD) is inversely related to gestational age at birth.
b) The onset of RDS can be as early as 6 hours after birth, and the symptoms include tachypnea, retractions, grunting, and oxygen desaturation.
c) Bronchopulmonary dysplasia is a disease of the newborn that manifests as a need for supplemental oxygen along with lower airway obstruction and air trapping, carbon dioxide retention, atelectasis, bronchiolitis, and bronchopneumonia.
d) Oxygen toxicity, barotrauma of positive-pressure ventilation on immature lungs, and endotracheal intubation have been reported as causative factors. Management of the patient’s oxygenation can be challenging.
e) Careful monitoring of the acid-base status and the use of increased peak inspiratory pressure and positive end-expiratory pressure may be needed to maintain oxygenation during surgery.
8. Cardiovascular system abnormalities
a) In evaluation of the neonate’s cardiovascular system, several variables should be examined: heart rate, blood pressure patterns, skin color, intensity of peripheral pulses, and capillary filling time.
b) Presence of a murmur or abnormal heart sound, low urine output, metabolic acidosis, dysrhythmias, or cardiomegaly, alone or in combination, raise the concern of some type of congenital heart lesion. These patients should be evaluated with a chest x-ray, EKG, and echocardiogram. The results of these diagnostic tests will allow for effective planning of the anesthetic, decreasing the possibility of complications.
c) The common syndromes associated with cardiac defects are listed in the following table.
d) Anesthetic implications of congenital heart disease in the neonate include the following:
(1) Direction and flow through any shunt
(2) Baseline oxygenation
(3) Dependence of the systemic or pulmonary circulation on flow through the ductus arteriosus
(4) The presence and size of any obstruction to blood flow
(5) Heart failure (high output, low output, or hypoxic)
(6) Drug therapy
(7) Antibiotic prophylaxis against bacterial endocarditis
9. Central nervous system abnormalities
a) An assessment of the CNS should include the status of the infants’ intracranial pressure and intracranial compliance.
b) Intraventricular hemorrhage (IVH) is almost exclusively seen in preterm babies; this occurs when there is spontaneous bleeding into and around the lateral ventricles of the brain.
c) The more preterm the neonate and the smaller the weight, the more likely one could find intraventricular hemorrhage.
d) The hemorrhage is usually the result of RDS, hypoxic-ischemic injury, and/or episodes of acute blood pressure fluctuation that rapidly increase or decrease cerebral blood flow. The classic example is laryngoscopy in the presence of inadequate anesthesia.
e) The symptoms of IVH include hypotonia, apnea, seizures, loss of sucking reflex, and a bulging anterior fontanelle. Particular evaluation of the neonate with meningomyelocele (spina bifida) will be discussed subsequently.
10. Preoperative labs
Neonates who are premature (<60 weeks postconceptual age), those with concurrent cardiopulmonary disease, and babies in whom major blood loss is anticipated during the surgical procedure should have serial hematocrits, electrolytes, blood gases, and serum osmolality measured. The test values will assist in the fluid, electrolyte, and blood replacement during the surgical procedure.
11. Preoperative treatment of significance for anesthesia
Many of the pre-existing conditions in the neonate will require medical treatment. Some of the preoperative drugs and their anesthetic implications are listed in the following table.
a) Parental preparation is important. In the case of institutions that do not have a neonatal intensive care unit, the patient will have been transferred in from another institution and the parents still may be in the institution where the baby was delivered.
b) It is imperative that the parents be prepared and the informed consent for anesthesia be obtained. Often this must be done via telephone or from the father who may have accompanied the neonate to the neonatal intensive care unit.
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