56: Neonatal Anesthesia

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CHAPTER 56 Neonatal Anesthesia

Rita Agarwal, MD, Jennifer F. Brunworth, MD

1 Why are neonates and preterm infants at increased anesthetic risk?

image Pulmonary factors. Differences in the neonatal airway, including large tongue and occiput, floppy epiglottis, small mouth, and short neck predispose infants to upper airway obstruction. The more premature the infant is, the higher the incidence of airway obstruction. The carbon dioxide response curve is shifted farther to the right in neonates than in adults (i.e., infants have a comparatively decreased ventilatory response to hypercarbia). Newborn vital capacity is about one half of an adult’s vital capacity, respiratory rate is twice that of an adult, and oxygen consumption is two to three times greater. Consequently opioids, barbiturates, and volatile agents have a more profound effect on oxygenation and ventilation in neonates than in adults.
image Cardiac factors. Newborn infants have relatively stiff ventricles that function at close to maximal contractility. Cardiac output is heart rate dependent, and neonates are highly sensitive to the myocardial depressant effects of many anesthetic agents, especially those that may produce bradycardia. Inhalational agents and barbiturates should be used cautiously.
image Temperature. Infants have poor central thermoregulation, thin insulating fat, increased body surface area–to-mass ratio, and high minute ventilation. These factors make them highly susceptible to hypothermia in the operating room. Shivering is an ineffective mechanism for heat production because infants have limited muscle mass. Nonshivering thermogenesis uses brown fat to produce heat, but it is not an efficient method to restore body temperature and increases oxygen consumption significantly. Cold-stressed infants may develop cardiovascular depression and hypoperfusion acidosis.
image Pharmacologic factors. Neonates have a larger volume of distribution and less tissue and protein binding of drugs than older children and adults. They also have immature livers and kidneys and a larger distribution of their cardiac output to the vessel-rich tissues. Neonates often require a larger initial dose of medication but are less able to eliminate the medication. Uptake of inhalation agents is more rapid, and minimum alveolar concentration is lower.

2 Do neonates have normal renal function?

Glomerular function of the kidneys is immature, and the concentrating ability is impaired. Renal clearance of drugs may be delayed. Extra salt and water are not handled well.

3 Why is it important to provide infants with exogenous glucose?

Neonates have low stores of hepatic glucose, and mechanisms for gluconeogenesis are immature. Infants who have fasted may develop hypoglycemia. Symptoms of hypoglycemia include apnea, cyanosis, respiratory difficulties, seizures, high-pitched cry, lethargy, limpness, temperature instability, and sweating.

4 What are the differences in the gastrointestinal or hepatic function of neonates?

Gastric emptying is prolonged, and the lower esophageal sphincter is incompetent; thus the incidence of reflux may be increased. Elevated levels of bilirubin are common in neonates. Kernicterus, a complication of elevated levels of bilirubin, may lead to neurologic dysfunction and even death in extreme cases. Commonly used medications such as furosemide and sulfonamide may displace bilirubin from albumin and increase the risk of kernicterus. Diazepam contains the preservative benzyl alcohol, which also may displace bilirubin. Hepatic metabolism is immature, and hepatic blood flow is less than that in older children or adults. Drug metabolism and effect may be prolonged.

5 What is retinopathy of prematurity?

Retinopathy of prematurity is a disorder that occurs in premature and occasionally full-term infants who have been exposed to high inspired concentrations of oxygen. Proliferation of the retinal vessels, retinal hemorrhage, fibroproliferation, scarring, and retinal detachment may occur, with decreased visual acuity and blindness. Premature and full-term infants should have limited exposure to high concentrations of inspired oxygen. Oxygen saturation should be maintained between 92% and 95%, except during times of greater risk for desaturation.

6 How is volume status assessed in neonates?

Blood pressure is not a reliable measure of volume in neonates. If the anterior fontanelle is sunken, skin turgor is decreased, and the infant cries without visible tears, the diagnosis is dehydration. Capillary refill after blanching of the big toe should be less than 5 seconds. The extremities should not be significantly cooler than the rest of the body. Finally the skin should look pink and well perfused—not pale, mottled, or cyanotic.

7 What problems are common in premature infants?

See Table 56-1.

TABLE 56-1 Common Problems in Premature Infants

Problem Significance
Respiratory distress syndrome Surfactant, which is produced by alveolar epithelial cells, coats the inside of the alveolus and reduces surface tension. Surfactant deficiency causes alveolar collapse. BPD occurs in about 20% of cases.
Bronchopulmonary dysplasia (BPD) Interstitial fibrosis, cysts, and collapsed lung impair ventilatory mechanics and gas exchange.
Apnea and bradycardia (A and B) This is the most common cause of morbidity in postoperative period. Sensitivity of chemoreceptors to hypercarbia and hypoxia is decreased. Immaturity and poor coordination of upper airway musculature also contribute. If apnea persists >15 sec, bradycardia may result and worsen hypoxia.
Patent ductus arteriosus (PDA) Incidence of hemodynamically significant PDA varies with degree of prematurity but is high. Left-to-right shunting through the PDA may lead to fluid overload, heart failure, and respiratory distress.
Intraventricular hemorrhage (IVH) Hydrocephalus usually results from IVH. Avoiding fluctuations in blood pressure and intracranial pressure may reduce the risk of IVH.
Retinopathy of prematurity See Question 5.
Necrotizing enterocolitis Infants develop distended abdomen, bloody stools, and vomiting. They may go into shock and require surgery.

8 What special preparations are needed before anesthetizing a neonate?

The room should be warmed at least 1 hour before the start of the procedure to minimize radiant heat loss. A warming blanket and warming lights also help to decrease heat loss. Covering the infant with plastic decreases evaporative losses. Forced-air warming blankets have been shown to be very efficient at keeping infants warm. They work equally well if the infant is placed on them or if the blanket is placed on the infant. Temperature should be monitored carefully because it is easy to overheat a small infant.

image Routine monitors in a variety of appropriately small sizes should be available. At least two pulse oximeter probes are helpful in measuring preductal and postductal saturation.
image Listening to heart and breath sounds with a precordial or esophageal stethoscope is invaluable.
image Calculate estimated blood volume, maintenance, and maximal acceptable blood loss.
image Placing 25 to 50 ml of balanced salt solution in a buretrol prevents inadvertent administration of large amounts of fluid.
image Five percent albumin and blood should be readily available.

9 What intraoperative problems are common in small infants?

See Table 56-2.

TABLE 56-2 Common Intraoperative Problems in Infants

Problem Possible causes Solution
Hypoxia
1. Short distance from cords to carina; ETT is easily dislodged or displaced into bronchus.
2. Pressure on abdomen or chest by surgeons may decrease FRC and vital capacity.

1. After intubation, place ETT into right main stem and, carefully listening to breath sounds, pull tube back. Tape ETT 1-2 cm above level of carina.
2. Inform surgeons when they are interfering with ventilation. Hand ventilation helps to compensate for changes in peak pressure.

Bradycardia
1. Hypoxia
2. Volatile agents
3. Succinylcholine
1. Preoxygenate before intubation or extubation; all airway manipulations should be performed expeditiously
2. Minimize amount of volatile agent administered, especially halothane.
3. Give atropine before administering succinylcholine to blunt vagal effects.
Hypothermia See Question 1. Warm operating room; have warming blanket, warming lights, warm fluids, humidifier; keep infant covered whenever possible. Hypotension
1. Bradycardia
2. Volume depletion
1. Treat bradycardia with anticholinergics and ensure oxygenation.
2. Many neonatal emergencies are associated with major fluid loss. Volume status should be carefully assessed, with replacement as needed

ETT, Endotracheal tube; FRC, functional residual capacity.

10 What are the most common neonatal emergencies?

Tracheoesophageal fistula (TEF) Gastroschisis
Congenital diaphragmatic hernia (CDH) Patent ductus arteriosus (PDA)
Omphalocele Intestinal obstruction
Pyloric stenosis  

11 Discuss the incidence and anesthetic implications of congenital diaphragmatic hernia

image The incidence is 1 to 2:5000 live births.
image The diaphragm fails to close completely, allowing the peritoneal contents to herniate into the thoracic cavity. Abnormal lung development and hypoplasia usually occur on the side of the hernia but may be bilateral.
image The majority of hernias occur through the left-sided foramen of Bochdalek.
image Associated cardiovascular abnormalities present in 23% of patients.
image Patients present with symptoms of pulmonary hypoplasia. The severity of symptoms and prognosis depend on the severity of the underlying hypoplasia.
image Mask ventilation may cause visceral distention and worsen oxygenation. The infant should be intubated while awake. Low pressures must be used for ventilation to prevent barotrauma. Pneumothorax of the contralateral (healthier) lung may occur when high pressures are needed. Some patients may require high-frequency ventilation or extracorporeal membrane oxygenation.
image A nasogastric tube should be used to decompress the stomach.
image A transabdominal approach is used for the repair.
image Good intravenous (IV) access is mandatory. An arterial line may be necessary if the infant has significant lung or cardiac abnormalities.
image Pulmonary hypertension may complicate management by impairing oxygenation and decreasing cardiac output. Most patients need to remain intubated in the postoperative period.
image Opioids and muscle relaxants should be the primary agents used. Inhalational agents may be used to supplement the anesthetic if tolerated by the infant.

12 Which congenital anomalies are associated with tracheoesophageal fistula?

TEFs may occur alone or as part of a syndrome. The two most common syndromes are the VATER and the VACTERL syndromes. Patients with VATER have vertebral anomalies, imperforate anus, tracheoesophageal fistula, and renal or radial abnormalities. Patients with VACTERL have all of the above in addition to cardiac and limb abnormalities.

13 How should patients with tracheoesophageal fistula be managed?

image Patients usually present with excessive secretions, inability to pass a nasogastric tube, and regurgitation of feedings. Respiratory symptoms are uncommon.
image Positive-pressure ventilation may cause distention of the stomach. In a spontaneously breathing patient either an awake intubation or inhalational induction may be carried out.
image The endotracheal tube (ETT) should be placed into the right main stem and gradually withdrawn until bilateral breath sounds are heard. The stomach should be auscultated to ensure that it is not overinflated. If the infant has significant respiratory distress because of overinflation of the stomach, it may be necessary to perform a gastrostomy before anesthetizing the patient.
image An arterial line is frequently not necessary in an otherwise healthy infant with no other congenital anomalies. In selected patients it may be helpful to monitor blood gas values.
image Pulse oximetry is invaluable. Probes should be placed at a preductal (right hand or finger) and postductal site (left hand or feet).
image Once the airway has been secured, the infant is placed in the left lateral decubitus position. Placing a precordial stethoscope on the left chest helps to detect displacement of the ETT.
image A right-sided thoracotomy is made, and the fistula is divided. If possible, the esophagus is reanastomosed; if not, a gastrostomy tube is placed.
image It is desirable to extubate the infant as soon as possible to prevent pressure on the suture line.

14 What are the differences between omphalocele and gastroschisis?

An omphalocele is a hernia within the umbilical cord caused by failure of the gut to migrate into the abdomen from the yolk sac. The bowel is completely covered with chorioamnionic membranes but otherwise usually normal. Patients with omphalocele frequently have associated cardiac, urologic, and metabolic anomalies.

In gastroschisis the bowel is not covered with chorioamnionic membranes; often there is an inflammatory exudate, and the bowel anatomy may be abnormal. The exact cause of gastroschisis is unknown; it may be to the result of vascular occlusion of blood supply to the abdominal wall or fetal rupture of an omphalocele.

15 How are patients with omphalocele or gastroschisis managed in the perioperative period?

image It is important to prevent evaporative and heat loss from exposed viscera. The exposed bowel should be covered with warm, moist saline packs and Saran wrap until the time of surgery. The operating room should be warmed before the arrival of the infant. Warming lights and a warming blanket help to decrease conductive and radiation loss. Covering the head and extremities with plastic prevents evaporative loss.
image Respiratory distress is uncommon; therefore infants usually arrive in the operating room breathing spontaneously. Awake intubation or rapid-sequence induction quickly establishes airway control.
image Ventilation is controlled with muscle relaxants to facilitate return of the bowel into the abdomen.
image After intubation a nasogastric tube should be placed if not already present.
image Patients need good IV access to replace third-space and evaporative losses. An arterial line can be helpful.
image Once the surgeons begin to put the viscera into the abdomen, the ventilatory requirements change. Hand ventilation during this phase allows the anesthesiologist to feel peak airway pressures and changes in airway pressures. If peak airway pressures are greater than 40 cm H2O, the surgeons must be notified.
image The abdominal cavity may be too small for the viscera. Venous return from or blood flow to the lower extremity may be compromised. A pulse oximeter on the foot helps to detect such changes. Renal perfusion may decrease and manifest as oliguria.
image If primary closure is not possible, the surgeons choose either to do a fascial (skin) closure or place a synthetic mesh silo over the defect. Both approaches necessitate return trips to the operating room for the final corrective procedure.
image Patients usually remain intubated after surgery.

16 How does pyloric stenosis present?

Pyloric stenosis is a common surgical problem, occurring in 1 out of 300 live births. First-born males are more commonly affected, and it usually presents between 2 and 6 weeks of age. Patients present with persistent vomiting. Dehydration, hypochloremia, and metabolic alkalosis can develop. Continued severe vomiting and dehydration can lead to metabolic acidosis. An olivelike mass can be felt in the epigastrium. Confirmation of the diagnosis by barium swallow roentgenogram has largely been replaced by abdominal ultrasound. Surgeons may choose to repair the pylorus laparoscopically or by an open approach.

17 Discuss the perioperative management of patients with pyloric stenosis

image Electrolyte and volume imbalances need to be corrected before taking the patient to the operating room.
image A gastric tube should be placed, and continuous suction applied. The patient may have a large gastric volume of oral x-ray film contrast.
image Patients are at risk for aspiration; therefore rapid-sequence intubation or modified rapid-sequence intubation should be performed. Awake intubation in this situation has been associated with greater desatuaration and a longer time to intubate
image Choice of anesthetic agents and muscle relaxants will be guided by the speed of the surgeon (duration of surgery can be 10 to 60 minutes).
image Opioids are usually unnecessary and should be avoided intraoperatively

18 Are there any benefits to specific ventilator strategies in neonates?

Evidence has begun to emerge that strongly supports the use of lung protective ventilation (8ml/kg) in the management of neonates with respiratory distress syndrome (RDS), meconium aspiration syndrome, or congenital diaphragmatic hernia. Injury that has resulted in heterogeneous lung mechanics may cause a particular susceptibility to overdistention because of small absolute lung volumes and a highly compliant chest wall. Regional overdistention and lung stretch from large tidal volumes and elevated airway pressures may be more significant in neonates than adults because of the difference in chest wall compliance and abdominal compartment pressures. In addition to barotrauma caused by high airway pressure, atelectotrauma, related to repeated alveolar recruitment and derecruitment, have been identified as potentially injurious to the lung in patients at risk for RDS.

19 At what age should the former premature infant be allowed to go home after surgery?

Premature infants are at increased risk for the development of postoperative apnea even after relatively minor surgery. Postoperative apnea has been reported in ex-premature infants up to 60 weeks’ postconceptual age (PCA). Côté and associates showed that, in ex-premature infants born at a gestional age of 32 weeks undergoing inguinal herniorrhaphy, the risk of postoperative apnea was not less than 1% until 56 weeks’ PCA. Anemia appropriate for gestational age or high-for−gestational age infants and a history of continuing apnea at home increased the risk of postoperative apnea.

KEY POINTS: Neonatal Anesthesia image

1. Neonates are at increased anesthetic risk because they:

image Desaturate quickly.
image Are more prone to airway obstruction.
image Have noncompliant ventricles and depend on adequate heart rate to maintain cardiac output.
image Can get hypothermic very quickly.
image Have immature kidney and liver function, which affects the pharmacology of administered medications.

2. Common neonatal emergencies include:

TEF Gastroschisis
CDH PDA
Omphalocele Intestinal obstruction
Pyloric stenosis  

3. Careful preparation for anesthetizing neonates includes:

image Warming the room, having warming lights, blankets, and convection air warming blankets available to maintain body heat.
image Having multiple sizes available for the standard monitoring devices.
image Estimating fluid maintenance, deficit, blood volume, and maximal acceptable blood loss before the start of the case.
image Limiting the amount of volume placed in the IV buretrol to prevent accidental overhydration

4. All pyloric stenosis patients:

image Should be treated as having full stomachs. Always suction the stomach before induction.
image Usually present with metabolic alkalosis, but if very dehydrated may present with metabolic acidosis.
image Volume and electrolyte imbalances need to be corrected before they are brought to the operating room for surgical correction.
image Opioids are usually unecessary and should be avoided intraoperatively.

20 Does regional anesthesia protect the patient from developing postoperative anesthesia?

Spinal anesthesia without supplemental sedation has been associated with less apnea than general anesthesia. Caudal epidural blockade may also be used. The addition of sedation may increase the incidence of postoperative apnea.

SUGGESTED READINGS

1. Côté C.J., Zaslavsky A., Downes J.J., et al. Postoperative apnea in former preterm infants after inguinal herniorrhaphy: A combined analysis. Anesthesiology. 1995;82:809-822.

2. Feldman J.M., Davis P.J. Do new anesthesia ventilators deliver small tidal volumes accurately during volume-controlled ventilation? Anesth Analg. 2008;106:1392-1400.

3. Schultz M.J., Haitsma J.J., Slutsky A.S., et al. What tidal volumes should be used in patients without acute lung injury? Anesthesiology. 2007;106:1226-1231.

4. Vitali S.H., Arnold J.H. Bench-to-bedside review: ventilator strategies to reduce lung injury—lessons from pediatric and neonatal intensive care. Crit Care. 2005;9:177-183.

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58: Congenital Heart Disease 59: Fundamentals of Obstetric Anesthesia 34: Heart Failure 5: Electrolytes 76: Electroconvulsive Therapy 41: Acute Respiratory Distress Syndrome (ARDS)