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Chapter: Clinical Anesthesiology: Anesthetic Management: Obstetric Anesthesia

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Anesthesia for Neonatal Resuscitation

Anesthesia for Neonatal Resuscitation
1. General Care of the Neonate 2. Meconium-Stained Neonates 3. Care of the Depressed Neonate

NEONATAL RESUSCITATION

 

1. General Care of the Neonate

 

One healthcare provider whose sole responsibility is to care for the neonate and who is capable of provid-ing resuscitation should attend every delivery. As the head is delivered, the nose, mouth, and pharynx are suctioned with a bulb syringe. After the remainder of the body is delivered, the skin is dried with a ster-ile towel. Once the umbilical cord stops pulsating or neonatal breathing is initiated, the cord is clamped and the neonate is placed in a radiant warmer with the bed tilted in a slight Trendelenburg position.

Neonatal evaluation and treatment are carried out simultaneously (Figure 41–5). If the neonate is obviously depressed, the cord is clamped early and resuscitation is initiated immediately. Breathing normally begins within 30 s and is sustained within 90 s. Respirations should be 30–60 breaths/min and the heart rate 120–160 beats/min. Respirations are assessed by auscultation of the chest, whereas heart rate is determined by palpation of the pulse at the base of the umbilical cord or auscultation of the pre-cordium. It is critically important to keep the neo-nate warm.

 

In addition to respirations and heart rate, color, tone, and reflex irritability should be evalu-ated. The Apgar score (Table 41–7), recorded at 1 min and again at 5 min after delivery, remains the most valuable assessment of the neonate. The 1-min score correlates with survival, whereas the 5-min score has limited relationship to neurologi-cal outcome.

 

Neonates with Apgar scores of 8–10 are vig-orous and may require only gentle stimulation (flicking the foot, rubbing the back, and additional drying). A catheter should first be gently passed


through each nostril to rule out choanal atresia, and then through the mouth to suction the stomach and rule out esophageal atresia.

2. Meconium-Stained Neonates

 

The presence or absence of meconium in the amni-otic fluid (approximately 10–12% of deliveries) changes the immediate management of the neonate at birth. Fetal distress, particularly after 42 weeks of gestation, is often associated with release of thick meconium into the fluid. Fetal gasping during stress results in entry of a large amount of meconium-tainted amniotic fluid into the lungs. When the neonate initiates respiration at birth, the meconium moves from the trachea and large airways downtoward the periphery of the lung. Thick or partic-ulate meconium may obstruct small airways and cause severe respiratory distress in 15% of meco-nium-stained neonates. Moreover, these infants can develop persistent fetal circulation.

 

Unless the neonate has absent or depressed respirations, thin watery meconium does not require suctioning beyond careful bulb suctioning of the oropharynx when the head emerges from the perineum (or from the uterus at cesarean section). When thick “pea soup” meconium is present in the amniotic fluid, however, some clinicians intubate and suction the trachea immediately after delivery but before the first breath is taken. If the baby is not vigorous, tracheal suctioning is recommended when meconium is present. Tracheal suctioning of the thick meconium is accomplished by a special suctioning device attached to the endotracheal tube as the tube is withdrawn. If meconium is aspirated from the trachea, the procedure should be repeated until no meconium is obtained—but no more than three times, after which it is usually of no further benefit. The infant should then be given supplemen-tal oxygen by face mask and observed closely. The stomach should also be suctioned to prevent pas-sive regurgitation of any meconium. Newborns with meconium aspiration have an increased incidence of pneumothorax (10% compared with 1% for all vagi-nal deliveries).

 

3. Care of the Depressed Neonate

 

Approximately 6% of newborns, most of whom weigh less than 1500 g, require some form of advanced life support. Resuscitation of the depressed neonate requires two or more persons— one to manage the airway and ventilation and another to perform chest compressions, if neces-sary. A third person greatly facilitates the placement of intravascular catheters and the administration of fluids or drugs. The anesthesiologist caring for the mother can render only brief assistance and only when it does not jeopardize the mother; other per-sonnel are, therefore, usually responsible for neona-tal resuscitation.

 

Because the most common cause of neonatal depression is intrauterine asphyxia, the empha-sis in resuscitation is on respiration. Hypovolemia is also a contributing factor in a significant num-ber of neonates. Factors associated with hypovole-mia include early clamping of the umbilical cord, holding the neonate above the introitus prior to clamping, prematurity, maternal hemorrhage, pla-cental transection during cesarean section, sepsis, and twin-to-twin transfusion.

 

Failure of the neonate to quickly respond to respiratory resuscitative efforts mandates vascular access and blood gas analysis; pneumothorax (1% incidence) and congenital anomalies of the airway, including tracheoesophageal fistula (1:3000–5000 live births), and congenital diaphragmatic hernia (1:2000–4000) should also be considered.

 

Grouping by the 1-min Apgar score greatly facilitates resuscitation: (1) mildly asphyxiated neo-nates (Apgar score of 5–7) usually need only stimu-lation while 100% oxygen is blown across the face;moderately asphyxiated neonates (Apgar score of 3–4) require temporary assisted positive-pressure ventilation with mask and bag; and (3) severely depressed neonates (Apgar score of 0–2) should be immediately intubated, and chest compressions may be required.

 

Guidelines for Ventilation

 

Indications for positive-pressure ventilation include apnea, (2) gasping respirations, (3) persistent central cyanosis with 100% oxygen, and (4) a per-sistent heart rate less than 100 beats/min. Excessive flexion or extension of the neck can cause airway obstruction. A 1-in.-high towel under the shoulders may be helpful in maintaining proper head posi-tion. Assisted ventilation by bag and mask should be at a rate of 30–60 breaths/min with 100% oxy-gen. Initial breaths may require peak pressures of up to 40 cm H2O, but pressures should not exceed 30 cm H2O thereafter. Adequacy of ventilation should be checked by auscultation and chest excur-sions. Gastric decompression with an 8F tube often facilitates ventilation. If after 30 s the heart rate is over 100 beats/min and spontaneous ven-tilations become adequate, assisted ventilation is no longer necessary. If the heart rate remains less than 60 beats/min or 60–80 beats/min without an increase in response to resuscitation, the neonate is intubated and chest compressions are started.

If the heart rate is 60–80 beats/min and increasing, assisted ventilation is continued and the neonate is observed. Failure of the heart rate to rise above 80 beats/min is an indication for chest compres-sions. Indications for endotracheal intubation include ineffective or prolonged mask ventilation and the need to administer medications.

 

Intubation (Figure 41–6) is performed with a Miller 00, 0, or 1 laryngoscope blade, using a 2.5-, 3-, or 3.5-mm endotracheal tube (for neonates <1 kg, 1–2 kg, and >2 kg, respectively). Correct endotracheal tube size is indicated by a small leak with 20 cm H2O pressure. Right endobronchial intubation should be excluded by chest ausculta-tion. The correct depth of the endotracheal tube (“tip to lip”) is usually 6 cm plus the weight in kilo-grams. Oxygen saturation can usually be measured by a pulse oximeter probe applied to the palm. Capnography is also very useful in confirming endotracheal intubation. Transcutaneous oxygen sensors are useful for measuring tissue oxygenation but require time for initial equilibration. Use of a laryngeal mask airway (LMA#1) has been reported


in neonates weighing more than 2.5 kg and may be useful if endotracheal intubation is difficult (eg, Pierre Robin syndrome).

Guidelines for Chest Compressions

 

Indications for chest compressions are a heart rate that is less than 60 beats/min or 60–80 beats/min and not rising after 30 s of adequate ventilation with 100% oxygen.

 

Cardiac compressions should be provided at a rate of 120/min. The two thumb/encircling hands technique (Figure 41–7) is generally pre-ferred because it appears to generate higher peak systolic and coronary perfusion pressures. Alternatively, the two-finger technique can be used (Figure 41–8). The depth of compressions should be approximately one third of the anterior–poste-rior diameter of the chest and enough to generate a palpable pulse.

 

Compressions should be interposed with venti-lation in a 3:1 ratio, such that 90 compressions and 30 ventilations are given per minute. The heart rate should be checked periodically. Chest compressions should be stopped when the spontaneous heart rate exceeds 80 beats/min.


Vascular Access

 

Cannulation of the umbilical vein with a 3.5F or 5F umbilical catheter is easiest and the preferred tech-nique. The tip of the catheter should be just below skin level and allow free backflow of blood; further advancement may result in infusion of hypertonic solutions directly into the liver. A peripheral vein or even the endotracheal tube can be used as an alter-nate route for drug administration.

 

Cannulation of one of the two umbilical arteries allows measurement of blood pressure and facilitates blood gas measurements but may be more difficult. Specially designed umbilical artery catheters allow continuous Pao2 or oxygen saturation monitoring as well as blood pressure. Care must be taken not to introduce any air into either the artery or the vein.

 

Volume Resuscitation

Some neonates at term and nearly two thirds of premature infants requiring resuscitation are hypo-volemic at birth. Diagnosis is based on physical examination (low blood pressure and pallor) and a poor response to resuscitation. Neonatal blood pres-sure generally correlates with intravascular volume and should therefore routinely be measured. Normal blood pressure depends on birth weight and varies from 50/25 mm Hg for neonates weighing 1–2 kg to 70/40 mm Hg for those weighing over 3 kg. A low blood pressure suggests hypovolemia. Volume expan-sion may be accomplished with 10 mL/kg of lactated Ringer’s injection, normal saline, or type O-negative blood cross-matched with maternal blood. Less common causes of hypotension include hypocalce-mia, hypermagnesemia, and hypoglycemia.

 

Drug Therapy

 

A. Epinephrine

 

Epinephrine, 0.01–0.03 mg/kg (0.1–0.3 mL/kg of a 1:10,000 solution), should be given for asystole or a spontaneous heart rate of less than 60 beats/min in spite of adequate ventilation and chest compressions. It may be repeated every 3–5 min. Epinephrine may be given in 1 mL of saline via the endotracheal tube when venous access is not available.

B. Naloxone

 

Naloxone, 0.1 mg/kg intravenously or 0.2 mg/kg intramuscularly, is given to reverse the respiratory depressant effect of opioids given to the mother in the last 4 h of labor. Withdrawal symptoms may be precipitated in babies of mothers who chronically consume prescribed or illicit opioids.

C. Other Drugs

 

Other drugs may be indicated only in specific settings. Sodium bicarbonate (2 mEq/kg of a 0.5 mEq/mL 4.2% solution) should usually be given only for a severe metabolic acidosis documented by blood gas measurements and when ventilation is adequate. It may also be administered during prolonged resuscitation (>5 min)—particularly if blood gas measurements are not readily available. The infusion rate should not exceed 1 mEq/kg/min to avoid hypertonicity and intracranial hemorrhage. As noted above, in order to prevent hypertonicity-induced hepatic injury, the umbilical vein catheter tip should not be in the liver. Calcium gluconate mg/kg (CaCl 2, 30 mg/kg) should be given only to neonates with documented hypocalcemia or those with suspected magnesium intoxication (from maternal magnesium therapy); these neonates are usually hypotensive, hypotonic, and appear vasodi-lated. Glucose (8 mg/kg/min of a 10% solution) is given only for documented hypoglycemia because hyperglycemia worsens hypoxic neurological defi-cits. Blood glucose should be measured because up to 10% of neonates may have hypoglycemia (glucose <35 mg/dL), particularly those delivered by caesarean section. Dopamine may be started at 5 mcg/kg/min to support arterial blood pressure. Lastly, surfactant may be given through the endotracheal tube to pre-mature neonates with respiratory distress syndrome.

 

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