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Respiratory Support in Neonates and Infants
Initial stabilization maneuvers include mild tactile stimulation, head positioning, and suctioning of the mouth and nose followed as needed by
Neonates who cannot be oxygenated by any of these means may require a full cardiac evaluation to exclude congenital heart disease and treatment with high-frequency oscillatory ventilation, nitric oxide, extracorporeal membrane oxygenation, or a combination.
O2 may be given using a nasal cannula, face mask, or O2 hood, with O2 concentration set to achieve a Pao2 of 50 to 70 mm Hg in preterm infants and 50 to 80 mm Hg in term infants or an O2saturation of 90 to 94% in preterm infants and 92 to 96% in term infants. Lower Pao2 in preterm infants provides almost full saturation of Hb, because fetal Hb has a higher affinity for O2; maintaining higher Pao2 increases the risk of retinopathy of prematurity (see Retinopathy of Prematurity ). No matter how O2 is delivered, it should be warmed (36 to 37° C) and humidified to prevent secretions from cooling and drying and to prevent bronchospasm.
An umbilical artery catheter (UAC) is usually placed for sampling ABGs in neonates who require fraction of inspired O2 (Fio2) ≥ 40%. If a UAC cannot be placed, a percutaneous radial artery catheter can be used for continuous BP monitoring and blood sampling.
Neonates who are unresponsive to these maneuvers may require fluids to improve cardiac output and are candidates for CPAP ventilation or bag-and-mask ventilation (40 to 60 breaths/min). If the infant does not oxygenate with or requires prolonged bag-and-mask ventilation, endotracheal intubation with mechanical ventilation is indicated, although very immature neonates (eg, < 28 wk gestation or < 1000 g) are typically begun on ventilatory support immediately after delivery so that they can receive preventive surfactant therapy. Because bacterial sepsis is a common cause of respiratory distress in neonates, it is common practice to draw blood cultures and give antibiotics to neonates with high O2 requirements pending culture results.
CPAP delivers O2 at a positive pressure, usually 5 to 7 cm H2O, which keeps alveoli open and improves oxygenation by reducing the amount of blood shunted through atelectatic areas while the infant breathes spontaneously. CPAP can be provided using nasal prongs and various apparatuses to provide the positive pressure; it also can be given using an endotracheal tube connected to a conventional ventilator with the rate set to zero. CPAP is indicated when Fio2≥ 40% is required to maintain acceptable Pao2 (50 to 70 mm Hg) in infants with respiratory disorders that are of limited duration (eg, diffuse atelectasis, mild respiratory distress syndrome, lung edema). In these infants, CPAP may preempt the need for positive pressure ventilation.
NIPPV (see also Overview of Mechanical Ventilation : Noninvasive positive pressure ventilation (NIPPV)) delivers positive pressure ventilation using nasal prongs or nasal masks. It can be synchronized (ie, triggered by the infant's inspiratory effort) or nonsynchronized. NIPPV can provide a back-up rate and can augment an infant's spontaneous breaths. Peak pressure can be set to desired limits. It is particularly useful in patients with apnea to facilitate extubation and to help prevent atelectasis.
Endotracheal tubes are required for mechanical ventilation (see also Airway Establishment and Control : Endotracheal tubes):
Intubation is safer if O2 is insufflated into the infant’s airway during the procedure. Orotracheal intubation is preferred. The tube should be inserted such that the
The endotracheal tube is properly placed when its tip can be palpated through the anterior tracheal wall at the suprasternal notch. It should be positioned about halfway between the clavicles and the carina on chest x-ray, coinciding roughly with vertebral level T2. If position or patency is in doubt, the tube should be removed and the infant should be supported by bag-and-mask ventilation until a new tube is inserted. Acute deterioration of the infant’s condition (sudden changes in oxygenation, ABGs, BP, or perfusion) should trigger suspicion of changes in the position of the tube, patency of the tube, or both.
Ventilators can be set to deliver fixed pressures or volumes; can provide assist control (AC, in which the ventilator is triggered to deliver a full breath with each patient inspiration) or intermittent mandatory ventilation (IMV, in which the ventilator delivers a set number of breaths within a time period, and patients can take spontaneous breaths in between without triggering the ventilator); and can be normal or high frequency (delivering 400 to 900 breaths/min). Optimal mode or type of ventilation depends on the infant’s response. Volume ventilators are considered useful for larger infants with varying pulmonary compliance or resistance (eg, in bronchopulmonary dysplasia), because delivering a set volume of gas with each breath ensures adequate ventilation. AC mode is often used for treating less severe pulmonary disease and for decreasing ventilator dependence while providing a small increase in airway pressure or a small volume of gas with each spontaneous breath. High-frequency jet, oscillatory, and flow-interrupter ventilators are used in extremely premature infants (< 28 wk) and in some infants with air leaks, widespread atelectasis, or pulmonary edema (see Pulmonary Edema ).
Initial ventilator settings are estimated by judging the severity of respiratory impairment. Typical settings for an infant in moderate respiratory distress are Fio2= 40%; inspiratory time (IT) = 0.4 sec; expiratory time =1.1 sec; IMV or AC rate = 40 breaths/min; peak inspiratory pressure (PIP) = 15 cm H2O for very low-birth-weight infants and up to 25 cm H2O for near-term infants; and positive end-expiratory pressure (PEEP) = 5 cm H2O. These settings are adjusted based on the infant’s oxygenation, chest wall movement, breath sounds, and respiratory efforts along with arterial or capillary blood gases.
Patient-triggered ventilation often is used to synchronize the positive pressure ventilator breaths with the onset of the patient’s own spontaneous respirations. This seems to shorten the time on a ventilator and may reduce barotrauma. A pressure-sensitive air-filled balloon attached to a pressure transducer (Graseby capsule) taped to the infant’s abdomen just below the xiphoid process can detect the onset of diaphragmatic contraction, or a flow or temperature sensor placed at the endotracheal tube adapter can detect the onset of a spontaneous inhalation.
Ventilator pressures or volumes should be as low as possible to prevent barotrauma and bronchopulmonary dysplasia; an elevated Paco2 is acceptable as long as pH remains ≥ 7.25 (permissive hypercapnia). Likewise, a Pao2 as low as 40 mm Hg is acceptable if BP is normal and metabolic acidosis is not present.
Adjunctive treatments used with mechanical ventilation in some patients include
Paralytics (eg, vecuronium or pancuronium bromide 0.03 to 0.1 mg/kg IV q 1 to 2 h prn [with pancuronium, a test dose of 0.02 mg/kg is recommended in neonates]) and sedatives (eg, fentanyl 1 to 4 mcg/kg IV push q 2 to 4 h or midazolam 0.05 to 0.15 mg/kg IV over 5 min q 2 to 4 h) may facilitate endotracheal intubation and can help stabilize infants whose movements and spontaneous breathing prevent optimal ventilation. These drugs should be used selectively, however, because paralyzed infants may need greater ventilator support, which can increase barotrauma. Inhaled nitric oxide 5 to 20 ppm may be used for refractory hypoxemia when pulmonary vasoconstriction is a contributor to hypoxia (eg, in idiopathic pulmonary hypertension, pneumonia [see Neonatal Pneumonia], or congenital diaphragmatic hernia [see Diaphragmatic Hernia ]) and may prevent the need for extracorporeal membrane oxygenation (see Soft-Tissue Injuries : Extracorporeal membrane oxygenation (ECMO)).
Weaning from the ventilator can occur as respiratory status improves. The infant can be weaned by lowering
Continuous-flow positive pressure ventilators permit the infant to breathe spontaneously against PEEP while the ventilator rate is progressively slowed. As the rate is reduced, the infant takes on more of the work of breathing. Infants who can maintain adequate oxygenation and ventilation on lower settings typically tolerate extubation. The final steps in ventilator weaning involve extubation, possibly support with nasal (or nasopharyngeal) CPAP or NIPPV, and, finally, use of a hood or nasal cannula to provide humidified O2 or air.
Very low-birth-weight infants may benefit from the addition of a methylxanthine (eg, aminophylline, theophylline, caffeine) during the weaning process. Methylxanthines are CNS-mediated respiratory stimulants that increase ventilatory effort and may reduce apneic and bradycardic episodes that may interfere with successful weaning. Caffeine is the preferred agent because it is better tolerated, easier to give, safer, and requires less monitoring. Corticosteroids, once used routinely for weaning and treatment of chronic lung disease, are no longer recommended in premature infants because risks (eg, impaired growth and neurodevelopmental delay) outweigh benefits. A possible exception is as a last resort in near-terminal illness, in which case parents should be fully informed of risks.
ECMO is a form of cardiopulmonary bypass used for infants who cannot be oxygenated adequately or ventilated with conventional ventilators. Eligibility criteria vary by center, but in general, infants should have reversible disease (eg, persistent pulmonary hypertension of the newborn [see Persistent Pulmonary Hypertension of the Newborn ], congenital diaphragmatic hernia, overwhelming pneumonia) and should have been on mechanical ventilation < 7 days.
After systemic heparinization, blood is circulated through large-diameter catheters from the internal jugular vein into a membrane oxygenator, which serves as an artificial lung to remove CO2and add O2. Oxygenated blood is then circulated back to the internal jugular vein (venovenous ECMO) or to the carotid artery (venoarterial ECMO). Venoarterial ECMO is used when both circulatory support and ventilatory support are needed (eg, in overwhelming sepsis). Flow rates can be adjusted to obtain desired O2 saturation and BP.
ECMO is contraindicated in infants < 34 wk, < 2 kg, or both because of the risk of intraventricular hemorrhage with systemic heparinization. Complications include thromboembolism, air embolization, neurologic (eg, stroke, seizures) and hematologic (eg, hemolysis, neutropenia, thrombocytopenia) problems, and cholestatic jaundice.
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