CPAP is usually administered by means of a ventilator or stand-alone CPAP delivery system. Any system used to deliver CPAP should allow continuous monitoring of the delivered pressure, and be equipped with safety alarms to indicate when the pressure is above or below the desired level. Alternatively, CPAP may be delivered by a simplified system providing blended oxygen flowing past the infant’s airway, with the end of the tubing submerged in 0.25% acetic acid in sterile water solution to the desired depth to generate pressure (“bubble CPAP”). Stand-alone variable flow CPAP devices, in which expiratory resistance is decreased via a “fluidic flip” of flow at the nosepiece during expiration, are also available.

General characteristics. A continuous flow of heated, humidified gas is circulated past the infant’s airway, typically at a set pressure of 3 to 8 cm H₂O, maintaining an elevated end-expiratory lung volume while the infant breathes spontaneously. The air—oxygen mixture and airway pressure can be adjusted. Variable flow CPAP systems may decrease the work of breathing and improve lung recruitment in infants on CPAP, but have not been shown to be clearly superior to conventional means of delivery. CPAP is usually delivered by means of nasal prongs, nasopharyngeal tube, or nasal mask. Endotracheal CPAP should not be used, because the high resistance of the endotracheal tube increases the work of breathing, especially in small infants. Positive-pressure hoods and continuous-mask CPAP are not recommended.

General characteristics. A continuous flow of heated and humidified gas is circulated past the infant’s airway; the gas is a mixture of air, blended with oxygen to maintain the desired oxygen saturation level. Peak inspiratory pressure (PI or PIP), positive end-expiratory pressure (PEEP), and respiratory timing (rate and duration of inspiration and expiration) are selected.

General characteristics. These ventilators combine the features of pressure-limited, time-cycled, continuous flow ventilators with an airway pressure, airflow, or respiratory movement sensor. By measuring inspiratory flow or movement, these ventilators deliver intermittent positivepressure breaths at a fixed rate, in synchrony with the baby’s inspiratory efforts (“synchronized IMV,” or synchronized intermittent mandatory ventilation [SIMV]). During apnea, SIMV ventilators continue to deliver the set IMV rate. In patient-triggered ventilation, a positive pressure breath is delivered with every inspiratory effort. As a result, the ventilator delivers more frequent positive pressure breaths, usually allowing a decrease in the inspiratory pressure (PIP) needed for adequate gas exchange. During apnea, the ventilator in patient-triggered mode delivers an
operator-selected IMV (“control”) rate. In some ventilators, synchronized IMV breaths can be supplemented by pressure-supported breaths in the spontaneously breathing infant. Ventilators equipped with a flow sensor can also be used to monitor delivered VT continuously by integration of the flow signal.

Indications. SIMV can be used when a conventional pressure-limited ventilator is indicated. If available, it is the preferable mode of ventilator therapy in infants who are breathing spontaneously while on IMV. The indications for assist/control and pressure support ventilation have not been established, although many neonatal intensive care units (NICUs) use these modes as initial ventilator support because of perceived advantages of using lower peak inspired pressure and smaller VTs.

General characteristics. Volume-cycled ventilators are similar to pressurelimited ventilators, except that the operator selects the volume delivered rather than the PIP. “Volume guarantee” is a mode of pressure-limited SIMV, in which the ventilator targets an operator-chosen VT (usually 4—6 mL/kg) during mechanically delivered breaths. Volume guarantee allows rapid response of the ventilator pressures to changing lung compliance, and may be particularly useful in infants with RDS who receive surfactant therapy.

Advantages. The pressure automatically varies with respiratory system compliance to deliver the selected VT, theoretically minimizing variability in minute ventilation.

Indications. Volume-cycled ventilators may be useful if lung compliance is rapidly changing, as would be seen in infants receiving surfactant therapy.

General characteristics. Available high-frequency ventilators are similar despite considerable differences in design. All are capable of delivering extremely rapid rates (300-1,500 breaths/minute, 5-25 Hz; 1 Hz = 60 breaths/minute), with VTs equal to or smaller than anatomic dead space. These ventilators apply continuous distending pressure to maintain an elevated lung volume; small VTs are superimposed at a rapid rate. HFJ ventilators are paired with a conventional pressure-limited device, which is used to deliver intermittent “sigh” breaths to help prevent atelectasis. “Sigh” breaths are not used with HFO ventilation. Expiration is passive (i.e., dependent on chest wall and lung recoil) with HFFI and HFJ machines, while expiration is active with HFO. The mechanisms of gas exchange are incompletely understood.

Disadvantages. Despite theoretical advantages of HFV, no significant benefit of this method has been demonstrated in routine clinical use over more conventional ventilators. Only one rigorously controlled study found a small reduction in BPD in infants at high risk treated with high-frequency oscillatory ventilation (HFOV) as the primary mode of ventilation. This experience is likely not generally applicable, however, as other studies have shown no difference. These ventilators are more complex and expensive, and there is less long-term clinical experience. The initial studies with HFO suggested an increased risk of significant intraventricular hemorrhage, although this complication has not been observed in recent clinical trials. Studies comparing the different types of high-frequency ventilators are unavailable; therefore, the relative advantages or disadvantages of HFO, HFFI, and HFJ, if any, are not characterized.

Indications. HFV is primarily used as a rescue therapy for infants failing conventional ventilation. Both HFJ and HFO ventilators have been shown to be superior to conventional ventilation in infants with air leak syndromes, especially PIE. Because of the potential for complications and equivalence to conventional ventilation in the incidence of BPD, we do not use high-frequency ventilation as the primary mode of ventilatory support in infants.

Recently delivered premature infant with minimal respiratory distress and low supplemental oxygen requirement (to prevent atelectasis)

Respiratory distress and requirement of FiO₂ above 0.30 by hood

FiO₂ above 0.40 by hood

Initial stabilization in the delivery room for spontaneously breathing, extremely premature infants (25—28 weeks’ gestation)

Initial management of premature infants with moderately severe respiratory distress

Clinically significant retractions and/or distress after recent extubation

In general, infants with RDS who require FiO₂ above 0.35 to 0.40 on CPAP should be intubated, ventilated, and given surfactant replacement therapy. In some NICUs, intubation for surfactant therapy in infants with RDS is followed by immediate extubation to CPAP. We generally use mechanical ventilation for all infants who are given surfactant.

After extubation to facilitate maintenance of lung volume

Frequent intermittent apnea unresponsive to drug therapy

Early treatment when use of mechanical ventilation is anticipated because of deteriorating gas exchange

Relieving “increased work of breathing” in an infant with signs of moderateto-severe respiratory distress

Administration of surfactant therapy in infants with RDS

Prolonged apnea

PaO₂ below 50 mm Hg, or FiO₂ above 0.80. This indication may not apply to the infant with cyanotic congenital heart disease.

PaCO₂ above 60 to 65 mm Hg with persistent acidemia

General anesthesia

FiO₂. The goal is to maintain adequate tissue oxygen delivery. Generally, this can be accomplished by achieving a PaO₂ of 50 to 70 mm Hg and results in a hemoglobin saturation of 88% to 95% (see Fig. 29.1). Increasing inspired oxygen is the simplest and most direct means of improving oxygenation. In premature infants, the risk of retinopathy and pulmonary oxygen toxicity argue for minimizing PaO₂. For infants with other conditions, the optimum PaO₂ may be higher. Direct pulmonary oxygen toxicity begins to occur at FiO₂ values greater than 0.60 to 0.70.