Care of the Neonate on Nasal Continuous Positive Airway Pressure: A Bedside Guide

Respiratory Distress Syndrome

Respiratory distress syndrome is primarily caused by a deficiency of surfactant. Surfactant decreases alveolar surface tension, decreasing the pressure needed to inflate and keep alveoli open. The quantity and quality of surfactant is lower with decreasing gestational age. Portions of surfactant can be synthesized during the saccular phase of lung development, between 27 and 36 weeks’ gestation, but most infants born before 34 weeks’ gestation do not have adequate surfactant to support extrauterine life without respiratory support because mature levels of pulmonary surfactant are not usually present until after 35 weeks’ gestation. ^17–19 In addition to prematurity, surfactant deficiency can be associated with the following ²⁰ :

Surfactant deficiency results in increased work of breathing as the neonate tries to generate enough pressure to open alveoli and inflate the lungs. This increase in work of breathing is accentuated by the increase in chest wall compliance seen in both preterm and term infants. ^21,22 In addition to having a highly compliant chest wall, premature infants are prone to central and obstructive apnea, ²³ and mature alveoli are not present until 36 weeks’ gestation. ²⁰ These factors all contribute to diffuse atelectasis, which results in decreased lung compliance and a low functional residual capacity (FRC), ultimately causing a mismatch of ventilation and perfusion. Blood bypasses collapsed, unoxygenated alveoli, causing a ventilation-to-perfusion mismatch resulting in hypoxemia (Figure 1). This hypoxemia can then contribute to an increase in pulmonary vascular resistance, resulting in increased right-to-left shunting of deoxygenated blood through the foramen ovale and ductus arteriosus, further worsening arterial hypoxemia and ultimately resulting in respiratory failure.

FIGURE 1

Ventilation–perfusion scenarios in the newborn lung.

Abbreviation: TTN = transient tachypnea of the newborn.

Respiratory distress syndrome presents with increased work of breathing, desaturation, and cyanosis immediately at or shortly after birth. The signs of RDS tend to progress over the first 24–72 hours of life and then begin to stabilize and improve as the newborn’s body starts to produce surfactant in response to birth. Exogenous surfactant can be given via endotracheal intubation or minimally invasive methods, but early CPAP has been shown to decrease the need for intubation and surfactant administration. ^24,25 Antenatal glucocorticoids promote the maturation of alveoli and surfactant production and have significantly decreased the incidence and severity of RDS in very premature and late-preterm infants. ^26,27 Nasal continuous positive airway pressure maintains and can even increase FRC by exceeding the closing capacity of the lungs. Therefore, nCPAP can improve ventilation and ventilation–perfusion mismatch, prevent progressive arterial hypoxemia, decrease respiratory muscle fatigue, and ultimately reduce the failure seen in the setting of RDS. ²³

Transient Tachypnea of the Newborn

Transient tachypnea of the newborn is a result of the failure of adequate lung fluid clearance at birth. It is an increase in sodium and lung fluid reabsorption during labor and delivery rather than the mechanical squeezing of the fetus passing through the birth canal that clears the excess fluid in the fetus’s lungs. ²⁸ Fetal lung fluid is produced by the lung itself, and amniotic fluid rarely enters the developing lung except during fetal distress. ²³ The rate of secretion of lung fluid starts to decrease two to three days before birth, with nearly two-thirds of the total clearance of fluid occurring during labor. ^23,29 The onset of labor stimulates the pulmonary epithelium to change from a chloride-secreting membrane to a sodium-absorbing membrane, resulting in absorption of fetal lung fluid. ²⁸ This process is developmentally regulated, with premature infants being less able to clear fetal lung fluid. The accumulated fluid leads to compression of compliant airways, gas trapping, hypoxemia from ventilation–perfusion mismatch, and hypercarbia from interference with alveolar ventilation. ²³

Transient tachypnea of the newborn typically appears as tachypnea within two hours of birth and resolves by 72 hours after birth, with respiratory improvement coinciding with the natural diuresis that tends to occur around this time period. Transient tachypnea of the newborn occurs more frequently in infants after an elective cesarean birth, because these infants are born without the benefit of labor. Changes in stress hormones and the rapid clearance of fetal lung fluid, largely through sodium reabsorption, are inadequate or not present in preterm gestations or the absence of labor, which places the neonate at risk for respiratory distress. ³⁰ Transient tachypnea of the newborn also occurs more frequently in twin pregnancies, preterm birth, maternal diabetes, and maternal asthma. Male sex and higher birth weights are associated with an increased incidence of TTN. ^31,32 Nasal continuous positive airway pressure improves oxygenation in infants with TTN by stenting open airways, increasing alveolar pressure to expand alveoli, and promoting clearance of lung fluid, which decreases ventilation–perfusion mismatch (see Figure 1).

Persistent Pulmonary Hypertension of the Newborn

Persistent pulmonary hypertension of the newborn is a result of the neonate’s inability to decrease pulmonary vascular resistance after birth. During intrauterine life, pulmonary vascular resistance is high because little blood flow needs to go to the lungs in the absence of breathing air. Therefore, the fetus lives in a relatively hypoxic environment. With the first breaths at birth, oxygen in the air is introduced through the lungs to the pulmonary vasculature, resulting in vasodilation and a decrease in pulmonary artery pressures. Blood flow to the lungs is then increased.

With PPHN, pulmonary pressures fail to decrease in the newborn, leading to right-to-left shunting of deoxygenated blood across the foramen ovale and ductus arteriosus, resulting in cyanosis. This hypoxemia leads to respiratory distress as the infant attempts to compensate for the decreased oxygen levels and attempts to open alveoli to increase oxygen delivery to the pulmonary vasculature. Neonates with PPHN typically present with tachypnea and cyanosis. Because of right-to-left shunting, differential pre- and postductal saturations are common. Arterial blood gases show severe hypoxemia and oxygen desaturation, often with normal carbon dioxide tensions. ³³ Nasal continuous positive airway pressure is used in the treatment of PPHN to provide both lung inflation and oxygenation, which results in a decrease in pulmonary vascular resistance.

Constant Flow/Ventilator-Derived nCPAP

Constant flow/ventilator-derived nCPAP is one of the oldest forms of CPAP and uses a ventilator to provide a set flow and positive end expiratory pressure (PEEP). It has been in use the longest; however, it can be associated with an increase in work of breathing when compared with variable flow delivery systems. Because the flow does not vary with the infant’s respiratory cycle with this delivery system, the infant must work harder to exhale against the positive pressure. ³⁶ Other forms of delivering nCPAP have gained favor over the years. Bubble nCPAP, in particular, has been shown to have several advantages over ventilator-derived constant flow nCPAP. ^37–40

Variable Flow nCPAP/Infant Flow

With variable flow or fluidic flip nCPAP, a device (driver) incorporates an oxygen blender, flowmeter, and pressure monitor to deliver the necessary amount of nCPAP. Variable flow systems allow for increased pressure support during inhalation and decreased resistance during exhalation. This can result in increased lung volumes, improved lung compliance, decreased work of breathing, and improved lung recruitment when compared with constant flow systems. ⁴¹ This system has many advantages including pressure display, alarms, and an internal pressure relief valve that allows for a more constant pressure delivery while minimizing excessive pressure delivery. This device is well tolerated and effective. ^42,43

Bubble nCPAP

Bubble nCPAP uses positive pressure by immersing the expiratory tubing in a water column to deliver pressure. With bubble nCPAP, there is not a machine that delivers nCPAP; rather, the depth in centimeters of the expiratory tubing delivers the desired PEEP. A flowmeter attached to a blender and cylinder with water (acetic acid can be used to deter bacterial growth) is the mechanism for positive pressure generation (Figure 2). There are no alarms for this setup; therefore, vigilance at the bedside is required to assure proper connections, positioning, pressure delivery, and respiratory support. Bubble nCPAP delivers mechanical oscillatory vibrations that simulate ventilation in a similar way to high-frequency ventilation. ⁴⁴ With bubble nCPAP, nonrecruited areas of the lung may open and air exchange may be improved because of the variable frequency and amplitude of the pressure oscillations. ²³ These pressure oscillations provide enhanced ventilation, and Lee and colleagues ³⁸ found that bulk tidal volumes, respiratory rates, and minute ventilation were lower in premature infants supported with bubble nCPAP when compared with ventilator nCPAP. In addition, there was no statistically significant difference in transcutaneous carbon dioxide pressure or oxygen saturations between the two groups. ³⁸ Infants using bubble nCPAP have also been shown to have fewer complications, a decreased need for intubation, less likelihood of respiratory failure, and shorter hospital stays, all at a lower cost than ventilator-derived nCPAP. ^37,39,40 Although initially employed in premature infants, bubble nCPAP is now being used for infants of all gestations.

FIGURE 2

CPAP delivery apparatus.

Heated Humidified High-Flow Nasal Cannula

Heated humidified high-flow nasal cannula is an alternative method to deliver continuous distending pressure without nCPAP. Heated humidified high-flow nasal cannula was developed as an alternative to nCPAP systems because of perceived improved patient tolerance and ease of use. ¹² Heated humidified high-flow nasal cannula uses a flowmeter and heated, humidified oxygen delivered at high rates via nasal cannula prongs. The flow rate needed is determined by the physician or advanced practice nurse based on the clinical needs of the patient. Our group uses flow rates ranging from 2 to 5 L/minute. A recent Cochrane review found that in comparison with other forms of noninvasive respiratory support, high-flow nasal cannula has similar rates of efficacy for preventing extubation failure, death, and chronic lung disease. The review also found that nasal trauma and potential pneumothorax are also decreased with the use of high-flow nasal cannula. ⁴⁵ The primary concern with HHHFNC centers on the highly variable pressure delivery because it is the flow rate and not the exact pressure that is delivered in this system; the high-flow air generates a continuous positive airway pressure, but the amount of pressure generated is not measured or regulated. Iyer and Mhanna ⁴⁶ showed a significant linear association between flow rate and distending pressures in premature infants with a mean gestational age of 26.6 weeks, but commented that the pressures generated by a specific flow rate were variable. Heated humidified high-flow nasal cannula is predominantly used when weaning the neonate from nCPAP; however, Yoder and associates found that HHHFNC had the same clinical efficacy and safety when compared with nCPAP in neonates ≥ 28 weeks’ gestation. ⁴⁷ Several studies have shown HHHFNC is well tolerated by premature infants, may improve growth, and did not increase the risk of death, BPD, or other outcomes. ^12,47 However, the effective use of HHHFNC has been debated because a large meta-analysis of clinical trials did not show HHHFNC as equivalent or superior to nCPAP, and concluded that the safety and efficacy of HHHFNC in extremely preterm and mildly preterm infants still needs to be established. ⁴⁵ Therefore, many institutions choose to only use HHHFNC in infants >32 weeks corrected gestational age who are in a convalescent phase.

Skin/Tissue Integrity

There are many potential pressure points on the head and face when using CPAP. The nares, columella, and nasal septum are particularly at risk for injury because of the positioning of prongs or a mask. Properly fitted prongs will avoid pressure on these high-risk areas as well as prevent excess movement and rubbing. A properly sized and positioned mask is needed to prevent slipping and pressure injury. With a mask, pressure injury can occur to the nasal bridge and/or to the nares and columella. In addition, the mask can slide upward and obstruct the nares. Depending on the hat and strap apparatus used, pressure may also occur on the cheeks, scalp, chin, and ears. Therefore, it is important to remove the hat and chin strap completely to do a full assessment.

Effectiveness of nCPAP Delivery and Support of Ventilation

Regular assessments of the neonate’s color, work of breathing, and oxygen saturation are mandatory, as is evaluating respiratory rate, symmetry of chest movement, and breath sounds. Retractions, grunting, and increased work of breathing need immediate attention and may necessitate an increase in ventilatory support. When auscultating breath sounds, the clinician should be able to hear the CPAP bubbling or roar throughout the entire chest when CPAP is being delivered appropriately. Unequal chest movement or a sudden increase in respiratory rate and/or work of breathing may indicate a pneumothorax or other pulmonary complication.

Proper nCPAP Positioning and Equipment Application

The hat should be at the brow line (Figure 3), cover the ears (ensure the ears are not folded over), and reach the base of the neck. The hat should fit snugly so it will hold the CPAP apparatus in place but not be so tight that it causes blanching of the skin or pulls up on the CPAP mask/prongs, lifting the nose toward the forehead. The lateral straps should have equal tension on them and should not cut into or cause an indentation in the facial cheeks. The nCPAP circuit should be secured so that any condensation drains toward the nCPAP unit and the tubing does not slip out of the incubator, causing tension against the headgear and the baby’s face.

FIGURE 3

Proper CPAP positioning. Developmental aids are used to “nest” the infant; the hand is placed under the chin to help keep the mouth closed without the aid of a chin strap. A properly fitting mask is used with at least 2–4 mm of space between the lower aspect of the mask (or crossbar of the prongs) and columella/nares, CPAP straps fit snugly over the cheeks but do not compress or cut into facial tissue. The CPAP hat is covering the brow.

Positioning the neonate so the mouth remains closed is important because an open mouth may decrease the pressure delivered and increase the possibility of respiratory distress. Placing the neonate in the prone position with his/her hand tucked underneath the chin may help keep the mouth closed. Using a roll under the neck or chest may help keep the airway patent by facilitating flow past the nasopharyngeal level. A chin strap is also helpful to use when the infant’s mouth habitually remains open. When using a chin strap, it is important that it is positioned underneath the bony portion of the chin and not over the fleshy portion of the hypopharynx region because this may cause airway obstruction and place the infant at risk for aspiration.

Manufacturers supply a template for proper selection of the size of nasal prongs and masks. The template and choices for the different sizes differ based on the manufacturer. Nasal prongs should fill the entire nares but not cause blanching. There should be a small (several millimeters) cushion of air between the nasal septum and the base (crossbar) of the prongs. The nares should be kept clear of secretions but deep suctioning should be minimized to avoid trauma and resultant edema of the nasal mucosa. The mask should cover the entire nose, yet be small enough to sit flush with the face and not slide. The mask should not fit too tightly; it should not cause indentations and pressure on the nasal bridge or ride up and occlude the nares. ⁴⁰ Alternating the use of mask and prongs can help minimize pressure injuries.

Abdominal Distention

Early in the use of nCPAP for neonates, there was concern for increased risks of gastrointestinal perforation and necrotizing enterocolitis, but this has not been seen in recent studies. ^34,48 The use of nCPAP, however, has been associated with abdominal distention in neonates, especially those born prematurely. This is a result of air being pushed into the stomach and is complicated by the gastrointestinal dysmotility commonly seen in sick and premature neonates. It is important to continually assess the abdomen for distention, discoloration, and tenderness. An appropriately sized orogastric tube (at least 8 Fr, if permitted by the infant’s size) should always be in place when nCPAP is in use. This will allow for the escape of gastric air that is under pressure. If this gastric air reaches the intestines, it causes gaseous distention of the bowel that will only be removed when the infant passes the air rectally. Feeding tolerance should also be monitored closely and the orogastric tube should be allowed to vent between feedings.