Use of CPAP in Premature Babies

Abstract

Respiratory distress syndrome (RDS) is the most common respiratory disorder of preterm infants and is a major course of neonatal mortality and morbidity. The combined use of antenatal steroids and early continuous positive airway pressure (CPAP) are considered the gold standard for the prevention and treatment of RDS in the preterm infant. CPAP used in the spontaneous breathing neonate maintains adequate functional residual capacity within the alveoli to prevent atelectasis and support gas exchange CPAP is most commonly delivered using bi-nasal short prongs or a nasal mask. Pressure is generated using a variety of devices. CPAP is generally well tolerated, in part because infants are preferential or “obligatory nasal breathers”. CPAP has revolutionised the outcome in premature babies by reducing the need for mechanical ventilation and the use of surfactant. Prophylactic or early CPAP in the delivery room reduces the need for surfactant and mechanical ventilation by nearly 50%. CPAP is an attractive option for supporting neonates with respiratory distress, because it preserves spontaneous breathing, does not require endotracheal intubation, and may result in less lung injury than mechanical ventilation.

1. Introduction

Globally around 2.4 million newborns died in 2020 of which 75% of neonatal deaths occur within the first week of life. In 2017 most neonatal deaths occurred as a result of either preterm birth, intrapartum complications such as birth asphyxia or failing to breath, infections and/or lethal congenital malformations [1].

Respiratory distress syndrome (RDS) in the newborn is one of the major causes of neonatal mortality and morbidity. RDS is due to a lack of surfactant in the lungs of the preterm baby and this usually develops in the first 24 h of life. Positive pressure ventilation has been found to be an effective form of treatment for this condition [2].

In women at risk of preterm birth treatment the use of antenatal corticosteroids has been proven to reduce perinatal and neonatal death, RDS and Intraventricular haemorrhages (IVH) [3]. The combined use of antenatal steroids and early continuous positive airway pressure (CPAP) are considered the gold standard for the prevention and treatment of RDS in the preterm infant [4, 5].

2. CPAP

2.1 What is nasal CPAP?

Nasal continuous airway pressure (CPAP) is a non-invasive form of respiratory support for the spontaneously breathing infant with lung disease. In this situation CPAP provides a constant distending pressure during both the inhalation and expiration phases thereby reducing the need for intubation and mechanical ventilation [6].

CPAP imitates the natural physiologic reflex called “grunting,” which is forced expiration against a closed glottis that occurs with infants with poor lung compliance and low end-expiratory volume who uses this physiological mechanism to try to maintain a higher end expiratory volume [7].

The infants tongue and soft palate forms an anatomic seal thereby maintaining the CPAP pressure in the babies lungs [8].

CPAP maintains functional residual capacity (FRC) and supports gas exchange in the neonatal lungs thereby reducing the incidence of apnoea, improves the work of breathing and reduces lung damage [9].

CPAP was first used to support the breathing of preterm infants in 1971 [10]. Gregory used Endotracheal tubes for his CPAP study in 20 infants weighing between 930 and 3800 g. All these infants had severe RDS and were breathing spontaneously. Gregory used pressures up to 12 mmHg via the ETT in 18 of the infants and for the other 2 infants he used a pressure chamber placed around the infants head. He noted that increasing the PEEP (positive end expiratory pressure) caused a reduction in the minute ventilation. However there was not much change in the babies pH, CO₂ tension, blood pressure or lung compliance.

2.2 How does CPAP benefit infants with RDS?

The surfactant deficiency in RDS causes collapse of the terminal airways in the babies lungs leading to a reduction in the functional residual capacity. This results in an increase in the ventilation-perfusion mismatch and thereby an increase in the work of breathing [11].

CPAP reduces upper airway obstruction by the decrease in pulmonary vascular resistance and increasing the thoracic gas volume [12, 13, 14].

CPAP also decreases left to right shunting by increasing right ventricular output while not significantly affecting the left ventricular output and pulmonary vascular resistance [15].

CPAP also produces a rise in Pa02 (with no significant change in PCO2) and maintains the Positive End Expiratory Pressure (PEEP) thereby reducing atelectasis, increasing the surface area of the alveolus and thereby an improvement in the ventilation-perfusion mismatch [16, 17]. The rise in Pa02 and the resulting regulation in both rate and dept. of respiration generally results in a cessation of grunting with 15 min of commencing CPAP. CPAP thereby improves the infants ability to cope with increasing respiratory loads through the Hering-Breuer reflex [18].

CPAP in most instances is applied at pressures between 4 and 6 cm H₂O however, in infants with poor lung compliance, CPAP of pressures from 8 to 10 cm H₂O have been used. The higher pressures might result in overdistension that affects gas exchange and damage to the terminal airways may result in pneumothorax. It is uncertain what the optimum CPAP levels should be as this varies with the age of the infant and the severity of RDS [19].

2.3 Use of CPAP in neonates

CPAP is commonly used in neonates with the following conditions:

1. RDS

   Prophylactic CPAP i.e. CPAP started immediately after delivery in preterm or low birth weight infant or within the first 15 min of life (before the onset of respiratory disease) has been shown to reduce the incidence of BPD (bronchopulmonary disease), the combined outcome of death or BPD, and the need for mechanical ventilation [20, 21].

   In preterm or low birth weight infants with established respiratory distress, CPAP reduces the incidence of respiratory failure, the use of mechanical ventilation and mortality however there is an increased rate of pneumothorax compared to spontaneous breathing with supplemental oxygen [3].

2. Post extubation

   NCPAP can also be used as “step-down” therapy to provide respiratory support following extubation after mechanical ventilation. These infants have a less likelihood of developing respiratory failure and having the need for reintubation and mechanical ventilation. The reason for this may be due to the fact that CPAP maintains lung volumes, causes airflow stimulation of the nasal passage and upper airway and by reducing apnoea in the preterm infant [22, 23].

3. Apnoea

   CPAP decreases both obstructive and a combination of obstructive and central apnoea and prevents hypoxia. Central apnoea by itself is not affected by CPAP. Miller postulated that CPAP reduces upper airway obstruction by splinting the pharyngeal airway [24].

2.4 CPAP apparatus

CPAP has two main components: a device to generate pressure and a patient interface used to deliver pressure.

CPAP devices include:

Variable flow devices ie devices that generate CPAP by a jet of blended air delivered by the Infant Flow Driver. This system requires air flows in excess of 8 L/min in order to generate positive end expiratory pressures of 5 cm H₂O.

Constant or continuous flow examples of which are bubble CPAP and ventilator CPAP.

With bubble CPAP the PEEP is maintained by immersing the distal end of the expiratory tubing in water. The pressures are determined by the depth of the tubing in the water. For example 5 cm below the surface equals to 5 cm H₂O blended humidified gas oxygen or air is delivered by nasal prongs or nasal masks and as air flows out of the infant via the expiratory tubing it gives its characteristic bubbling [1, 3, 25]. Bubble CPAP is inexpensive and is easy to adapt for newborns [3]; however, if the interface is not well adapted or if there is leakage through the nose or mouth, the PEEP is not guaranteed.

Studies have shown that there is little difference in terms of respiratory rate, heart rate, blood pressure or comfort scores between the use of continuous flow CPAP and variable flow CPAP [8, 26, 27, 28, 29, 30, 31].

Many neonatal units use CPAP pressures delivered between 5 and 6 cm H₂O. Some units use starting pressures of 8 cm H₂O. Elgellab noted that CPAP pressures of 8 cm H₂O improved the thoraco-abdominal synchrony, lowered the respiratory rate and increased the tidal volume of preterm infants with respiratory failure [18].

For preterm infants with poorly compliant lungs, higher CPAP pressures 32 (e.g. 8 cm H₂O may be needed 3 as the first line of support immediately after birth or at the start of the respiratory distress with escalation to intubation and mechanical ventilation if CPAP fails.

2.5 CPAP delivery

The most common interfaces for CPAP delivery include:

Short binasal prongs that fits directly into the nostrils or nasal mask. Other interfaces used included single nasal prongs and nasopharyngeal prongs which uses a nasopharyngeal tube (NGT) in which the tip of the tube sits in the nasopharynx thereby bypassing the nasal cavity [32, 33].

Short binasal prongs when compared to single nasal prongs and nasopharyngeal prongs showed that there was a decrease in the babies oxygen requirement and respiratory rate thereby reducing the need for reintubation [23, 34, 35]. Endotracheal tubes are still used to deliver CPAP when the infants have facial anomalies such as bilateral cleft lip and or palate [2].

The problem with binasal prongs however is that it must be fitted snugly which can lead to injury to the nares and nasal septum [35, 36].

With the nasal mask, this is placed over the babies nose and mouth forming a good seal.

When compared to binasal prongs, nasal masks decreased the incidence of moderate-to-severe BPD and the need for surfactant. However there were no differences in mortality or other morbidities [7, 30].

CPAP failure i.e. babies requiring mechanical ventilation while on CPAP is defined when one or more of the following conditions arise: persistent or frequent apnoeic episodes, PaCO2 of ≥60 mm Hg (8.3 kPa), FiO2 of ≥0.6 to maintain acceptable oxygen saturation. 14% to as high as 40% of infants with respiratory distress who have initially been started on CPAP may need to be intubated and ventilated. CPAP failure was associated with an increased rate of pneumothorax, death, bronchopulmonary dysplasia (BPD) and other morbidities compared with those managed on CPAP alone [37, 38, 39].

2.6 Contraindications in the use of CPAP in babies

This includes upper airway abnormalities such as choanal atresia, cleft palate and trachea oeophageal fistula.

Babies in shock i.e. cardiovascular instability.

Frequent apnoeic episodes with bradycardia and desaturations.

Respiratory failure PCO2 of >60 mmHg FiO2 > 0.6 to maintain an acceptable O2 saturation.

Congenital diaphragmatic hernia as the gastric distension caused by CPAP can result in further compromise of the organs in the chest.

Complications that can occur with CPAP giving rise to inefficient delivery include [40]

• Kinking of nasopharyngeal tube (in NP CPAP) and/or delivery circuit.

• Obstruction of the binasal nasal prongs with mucus plugging.

• Displacement of the nasal prongs/mask.

• Skin irritation of the face from the securing tapes.

• Pressure necrosis around nostrils and distortion of the nasal septum.

• Pressure necrosis around head/ears due to improperly secured bonnets or CPAP head harnesses.

• Air leaking around the prongs due to the mouth being open which may result in loss of desired pressure and decrease in delivered oxygen concentration.

• Pneumothorax or pneumomediastinum especially in the extremely low birth weight babies.

• Extremely high CPAP levels resulting in a decrease in the venous return and therefore reducing the babies cardiac output.

• Feed intolerance following gastric distension (CPAP belly) as the delivered gas enters the stomach and gastrointestinal tract.

2.7 CPAP and surfactant

Studies have shown that in babies with moderate to severe respiratory distress syndrome the combination of nasal continuous positive airway pressure (nCPAP) and a single dose of surfactant reduces the need for intubation and mechanical ventilation [36].

Methods of delivering surfactant to an infant on CPAP include:

INSURE method (INtubation-SURfactant-Extubation), Surfactant administration via thin catheter and Nebulized surfactant [41].

The INSURE method (INtubation-SURfactant-Extubation) is done by intubating the infant, administrating surfactant via the endotracheal tube followed by a short period of mechanical ventilation, extubation and then onto CPAP. This is done at the onset of RDS [42] Stevens suggest that in spontaneously breathing preterm infants with RDS the INSURE method of surfactant administration followed by early extubation to NCPAP is preferable to traditional intubation and surfactant treatment and keeping the baby on the ventilator. INSURE reduces the need for mechanical ventilation. Its also reduces the incidence of pneumothorax and BPD.

Surfactant administration via thin catheter (S-TC) encompasses any method in which a thin catheter, narrower than a standard endotracheal tube (ETT), is passed through the vocal cords to allow surfactant instillation. The most commonly used methods are [43].

A flexible thin catheter and Magill’s forceps (Cologne method), as described by Kribs and colleagues [33], flexible thin feeding tube without Magill’s forceps (take care method), as described by Kanmaz and colleagues, semi-rigid thin catheter (Hobart method), as described by Dargaville and colleagues [30]; and modifications of the above methods.

Differences of the various methods may be encountered in (1) the pre-medication used, (2) the means of laryngoscopy used, including videolaryngoscopy, (3) the type of catheter, (4) the method used to guide the catheter through the vocal cords, (5) the approach to surfactant delivery (bolus versus infusion, rapid versus slow), (6) the surfactant preparation, (7) the surfactant dose, and (8) the approach to respiratory management before, during, and after the technique, including the type of non-invasive respiratory support used. It is expected that infants are spontaneously breathing, and therefore positive-pressure inflations are not required for surfactant dispersal. Unlike an ETT, a thin catheter is unsuitable for delivery of positive-pressure inflations.

Several different acronyms may be used for the above methods, including:

• MIST (minimally invasive surfactant therapy);

• LISA (less invasive surfactant administration);

• SurE (surfactant without endotracheal tube);

• MISA (minimally invasive surfactant administration); and

• NISA (non-invasive surfactant administration).

Abdel-Latif et al. concluded in his Cochrane review that surfactant therapy via thin catheter (S-TC) compared to surfactant via endotracheal tube (ETT) reduced the incidence of the combined outcome of death or bronchopulmonary dysplasia (BPD) at 36 weeks’ postmenstrual age (PMA) [31].

2.8 Nebulised surfactant

This method is carried out when Aerosolised surfactant is given to the neonate via a customised vibrating membrane nebuliser positioned between the mask and the bubble nCPAP circuit. Minocchieri et al. showed that nebulised surfactant administered in the first 4 h of life to very and moderately preterm infants with mild RDS may benefit these babies [44]. These findings require confirmation in a adequately powered randomised controlled trial evaluating the benefits of nebulised surfactant in infants with mild to moderate respiratory distress [44].

3. Conclusion

In conclusion CPAP is a safe and effective method of noninvasive ventilation in the preterm infant with RDS and it reduces the need for assisted ventilation by almost half, and substantially reduced the use of surfactant. CPAP is a simple and inexpensive form of treatment to implement and hence has implications for use in low- and middle-income countries (LMIC).

Conflict of interest

The author declares no conflict of interest.