Use of CPAP in Premature Babies

*Prema Subramaniam*

### **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.

**Keywords:** CPAP, RDS, prematurity, reduction in mortality and morbidity, surfactant

#### **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 [12–14].

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].
