Analysis of distal airway pressure changes in a simulation model of continuous positive airway pressure (CPAP).

摘要

Background: Nasal continuous positive airway pressure (CPAP) is commonly used to treat respiratory failure in newborns with excellent results; however, pneumothorax is frequently reported, varying in frequency from 1.4% to 10.3%.Methods: In this study, we used a lung simulator to determine the cause of this variability by measuring the pressure in the CPAP system and in the interior of one balloon to simulate the lung, with repeat measurements with the nasal prongs sealed and unsealed. In addition, crying was simulated by blowing through a hole that simulated the mouth.Results: We found that when the nasal prongs were used, unsealed simulator distension existed. However, the pressure remained at zero when the nostrils were sealed, indicating that the pressure inside the simulated lung was equal to that inside the system. Simulated crying increased the pressure 4-fold.Conclusions: We conclude that the seal in the nostrils is a factor for the effectiveness of the procedure and increases the risk of pneumothorax, as well as alter the results of studies on nasal CPAP. Nostril seals should be considered for future studies on the efficacy and safety of nasal CPAP. Introduction Continuous positive airway pressure (CPAP) is one of the most popular techniques described to treat newborn respiratory failure; it has been used since 1971 when Gregory and his colleagues demonstrated that orotracheal CPAP with an anesthesia bag improved oxygenation in preterm infants with respiratory distress. Subsequently, different devices were developed to provide CPAP [1-5]. In subsequent years, mechanical ventilation replaced CPAP as the most common form of ventilatory support. However, in the past several years, CPAP has been shown to have some important advantages over mechanical ventilation, including lower risk of lung injury [6-10].In the last three decades, in parallel with the evolution of different forms of ventilation, ventilatory goals have evolved. Initially, the goal was to reduce mortality, and in the 1980s, the goal was to reduce neurological damage. In the 1990s, the goal was to prevent lung damage, and currently, the goals are to minimize lung injury and complications of mechanical ventilation [11]. CPAP is one of the strategies used to achieve the above objectives. In recent years, the acceptance of CPAP has increased and several articles assessing the efficacy and safety of the procedure have been published [12-23] However, there are only a few studies regarding the physiological basis of CPAP [24,25], and little is known about how to best manage patients [26]. This lack of physiological knowledge has led to conflicting clinical results and the development of a great number of dispositives for the everyday treatment of newborns [27-30]. Background It has been accepted that the severity of lung disease is related to gestational age. In severely immature newborns, higher oxygen gradients are needed, therefore increasing the need for mechanical ventilation and consequently increasing the risk of lung damage [31].Despite the variety of interfaces available to apply CPAP [32,33], nasal prongs are the most common method, with reports suggesting that nasal prongs should be as wide as possible to reduce resistance and fit the nostril snugly without air leakage or tissue damage [34].Although nasal CPAP is a widely accepted ventilatory strategy [35-38], there are some unclear aspects regarding its application. The delivered intra-prong pressure in bubble CPAP is assumed to be represented by the submersion depth of the expiratory tubing [39]. However, Chilton and Brooks [40] and De Paoli et al [41] reported a reduction of about 50% in pharyngeal pressure in infants with open mouths. The intensity of bubbling appears to have no effect on oxygenation and CO2 in some studies [31], but others mention it as an important determinant of oxygenation.(25) Moreover, it was found that prong pressure during nasal CPAP delivery is variable and depends on the