Pressure Support Ventilation and Other Approaches to Overcome Imposed Work of Breathing

Abstract

After completing this article, readers should be able to: 1. Delineate some of the patient-ventilator interactions that occur during synchronized mechanical ventilation. 2. List the factors that influence the work of breathing. 3. Describe various triggering mechanisms and their advantages and disadvantages. 4. List the modalities employed to reduce the added work of breathing during mechanical ventilation. The availability of an amazing number of ventilator modes, techniques, and devices characterizes the state of the art in neonatal ventilatory support at the outset of the 21st century. Unfortunately, the engineering advances in developing devices with complex capabilities have outpaced our understanding of how and when to use them optimally. One important aspect of mechanical respiratory support that has received limited attention is the added work of breathing imposed by mechanical ventilators. Respiratory support with mechanical ventilation requires the use of endotracheal tubes, and synchronization of ventilation requires triggering devices, both of which impose additional work of breathing on the infant, who already is in respiratory failure. Thus, careful consideration of patient-ventilator interactions during synchronized ventilation and the factors that influence the work of breathing is essential. Work of breathing consists of the work required to overcome the elastic forces and resistance to gas flow. Elastic work is determined by lung compliance and is highly variable. Optimization of lung volume and surfactant replacement therapy are the two major interventions available to improve lung compliance and decrease the elastic work of breathing. Resistance can be divided into airway resistance and the added resistance of the ventilator circuit, triggering mechanism, and endotracheal tube. Airway resistance varies and may be high in infants who have meconium aspiration or chronic lung disease. In this article, we focus on the imposed work of breathing by the ventilator and endotracheal tube. The consequences of high endotracheal tube resistance include risk of air-trapping, …