Noninvasive ventilation techniques augment alveolar ventilation without an indwelling artificial airway. This is accomplished with either negative (subatmospheric) or positive pressure administered via an external interface. Mechanical ventilation emerged first with negative pressure ventilation in 1830, predating the development of artificial airways. It had a long history of success in treating polio patients in respiratory failure. The concept of body ventilation later evolved to include positive pressure ventilation delivered via external masks covering some combination of the nose and mouth.
Noninvasive positive pressure ventilation (NPPV) has several advantages when compared with negative pressure ventilation. Its system components are small and portable, are easy to use and easy to fit, and cause less discomfort and avoid upper airway obstruction, unlike negative-pressure ventilators. In recent years, new technologies have become available that allow both short- and long-term use of NPPV in children.
These devices allow delivery of airflow under pressure, with or without supplemental oxygen, for gas exchange without an invasive airway. With the increased level of acuity seen in many pediatric hospitals as well as increasing numbers of technology-dependent children, hospitalists need to familiarize themselves with the indications and the technologies available in the hospital, delivery room, and emergency department, during transport, and in the special care and intensive care units.
MODES OF NONINVASIVE VENTILATION
A number of different devices are available, each with advantages and disadvantages. In general, most devices for noninvasive ventilation are pressure (rather than volume) controlled, with limited adjustment options.
CONTINUOUS POSITIVE AIRWAY PRESSURE
Devices for continuous positive airway pressure (CPAP) provide a continuous flow of delivered air to generate a preset pressure throughout the entire respiratory cycle. As illustrated in Figure 195-1, CPAP provides a constant airflow at a set supra-atmospheric pressure, superimposed on a patient’s spontaneous breaths. The additional airflow raises inspiratory pressures and applies a positive end-expiratory pressure, overall increasing mean airway pressure. The additional end-expiratory distending pressure helps prevent airway collapse and resultant atelectasis, in turn increasing the patient’s functional residual capacity. These effects have been shown to improve oxygenation and lessen work of breathing. CPAP does not directly increase tidal volume, however, and as such it provides respiratory support but not truly assisted ventilation.1,2
Respiratory air flow with various modes of noninvasive ventilation. NPPV, noninvasive positive pressure ventilation; CPAP, continuous positive airway pressure.
BILEVEL POSITIVE AIRWAY PRESSURE
Bilevel positive airway pressure devices (e.g. BiPAP, Respironics Corporation) can provide different set pressures during inspiration and expiration.3 The pressure difference between expired positive airway pressure (EPAP) and inspired positive airway pressure (IPAP) serves to increase tidal volume and hence minute ventilation (see Figure 195-1).
Bilevel NPPV is commonly delivered in either ...