Acute respiratory distress is a frequent problem encountered by emergency physicians and intensivists. Often the clinician must act to ensure adequate oxygenation and ventilation before a definitive diagnosis is achieved. The treatment of acute respiratory distress requires an aggressive approach that entails use of medications, oxygen, and often positive pressure ventilation. Historically, patients who required positive pressure ventilation underwent endotracheal intubation (ETI) and were placed on a mechanical ventilator. However, over the past decade there has been an increased use of noninvasive positive pressure ventilation (NIV).1,2 As opposed to ETI, NIV uses an external mask interface to deliver positive pressure to the patient.
NIV and ETI with conventional ventilation are not synonymous alternatives; NIV is not warranted when the airway needs to be secured. Rather, NIV should be considered an additional tool that can augment medical care to possibly prevent ETI. This chapter will discuss the use of NIV in the emergency medicine patient with acute respiratory distress.
There are two major types of NIV (or noninvasive positive pressure ventilation) that are used in the prehospital and emergency medicine setting: continuous positive airway pressure (CPAP) and bilevel positive airway pressure (BiPAP).
CPAP provides continuous positive airway pressure throughout the entire respiratory cycle (see Figure 6-1). There are small variations in pressure that are dependent on patient respiratory effort: a drop in pressure that occurs with each spontaneous inspiration and a rise in pressure that occurs with each exhalation. The set pressure will very closely approximate mean airway pressure (Pma). The amount of flow or tidal volume (Tv) will depend on patient effort, lung compliance, and the fit of the mask.
Continuous positive airway pressure (CPAP). CPAP set at 5. Patient breathing spontaneously, with approximately 200 cm3 tidal volume (Vt). Mean airway pressure (Pma) is approximately 5 cm H2O. Pressure and Vt tracings are ideal.
BiPAP consists of two applied pressures: inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP) (see Figure 6-2). EPAP is similar to applied positive end-expiratory pressure (PEEP) on the mechanical ventilator, maintaining positive pressure throughout the expiratory cycle. IPAP provides a higher positive pressure during inspiration to support the work of breathing and augment ventilation.
Bilevel positive airway pressure (BiPAP). Inspiratory positive airway pressure (IPAP) set at 10 cm H2O. Expiratory positive airway ressure (EPAP) set at 5 cm H2O. Pressure support (PS), IPAP – EPAP is 5 cm H2O. Mean airway pressure (Pma) is approximately 7 cm H2O. Patient breathing spontaneously; Vt is approximately 300 cm3. Pressure and Vt tracings are ideal.
CPAP and EPAP: Opening the Lung ...