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INTRODUCTION

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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 that required positive pressure ventilation underwent endotracheal intubation (ETI) and were placed on a mechanical ventilator. However, over the past two decades, there has been an increased use of noninvasive positive pressure ventilation (NIPPV).1,2 As opposed to ETI, NIPPV uses an external mask interface to deliver positive pressure to the patient.

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NIPPV and ETI with conventional ventilation are not synonymous alternatives; NIPPV is not warranted when the airway needs to be secured and when higher levels of positive pressure are required. Rather, NIPPV should be considered an additional tool that can augment medical care to possibly prevent ETI. This chapter will discuss the use of NIPPV in the emergency medicine patient with acute respiratory distress.

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PHYSIOLOGY OF NIPPV

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Nomenclature

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There are two major types of NIPPV that are used in the pre-hospital and emergency medicine setting: continuous positive airway pressure (CPAP) and bi-level positive airway pressure (BiPAP).

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CPAP is provided throughout the entire respiratory cycle (see Figure 7-1). There are small variations in pressure that are dependent on patient respiratory effort. 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.

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FIGURE 7-1

Continuous Positive Airway Pressure (CPAP). CPAP set at 5. Patient breathing spontaneously, with approximately 200 cc tidal volume (VVT). Mean Airway Pressure (Pma) is approximately 5 cm H2O. Pressure and TV tracings are ideal.

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BiPAP consists of two applied pressures: inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP) (see Figure 7-2). 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.

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FIGURE 7-2

Bilevel Positive Airway Pressure (BiPAP). Inspiratory Positive Airway Pressure (IPAP) set at 10 cm H2O. Expiratory Positive Airway Pressure (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, TV is approximately 300 cc. Pressure and VTV tracings are ideal.

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CPAP and EPAP: Opening the Lung and Keeping It Open

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CPAP and ...

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