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46 AUGUST 2017 | EMSWORLD.com CONTINUING EDUCATION O ver the years, continuous posi- tive air way pressure (CPAP) has become an accepted and routinely used prehospital emer- gency treatment for acute respiratory fail- ure. Evidence shows noninvasive ventilatory management can reduce intubation rates and improve patient recovery, 1 and with the arrival of CPAP several years ago, many alterations and advances have improved this therapy, resulting in better patient out- comes. Among these advances has been bilevel positive airway pressure, or BiPAP. BiPAP, more commonly observed in hos- pital emergency departments and intensive care units, has also made its way to the pre- hospital setting. 2 Many prehospital provid - ers seem to have a natural curiosity about this lifesaving intervention. This article will discuss the pulmonary mechanism of BiPAP, how it differs from CPAP and tech- nical aspects providers can utilize in their practice where BiPAP is offered. Pulmonary Mechanics As the name implies, bilevel positive airway pressure offers two different levels of noninvasive pressure that correspond to the respiratory cycle. These levels are called the inspiratory positive airway pres- sure (IPAP) and expiratory positive airway pressure (EPAP). These are also known as the inspiratory baseline and the expiratory baseline pressures. When a patient receives BiPAP, the noninvasive ventilator functions to provide a preset expiratory pressure dur- ing the expiratory phase and a preset inspi- ratory pressure during the inspiratory phase of the respiratory cycle. This mechanism creates an astonishingly powerful method of reducing the patient's work of breathing and increasing the func- tional residual capacity (FRC) of the lungs (FRC is the volume of air left in the lungs at the end of exhalation). 3 It is important to note there are two separate physiological processes working in the lungs: ventilation and oxygenation. Ventilation specifically deals with the removal of carbon diox- ide from the lungs. The effectiveness of ventilation is measured by arterial carbon dioxide levels, or PaCO 2 ; in the prehospital environment this is often correlated with end-tidal carbon dioxide, or EtCO 2 . From a mechanical ventilation standpoint, ven- tilation is monitored and even controlled by adjusting values such as tidal volume, minute ventilation and respiratory rate. Oxy- genation specifically deals with the ability of the lungs to deliver oxygen to the pulmo- nary capillaries. Oxygenation is measured most accurately by obtaining the partial pressure of arterial oxygen, or PaO 2 ; this is most commonly related to the patient's SpO 2 value in the prehospital environment. In mechanical ventilation the PaO 2 and/or SpO 2 is improved by increasing the posi- tive end expiratory pressure (PEEP, which coincidentally is directly proportional to the FRC in the lungs) and the fraction of inspired oxygen (FiO 2 , 21%–100%). The removal of carbon dioxide in BiPAP is done through the use of pressure support. Pressure support is a value determined by the difference between IPAP and EPAP (Figure 1). Pressure support is primarily used for ventilation, meaning it's inversely proportional to arterial carbon dioxide lev- els. As pressure support increases, PaCO 2 should decrease; when pressure support decreases, PaCO 2 should increase. The pressure support is directly proportional to tidal volume: As pressure support increases, tidal volume should increase, and vice versa. Patients who present in the latter stag- es of acute respiratory failure often pres- ent with arterial blood gases reflective of uncompensated respiratory acidosis, usual- ly as a result of decreased tidal volumes and minute ventilation due to muscle fatigue and/or abnormal ventilatory rates. BiPAP may benefit these patients by accelerating their recovery from respiratory failure. 4 The ventilating pressure support augments the patient's compromised respiratory effort by alleviating muscle demand for ventilation. Thus, the addition of pressure support utiliz- ing IPAP effectively and safely ventilates the patient, much in the same way bag-valve This CE activity is approved by EMS World, an organization accredited by the Commission on Accreditation for Pre-Hospital Continuing Education (CAPCE), for 1 CEU upon successful completion of the post-test available at EMSWorldCE.com . Test costs $6.95. Questions? E-mail editor@EMSWorld.com. • Provide an introduction and overview of bilevel positive airway pressure (BiPAP) • Identify differences in mechanism and applications between BiPAP and continuous positive airway pressure (CPAP) • Outline the technical components of BiPAP administration for prehospital providers Objectives BiPAP Essentials for Prehospital Providers Utilizing bilevel positive airway pressure in the management of pulmonary emergencies By Dustin Britt, AAS, RRT-ACCS, CPFT, NRP, FP-C