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EMSWORLD.com | AUGUST 2017 49 between 30%–50% (which is roughly equivalent to using a nasal cannula for oxygenation), and maintain SpO 2 levels. Oxygen toxicity has become a hot topic in prehospital literature; make all attempts to avoid excessive oxygen administration. In mechanical ventilation, the amount of PEEP used often corresponds with the level of FiO 2 required. For example, when using high levels of PEEP, a lower amount of oxygen is needed to maintain oxygenation, and vice versa for circumstances using low levels of PEEP. The same concept holds true for non- invasive BiPAP. Clinicians may titrate EPAP according to the amount of FiO 2 required to maintain SpO 2 or PaO 2 . Most sources rec- ommend maximum EPAP levels between 10–15 cm H 2 O, and of course FiO 2 can be adjusted to maintain appropriate SpO 2 . 13 Patients requiring high levels of both EPAP and FiO 2 may have decompensated to the point where intubation and invasive mechanical ventilation are required. 13 Prehospital Clinical Applications A common complaint of 9-1-1 callers is respiratory distress or difficulty breathing. Since this has a high occurrence, it's impor- tant for prehospital providers to know when BiPAP is appropriate for those experiencing it. First and foremost, BiPAP is not indicated for patients who are unable to maintain their airway, are hemodynamically unstable, have an altered level of consciousness or are apneic or require immediate intubation. Complications or adverse effects of BiPAP include gastric distention, hypotension, anxi- ety and (less likely) pneumothorax. 12 COPD is an obstructive disorder charac- terized by increased airway resistance and decreased expiratory flow rates. This makes it difficult for COPD patients to fully exhale their tidal volume. Although most people associate it with smoking and emphysema, COPD is actually an umbrella term that includes other respiratory conditions, such as asthma and chronic bronchitis. During an exacerbation of this disease, increased airway resistance leads to air trapping and a retained volume of air in the distal airways and alveoli. As the exacerbation worsens, trapped gases decrease the volume of air the patient can inspire. The solution to this is to open the airways and maintain their patency. This can be done with medications such as bronchodila- tors, steroids and smooth muscle relaxers. However, BiPAP offers the ability to "stint" airways by providing PEEP. This maintains the patency of lower airways and allows the patient to exhale with much more ease. The addition of pressure support decreases muscle fatigue by augmenting the amount of work the patient performs to breathe. Patients in acute respiratory failure, a com- mon occurrence with COPD, benefit from the pressure support because it decreases arterial carbon dioxide by increasing the patient's tidal volume with the increased positive pressure during the inspiratory phase of the respiratory cycle. Patients with congestive heart failure and/or pulmonary edema benefit greatly from BiPAP. 10 Not only does BiPAP decrease muscle fatigue, increase tidal volume and maintain alveolar/distal airway patency, 11 but therapeutically BiPAP benefits "wet" lungs by decreasing central venous return. This decreases the amount of circulat- ing blood volume that goes through the pulmonar y vasculature, which in turn decreases hydrostatic vessel pressure and prevents fluid from crossing the capillary membrane in the alveoli and flooding the interstitial spaces. The decreased venous return is caused by the PEEP or, in the case of BiPAP, the EPAP. The increased expiratory pressure increases intrathoracic pressures, putting stress on the venous return system, decreasing central venous pressures. This increased EPAP increases the functional residual capacity of the lungs, leading to an increase in arterial oxygen and/or SpO 2 . Note also that pulmonary edema does not have to be a result of CHF for BiPAP to be effective. Other causes of noncardiogenic pulmonary edema, such as acute respiratory distress syndrome (ARDS), sepsis/systemic inflammatory response syndrome and renal failure (with fluid overload) with respiratory distress, warrant noninvasive ventilation if immediate intubation is not required. When differentiating the appropriate use of CPAP versus BiPAP, it is important to consider whether the patient is suffering from type 1 or type 2 respiratory failure. In type 1 (hypoxemic) respiratory failure, the patient suffers from hypoxemia alone, usu- ally defined as a PaO 2 less than 50 mmHg. 14 In type 2 (ventilatory/hypercapnic) respira- tory failure, the patient suffers from hyper- capnia, usually defined as a PaCO 2 greater than 50 mmHg, which can be accompanied by type 1. 14 CPAP itself is an effective first- line agent for type 1 patients, as it is effective for increasing FRC by applying PEEP. 12 Type 2 patients are recommended to be placed on BiPAP as an effective means of improv- ing gas exchange and normalizing arterial blood gases. 12 When considering changes in practice and purchasing equipment, it may be prudent to utilize devices that can pro- vide BiPAP since BiPAP utilizes EPAP, which essentially is PEEP. This may be why BiPAP does not display a clinical benefit in out- comes over CPAP in cases of acute cardio- genic pulmonary edema that may initially present as type 1 respiratory failure. 4 Conclusion This article in no way fully expresses the scope and technical aspects of bilevel posi- tive airway pressure ventilation. The reader is encouraged to seek further knowledge through reading, clinical observation and skill practice. BiPAP is an amazing innovation in the treatment of pulmonary disorders. It is proven to prevent and delay endotracheal intubation in patients experiencing acute respiratory failure. Paramedics interested in providing advanced emergency and criti- cal care in the field will find BiPAP a tool that can be applied in situations where emer- gency CPAP may have been used. With the proper training, didactic opportunity and clinical practice, prehospital providers can and should be comfortable applying this therapy with the potential to reduce the burdens of endotracheal intubation and respiratory arrest in patients experiencing pulmonary disease exacerbations. For a list of references view the full article here: http://www.emsworld.com/article/218042. ABOUT THE AUTHOR Dustin Britt, A AS, RRT-ACCS, CPFT, NRP, FP-C, is a paramedic with Stanly County EMS and a respiratory therapist with Carolinas Healthcare System in Albemarle, N.C. His recent experience includes working as a flight paramedic with Eagle Air Med in Gallup, N.M.