Evidence-Based EMS: Out-of-Hospital BiPAP vs. CPAP

It’s that crazy weather again. One minute it’s a beautiful sunny day, and the next it’s freezing rain. As you bundle up for the cold weather, you get dispatched to a 75-year-old male with difficulty breathing. You arrive on scene to find a thin, frail elderly man sitting in the kitchen, leaning forward with elbows propped on the table. He struggles to say, “I can’t breathe.”

On exam you note pursed-lip breathing with a prolonged expiratory phase. He has intercostal retractions, diffuse wheezing with rales bilaterally, with pitting edema in his lower extremities. Initial vital signs are a pulse of 130, blood pressure of 165/60, respiratory rate of 25, and a pulse oximetry reading of 85% on room air. His medical history is significant for severe COPD and congestive heart failure.

While you debate whether this is a COPD or CHF exacerbation, you decide to put the patient on continuous positive airway pressure (CPAP) while administering nebulized albuterol. The patient is still anxious with labored breathing, but his pulse ox improves to 90%. On arrival at the hospital, the emergency department physician immediately orders the respiratory therapist to switch from your CPAP to biphasic positive airway pressure (BiPAP).

You’ve seen this switch occur on multiple occasions when you’ve brought in a patient on CPAP and wonder why the ED always switches to BiPAP. Is BiPAP really that much better than CPAP? If so, should we be using BiPAP in the EMS world?

Background

As a quick review, patients in acute respiratory distress have a problem with oxygenation, ventilation or both. Oxygenation is the process of providing oxygen to the patient. However, pathologies like COPD and CHF may require more than just oxygenation as a result of alveolar disease preventing appropriate diffusion of oxygen and carbon dioxide across the alveolar membranes (i.e., pulmonary edema and bronchoconstriction). This is when ventilation becomes important. Ventilation can be thought of as the actual physiologic process of breathing, which is inhalation, diffusion of gases and exhalation.

Ventilation and oxygenation are important for understanding the utility of noninvasive positive pressure ventiliaton (NIPPV). NIPPV is a form of mechanical ventilation delivered through the use of tight-fitting nasal or facial masks that does not require endotracheal intubation. It can be delivered in two forms: CPAP or BiPAP.⁷ CPAP provides a continuous pressure of oxygen to the alveoli. This constant pressure provides oxygen directly to the lungs, prevents alveolar collapse, and may even open up previously closed alveoli (alveolar recruitment). In essence, CPAP primarily provides oxygenation and may indirectly influence ventilation by allowing alveoli to remain or become available.⁷ As a result of this constant pressure throughout the respiratory cycle, the patient has to overcome this pressure during exhalation. Thus, CPAP is limited by the patient’s ability to overcome the very pressure CPAP provides.

Here is where BiPAP can help. BiPAP provides CPAP, but senses and adjusts the oxygen pressure to the patient’s breathing cycle. The oxygen pressure increases during inhalation to provide maximal alveolar recruitment but decreases during exhalation to ease breathing while keeping alveoli open with its adjustable CPAP function. In essence, BiPAP provides greater control for acute respiratory distress and may provide better gas exchange to optimize cardiopulmonary performance. Thus, many hospitals use BiPAP for this very reason: better control.

The use of BiPAP is further supported by a 2004 Cochrane review in which the authors examined 14 randomized controlled trials in which standard medical therapy (SMT)—defined as supplemental oxygen, bronchodilators, steroids and antibiotics—was compared to BiPAP in patients with COPD. With a total of 758 patients analyzed, the authors found a 48% reduction in the risk of mortality for patients treated with BiPAP. This demonstrated a number needed to treat (NNT) of 10, meaning that for every 10 patients treated with BiPAP, one life was saved compared to SMT alone. This review also demonstrated a 60% decrease in the risk of intubation with a NNT of 4.⁸

Clearly this review supports the use of BiPAP as a first-line NIPPV therapy in treating COPD. Before we claim that BiPAP is superior, though, let’s remember that this review did not specifically compare the use of CPAP against the use of BiPAP. So let’s look at the evidence comparing the two before we throw our CPAP machines out the window.

In-Hospital Evidence

To begin, there are studies that showed worse outcomes with BiPAP compared to CPAP. In 2012, Brazilian researcher Juliana Nalin de Souza Passarini demonstrated an increased need for endotracheal intubation in patients who received BiPAP compared to those who received CPAP in treatment of acute cardiogenic pulmonary edema (ACPE) and COPD exacerbation.¹⁰ However, this study was limited by a nonrandomization of subjects, leading to bias in the patients who received BiPAP and CPAP. This was demonstrated when the authors concluded that the increased need for intubation was likely due to greater disease severity in those patients who received BiPAP. Despite these limitations, this study still demonstrated that a majority of patients managed with NIPPV avoided the need for endotracheal intubation.

In contrast, an older, more methodologically sound study stated that BiPAP may provide slightly better results than CPAP. These authors attempted to evaluate whether BiPAP improved ventilation, acidemia and dyspnea more rapidly than CPAP in patients with ACPE by measuring vital signs and specific blood lab values. What makes this manuscript methodologically superior to the former study is that it was a randomized, controlled, double-blinded study, so bias was kept to a minimum. The authors concluded that BiPAP improves ventilation and vital signs quicker than CPAP. However, they added a word of caution after discovering a relationship with having a myocardial infarction (MI) and the use of BiPAP.⁶ Fortunately, a meta-analysis nine years later demonstrated this relationship of new-onset MI and BiPAP utilization did not reach statistical significance.⁵

However, many who support CPAP state that both interventions lack a difference in meaningful outcomes (i.e., the need for intubation and/or effect on mortality). One such study compared BiPAP to CPAP in 200 patients with ACPE. The authors discovered that BiPAP was associated with faster resolution of respiratory failure (159 vs. 210 mins.). However, there was no difference in mortality or rate of intubation in BiPAP and CPAP patients. In essence, CPAP may be just as good as BiPAP in the long run.⁸

Furthermore, a recent article in the New England Journal of Medicine further supported that CPAP is just as beneficial as BiPAP in terms of meaningful outcomes. The objective was to determine whether noninvasive ventilation reduced mortality and whether there were important differences in outcomes associated with the method of treatment (CPAP or BiPAP). The authors discovered that 11.7% of patients on CPAP and 11.1% of patients on BiPAP either died or were intubated. This small difference was not statistically significant, and the authors concluded CPAP can be just as effective as BiPAP in short-term (seven-day) mortality.⁴

Before we say that CPAP can be just as good as BiPAP, though, let’s look at the prehospital evidence.

Prehospital Evidence

Although limited in number of studies, the prehospital evidence for the utility of BiPAP and CPAP shows comparable results to the in-hospital research. The University of Sheffield’s Steve Goodacre, et al., published a systematic review comparing OOH CPAP and BiPAP to SMT. There was an overall reduction in mortality and intubation rate when compared to SMT, but they found no statistical difference with the use of BiPAP and CPAP. While this review seems to be the most complete to date, the authors noted, “The analysis of BiPAP in particular involved fewer studies and fewer patients (190 receiving BiPAP vs. 610 receiving CPAP).”³ Additionally, Sheffield’s Abdullah Pandor and colleagues provided a similar systematic review that showed a decrease in mortality and need for intubation in the CPAP group that was similar to the BiPAP group.⁹

Bottom Line

After looking at the evidence of BiPAP against CPAP, the only advantage BiPAP appears to provide is a decreased time to resolution of respiratory symptoms, vital signs and improvement of laboratory values. However, keep in mind that this difference doesn’t occur until late in the treatment course. While this shouldn’t affect most EMS systems with short transport times, some rural EMS systems may take the long-term effects of BiPAP into consideration given their longer transport times. Otherwise, current evidence demonstrates minimal benefit to BiPAP over CPAP.

What we do know is that BiPAP provides better outcomes in patients with COPD when compared to SMT, and CPAP may be better for ACPE. However, the studies reviewed in this article have not shown a clear or consistent advantage to BiPAP over CPAP in clinically significant outcomes such as decreased mortality, need for intubation, ICU admission and length of hospital stay.

As a prehospital provider, it is always a good to question yourself, broaden your differential impression for acute respiratory failure and maintain that inquisitive mind. With the evidence reviewed here, the hospital changing your prehospital CPAP to BiPAP every time should not distress you. In the short run, CPAP is just as good as BiPAP. The next time you are faced with a patient with acute respiratory distress, the best thing you can do is relax, remember your training and think about what you can do to best help your patient. If you decide CPAP is the way to go, you now have the evidence to support your decision.

References

1. Baird JS, Ravindranath TM. Out-of-hospital noninvasive ventilation: epidemiology, technology and equipment. Pediatr Rep, 2012 Apr 2; 4(2): e17.

2. Cross AM, Cameron P, Kierce M, Ragg M, Kelly AM. Non-invasive ventilation in acute respiratory failure: a randomised comparison of continuous positive airway pressure and bi-level positive airway pressure. Emerg Med J, 2003 Nov; 20(6): 531–4.

3. Goodacre S, Stevens JW, Pandor A, et al. Prehospital noninvasive ventilation for acute respiratory failure: systematic review, network meta-analysis, and individual patient data meta-analysis. Acad Emerg Med, 2014 Sep; 21(9): 960–70.

4. Gray A, Goodacre S, Newby D, et al. Noninvasive Ventilation in Acute Cardiogenic Pulmonary Edema. N Engl J Med, 2008; 359: 142–51.

5. Ho KM, Wong K. A comparison of continuous and bi-level positive airway pressure non-invasive ventilation in patients with acute cardiogenic pulmonary oedema: a meta-analysis. Crit Care, 2006; 10(2): R49.

6. Kollef M, Isakow W. The Washington Manual of Critical Care, 2nd ed. Philadelphia: Lippincott Williams & Wilkins, 2012.

7. Mehta S, Jay GD, Woolard RH, et al. Randomized, prospective trial of bilevel versus continuous positive airway pressure in acute pulmonary edema. Crit Care Med, 1997 Apr; 25(4): 620–8.

8. Nouira S, Boukef R, Bouida W, et al. Non-invasive pressure support ventilation and CPAP in cardiogenic pulmonary edema: a multicenter randomized study in the emergency department. Intensive Care Med, 2011; 37(2): 249–56.

9. Pandor A, Thokala P, Goodacre S, et al. Pre-hospital non-invasive ventilation for acute respiratory failure: a systematic review and cost-effectiveness evaluation. Health Technol Assess, 2015 Jun; 19(42): 1–102.

10. Passarini JN, Zambon L, Morcillo AM, et al. Use of non-invasive ventilation in acute pulmonary edema and chronic obstructive pulmonary disease exacerbation in emergency medicine: predictors of failure. Rev Bras Ter Intensiva, 2012 Sep; 24(3): 278–83.

11. Ram FS, Picot J, Lightowler J, Wedzicha JA. Non-invasive positive pressure ventilation for treatment of respiratory failure due to exacerbations of chronic obstructive pulmonary disease. Cochrane Database Syst Rev, 2004; (1):CD004104

Hawnwan Philip Moy, MD, is an assistant medical director of the Saint Louis City Fire Department and emergency medicine clinical instructor and core faculty of the EMS Section of the Division of Emergency Medicine at Washington University in St. Louis, MO. He completed his emergency medicine residency at Barnes Jewish Hospital/Washington University in St. Louis and his EMS fellowship at the University of North Carolina in Chapel Hill.

Blake Bruton, MD, earned his Doctor of Medicine degree from the University of Arkansas for Medical Sciences. He is currently in his second year of emergency medicine residency at Washington University in St. Louis. He is a certified Advanced Trauma Life Support instructor for the American College of Surgeons. His current interests include prehospital care, trauma resuscitation, bedside ultrasound and pediatric emergency medicine.