Prehospital Use of CPAP

It’s 3 a.m. on an unusually slow night. Your partner is dozing on the couch, and you’re watching your fifth consecutive Cops rerun when the hotline rings. “Rise and shine,” says the dispatcher. “Difficulty breathing, cardiac history, 84-year-old female at St. Anthony’s Towers, apartment 906.”

You know you’ve been to this apartment before and cared for a patient with congestive heart failure. On the way, you discuss with your partner how you’re surprised she survived her last trip to the hospital when she was intubated in the emergency department. You’re both prepared for a priority patient.

An excited neighbor in a nightgown meets you at the elevator and guides you to the apartment. You hear the familiar gurgling sounds of rales from the hallway, and inside find Mrs. Miller seated upright on her bed. She is pale, diaphoretic and struggling for every breath. “I....need...the...mask...!” she tells you between gasps. A quick assessment reveals that she woke up short of breath, just as she has before when her “lungs filled up.” She denies chest pain and has a long list of medications that includes nitroglycerin and furosemide.

Your partner immediately places her on a NRB mask and obtains a set of vitals, while you assemble a continuous positive airway pressure (CPAP) circuit. Her heart rate is 140, sinus tachycardia on the monitor, pulse ox 82%, respiratory rate 36 with coarse rales in all lung fields, and BP 210/150. You connect the CPAP tubing to your portable oxygen tank, administer a spray of nitroglycerin under her tongue, and place the tight-fitting mask on her face, while your partner obtains IV access. A few minutes after the mask is applied, she becomes less anxious and nods her head when you ask if it is easier to breathe. You apply an inch of nitroglycerin paste to her chest, administer 40 mg of furosemide IV and package her onto the stretcher. You reassess her vitals en route to the hospital; she now has a heart rate of 128, pulse ox 100%, respiratory rate 24, BP 178/94, and you obtain a 12-lead ECG that shows 1 mm of ST depression in leads I, aVL, V5 and V6. You administer another spray of nitroglycerin and call the hospital to advise that your patient is on CPAP. They give you a room assignment and assure that a respiratory therapist will be standing by.

At the hospital, Mrs. Miller is transferred to a BiPAP machine, given more furosemide and started on a nitroglycerin infusion. Her skin color is almost back to normal now, and she is not nearly as diaphoretic. As you say goodbye to her, she thanks you several times, now able to speak much easier.

Introduction

Because respiratory distress is one of the most common causes for calling 9-1-1, EMS providers have several tools to treat and improve discomfort before arriving at the hospital. Once a differential diagnosis can be made for the cause of the breathing difficulty, high-flow oxygen and appropriate medications usually help alleviate it. However, some patients are in such profound distress that their breathing must be assisted with a bag-valve mask, followed by intubation. While often necessary for survival, endotracheal intubation is an invasive procedure that carries a host of drawbacks and complications. Noninvasive ventilatory support is emerging in the prehospital setting as an effective treatment option for patients who need some support for breathing but can still maintain an airway. In cases of acute pulmonary edema from congestive heart failure, COPD and asthma exacerbations, it has been shown to decrease the need for endotracheal intubation and relieve symptoms.1–6 Noninvasive ventilatory support is delivered by continuous positive airway pressure (CPAP) and bilevel positive airway pressure (BiPAP) devices. This article explains the physiologic advantages to noninvasive ventilatory support, the equipment it involves and how it is applied, and reviews some of the current research on its use.

Airway Management Options

Endotracheal intubation has been the standard method used to assist ventilation in the patient who is in danger of respiratory arrest or remains hypoxic after other interventions have failed. It provides definitive airway control and a method of precisely titrating respiratory rate and tidal volume. It can also adjust the positive end expiratory pressure (PEEP), which is pressure in the lungs at the end of expiration that keeps collapsing airways open.7,8

Intubation can be difficult to accomplish in the field, however, with a patient who is still breathing and has a gag reflex. If medications are not available to facilitate intubation, you must wait until the patient becomes so fatigued and hypoxic that he loses his gag reflex before attempting an oral intubation. If medications are used and intubation attempts are unsuccessful, the results can be deadly.7 Another option for the breathing patient is nasal intubation, which can cause bleeding that compromises the airway. Hypoxia, lethal dysrhythmias, tracheal trauma and aspiration are potential complications of either method.3,7 Even when intubation is successful, intubated patients lose the warming and humidifying functions of the upper airway until they can be placed on a ventilator. While intubated and on a ventilator, patients are unable to talk, must remain sedated while they are weaned off, and are at an increased risk of pneumonia.3,4 Even though intubation will provide adequate ventilation and is often lifesaving, it is advantageous to avoid it if less-invasive options are available.

CPAP is emerging as a noninvasive option for EMS providers to provide respiratory support through a mask rather than an ET tube. It can get patients through their crisis without their having to be intubated, or at least buy some time until intubation is needed. CPAP is the most common form of noninvasive ventilatory support utilized in the prehospital environment because of the small size of the equipment needed and oxygen-powered generator. It delivers continuous positive air pressure, usually at 10 cm H2O throughout the respiratory cycle.3 It is also used in the home to treat obstructive sleep apnea, where it works by preventing the upper airway structures from collapsing and stops subsequent hypoxic episodes that disrupt the sleep cycle. It has more recently been studied for emergent treatment of respiratory distress as a means of decreasing the patient’s work of breathing. This is different from BiPAP, which delivers two levels of positive pressure during the different phases of the respiratory cycle. If CPAP is set for 10 cm H2O throughout the respiratory cycle, BiPAP might deliver 15 cm H2O during inspiration and 5 cm H2O during expiration.3–5,7 While BiPAP units, which are used most often in hospitals, can provide more relief, they are less practical for field use because they are larger, more expensive and require more energy.7 An extensive discussion of BiPAP is beyond the scope of this article.

Prehospital Research of CPAP

While endotracheal intubation is generally viewed as a last resort for respiratory distress, emergency department studies of CPAP show that it seems to have the most benefit when initiated early.1,2 Logically, this would carry over to the field and even be useful in systems with short transport times.2 A few clinical trials have studied prehospital use of CPAP, and all show a decrease in intubations and symptom improvement with no major complications.1,2

The most recent major study took place in Helsinki, Finland, where CPAP has been used for over 10 years on physician-staffed mobile intensive care units to treat acute pulmonary edema from CHF. Patients who received CPAP had improved oxygenation (increased SpO2) and lowered respiratory rate, heart rate and systolic blood pressure. While the diagnosis of acute pulmonary edema was confirmed in the hospital in only 69% of the patients in the study who received CPAP, the patients who were initially misdiagnosed do not appear to have been harmed by the CPAP.1

Other studies have taken place in the United States—one in Cincinnati, OH, where a prospective case series analysis studied its effectiveness in treating acute pulmonary edema from CHF. CPAP was added to the Cincinnati Fire Department’s CHF protocol for patients believed to be in imminent need of intubation. This study showed an increase in pulse oximetry readings, no patients were intubated in the field, and no complications were attributed to CPAP. Also, the paramedics who participated in the study reported no technical or logistical problems with the CPAP system.2 Another trial evaluated CPAP’s effectiveness through a review of run reports over a two-month period before and after it was implemented. It was utilized for severe respiratory distress of any etiology, and the CPAP group had significantly fewer intubations.9

How It Works

CPAP has been most studied as a treatment option for patients with pulmonary edema from congestive heart failure, where distress is caused by increased vascular pressure from the failing left ventricle that forces interstitial fluid into the alveoli. This fluid not only impedes oxygen exchange, but it washes out the surfactant that holds alveolar sacs open, allowing them to collapse. CPAP increases pressure in the lungs and holds open collapsed alveoli, pushes more oxygen across the alveolar membrane, and forces interstitial fluid back into the pulmonary vasculature.1–3 This improves oxygenation, ventilation and ease of breathing. In addition, the increased intrathoracic pressure decreases venous return to the heart and reduces the overwhelming preload (pressure in the ventricles at the end of diastole). It also lowers the pressure that the heart must pump against (afterload), both of which improve left ventricular function.1–3

The mechanism by which CPAP can be useful in treating COPD and asthma is less understood. In these patients, respiratory distress is caused by constriction of the lower airways from an irritant (bronchoconstriction), collapse of the alveolar walls from disease and plugged airways from excess mucus secretion. Patients with COPD are often unable to completely empty their lungs during expiration, which leaves positive pressure in the airways at the end of expiration. This is known as intrinsic positive end expiratory pressure (PEEP) that is usually about 5 cm H2O. It must be overcome before negative pressure can be generated to inhale more air.4,5 These patients will exhale through pursed lips to keep the airways open. With CPAP applied, this pressure is overcome mechanically and the workload is taken off of the patient.4,5 In addition to reinflating collapsed alveoli, CPAP delivers more oxygen, can pop the obstructing mucus secretions, and delivers nebulized medications more effectively.4

Directions for Use

While equipment varies among manufacturers, CPAP sets designed for field use are powered by an oxygen source that can deliver 50 psi. Some generators have a fixed flow rate, while others can be adjusted. The percentage of oxygen delivered (FiO2) usually starts at 30% and can be increased, depending on the needs of the patient. The rest of the equipment comes in a prepackaged kit, which includes a face mask, corrugated tubing, bacteria filter and PEEP valve.

When applying CPAP to a patient, start by connecting the circuit to the oxygen source according to the manufacturer’s directions. Next, apply the mask with the enclosed straps and ensure that there is an airtight seal similar to a bag-valve mask. Once a seal is achieved, install the PEEP valve and adjust the FiO2 as needed. Many patients have been on CPAP before and will ask for it; for others, it can be scary and they must be coached through the experience. Explain that it will feel like they are sticking their head out of a car window, and encourage them to breathe in through their nose and exhale through their mouth against the pressure. They may also hold the mask themselves to get used to it before the straps are applied. Once applied, the mask may be removed for a few seconds to administer sublingual nitroglycerin, and the corrugated tubing can be cut to install a nebulizer. While this may seem cumbersome, with practice it can be accomplished very quickly and will not significantly delay scene time.

Who Needs CPAP?

While some protocols have specific guidelines for when CPAP should be applied, it is generally indicated for a patient in moderate to severe respiratory distress who is completely alert and able to maintain his airway.3,4,8 While most patients improve shortly after CPAP is applied, remember that it is helping alleviate symptoms more than the underlying problem. It must be used as an adjunct to medications, and some patients will still deteriorate after it is applied.3,4 While CPAP makes it easier for patients to breathe, it is not a ventilator and does not breathe for them. Therefore it is contraindicated in cases of hypoventilation, decreased mentation or any potential airway compromise, such as vomiting.3,4 These patients are past the point where CPAP can be effective, and must have their ventilations assisted with a bag-valve mask and be intubated. It is also not appropriate for minor asthma and COPD exacerbations that quickly respond to medications.

Complications and Side Effects of CPAP

While virtually all of the clinical trials evaluating CPAP show only minor complications and side effects, there are a few things to watch for. The most common problem is anxiety; a few patients will not tolerate it despite coaching. In these cases, it should be removed. Because CPAP increases intrathoracic pressure, there is a theoretical risk of hypotension and a pneumothorax. You must continually reassess for these conditions, although neither has been demonstrated to be a problem in the current EMS research. Another theoretical consideration is gastric distension. In the awake patient, this is generally not a concern until positive pressure reaches 25–30 cm H2O, which is higher than CPAP should ever be set.2,3,6 Other complaints include sinusitis, skin abrasions and conjunctivitis, all of which can be minimized with a proper mask size and seal.2

CPAP can rapidly deplete portable oxygen supplies, especially if the FiO2 is increased. It is important to monitor the amount of pressure available in both portable and on-board tanks. Once CPAP is started, it should be continued, so it may be a good idea to move the patient to the ambulance before applying it. Give the hospital staff advance notice so they can have their equipment ready.

Summary

When used correctly, CPAP has been shown to alleviate symptoms and decrease the need for intubation for patients with CHF, COPD and asthma. It is safe, portable and easy to apply. CPAP does not replace intubation, but rather is a less-invasive means of providing respiratory support while medications work to correct the underlying cause of distress.

References

  1. Kallio T, Kuisma M, et al. The use of prehospital continuous positive airway pressure treatment in presumed acute severe pulmonary edema. Prehosp Emerg Care 7:209–213, 2003.
  2. Kosowsky J, Stephanides S, et al. Prehospital use of continuous positive airway pressure (CPAP) for presumed pulmonary edema: A preliminary case series. Prehosp Emerg Care 5:190–196, 2001.
  3. Kosowsky J, Storrow A, Carleton S. Continuous and bilevel positive airway pressure in the treatment of acute cardiogenic pulmonary edema. Am J Emerg Med 18:91–95, 2000.
  4. Pollack C. Noninvasive ventilatory support in the emergency department. Manual of Emergency Airway Management. Philadelphia: Lippincott, Williams and Wilkins, 2000.
  5. Rapparo S. Use of CPAP and BiPAP in acute respiratory failure. The Berries. http://theberries.ns.ca/Archives/CPAP.html.
  6. Hanley M, Welsh C. Current Diagnosis and Treatment in Pulmonary Medicine. New York, NY: McGraw-Hill Medical Publishing, 2003.
  7. Margolis G. Airway Management, Paramedic. Sudbury, MA: Jones and Bartlett Publishers, 2004.
  8. Bledsoe B, Porter R, Cherry R. Paramedic Care: Principles & Practices. Upper Saddle River, NJ: Brady Prentice Hall, 2001.
  9. Bailey P, Sweeney T, et al. Prehospital CPAP reduces the need for endotracheal intubation. Poster Presentation. Prehosp Emerg Care 7:166, 2003.

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