In normal respiration, the contraction of external intercostal muscles and the diaphragm increases the lung volume, creating negative pressure that results in the movement of air to the alveoli. The relaxation of the external intercostal muscles and diaphragm restores the thoracic cavity to preinspiratory volume, increasing pressure in the lungs and generating exhalation. This movement of air in and out of the lungs, known as pulmonary ventilation, provides the necessary oxygen to the alveoli and eliminates carbon dioxide. Pulmonary ventilation maintains optimal partial pressure of each gas, allowing gas exchange at the level of the alveoli and pulmonary capillaries.

Some of the most common calls to emergency medical services are associated with respiratory complaints [1–4]. Differential diagnosis includes neurological issues (e.g., head trauma, drugs, and cerebrovascular accidents), upper airways (e.g., swelling, blockage by a foreign body, and trauma), lower airways (e.g., asthma and chronic obstructive pulmonary disease (COPD)), alveoli, and possible impairment in pulmonary circulation resulting from pulmonary embolism. Congestive heart failure and COPD make up the largest percentage of respiratory emergencies. In the United States, approximately one million patients per year are treated by paramedics for acute congestive heart failure [5].

Dyspnea, or shortness of breath, accounts for 10–13 % of emergency medical service calls [6]. Standard care for dyspnea in the prehospital setting typically involves supplemental oxygen and beta agonist nebulizer therapy. Vasopressors and diuretics may also be employed, depending on the emergency medical service protocol and responder skill level.

Respiratory failure occurs when the lungs can no longer provide adequate oxygenation, generally resulting in tachypnea, hypoxemia, hypercapnia, and perceived dyspnea. Severe respiratory failure has been managed in the prehospital setting by endotracheal intubation, an invasive procedure that requires sedation and advanced skills. Endotracheal intubation may be difficult and dangerous because of the presence of contact-protective airway reflexes [7] and is associated with multiple complications, such as oral lacerations, aspiration, tube malposition, barotrauma, and ventilator-associated pneumonia. The poorly controlled environment of the prehospital setting increases the likelihood of these complications.

Trauma and pneumothorax may present with the symptom of dyspnea. The presence of trauma is generally easily discerned, and presentation of significant pneumothorax typically involves tracheal deviation and unilateral loss of breath sounds. More perplexing are the life-threatening medical causes of dyspnea, such as exacerbations of COPD, asthma, pneumonia, pulmonary embolism, cardiac ischemia, and acute cardiogenic pulmonary edema (ACPE) (COPD and ACPE are the most common). The uncertain etiology of medically induced dyspnea complicates its management in the prehospital setting.

Improving alveolar ventilation is a critical step for delivering oxygenated blood to the tissue. Different techniques for accomplishing this have been introduced over the years, ranging from provision of supplemental oxygen to endotracheal intubation. With recent advances, noninvasive positive-pressure ventilation (NIV), a technique introduced in 1981 by Sullivan and colleagues to provide alveolar ventilation without creation of an invasive airway, has emerged as an efficient alternative to endotracheal intubation with mechanical ventilation; NIV also has a lower rate of complications such as pneumonia, vocal injury, and tracheal stenosis than invasive techniques [8].

Unlike bag valve mask ventilation, the most basic form of NIV, which is typically used for pre-oxygenation of a patient prior to endotracheal intubation, two types of NIV are used in lieu of endotracheal intubation. The first type, continuous positive airway pressure, applies supportive pressure in a uniform fashion during both the inspiratory phase and the expiratory phase. The second type, bi-level positive airway pressure, alternates different levels of inspiratory and expiratory pressure. Both types typically provide pressure support of 4–20 cmH₂O, usually via a face mask, although helmets and nasal cannulas can also be used [9]. Because BiPaP matches the patient’s spontaneous respiratory drive, in certain patients NIV may be more efficient than endotracheal intubation and controlled mechanical ventilation [10]. In addition, the training required to deliver NIV is less extensive than the training required for endotracheal intubation.

Over the past several years, NIV modalities have proven to be effective in management of acute respiratory failure. NIV decreases the effort required for breathing through several mechanisms. It improves pulmonary compliance and reduces the ventilation/perfusion mismatch. Smaller, pliable airways are stented open. This allows for recruitment and ventilation of atelectatic alveoli. The increased intrathoracic pressure decreases venous return, transmural pressure, and afterload, which improves cardiac function. Edema is shifted back into the vascular system [10].