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The approach to a patient with difficulty breathing must always begin with addressing immediate life threats (e.g., hypoxemia, upper airway obstruction, tension pneumothorax). After this primary assessment, possible causes of the presentation can be considered to guide specific therapy. Accurate diagnosis of the cause of dyspnea in prehospital settings remains difficult. Studies have shown that EMS professionals often struggle with determining the etiology of dyspnea [4, 5]. Prehospital treatment must find a balance between disease severity, diagnostic certainty, and the likelihood of benefit versus harm. Among 144 patients given furosemide in the field, it had been given appropriately only 58% of the time to patients with a subsequent diagnosis of congestive heart failure [6]. Inappropriate administration occurred 42% of the time and was potentially harmful 17% of the time [6].

Much of the assessment of disease severity comes from general observation of the patient, supplemented by physical examination and close monitoring of vital signs, cardiac rhythm, pulse oximetry (SpO₂), and waveform capnography. Talking to a patient to assess how many words the patient can speak at a time, whether there is associated diaphoresis, and if the patient appears to be fatiguing can be helpful clues for potential deterioration. If the initial assessment reveals the possibility of impending respiratory failure, appropriate supplemental ventilation should be considered, including the use of noninvasive positive‐pressure ventilation (NIPPV) or bag‐valve‐mask ventilation in conjunction with oral/nasopharyngeal airways, supraglottic devices, or endotracheal intubation.

Once disease severity and the immediate needs have been addressed, the next step is to categorize the underlying cause. The four most common categories for respiratory distress are upper airway obstruction, small airway obstruction (e.g., chronic obstructive pulmonary disease [COPD] and asthma), cardiovascular etiologies (e.g., acute decompensated heart failure [ADHF], sympathetic crashing acute pulmonary edema [SCAPE], acute coronary syndrome, pulmonary embolism), and pneumonia. Additional medical conditions that can lead to acute respiratory distress are listed in Box 5.1.

Acute coronary syndrome is an important consideration among these disparate causes of shortness of breath. It can present as cardiogenic shock with acute pulmonary edema and cause subjective dyspnea without severe cardiac function impairment. Dyspnea associated with acute coronary syndrome may not be accompanied by chest discomfort and is more common in women, older individuals, and diabetics [7, 8]. Dysrhythmias can also cause dyspnea. They are readily diagnosed by cardiac monitoring. If time and the patient's condition allow, a 12‐lead ECG may guide treatment and destination decisions for the dyspneic patient. Sepsis can also present with respiratory distress due to fever, increased oxygen consumption, and compensation of underlying lactic acidosis. Toxic exposures can cause respiratory distress, either through direct irritation of the respiratory tract or secondarily by central or autonomic nervous system impairment of respiratory function. Tachypnea and subjective dyspnea may also be compensatory for an underlying metabolic acidosis, as with diabetic ketoacidosis or salicylate toxicity. If these acidotic patients require intubation and mechanical ventilation, it is important to continue to hyperventilate them after securing the airway to maintain their preexisting respiratory compensation. This can be facilitated through the early and continued use of continuous waveform capnography monitoring. Neuromuscular diseases such as myasthenia gravis and Guillain Barré syndrome are rare causes of inadequate ventilation and respiratory failure. Although diagnoses of exclusion, shortness of breath is also a common manifestation of anxiety disorders, panic attacks, and psychogenic hyperventilation.