Dyspnea is defined as abnormal or uncomfortable breathing in the context of what is normal for a person according to his or her level of fitness and exertional threshold for breathlessness. Dyspnea is a common symptom and can be caused by many different conditions. Dyspnea can be acute with an asthma exacerbation, acute myocardial infarction, pulmonary embolus or upper airway obstruction. Chronic causes of dyspnea include COPD, interstitial lung disease, cancer and sarcoidosis.
Epidemiology: 3-6% of all emergency department visits, 15-20% of all hospital admissions, 85% of cases are: COPD, pneumonia, cardiac ischemia, interstitial lung disease/CHF or psychogenic and 30% are multifactorial.
Part 2 of this series will cover the more common causes of dyspnea. However, here in Part 1, we will touch on some of the causes of dyspnea that can initially be overlooked and missed. Including airway obstruction and toxins, as well as neurologic, metabolic, hematologic and psychiatric causes.
Causes of Airway Obstruction may include retropharyngeal abscess, angioedema, inhalation burn injuries, aspiration of foreign body or epiglottitis. These patients may initially present with mild subjective symptoms such as sore throat and neck pain which can progress to coughing, hoarseness of voice, stridor (image), drooling, tripoding and retractions.
Neuromuscular disease may present as dyspnea due to weakness of the muscles of breathing. Consider causes such as myasthenia gravis (image), Guillain-Barre syndrome or wound botulism.
Anemia, whether a gastrointestinal bleed or post-chemotherapy, is a very common hematologic cause of dyspnea.
Toxins such as Carbon monoxide (CO) toxicity ,may present with flu-like symptoms. Symptoms may also be shared by several members in the same home or workplace. Methemoglobinemia (MetHb) can be precipitated by medications that are strong oxidizing agents like topical anesthetics (benzocaine or Pyridium) and certain antibiotics. Methemoglobinemia and carbon monoxide poisoning, like anemia, results in a global decrease in the amount of oxygen that the blood can carry to the tissues. Aspirin toxicity can cause a metabolic acidosis which indirectly can result in dyspnea and hyperventilation.
Metabolic causes of dyspnea, the most common being a metabolic acidosis, can be caused by sepsis, diabetic ketoacidosis or toxins such as aspirin and toxic alcohol like methanol. Patients may present with rapid and deep Kussmaul respirations.