The etiology of dyspnea is usually advanced malignant disease, although other risk factors include ascites, chronic obstructive pulmonary disease, deconditioning, and pneumonia. Dyspnea occurs when more respiratory effort is necessary to overcome obstruction or restrictive disease (e.g., tumor or pleural effusions), when more respiratory muscles are required to maintain adequate breathing (e.g., neuromuscular weakness or cachexia), or when there is an increase in ventilatory need (e.g., hypercapnia or metabolic acidosis).
Opioids decrease the perception of air hunger, regardless of the underlying pathophysiology and without causing respiratory depression. This relief is dose related and, experimentally, is reversible by naloxone, an opioid antagonist. Very low doses of opioid, such as morphine 2.5 mg orally, may provide relief in opioid-naïve patients. Higher doses may be indicated in patients who have more intense dyspnea or in patients who are using opioids for pain. As with pain control, gradual upward titration may be needed to provide relief, particularly as symptoms progress.
The use of nebulized opioids for control of dyspnea remains controversial. Nebulized morphine has been administered in the belief that this route would deliver the opioid directly to opioid receptors isolated within the lung. Initial uncontrolled clinical trials and case reports described efficacy using this technique. However, controlled trials have not confirmed these positive results, and as a result, nebulized morphine is generally not indicated. Initial trials of nebulized fentanyl, a lipophilic opioid, suggest efficacy.[Level of evidence: II]
A randomized controlled trial of oxygen delivered versus room air, both delivered by nasal cannula and worn at least 15 hours per day over a 7-day period, demonstrated no differences in breathlessness, with no difference in side effects between the two groups. In light of the lack of benefit of oxygen therapy, the investigators recommended that less burdensome therapies be selected. Supplemental oxygen appears to be useful only when hypoxemia is the underlying cause of dyspnea and is not effective in relieving symptoms of dyspnea in people who do not have hypoxemia.[52,53] Alternate strategies include positioning a cool fan toward the patient's face and repositioning the patient into an upright posture. Cognitive behavioral therapies such as relaxation, breathing control exercises, and psychosocial support may be effective in relieving dyspnea, although patients in the final hours of life may have limited capacity to participate in these techniques.[Level of evidence: I]