Chronic critically ill dyspneic patients: mechanisms and clinical measurement.

Dyspnea is a multidimensional, subjective perception of breathing difficulty commonly seen in patients who are critically or terminally ill. Understanding the mechanisms and assessment of dyspnea will help nurses in advanced practice roles to successfully manage these patients. Major mechanisms of dyspnea include stimulation of the chemoreceptors, stimulation of chest wall and intrapulmonary receptors, and increased sense of effort (also termed increased respiratory motor command). The causes of dyspnea are multifactorial, including numerous clinical conditions and aggravating situations that promote dyspnea. Assessment of dyspnea includes an accurate history of timing, precipitating factors, associated symptoms, alleviating factors, intensity and quality of the symptom. Measurement tools for dyspnea include both unidimensional and multidimensional tools, as well as tools that measure changes in the perception of dyspnea. Most tools have been tested for reliability and validity on healthy subjects or on patients with chronic obstructive pulmonary disease and, therefore, should be used with caution in critically or terminally ill patients.