Increased Ventilatory Demand

Ventilatory demand is increased because of increased physiologic dead space resulting from reduction in the vascular bed, hypoxemia and severe deconditioning with early metabolic acidosis (with excessive hydrogen ion stimulation), alterations in carbon dioxide output (V co ₂ ) or in the arterial partial pressure of carbon dioxide (P co ₂ ) set point, and nonmetabolic sources such as increased neural reflex activity or psychological factors such as anxiety and depression.

Impaired Ventilation

Impaired mechanical responses result in restrictive and obstructive ventilatory deficits. A restrictive ventilatory defect is caused by decreased distensibility of the lung parenchyma, pleura, or chest wall (parenchymal disease or reduced chest compliance) or by a reduction in the maximum force exerted by the respiratory muscles (muscle weakness). An obstructive ventilatory deficit refers to impedance of the flow of air. Both structural changes (external compression or internal obstruction) and functional changes (bronchoconstriction) can lead to progressive narrowing of the airways. Patients may also have a mixed restrictive and obstructive disorder. Box 15-1 outlines the pathophysiologic mechanisms of dyspnea with potential clinical causes in persons with advanced cancer and other end-stage diseases.

Special End-of-Life Considerations

Asthenia and generalized muscle weakness are common in patients with advanced COPD and other end-stage diseases. Exercise capacity is limited by abnormalities in either endurance or weakness of the skeletal muscles in patients with chronic heart failure, COPD, and cancer. Both peripheral muscle and respiratory muscle strength are reduced in patients with cardiorespiratory diseases and cancer, and muscle strength is a significant contributor to the intensity of exercise-induced dyspnea. Patients with chronic heart failure have abnormal skeletal muscle metabolism during exercise and significant ultrastructural skeletal muscle abnormalities that affect both the respiratory and the peripheral muscles.

Cachexia is a common final presentation of several chronic conditions, including cancer, COPD, chronic heart failure, acquired immunodeficiency syndrome, and renal failure. Cachexia differs from simple nutritional imbalance because there are modifications in the metabolism of proteins, lipids, and carbohydrates, with a preferential loss of muscle tissue over fat, enhanced protein degradation, and unresponsiveness to nutritional interventions. Weakness of both respiratory and peripheral muscles can result from impaired nutritional status.

Neurologic paraneoplastic syndromes can contribute to the development of dyspnea in patients with cancer. Thirty percent of patients with malignant thymoma have myasthenia gravis that can weaken respiratory muscles and cause respiratory failure. Eaton-Lambert syndrome, associated with lung, rectal, kidney, breast, stomach, skin, and thymus cancers, can also produce respiratory muscle weakness and result in dyspnea.

For patients with advanced cancer and other end-stage diseases, there is an interrelationship between psychological factors and dyspnea. Breathlessness may evoke anxiety or fear, and emotions may contribute to dyspnea either by increasing respiratory drive or altering the perceptions of breathlessness. Anxiety, depression, fatigue, and psychological ability to cope with disease have been noted as predictors of dyspnea in patients with advanced lung cancer. In general, anxious, obsessive, depressed, and dependent persons appear to experience dyspnea that is disproportionately severe relative to the extent of the pulmonary disease.

Patient Reports

Because dyspnea is a subjective experience, the key to assessment is the patient’s report of breathlessness through the use of unidimensional instruments and descriptions related to its effect on level of activity. Individuals with comparable degrees of functional lung impairment may experience considerable differences in how they perceive the intensity of dyspnea. Factors such as adaptation, differing physical characteristics, and psychological conditions can modulate both the quality and the intensity of the person’s perception of breathlessness. Therefore, medical personnel must ask for and accept the patient’s assessment, often without measurable physical correlates.

To determine the presence of dyspnea, it is important to ask more than “Are you short of breath?” Patients often respond in the negative to this simple question either because the activity that they are performing at that moment is not causing dyspnea or because they have limited their physical activity to ensure that they do not experience breathlessness. It is therefore important to ask about shortness of breath in relation to specific activities (e.g., walking at the same speed as someone else of your age, walking upstairs, or eating).

Qualitative Aspects of Dyspnea

Dyspnea is also not a single sensation. Clinical investigations suggest that the sensation of breathlessness encompasses several qualities that may, as in the assessment of pain, allow discrimination among the various causes. For example, in assessing pain, descriptors such as “burning” or “shooting” suggest a neuropathic etiology. Similarly, the descriptor “My chest feels tight” has been associated with asthma and “My breathing requires effort/work” with lymphangitic carcinomatosis. Although studies have noted association of specific sets of descriptor clusters with different pathologies, there is significant overlap across chronic medical conditions and a lack of consistency within medical conditions. Research to date does not support the use of descriptors as a tool for delineating differential diagnosis or targeting treatment, but the language used by breathless patients may provide another dimension to understand and evaluate their experience.

Clinical Assessment

Clinical assessment of dyspnea includes the patient’s report and history of the symptom and a focused physical examination. The assessment directs management and provides a baseline on which to evaluate the patient’s response to treatment. Table 15-1 outlines a general approach to the clinical assessment of dyspnea in palliative care patients.

The history includes the temporal onset (acute or chronic), pattern, severity and qualities of dyspnea, associated symptoms, precipitating and relieving events or activities, and response to medications. A history of smoking, underlying lung or cardiac disease, concurrent medical conditions, allergy history, and details of previous medications or treatments should be elicited. The physical, social, and emotional impact of dyspnea on the patient and family members and the coping strategies used are also important components of the history. The use of unidimensional or multidimensional tools to measure the quality and severity of dyspnea and its effect on functional ability can assist in assessment and monitoring the effects of treatment.

The Visual Analog Scale (VAS) is commonly used to measure perceived intensity of the dyspnea. This scale is usually a 100-mm vertical or horizontal line, anchored at either end with words such as “not at all breathless” and “very breathless”. Patients are asked to mark the line at the point that best describes the intensity of their breathlessness. The Edmonton Symptom Assessment Scale (ESAS) can also be used to measure perceived intensity of dyspnea. It uses a numeric 0 to 10 scale where 0 means no breathlessness and 10 means the worst possible breathlessness. Patients are asked to indicate the number that corresponds to their present intensity of breathlessness. The Modified Borg Scale (mBORG) has a 0 to 10 scale with nonlinear spacing of verbal descriptors of severity of breathlessness. Patients are asked to pick the verbal descriptor that best represents their perceived exertion. Conceived as a ratio scale (e.g., 4 is twice as severe as 2), the mBORG has theoretical advantages over numeric rating scales.

The Oxygen Cost Diagram is a visual analog scale that consists of a 100-mm vertical line used to measure the functional impact of breathlessness. Everyday activities such as walking, shopping, and bed-making are listed in proportion to their oxygen cost. Patients are asked to identify the level of activity that they cannot perform because it causes too much breathlessness. As dyspnea worsens, the score decreases. The Cancer Dyspnea Scale (CDS) is a 12-item questionnaire addressing sensations of effort (5 items), anxiety (4 items), and discomfort (3 items). Patients rate the severity of each item from 1 (not at all) to 5 (very much). It requires more time and effort to complete but can provide an understanding of the quality of breathlessness.

The physical examination should be performed with focus on possible underlying causes of dyspnea and the details obtained from the history. Particular attention should be directed at signs linked with certain clinical syndromes associated with common causes of dyspnea in people who have the patient’s particular underlying disease. For example, dullness to percussion, decreased tactile fremitus, and absent breath sounds are associated with pleural effusion in a person with lung cancer; elevated jugular venous pressure, an audible third heart sound, and bilateral crackles audible on chest examination are associated with congestive heart failure.

Accessory muscle use has been suggested as a physical finding that may reflect the intensity of dyspnea. Patients with COPD who were experiencing high levels of dyspnea were found to have significant differences in the use of accessory muscles as compared with patients with low levels of dyspnea, although there were no significant differences in respiratory rate, depth of respiration, or peak expiratory flow rates.

The choice of appropriate diagnostic tests should be guided by the stage of the disease, the prognosis, the risk-to-benefit ratios of any proposed tests or interventions, and the desire of the patient and family. If the person is actively dying or wants no further investigations or invasive or disease-oriented interventions, it is appropriate to palliate the symptom without further testing. If, however, the patient is at an earlier phase of illness, diagnostic tests helpful in determining the origin of dyspnea could include chest radiography; electrocardiography; pulmonary function tests; arterial blood gases; complete blood cell count; serum potassium, magnesium, and phosphate levels; cardiopulmonary exercise testing; and tests specific for underlying pathologic conditions (e.g., computed tomography angiogram for pulmonary embolism).