Introduction
Etiology
Assessment
Management of Dyspnea and Coughing
        Management of Underlying Causes
        Symptomatic Management
        General Support Measures
        Chronic Cough

Introduction

Dyspnea is defined as an uncomfortable awareness of breathing. It is a subjective experience involving many factors that modulate the quality and intensity of its perception. Patients with comparable degrees of functional lung impairment and disease burden may describe varying intensities of dyspnea. Patients use a host of different words and phrases to describe the sensation of breathlessness. Terms such as tightness and suffocating are sometimes used.[1]

Reports on the frequency of dyspnea also vary, depending on the setting and the extent of disease.[2] In one study, 49% of a general cancer population reported breathlessness, and 20% rated their breathlessness as moderate to severe.[3] Patients with advanced cancer experience this symptom more frequently and more intensely than do patients with limited disease. One study found that 75 of 135 patients with advanced cancer reporting to an outpatient palliative care clinic were experiencing moderate-to-severe dyspnea.[4] Breathlessness was a complaint at presentation in 60% of 289 patients with lung cancer.[5] Results of a large study showed that 70% of patients suffered from dyspnea in the last 6 weeks of life.[6] About one third of patients who could report the intensity of their dyspnea rated it as moderate to severe. Another study revealed that half of patients with advanced cancer scored their dyspnea as moderate to severe.[7]

The pathophysiological mechanisms of breathlessness are numerous and complex.[8] Peripheral and central mechanisms as well as mechanical and chemical pathways are involved.

The direct causes of dyspnea in patients with advanced cancer are numerous; categorizing them can assist in the etiologic work-up. One approach is to divide direct causes into the following four groups:

1. Direct tumor effects such as intrinsic or extrinsic airway obstruction, pleural involvement, parenchymal involvement either by primary or metastatic disease, and superior vena cava syndrome.



2. Indirect tumor effects such as pneumonia or a pulmonary embolus.



3. Treatment-related causes such as pulmonary fibrosis secondary to radiation therapy or chemotherapy or chemotherapy-induced cardiomyopathy.



4. Causes unrelated to the cancer. These include chronic obstructive airway disease and congestive heart failure.

One study found that in patients experiencing dyspnea from advanced cancer, a median of five different abnormalities could have contributed to their shortness of breath.[7] Spirometry was abnormal in 93% of 100 patients examined, with 5% having obstructive patterns, 41% restrictive patterns, and 47% mixed patterns; 49% of patients had lung cancer, 91% had abnormal chest radiographs, and 65% had parenchymal or pleural involvement. These results indicate that a subset of patients will experience shortness of breath without any apparent lung involvement. The potentially correctable causes of dyspnea included hypoxia (40%), anemia (20%), and bronchospasm (52%). No significant association between the type of respiratory impairment and the degree of dyspnea was found. Most of these patients were current or former smokers. Most patients also had a significant lowering of their maximum inspiratory pressures, suggesting severe respiratory muscle dysfunction. This finding was duplicated in another study.[4] Of patients admitted to hospice care, 34% had histories of cardiac disease and 24% had histories of respiratory disease.[6] Only 39% of terminally ill patients who reported dyspnea had lung or pleural involvement. The etiology of dyspnea could not be clearly identified in approximately one quarter of patients. Another study found that 49% of lung cancer patients presented with airflow obstruction.[9,7]

Respiratory muscle dysfunction is an underrecognized factor contributing to dyspnea. Causes of respiratory muscle dysfunction include neuromuscular disease, malnutrition, and deficiencies of potassium, magnesium, and inorganic phosphate.[10] Poor oxygenation, muscle fatigue, abnormal cortisol and catecholamine levels, and circulating cytokines are also implicated.

Although it is commonly believed that anxiety is associated with breathlessness, researchers found that anxiety and shortness of breath do not invariably go together.[7] One study demonstrated that the involvement of the lungs by cancer, anxiety, and poor maximal inspiratory pressures were correlates of the intensity of dyspnea in patients with advanced cancer.

The multidimensional nature of dyspnea must be noted in the complicated assessment of this symptom. Objective signs such as tachypnea or the use of accessory breathing muscles frequently do not match a patient’s perception of dyspnea and the degree of functional impairment it causes. Numerous factors, including psychosocial issues, may affect a patient’s experience of dyspnea. Pulmonary function tests, with few exceptions, play a limited role in the assessment of this syndrome. Lack of a clear understanding of the pathophysiological mechanisms underlying dyspnea hampers the clinician's overall ability to effectively manage it.[8,11]

There is no consensus on what constitutes the best instrument for assessing dyspnea. Visual analog and numerical rating scales appear to be useful and are commonly utilized.[8,11] The Borg Scale is occasionally utilized.[11] The Cancer Dyspnea Scale is a multidimensional instrument, initially developed in Japan for patients with lung cancer and later translated into Swedish. The scale has been shown to be valid and reliable in patients with advanced lung cancer. The subscales measure sense of effort (physical dimension), sense of anxiety (psychological dimension), and sense of discomfort.[12] These tools are limited, however, because they are unidimensional and do not account for the relative contribution of different factors to a patient’s perception of breathlessness. Assessment should include the impact of dyspnea on the patient’s functional status.

A comprehensive history and examination are essential to an accurate assessment of dyspnea.[8,11] The temporal onset, qualities of the symptom, associated symptoms, precipitating and relieving events or activities, and responses to medications should be reviewed. Sudden onset may herald a pulmonary embolism or infection, whereas gradual onset may suggest the development of a pleural effusion. A history of obstructive airways or cardiac disease can shed some light on possible underlying causes. Investigations such as measuring oxygen saturation can be useful in determining whether a patient is hypoxic. In the setting of advanced, incurable cancer, arterial blood gasses play a limited role.

Diagnostic tests that may help to determine the etiology of dyspnea include chest imaging by radiography, computer-assisted tomography, complete blood counts, oxygen saturation at rest and with exercise and, to a much lesser extent, pulmonary function tests. Maximal inspiratory pressure (MIP) measurements may be helpful, particularly if no apparent cause can be found.[7] MIP is a reliable functional test of the strength of the diaphragm and other respiratory muscles.

As with all symptoms, it is essential to identify and treat the underlying cause(s) of dyspnea if possible and when appropriate. Examples of specific underlying causes (some of them potentially reversible) and their treatments include the following:

• Tumor obstruction (upper airways, bronchus, or superior vena cava): Radiation therapy, hormone therapy, or chemotherapy for sensitive tumors. Bronchoscopically guided cauterization or laser ablation of intraluminal masses in large airways can be considered when such technology and expertise is available.[13] Stenting of large airways with expandable stents when the obstruction is extraluminal has been described.



• Carcinomatous lymphangitis: A trial of corticosteroids, e.g., dexamethasone. The optimal dose is not clear. Chemotherapy should be considered in sensitive cancers.



• Bronchospasms: Bronchodilators. The indiscriminate use of bronchodilators, particularly in the absence of bronchospasm, is discouraged. The treatment of underlying chronic obstructive disease should be optimized with bronchodilators and inhaled corticosteroids as appropriate, particularly because many patients may be current or former smokers.



• Pleural effusions: Pleural aspiration by thoracentesis or chest drain. Pleurodeses in selected patients with recurrent effusions should be considered. Indwelling catheters are now available for patients with recurrent effusions who are not suitable for pleurodesing.



• Gross ascites: Abdominal paracentesis.



• Cardiac failure: Diuretics and other drugs as appropriate.



• Chest infections: Antibiotics and chest physiotherapy when appropriate.



• Anemia: Blood transfusions in select patients.

Symptomatic management of dyspnea is based primarily on oxygen therapy, drug therapy, and general measures of support and counseling.

Patients who are hypoxic on room air are likely to benefit from oxygen therapy, probably through a decrease in the chemoreceptor input to the respiratory center and the brain cortex. In two controlled trials, cancer patients with dyspnea who were randomized in a crossover design showed significant improvement in their dyspnea.[14,15] The role of oxygen in the treatment of nonhypoxia-related dyspnea in cancer patients is less clear.

Opioids represent an extremely effective treatment for dyspnea in cancer patients. Fear of side effects should not prevent the appropriate use of opioids in this setting. Most authorities believe that, if used appropriately, opioids do not hasten death in dyspneic cancer patients; rather, they reduce physical and psychological distress and exhaustion, and early use improves quality of life.[11,16] Clinically significant hypoventilation following opioid therapy depends largely on the history of previous exposure to opioids and the rate of increase of the opioid dose. As with opioid use in pain management, the principles of starting at a regular low dose in opioid-naïve patients followed by appropriate dose titration applies. Opioid therapy for dyspnea is administered similarly to, and often concurrent with, opioid therapy for pain control. Most of the available evidence supports the role of opioids in relieving dyspnea in malignant and nonmalignant conditions.[17-21]

Anecdotal and experimental evidence suggest a role for nebulized opioid administration in the treatment of dyspnea.[22-24] Opioid receptors are present on sensory nerve endings in the airways; however, nebulization is an inefficient way of administering drugs.[22] Pharmacokinetic studies suggest that the systemic bioavailability of nebulized morphine is extremely poor and erratic, varying from 4% to 8%.[25] Some patients may experience claustrophobia. Available evidence does not support the clinical use of nebulized opioids. More clinical trials are needed to better determine the role of this mode of treatment.

Other options suggested for symptomatic treatment include methylxanthines, sedatives, tranquilizers, nebulized local anesthetics, and antiprostaglandins. The role of methylxanthines in cancer-related dyspnea has not been clarified. Chlorpromazine and promethazine have been shown to decrease dyspnea without affecting ventilation in noncancer patients, but their role in cancer-related dyspnea is unclear. Four out of five randomized controlled trials failed to demonstrate any benefit for using benzodiazepines in cancer patients.[11,26] One randomized single-blind study suggests that the combination of two scheduled medications (subcutaneous morphine and subcutaneous midazolam) and one as needed (subcutaneous morphine) for episodes of breakthrough dyspnea is more effective than the other evaluated combinations for controlling breakthrough dyspnea and requires further study.[27] The role of benzodiazepines appears to be limited to treatment of dyspnea that is considered a somatic manifestation of a panic disorder or use when a patient has concurrent severe anxiety. No evidence supports the use of nebulized local anesthetics for the treatment of breathlessness.

In addition to adequate pharmacological therapies, a number of nonpharmacological measures are suggested. These include pursed-lip breathing, diaphragmatic breathing and muscle training, cold air directed across the cheek, meditation, relaxation training, biofeedback techniques, and psychotherapy. The effectiveness of these measures in relieving breathlessness appears to be variable.

In some patients, chronic coughing may be the source of major suffering.[11] Chronic cough can cause pain, interfere with sleep, aggravate dyspnea, and worsen fatigue. The causes of cough can be classified much like the causes of dyspnea. The optimal therapy for chronic cough is treatment of the underlying disorder. Cough-suppressing agents such as opioids are commonly utilized. Anecdotal evidence suggests a role for inhaled local anesthetics, which should be utilized judiciously and sparingly; they are unpleasant to the taste and obtund the gag reflex, and anaphylactic reactions to preservatives in these solutions have been documented. Opioid and nonopioid antitussives such as dextromethorphan may act synergistically, but further studies are required to confirm this hypothesis.[11] In cases of increased sputum production, expectorants and mucolytics have been employed, but the effects have not been well evaluated. Inhaled sodium cromoglycate has shown promise as a safe method of controlling chronic coughing related to lung cancer.[26]

References

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