Difficulties clinicians have in determining opioids for the management of pain are multifactorial. One consideration may be the growing public concern for prescription opioid abuse, potentially creating resistance to appropriate use of opioids by clinicians who fear legal or regulatory push back.
General principles in managing severe pain in the opioid-tolerant patient include the following: (1) calculating the morphine equivalent as a daily 24-hour dose; (2) determining the breakthrough dose, which is usually 10% to 15% of the calculated daily dose; (3) titrating doses upward if pain is not controlled, or if more than three breakthrough doses are being required daily; and (4) reducing the calculated conversion dose of a new opioid 25% to 50% when converting to a different opioid.12
The EP is frequently required to convert a patient’s oral opioid analgesic to an equivalent IV dose, and hydromorphone and morphine are the two most commonly used. The Table provides an approximation for this conversion.
Equianalgesic Dosing
Equianalgesic dosing is an important concept in pain management, especially for those patients already receiving opioids. There is great variation in the analgesic potency of the different opioids. The dose at which two opioids provide equivalent pain relief is the equianalgesic dose. Usually, this is standardized to 10 mg of parenteral morphine.13 Unfortunately, it is not uncommon for patients to be undertreated when switched to another opioid.
Nonpain Symptom Management
Nonpain symptoms that all EPs must know how to manage include constipation, dyspnea, nausea/vomiting, the so-called death rattle, and terminal delirium. In one study of reasons for ED visits by palliative care patients, the most common were dyspnea (26%), nausea/vomiting/constipation (17%), and uncontrolled pain (15%).14
Constipation
The most important adverse effect of opioids—one that does not improve or change during treatment—is constipation. Constipation in general—not just associated with opioids—has been ranked as one of the 10 most bothersome symptoms in the palliative care population, leading to discomfort, decreased quality of life, and potential small bowel obstruction or perforation.15 Unless contraindicated, a gastrointestinal stimulant such as senna, or an osmotic laxative such as lactulose, must be prescribed whenever an opioid is initiated. As the author (Galicia-Castillo) often notes, “The hand that writes the prescription for an opioid should be the hand that writes an Rx for a bowel regimen, or it becomes the hand that disimpacts the patient.”
The most recent Cochrane Review for the management of constipation in the palliative care population did not show any differences in the effectiveness among three commonly used laxatives: senna, docusate, and lactulose. This review did not evaluate polyethylene glycol, which is also commonly used.16 The addition of stool softeners, bisacodyl and nightly prune juice can also be helpful.10
Dyspnea
Dyspnea, the subjective feeling of breathing discomfort, is a common end-of-life complaint. Similar to pain, self-report is required for adequate assessment of dyspnea. Treatment recommendations include opioids, anxiolytics, and oxygen therapy.18 Opioids are the most widely studied treatment for dyspnea, demonstrating reduction in breathlessness in patients who have a variety of conditions, such as advanced chronic obstructive pulmonary disease, interstitial lung disease, cancer, and chronic heart failure.19
While many of the benefits of opioids are widely recognized and understood, the manner in which they improve symptoms of dyspnea is less well known. In addition, the evidence of effectiveness is limited to oral or parenteral morphine and fentanyl, and nebulized opioids have not been well studied. Oxygen treatments have been shown to reduce dyspnea in patients who suffer from hypoxemia; however, no benefit was found for patients who had only mild or no hypoxemia. A majority of dying patients did not experience a change in respiratory comfort after their supplemental oxygen was withdrawn. In these cases, when administration of oxygen is unnecessary, it may potentially introduce further discomfort to end-of-life patients by causing nasal dryness and impaired mobility.20
The use of benzodiazepines as the primary medication to manage dyspnea is unfounded, but may provide some benefit when used in conjunction with opioids.11 When indicated, a longer-acting agent (eg, clonazepam, with an initial starting does of 0.25 mg orally every 12 hours) may be used.4
Nausea and Vomiting
Nausea and vomiting have been reported by 16% to 68% of patients who had life-limiting illness, such as cancer, heart failure, renal failure, or acquired immunodeficiency syndrome.21 The etiology of nausea and vomiting is multifactorial in a dying patient. Assessment and treatment has been based on understanding how neurotransmitters are involved in the “emetic pathway,”22 but other pathways, such as a cytokine-mediated model of cancer symptoms, may also be important.23