Acute pain has a sudden onset, usually subsides quickly, and is characterized by sharp, localized sensations with an identifiable cause. Acute pain is a natural physiologic response to injury, useful in warning individuals of disease or harmful situations. This process is often seen as a signal that the body is invoking critical immunologic and physiologic responses to cellular or tissue damage. Concomitant physiologic responses include excessive sympathetic nervous system activity, such as tachycardia, diaphoresis, and increased blood pressure and respiratory rate. Acute pain is somewhat instructive and purposeful by signaling danger. Pain is usually brief and resolves within a few months of onset. Surgical intervention and trauma are common sources of acute pain.

When acute pain responses become unremitting, constant, or undertreated, the biologic responses outlive their usefulness and can lead to chronic pain. Patients with chronic pain become tolerant to the physiologic response seen in acute pain. In addition, these patients often do not appear to be suffering from pain. The body becomes tolerant to the autonomic indicators where heart rate, blood pressure, and respiratory rate normalize as pain persists. Undesired consequences, such as anxiety and depression, are often associated with constant, long-term pain. The goal of acute pain management is to avoid progression to a chronic pain state. Early pain control will often prevent the development of chronic pain.

Chronic pain is defined by the Institute of Clinical Systems Improvement as “pain without biological value that has persisted beyond the normal time and despite the usual customary efforts to diagnose and treat the original condition and injury” (Hooten et al., 2013). Chronic pain may have a verifiable source, as in patients with arthritis, diabetic peripheral neuropathy, and postherpetic neuralgia. In some patients, however, no evidence of structural or nerve damage exists to explain the reason for pain. In these patients, the pain is most likely from peripheral and central sensitization of the pain pathways, explained later in this chapter.

Evidence is now showing that chronic pain is primarily a biopsychosocial disease, with cognitive factors such as pain catastrophizing and anxiety having a strong correlation to pain and disability. The current biomedical approach focusing only on tissue and tissue injury as the cause for the pain has often been ineffective. Patients are often complicated and need an individualized approach to therapy.

Identifying and differentiating pain through careful history of the location, quality, chronicity, and presence of psychological comorbidities is important because treatment choices are dictated by the cause and type of pain. The primary goal of therapy in chronic pain is to decrease the pain to a tolerable level using a combination of various types of therapies to help improve function and quality of life. Examples of types of chronic pain are shown in Box 7.1.

The individual assessment of pain is extremely important for determining proper treatments as well as monitoring effectiveness over time. According to the National Institutes of Health (NIH), self-reporting by patients is “the most reliable indicator of the existence and intensity of pain” (Herr & Garand, 2001). Along with self-reporting, involving the caregiver’s assessment of pain, especially in the very young or noncommunicating older patient, may be helpful. The self-report should include a description of the pain, location, intensity/severity, aggravating and relieving factors, and effect of pain on quality of life. Assessment tools are recommended to be brief and easy to use in order to reliably document pain intensity and pain relief. These tools will also evaluate other factors effecting pain, such as the presence of psychological comorbidities. One routine clinical approach to pain assessment and management is summarized by the mnemonic PQRSTU (Box 7.2). Assessment tools should be used initially to obtain a baseline level of pain and impaired function. Follow-up assessments should be performed to measure the progress toward acceptable pain relief based on the individual functional goals of the patient.

Because pain is subjective and is not easily quantifiable, several tools are available to determine the quantity and quality of a patients’ pain. The various pain scales can be classified as single or multidimensional and self-report or observational. Common single-dimension tools include the visual analog
scale (VAS), numerical rating scale (NRS), and verbal description scale (Figure 7.2). The single-dimension scales evaluate the intensity of pain. However, single-dimensional scales alone do not take into account function, which may be a more reliable indicator of pain control, especially chronic pain. Multidimensional scales consider location, pattern, and affective responses in addition to a severity score alone. Examples of multidimensional scales include the Brief Pain Inventory and the Initial Pain Assessment Tool (Pasero & McCaffrey, 2011).

The information assessed, particularly from the NRS and VAS, is helpful in determining appropriate treatment and drug selection. The Institute for Clinical Systems Improvement (ICSI) and the NIH have published guidelines on the appropriate evaluation and treatment of acute and chronic pain. Pain is recommended to be assessed with a 0-to-10 scale to assess a patient’s current level of pain. Zero defines a pain-free state, and a 10 describes the most severe pain imaginable by the patient. Pain rated at 1 to 3 is classified as mild; 4 to 7, moderate; and 8 to 10, severe. Other validated scales are available for use in special populations, such as in children and adults unable to self-report.

Subsequent assessments should evaluate the effectiveness of the treatment plan. First, determine if the cause of increased pain is related to the progression of disease, disease treatments, or a new cause of pain, as in cancer that has metastasized. Unrelieved pain may also be due to the development of opioid tolerance where the same amount of pain requires increasing doses of opioids in order to provide relief. The assessment of the patient’s pain and the efficacy of the treatment plan should be ongoing, and the pain reports should be documented. Continued use of the same pain scale is crucial to the continued assessment of treatment progress and communication between health care providers.

Treatment options for pain control include nonpharmacologic and pharmacologic therapies. Box 7.3 lists treatments that complement medication management of pain. Often, a multimodal, multidisciplinary approach using a combination of both pharmacologic and nonpharmacologic treatments is necessary to reduce pain to an acceptable level and provide an improvement in function, especially when opioid therapies are used. Maximizing the patient’s quality of life and function, while minimizing adverse effects of treatments, is the goal of the pain management treatment plan. Individualization of drug regimens according to the type and severity of pain is essential principles when using medications to manage both acute and chronic pain states.

For mild to moderate pain, acetaminophen, aspirin, or a nonsteroidal anti-inflammatory drug (NSAID) is usually considered initial therapy. Acetaminophen is used for mild pain across all age groups, mainly due to its favorable side effect profile. NSAIDs are very effective in pain associated with inflammation. However, patients may be at risk for gastrointestinal (GI), cardiac, or renal toxicities. Discussion of risk versus benefits of NSAID therapies will be discussed later in this chapter.

For pain assessed as moderate to severe, combination opioids, such as oxycodone, hydrocodone, or codeine in combination with acetaminophen or ibuprofen, can be used. More potent opioids, such as morphine, hydromorphone, or fentanyl, are used for the treatment of severe pain. Moderate to severe pain can also be treated with low-dose opioids when a patient has contraindications to NSAIDs or acetaminophen. Opioids may be combined with other coanalgesic medications based on severity, description, and type of pain. The combination of an opioid with a coanalgesic medication may provide more pain control than either of the drug classes alone.

When developing a treatment plan, members of the health care team should take into account the preferences and needs of patients whose education or cultural traditions may impede effective treatment. Certain cultures have strong beliefs about pain and its management. Members of these cultures may hesitate to report unrelieved pain or may have alternative methods of treating pain. Clinicians should be aware of the unique needs and circumstances of patients from different age groups or various ethnic and cultural backgrounds. In addition, many biases to opioids continue to exist in some patients and prescribers. Patient and provider education may be effective in addressing cultural concerns and alleviating biases associated with pain treatments.

Pharmacologic treatment is the most common modality in pain control. However, nonpharmacologic options and therapies have been shown to be effective, especially in patients with chronic pain. Nonpharmacologic approaches include the use of therapies such as heat, cold, exercise, and physical therapy. Complementary therapies such as acupuncture, meditation, and massage may also be effective.

More data is emerging on how CNCP needs to be seen as a biopsychosocial and not a purely biological condition especially when pain has no obvious cause. Behavioral therapies, including systematic coping approaches and relaxation strategies, have been shown to be essential in these patients in order to improve function and quality of life. Transcutaneous electrical nerve stimulation therapy can be used to help control certain types of nerve-related pain. Treatment of difficult pain conditions that cannot be managed by noninvasive and/or pharmacologic treatments may require a consultation with a pain specialist or a pain psychologist to evaluate other options or interventions.

Assessment of pain intensity is important when determining initial analgesic therapies. Mild to moderate pain can be treated with lower-potency medications such as acetaminophen and NSAIDs. These agents can also be part of a multimodal therapy plan in combination with opioids for severe pain. Historically, aspirin had been used as a pain modality for short-term pain treatment. However, increased adverse effects limit its chronic use. Aspirin is mostly used today to prevent cardiac events and is not routinely used as first-line pain management therapy.

Combination opioids, ketorolac, and tramadol are commonly used to treat moderate pain. The combination opioids contain the addition of a “nonopioid,” such as acetaminophen or ibuprofen, creating a treatment ceiling dose (maximum dose). Low doses of strong opioids may also be utilized for moderate pain in patients who have contraindications for NSAIDs or tramadol.

Opioids are the most common therapy recommended for severe pain. Morphine is the gold standard and the most studied opioid. When used in equivalent doses, most pure opioids (mu receptor agonists) are equally effective in controlling pain, but individual variation may exist among patients. Morphine, oxycodone, hydromorphone, oxymorphone, and fentanyl are pure mu opioid agonists indicated for the treatment of severe pain. Morphine is considered the opioid of first choice unless a contraindication exists or the patient has failed prior morphine therapy. Meperidine is another opioid that has historically been utilized for the treatment of severe pain. Use of this agent is no longer recommended due to neurotoxicity associated with accumulation of the active metabolite in patients with renal insufficiency or with chronic use.

In most persistent pain cases, pain medications should be administered around the clock (ATC), with as-needed medications used to treat BTP. This recommendation is based on the finding that regularly scheduled medications maintain a constant level of drug in the body and help prevent a recurrence of pain. BTP medications are indicated when intermittent pain occurs despite ATC therapy.

An essential principle in using medications to manage chronic pain is to individualize medication regimens according to the type and severity of pain. For mild to moderate pain, acetaminophen or an NSAID is usually considered initial therapy. Management of moderate to severe pain may utilize a combination opioid, tramadol, or low doses of opioids. Severe pain is treated with higher-potency opioids, such as morphine, hydromorphone, or oxycodone. Various classes of coanalgesics, such as anticonvulsants and antidepressants, can also be utilized in combination with the opioids (Table 7.1).