Melzack and Wall’s gate-control theory (1965) first suggested that pain has emotional and cognitive components in addition to a physical sensation. According to this theory, gating mechanisms located along the central nervous system regulate or even block pain impulses. Pain impulses pass through when a gate is open and are blocked when a gate is closed. Closing the gate is the basis for nonpharmacological pain-relief interventions. You gain a useful conceptual framework for pain management by understanding the physiological, emotional, and cognitive influences on the gates. For example, factors such as stress and exercise increase the release of endorphins, often raising an individual’s pain threshold (the point at which a person feels pain). Because the amount of circulating substances varies with every individual, the response to pain varies.

As pain impulses ascend the spinal cord toward the brainstem and thalamus, the stress response stimulates the autonomic nervous system. Pain of low to moderate intensity and superficial pain elicit the fight-or-flight reaction of the general adaptation syndrome (see Chapter 37). Stimulation of the sympathetic branch of the autonomic nervous system results in physiological responses (Table 43-1). Continuous, severe, or deep pain typically involving the visceral organs (e.g., with a myocardial infarction or colic from gallbladder or renal stones) activates the parasympathetic nervous system. Sustained physiological responses to pain sometimes seriously harm individuals. Except in cases of severe traumatic pain, which causes a person to go into shock, most people adapt to their pain, and their physical signs return to normal. Thus patients in pain do not always have changes in their vital signs. Changes in vital signs more often indicate problems other than pain.

Body movements and facial expressions indicating pain include clenched teeth, holding the painful area, bent posture, and grimacing. Some patients cry or moan, are restless, or make frequent requests of a nurse. You soon learn to recognize patterns of behavior that reflect pain. This becomes especially important in patients who are unable to report their pain such as the cognitively impaired. However, lack of pain expression does not indicate that the patient is not experiencing pain (Pasero and McCaffery, 2011).

Acute pain is protective, has an identifiable cause, is of short duration, and has limited tissue damage and emotional response. It eventually resolves, with or without treatment, after an injured area heals. Because acute pain has a predictable ending (healing) and an identifiable cause, health team members are usually willing to treat it aggressively. Unrelieved acute pain can progress to chronic pain (Kehlet et al., 2006).

Acute pain seriously threatens a patient’s recovery by resulting in prolonged hospitalization, increased risks of complications from immobility (see Chapter 47), and delayed rehabilitation. Physical and psychological progress is delayed as long as acute pain persists because a patient focuses all energy on pain relief. Efforts aimed at teaching and motivating the patient toward self-care are often hampered until the pain is successfully managed. Complete pain relief is not always achievable, but reducing pain to a tolerable level is realistic. Thus a primary nursing goal is to provide pain relief that allows patients to participate in their recovery.

Unlike acute pain, chronic pain is not protective and thus serves no purpose. Chronic pain lasts longer than 6 months and is constant or recurring with a mild-to-severe intensity (Ackley and Ladwig, 2011). It does not always have an identifiable cause and leads to great personal suffering. Examples of chronic noncancer pain include arthritis, low back pain, myofascial pain, headache, and peripheral neuropathy. Chronic pain is usually non–life threatening. Sometimes an injured area healed long ago, yet the pain is ongoing and does not respond to treatment.

The possible unknown cause of chronic pain, combined with the unrelenting nature and uncertainty of its duration, frustrates a patient, frequently leading to psychological depression and even suicide. Chronic pain is a major cause of psychological and physical disability, leading to problems such as job loss, inability to perform simple daily activities, sexual dysfunction, and social isolation.

The person with chronic noncancer pain often does not show obvious symptoms and does not adapt to the pain. Rather, he or she seems to suffer more with time because of physical and mental exhaustion. Associated symptoms of chronic pain include fatigue, insomnia, anorexia, weight loss, apathy, hopelessness, and anger. Chronic pain creates the uncertainty of how one will feel from day to day. If there is no objective evidence to confirm the existence of pain, the “burden of proof” lies with the patient (Shaw, 2006). Health care workers are usually less willing to treat chronic noncancer pain with opioids, although a policy statement supports the use of opioids for it (Chou et al., 2009). In addition, the American Society of Anesthesiologists (2010) developed “Practice Guidelines for Chronic Pain Management,” which includes the use of opioids. Often a person with chronic pain who consults with numerous health care providers is labeled a drug seeker, when he or she is actually seeking adequate pain relief. This situation is called pseudoaddiction. Nurses need to discourage patients from having multiple health care providers for treating pain and refer them to pain specialists. Pain centers offer a holistic approach to chronic pain using both nonpharmacological and pharmacological strategies for pain management (Pasero and McCaffery, 2011).

Pain that occurs sporadically over an extended period of time is episodic pain. Pain episodes last for hours, days, or weeks. Examples are migraine headaches and pain related to sickle cell disease (Gruener and Lande, 2006).

Not all patients with cancer experience pain. For those who do, as many as 90% are able to have their pain managed with relatively simple means (Lehne, 2010). Some patients with cancer experience acute and/or chronic pain. The pain is nociceptive and/or neuropathic. Cancer pain is usually caused by tumor progression and related pathological processes, invasive procedures, toxicities of treatment, infection, and physical limitations. A patient senses pain at the actual site of the tumor or distant to the site, called referred pain. Assess reports of new pain by a patient with existing pain. Although the treatment of cancer pain has improved, undertreatment of cancer pain continues. Approximately 70% to 90% of patients with advanced cancer experience pain. Sixty percent of them report moderate-to-severe pain (Maxwell et al., 2005).

Identifying the cause of pain is the first step in successful treatment. Nociceptive pain includes somatic (musculoskeletal) and visceral (internal organ) pain. Neuropathic pain arises from abnormal or damaged pain nerves (Table 43-2). Each of these pathological processes has distinct pain characteristics. The pain assessment section discusses these further.

Idiopathic pain is chronic pain in the absence of an identifiable physical or psychological cause or pain perceived as excessive for the extent of an organic pathological condition. An example of idiopathic pain is complex regional pain syndrome (CRPS). Research is needed to better identify the causes of idiopathic pain, thus leading to a more effective treatment (Pasero and McCaffery, 2011).