The nerve action potentials of the nociceptors are transmitted by two fiber types (Figure 12-1). The myelinated A-delta fibers rapidly transmit the pain impulse (fast pain). This produces a sharp pain sensation. The unmyelinated C fibers are slower (slow pain) and are responsible for the diffuse burning or aching sensation of pain. C fibers also produce throbbing, deep visceral pain and the sensations associated with chronic pain. Both eventually terminate in the dorsal horn of the spinal cord. The majority of these transmissions terminate in the substantia gelatinosa. ⁴⁶

Many of the afferent fibers synapse with second-order neurons in the dorsal horn. There are three classes of second-order neurons in the dorsal horn. These are projection cells that will relay information to higher brain areas; excitatory interneurons, which relay nociceptive transmissions to other interneurons, other projection cells, or motor neurons involved with local reflexes; and inhibitory interneurons, which will modulate the transmission. ^{27.30. and 87.} The connection between the cells of the primary- and secondary-order neurons located here compose the “pain gate.” This gate postulated in the gate control theory regulates the transmission of pain impulses to the brain. It also helps to explain why many nonpharmacologic methods such as acupuncture and massage can assist in pain management. ⁴⁶

There are multiple pathways through the spinal cord that a pain impulse can go along to the brain, primarily the thalamus, which functions as the relay station for pain impulses. Two of these pathways are the neospinothalamic and the paleospinothalamic. The neospinothalamic is the primary pathway for the fast pain fibers. The fibers of this tract cross to the opposite side of the spinal cord and pass upward to the thalamus. This tract transmits the discriminating aspects of pain such as its location, intensity, and duration. ³⁰

The paleospinothalamic tract transmits the stimuli from the slower C fibers. Not all of these fibers cross over before ascending. The slower fibers make it more difficult to specifically localize pain sensations. ³⁰ Substance P has been identified as the main neurotransmitter associated with slow pain sensations.

The third-order neurons located in the thalamus, brain stem, and midbrain project to portions of the central nervous system (Figure 12-2). ⁴⁶ The sensory homunculus, located on the postcentral gyrus of the parietal lobe, is thought to be involved in the discriminative and cognitive components of pain. ⁴⁶ The frontal lobe also plays a role in pain perception and interpretation.

The limbic and the reticular tracts respond to pain signals. Stimulation of these areas of the brain will result in arousing the person to the danger, release of stress hormones, and emotional responses to pain.

The body has its own intrinsic means of managing pain. This occurs in the pain-inhibitory or antinociceptive response system. Afferent fibers stimulate the periaqueductal gray area, the magnus raphe nucleus, and the pain inhibitory complex in the anterior horn. This allows the body to manage debilitating pain and still survive. The gate control theory has assisted in explaining how pain can be modulated. There are sensory nerves within the dorsal horn that literally can compete with the pain sensory fibers to “modulate” their effect. Larger A-beta fibers in the dorsal horn can decrease the amplitude of the afferent pain fibers. This again explains how acupuncture, rubbing an injury, or the use of a topical medication can relieve pain. 30. ^{and 46.}Figure 12-3 illustrates pain modulation. ⁴⁶

Another method of modulating pain occurs through inhibitory neurotransmitters or antinociception response. When the nociceptors are stimulated by heat, toxic chemicals, or tissue injury, there is a threshold depolarization or a direct excitation. After the tissue is injured, the inflammatory response can initiate an indirect excitation.

The spinal cord, brain, and other areas of the body produce inhibitory neurotransmitters. Neurotransmitters that contribute to pain modulation, γ-aminobutyric acid (GABA) and glycine, inhibit pain impulses in the brain and spinal cord. Norepinephrine and serotonin inhibit pain impulses in the medulla and pons.

The human body also has its own endogenous opioids. Endogenous opioids are neuropeptides that inhibit pain impulse transmission in the brain and spinal cord. The receptor sites for these neurotransmitters are also the sites where exogenously administered opioids act. The four types of opioid neuropeptides are enkephalins, endorphins, dynorphins, and endomorphins. Until the late 1970s with the discovery of these peptides, there was little understanding as to how pain medications work, and research and discovery still continues today. Enkephalins are weaker than endorphins but more powerful than morphine and last longer. Dynorphins will generally impede pain impulses, and endomorphins are primarily antinociceptive. ⁸⁴

The specific opioid sites where these neurotransmitters work throughout the body are the mu (μ) (with subtypes μ-1 and μ-2), kappa (к), and delta (δ). Each of these receptor sites binds differently with distinctive types of opioids. ^{30. and 46.} Mu receptors inhibit the release of excitatory neurotransmitters. Beta receptors interact with enkephalins to modulate pain impulses. Kappa receptors produce sedation and some analgesia. ^{23. and 84.} Research has uncovered some other endogenous opioid peptides, as well as additional subtypes to the known opioid sites. A recently discovered opioid peptide is nociception/orphanin-FQ, which resembles the dynorphins. ²³

One of the reasons emergency nurses may inaccurately categorize patients as addicted is a misunderstanding of the terms addiction, tolerance, physical dependence, and pseudoaddiction.¹⁰³ It is important to accurately use these terms to avoid further confusion and inappropriate categorization that results in stigmatization of patients. In 2001 the American Society of Addiction Medicine, the American Academy of Pain Medicine, and the American Pain Society recommended the following definitions. ¹

Patients expect pain relief. In a study of adult ED patients with (n = 752) and without (n = 522) pain, patients reported the expectation that their pain would be reduced by 72%, and 18% of patients expected a 100% reduction in pain. There was no difference in expectation related to the severity of pain on arrival, age, or gender. 31. ^{and 55.} Expectations of pain relief between Hispanic and non-Hispanic white ED patients were compared, and no difference in pain-relief expectations was found; most patients expected a decrease in pain scores between 69 and 81 mm using a 100-mm visual analog scale. ⁵⁵ In another study 48 patients with acute abdominal pain were interviewed; 44% expected complete pain relief while in the ED. ¹²⁰

Patients also expect rapid analgesic management. In a single-site study, upon arrival in the ED 620 adult patients were asked to report a “reasonable” time before receiving an analgesic. At discharge they were asked if their pain-relief needs were met and to rate their overall satisfaction with ED care. The average “reasonable” time to initial analgesic reported for the group was 23 minutes and did not vary by chief complaint. Patients who reported having their pain-relief needs met were more satisfied with their overall ED care. ³³ In this era that has a strong focus on patient satisfaction, optimal pain management may help improve overall ED patient satisfaction scores. It is clear ED patients expect rapid and aggressive pain management.

It is impossible to provide optimal pain relief without conducting an excellent pain assessment. Pain assessment guides the selection of intervention (pharmacologic versus nonpharmacologic), and reassessment is the key to ultimate pain relief or reduction of pain to meet the patient’s desired goal. Pain assessment typically means obtaining a pain intensity score from the patient. The use of pain scales allows for the objective measurement of a subjective state. The numeric rating scale (0 to 10) is the most commonly used scale in the ED and has been validated for use with acute pain in the ED setting. ¹² It is sufficient for many but not all adults. ⁴⁹ Assessment tools should be age appropriate, and special consideration and scales, such as the face, legs, activity, cry, and consolability (FLACC) scale, should be given to assessing patients who are nonverbal. Although many assessment tools exist, it is not the intent of this chapter to review multiple tools but to present core principles of pain assessment. Many multidimensional tools are available and assess dimensions of pain other than pain intensity. Often their use is impractical in the ED setting. However, in addition to assessing pain intensity, the ED nurse should assess the chief complaint, type of pain (acute, chronic, cancer, and end-of-life pain), location of pain, duration, prehospital interventions, patient age, and cultural expression of pain.

Merely recording a pain score in the medical record does not provide pain relief. Nurses must believe the patient and initiate appropriate interventions aimed at reducing pain. A recent study reported that ED nurses underestimate the patient’s report of pain. In a single-center study of ED nurses and patients, ED nurses were asked to rate the patients’ pain, and nurses scored the patients’ pain an average of 2.4 points lower than the patient-reported score. ⁷⁸ Minimizing the patient-reported pain score may lead to inadequate interventions.

Establishing the link between pain assessment, pain management, and patient outcomes is critical. ³⁴ Several studies have examined the effect of a designated space in the medical record to record a pain score. The impact of recording a pain score on the actual provision of analgesics has been mixed. Nelson et al⁷⁰ found a significantly larger proportion of patients received analgesics during the ED visit after a documentation education intervention (25% before and 36% after). In a study of trauma patients with high pain scores, documentation of a pain assessment was associated with a higher rate of analgesic administration (60%) when compared with patients without documentation of a pain score (33%). ⁹³ In another ED, investigators implemented a chart template for nurse practitioners and physicians designed to improve pain assessment. Although documentation of pain assessments using the chart improved from 41% to 57% of patients, no difference in analgesic administration was noted and the number of analgesic prescriptions provided at discharge actually decreased. ⁷ In summary, documentation of pain scores is important; however, nurses must take the next step and assist in the selection of the appropriate intervention and reassessment of any intervention to make sure optimal pain management has been attained.

Establishing the optimal and individualized pain management goal early in the ED visit is important. A pain score of 0 at discharge or reduction in pain score from admission to discharge may or may not be the right goal. Patients should be involved in determining the pain management goal whenever possible. Fosnocht et al³³ examined this issue and recorded arrival and discharge pain scores and asked patients to report overall pain relief during the ED stay. There was no difference in change in pain scores between patients who did and did not report pain relief at discharge. These data demonstrate that a change in pain score alone cannot be used to evaluate the effectiveness of ED pain management.

Although it is critical to involve the patient in the selection of the pain management goal and plan or care, should nurses assume patients will ask for pain medications? Recent data report that 98% of patients with abdominal pain reported pain to either the physician or nurse, but only 33% specifically requested analgesics. ¹²⁰ Severity of pain intensity scores has also been found to be an unreliable indicator of whether or not patients requested analgesics. ¹⁴ These studies demonstrate that assessment cannot consist of recording a pain score alone. Emergency nurses have the opportunity to help establish a pain plan of care by actively engaging the patient in not only determining a pain management goal, but specifically inquiring if a patient would like analgesics.

The policy “Pain Management in the Emergency Department” written by the American College of Emergency Physicians outlines the following basic principles: pain management should begin rapidly and not be delayed by delays in diagnosis, opioids and nonopioids should be used, safety should be an important consideration, physician and patient education strategies should be developed, and ongoing research should be conducted. ³ These principles address fundamental points to guide pain management.

Nonpharmacologic interventions should be used as an adjunct when administering analgesics and, in some cases, may be sufficient in isolation. Some patients with mild pain may not require analgesic administration, and others may refuse analgesics; in one study, up to 15% of ED patients refused pain medications. ¹⁰² Many nonpharmacologic interventions are available; some are useful, and others may not be practical for use in EDs without specialized training (e.g., hypnosis). All nurses should be able to facilitate distraction, the use of physical therapies such as positioning and elevation of extremities, and the use of heat and cold therapies. Heat may be useful for chronic pain and patients with sickle cell pain episodes. Ice should always be used for acute pain caused by musculoskeletal injuries and is often useful for pain associated with acute back injuries. Distraction techniques include music therapy, reading materials, and conversation. It is important for emergency nursing leaders to ensure distraction materials are made available and are readily accessible to promote their use. Use of distraction techniques has been found to reduce pain scores in a sample of pediatric patients with minor musculoskeletal trauma, but not for adults. ^{104. and 107.} In a single-site study, adult patients reported they were satisfied with their pain management and would like to have the option of music distraction in future ED visits, despite no change in pain scores. ¹⁰⁷ Nonpharmacologic interventions play an important role in relieving pain for many ED patients.

Pharmacologic interventions are often required to meet the patient’s pain management goal. The ED nurse can help suggest the best analgesic agent, dose, and route for the individual patient. The patient’s chief complaint, age, medical history, allergies, pain history, and stated pain goal should help determine analgesic interventions.

Analgesics can be administered by several routes including oral, intravenous, subcutaneous, and patient-controlled analgesic pump. The use of intramuscular injections, especially when multiple doses will be required, is discouraged. Intramuscular injections are painful and associated with erratic absorption, tissue damage, and an increased risk for abscess development. ⁴ When oral analgesics are not sufficient or when the intravenous route is not available, the subcutaneous route should be used. ⁴ The subcutaneous route has a somewhat slower onset of action than intravenous, but it is equally effective and is commonly used with cancer and palliative care patients. The intravenous route is indicated for patients with severe pain who are receiving opioids, and it has a peak effect of 15 to 30 minutes for most agents. ⁴ Reassessment of pain and administration of additional doses should occur if the pain goal has not been met in 15 minutes. Although multiple priorities challenge the ED nurse, all efforts should be made to reassess pain 15 minutes after administration of an intravenous or subcutaneous agent and within 60 minutes of administering an oral agent. Additional oral agents cannot be provided for 2 hours after initial dose. Finally, patient-controlled analgesia (PCA) is an excellent method of providing opioid analgesics for patients who may require multiple and frequent doses. PCA provides patients with control over their pain management. Reports of use in the ED are limited. Nurses will require specific training, and the equipment and dosing cartridges should be made available in the department to promote use of PCA as a method of providing analgesia in the ED.

It is also important to select the correct analgesic agent. Acetaminophen, NSAIDs, and opioids are the mainstays of ED pain management. Acetaminophen is useful for the relief of mild to moderate pain without inflammatory components, can be administered orally or rectally, and does not irritate the gastric mucosa. ⁴ It is also included in many combination oral opioid analgesics, including codeine, oxycodone (Percocet), and hydrocodone (Norco and Vicodin). The maximum daily recommended dose of acetaminophen (4000 mg for normal healthy adults) often limits the number of oral acetaminophen-opioid medications that can be administered within 24 hours. Healthy patients who exceed 4000 mg of acetaminophen within 24 hours are at an increased risk for hepatic toxicity. ⁴ Emergency nurses have an opportunity to educate patients about the limitations of acetaminophen when patients are discharged with analgesic prescriptions that include acetaminophen.