Key Terminologies in Pain Management and Opioid Pharmacology

acute pain: pain that results from tissue damage that generally abates as healing occurs; serves as a warning signal that something is wrong or needs attention adjuvant analgesic agent: a substance or medication added to an analgesic medication regimen to improve analgesia (synonym: coanalgesic agent) agonist: a medication that binds to an opioid receptor mimicking the way endogenous substances provide analgesia agonist–antagonist: a type of opioid (e.g., nalbuphine and butorphanol) that binds to the kappa opioid receptor site acting as an agonist (capable of producing analgesia) and simultaneously to the mu opioid receptor site acting as an antagonist (reversing mu agonist effects) allodynia: pain due to a stimulus that does not normally provoke pain, such as touch; typically experienced in the skin around areas affected by nerve injury and commonly seen with many neuropathic pain syndromes antagonist: a medication that competes with agonists for opioid receptor binding sites; can displace agonists, thereby inhibiting their action breakthrough pain: a transitory increase in pain that occurs in the context of otherwise controlled persistent pain ceiling effect: an analgesic dose above which further dose increments produce no change in effect central sensitization: a key central mechanism of neuropathic pain; the abnormal hyperexcitability of central neurons in the spinal cord, which results from complex changes induced by the incoming afferent barrages of nociceptors and results in an increased nociceptive neuron response chronic or persistent pain: pain that may or may not be time limited but that persists beyond the usual course/time of tissue healing co-analgesic agent: one of many medications that can either improve the effectiveness of another analgesic agent or independently have analgesic action (synonym: adjuvant analgesic agent) comfort–function goal: the pain rating identified by the individual patient above which the patient experiences interference with function and quality of life (e.g., activities the patient needs or wishes to perform) efficacy: the extent to which a medication or another treatment “works” and can produce the intended effect—analgesia in this context half-life: the time it takes for the plasma concentration (amount of medication in the body) to be reduced by 50% (after starting a medication, or increasing its dose; four to five half-lives are required to approach a steady-state level in the blood, irrespective of the dose, dosing interval, or route of administration; after four to five half-lives, a medication that has been discontinued generally is considered to be mostly eliminated from the body) hydrophilic: a substance or medication that is readily absorbed in aqueous solution hyperalgesia: an increasingly intense experience of pain resulting from a noxious stimulus intraspinal: “within the spine”; refers to the spaces or potential spaces surrounding the spinal cord into which medications can be given lipophilic: a substance or medication that is readily absorbed in fatty tissues metabolite: the product of biochemical reactions during medication metabolism mu agonist: any opioid that binds to the mu opioid receptor subtype and produces analgesic effects (e.g., morphine); used interchangeably with the terms full agonist, pure agonist, and morphinelike medication multimodal analgesia or multimodal pain management: the intentional, concurrent use of more than one pharmacologic or nonpharmacologic intervention with different methods of action with the goal to achieve better analgesia while using lower doses of medications with fewer adverse effects neuraxial: of the central nervous system neuropathic (pathophysiologic) pain: pain caused by injury or dysfunction (lesion or disease) of one or more nerves of the peripheral or central nervous systems with resultant impaired processing of sensory input neuroplasticity: the ability of the peripheral and central nervous systems to change both structure and function as a result of noxious stimuli nociceptive (physiologic) pain: pain that is sustained by ongoing activation of the sensory system that conducts the perception of noxious stimuli; implies the existence of damage to somatic or visceral tissues sufficient to activate the nociceptive system nociceptor: a type of primary afferent neuron that has the ability to respond to a noxious stimulus or to a stimulus that would be noxious if prolonged nonopioid: refers to analgesic medications that include acetaminophen and nonsteroidal anti-inflammatory drugs (NSAIDs) NSAID: an acronym for nonsteroidal anti-inflammatory drug (pronounced “en said”) opioid: refers to morphine and other natural, semisynthetic, and synthetic medications that relieve pain by binding to multiple types of opioid receptors; term is preferred to “narcotic” opioid dose–sparing effect: occurs when a nonopioid or co-analgesic medication is prescribed in addition to an opioid, enabling the opioid dose to be lower without diminishing analgesic effects opioid-induced hyperalgesia: a phenomenon in which exposure to an opioid induces increased sensitivity, or a lowered threshold, to the neural activity conducting pain perception; it is the “flip side” of tolerance opioid naïve: denotes a person who has not recently taken enough opioid on a regular enough basis to become tolerant to the opioid’s effects opioid tolerant: denotes a person who has taken opioids long enough at doses high enough to develop tolerance to many of the opioid’s effects, including analgesia and sedation pain: an unpleasant experience that is either emotional or sensory resulting from actual or possible damage to tissues and is uniquely experienced and described by each person peripheral sensitization: a key peripheral mechanism of neuropathic pain that occurs when there are changes in the number and location of ion channels; in particular, sodium channels abnormally accumulate in injured nociceptors, producing a lower nerve depolarization threshold, ectopic discharges, and an increase in the response to stimuli physical dependence: the body’s normal response to administration of an opioid for 2 or more weeks; withdrawal symptoms may occur if an opioid is abruptly stopped or an antagonist is given placebo: any medication or procedure, including surgery, that produces an effect in a patient because of its implicit or explicit intent and not because of its specific physical or chemical properties preemptive analgesic agents: pre-injury pain treatments (e.g., preoperative epidural analgesia and preincision local anesthetic infiltration) to prevent the development of peripheral and central sensitization of pain refractory: nonresponsive or resistant to therapeutic interventions such as analgesic agents substance use disorder (SUD): problematic use of substances such as opioids, benzodiazepines, or alcohol based on identification of at least two of the diagnostic criteria listed by the American Psychiatric Association. It is characterized by craving the substance; continuing use despite harm; inability to stop using; and experiencing withdrawal symptoms when abruptly not using the substance; formerly known as addiction titration: upward or downward adjustment of the amount (dose) of an analgesic agent tolerance: a normal physiologic process characterized by decreasing effects of a medication at its previous dose, or the need for a higher dose of medication to maintain an effect withdrawal: result of abrupt cessation or rapid decrease in dose of a substance upon which one is physically dependent. It is not necessarily indicative of substance use disorder Pain serves as a survival tactic that guides individuals not only to avoid damage in the moment, but also to learn to avoid danger in the future (Martin, Power, Boyle, et al., 2017). Nurses in all settings play a key role in the management of pain as experts in assessment, medication administration, and patient education. They are uniquely positioned to assume this role as members of the health care team most consistently at the patient’s bedside. These characteristics have led to nurses’ distinction as the primary managers of patients who are experiencing pain (Curtis & Wrona, 2018). Fundamental Concepts Understanding the definition, effects, and types of pain lays the foundation for proper pain assessment and management. Definition of Pain The American Pain Society (APS, 2016) defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage” (p. 2). This definition describes pain as a complex phenomenon that can impact a person’s psychosocial, emotional, and physical functioning. The clinical definition of pain reinforces that pain is a highly personal and subjective experience: “Pain is whatever the experiencing person says it is, existing whenever he says it does” (McCaffery, 1968, p. 8). The self-report by the patient is the standard; it is considered to be the most reliable indicator of pain and the most essential component of pain assessment (DiMaggio, Clark, Czarenecki, et al., 2018).