Introduction
Inpatient pain management is a critical component of hospital care. Patients followed by an acute pain service are typically those who have undergone surgery, were involved in trauma, have a chronic medical condition that causes pain, such as pancreatitis, or are being managed for cancer pain. Traditional inpatient pain services have focused on postsurgical care. Warfield et al. (Anesthesiology, Oct 31, 1995, 83(5):1090–1094) noted that as many as 57% of adult patients reported pain was their primary fear before surgery and 77% reported experiencing pain after surgery. Enhanced Recovery After Surgery (ERAS) programs were introduced to allay these concerns and improve postsurgical outcomes. These programs are common in Europe and expanding in the United States to ensure patients have reasonable expectations for postoperative pain control, which may reduce the incidence of chronic postsurgical pain.
Pain Evaluation and Assessment
For patients admitted to the hospital, assessment for the source of pain should be undertaken. This may be obvious in postsurgical cases but challenging for acute and chronic pain conditions. A comprehensive chart review and careful history and physical examination can illuminate influencing factors contributing to an individual’s pain complaint. Other important information includes presence of allergies to pain medications, previous trials of pain medications (including prescriptions, herbal supplements, and over-the-counter medications), current medical status, mental health, and current or prior substance abuse.
Pain is a subjective phenomenon, characterized by individual experiences and variable expressions. Regular and routine pain assessment is essential to optimal pain management. There are many available scales that can be used for patients to communicate their symptoms. The most commonly used are the numeric rating scale in which patients rate their pain from 0 to10, and the verbal quantitative scale, when a description (no pain, moderate pain, severe pain, etc.) is given. The visual analog scale ( Fig. 12.1 ) requires patients to rate their pain on a horizontal line from no pain to worst possible pain . Other measures are also available, including the Simple Descriptive Pain Intensity Scale, the Numeric Pain Intensity Scale, and the faces scales, which include the Wong-Baker scale and the Oucher scale ( Fig. 12.1 ). The faces scales consisting of drawings (Wong-Baker) or photographs (Oucher) of young faces in certain pain states can be used to assess pain in children who lack the language or number sophistication to describe their pain. Currently, activity and function scales are becoming more common. These include the PEG: three-item brief screening scale ( Fig. 12.2 ) and the DVPRS (Defense and Veterans Pain Rating Scale).
Pain assessment in patients who are unable or lack the capacity to communicate verbally can be challenging. The Pain Assessment in Advance Dementia tool was developed to assist in pain assessment in patients with dementia, using observation of facial expression, vocalization, and physiologic indicators to create a pain scale score ( Fig. 12.3 ). Patients in intensive care units can be assessed with CPOT (Critical Care Pain Observation Tool), which considers compliance with ventilation, body movement, facial expressions, and vocalization ( Fig. 12.4 ). New metrics are being designed and tested to improve pain assessment, including the Clinically Aligned Pain Assessment (CAPA) developed by Donaldson and Chapman. The CAPA promotes patient conversations that incorporate comfort, sleep, function, changes in pain, and pain control. ( Fig. 12.5 )
Special Populations
Certain populations, including geriatric, pediatric, mentally disabled, physically disabled, and the opioid dependent, will require adjustments in the assessment and management of their pain complaints. Polypharmacy and impaired organ function are common in the geriatric population, requiring judicious prescribing. Assessment of pain is also challenging in the elderly due to dementia, delirium, or stoicism, which may contribute to undertreatment of pain. In physically or cognitively impaired patients, it can be difficult to assess pain and address pain complaints due to the potentially limited ability to communicate. An example where special precaution should be taken is when prescribing a controlled analgesia pump for a patient who is visually or physically impaired, as they may not be able to use the pump as directed. Patients in the intensive care unit setting may be physically impaired by endotracheal tubes, or cognitively impaired due to sedation, making adequate pain assessment more challenging. Those with mental health comorbidities, such as anxiety or depression, may be at higher risk for overdose due to drug-drug interactions as well as increased sensitivity to pain medications. Pain management in patients with a history of substance use disorder may also be challenging due to tolerance, drug-seeking behavior, and behavioral difficulties.
Pain Management
Route of Administration
In general, the least invasive route of drug administration is preferred. Typically, the least invasive route is the oral route; however, other minimally invasive methods include intranasal and transdermal routes. The transmucosal route is also available, but drug bioavailability is variable. More invasive and less preferred routes for medication administration include intramuscular and rectum administration. If immediate pain relief is needed, intravenous (IV), (PCA), patient-controlled epidural analgesia (PCEA), and regional anesthesia can be considered. It is important to reassess pain control after medication administration or intervention to assess for treatment effectiveness and adverse effects.
Medication Selection
Appropriate implementation of pharmacologic interventions can enhance pain control on the inpatient pain service. Providers should consider a multimodal approach to pain control including nonpharmacologic and pharmacologic interventions.
Acetaminophen
Acetaminophen is widely used for its antipyretic and analgesic effects. The exact mechanism of action of acetaminophen is unclear, but it weakly inhibits prostaglandin (PG) synthesis in vitro and may have antiinflammatory activity, earning the classification as a nonsteroidal antiinflammatory drug (NSAID). It is typically felt to work through a central mechanism with predominant effects on analgesia and fever control with limited antiinflammatory effects. Acetaminophen is commercially available as an IV solution, rectal suppository, and a variety of oral products. Acetaminophen is also available in oral formulations in combination with opioids (codeine, hydrocodone, oxycodone, etc.), that may provide synergy. The Federal Drug Administration set a daily dose limit of 4 g for acetaminophen, but caution should be exercised above 3 g, and less for patient with impaired liver function. The recommended oral dose is 500–1000 mg twice or three times daily.
NSAIDS
NSAIDs act peripherally to inhibit PG synthesis and provide antiinflammatory, antipyretic, and analgesic effects. NSAIDs are used for mild to moderate pain, and when combined with opioids, can be used for severe pain. With the growing concern for opioid use in the United States, NSAIDs are more prevalent in inpatient and outpatient settings. NSAIDs can assist in managing postoperative pain, leading to reductions in opioid use, time to first ambulation, and time to first bowel movement. , However, NSAIDs carry a black box warning for increased risk of serious cardiovascular thrombotic events and gastrointestinal adverse events, including bleeding, ulceration, and perforation. NSAIDs can cause kidney injury and reduced renal blood flow, may affect bone healing, and are contraindicated for perioperative use in coronary artery bypass surgery. There are several NSAID classes that vary in selectivity, potency, and formulation ( Fig. 12.6 ). The classes of NSAIDs include carboxylic acids (which include salicylic acid), propionic and acetic acids, anthranilic acid derivatives, and cyclooxygenase-2 selective (COX-2). Unlike other NSAIDs, aspirin specifically inhibits platelet aggregation and irreversibly blocks cyclooxygenase. Because each NSAID class has unique efficacy and side effect profiles, patients who did not respond to one class may respond to a drug in another class. NSAIDs are most commonly prescribed in oral formulations. Topical formulations of NSAIDs, including diclofenac and ketoprofen, show promising results when used for musculoskeletal conditions. An IV NSAID formulation, such as ketorolac, has been shown to have an equivalent analgesic effect to morphine in major abdominal surgery and reduce the use of opioid medications. Both ibuprofen and diclofenac are also available in an IV formulation for use in postsurgical pain.
Opioids
Opioids act on central receptors in the brain and spinal cord to mediate pain. Among the opioid receptors (mu (μ), kappa (κ), and sigma (σ)), mu receptors contribute significantly to analgesia and respiratory depression. A short-term trial of opioids in the acute postoperative period may be used along with a plan to reduce the medication as pain improves with healing. Often, the type and amount of opioid prescribed after common surgical procedures varies greatly, resulting in more medication prescribed than necessary after discharge. The incidence of persistent opioid use after minor or major surgical procedures is noted to be significantly higher (approximately 6%) than in the nonoperative group (0.4%) and associated with behavioral and pain disorders. In an attempt to offer guidelines to provide appropriate pain treatment, Overton et al. described utilizing a modified Delphi procedure to determine the maximum number of opioid tablets required at discharge for various surgical procedures. Furthermore, after the CDC guidelines for opioid prescribing was published, 31 states (as of March 2016) have implemented a 7-day limit for initial or postoperative prescriptions.
Short-acting opioids
Short-acting opioids are used for fast reduction of pain. Opioid regimens vary widely, but short-term judicious management with a sliding scale can assist in determining the opioid requirements. An example of sliding scale includes use of morphine sulfate-immediate release (IR) 5 mg po for mild pain (1–3/10), 10 mg po for moderate pain (4–6/10), or 15 mg for severe pain 7–10/10, given every 4–6 h. Similarly, oxycodone sliding scale can be used from 5 to 15 mg every 4–6 h using the same scale for mild, moderate, and severe pain in opioid naïve patients. Concurrent use of more than one short-acting opioid should be avoided due to an increase in adverse effects. If adequate pain control is not achieved despite dose increase, or side effects are intolerable, opioid rotation to another short-acting opioid should be considered. Medication regimens should also consider formulations that include acetaminophen, as acetaminophen is limited by the total 24-hour total amount (i.e., > 4 g/daily.). Clinician should be extra cautious when using opioids in older individuals per the Beers Criteria. , The Beers Criteria was first published in the American Journal of Geriatric Society in 1991 and last updated in 2019. It includes a list of medications that may be used with caution in older adults due to safety, drug-drug interactions, side effects, etc.
Patient-controlled analgesia and patient-controlled epidural analgesia
Patient controlled analgesia (PCA) and PCEA offers patients immediate pain relief and is considered the gold standard for postoperative pain control after major surgery. PCA and PCEA treatment allows self-administration of IV or epidural opioids, respectively, to provide individuals continuous (basal rate) and/or on-demand dosing with triggered bolus. The PCA and PCEA drug delivery units have built-in safety features such as time lock, maximum dose limits, and capnography. The delivery units also document medication use, including bolus frequency. Basal rate infusions should be avoided in opioid naïve patients due to increased risk of adverse effects, such as sedation and respiratory depression, but can be used with caution in patients on chronic opioids. Standard PCA often utilizes morphine but hydromorphone and fentanyl are options for patients with renal impairment. PCEA uses opioids or opioids in combination with anesthetics (i.e., bupivacaine). In complex abdominal, thoracic, and major gynecological cancer surgeries, PCEA is preferred due to improved postsurgical outcomes and superior pain relief with less sedative effects. During transition from IV opioids to oral formulations, it is recommended to allow approximately 90 min of overlap time for oral medication to reach steady state. The conversion ratio of opioids depends on the drug’s molecular weight, lipophilicity, and membrane permeability. The general conversion between different formulations is noted below and can be adjusted based on a patient’s tolerance and cross-reacting medications( Table 12.1 ).
| Properties | Ratio | Oral | IV | Epidural | Intrathecal | |
|---|---|---|---|---|---|---|
| Morphine | Hydrophilic | 1/10 | 30 mg | 10 mg | 1.0 mg | 0.10 mg |
| Hydromorphone | Intermediate | 1/5 | 5 mg | 1 mg | 0.2 mg | 0.04 mg |
| Fentanyl | Lipophilic | 1/3 to 1/5 | N/a | 100 μg | 33 μg | 6–10 μg |
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