1 Define acute pain

Pain is defined as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” Acute pain refers to pain of short duration (<3 months), usually associated with surgery, trauma, or an acute illness. Acute pain differs from chronic pain because:

Its cause is usually known.

It is usually temporary and located in the area of trauma or damage.

It resolves spontaneously with healing.

2 Why has acute pain been undertreated?

There are numerous reasons acute pain is typically undertreated. Physicians get very little education regarding pain management during the course of medical school and residency training. Many providers overestimate the risks associated with the use of opioids, such as respiratory depression and addiction. Health care providers are also often afraid of scrutiny from regulatory boards that they believe may result from regularly prescribing opioid narcotics. In reality, the fact that poorly treated pain may result in higher morbidity and mortality rates has become appreciated only recently. There is now a greater emphasis being placed on not undertreating pain; lawsuits have successfully been brought against physicians for not providing enough pain medication. Pain is now considered the fifth vital sign.

3 How is pain assessed?

Pain is subjective and cannot be measured even with the most sophisticated medical equipment. Changes in vital signs such as blood pressure or heart rate correlate poorly with the degree of pain control.

The magnitude of pain and the response to treatment can be monitored in several ways. A visual analog scale may be used in which the patient chooses a mark on a 10-cm line corresponding with the perceived amount of pain being experienced. Scales using color (from blue for minimal pain through violet hues to bright red for maximal pain) or numbers (from zero for no pain through ten for maximal pain) have been devised for adults (Figure 77-1). A scale of 10 faces, ranging from very happy to very sad, can be used in young children. The child points to the face matching the way he or she feels. Verbal descriptive scales such as the McGill Pain Questionnaire are useful both for clinical and research purposes. Functional ability is also a useful measure of pain. In some patients, especially those who also have chronic pain, assessing ability to perform regular functions such as activities of daily living, performing at work, or ability to participate in leisure activities may be more useful than collecting pain scores. In a hospital setting the number of times a patient spontaneously leaves the room may provide a more accurate assessment than pain scores. Pain scores with activity may be a more sensitive measure of analgesia because it is easier to control pain at rest. The pain scale can be used to ensure that an intervention such as an increased dose of opioids is effective in decreasing the patient’s pain.

Figure 77-1 Pain scales for children and adults.

(From Wong D, Whaley L: Clinical manual of pediatric nursing, St. Louis, 1990, Mosby.)

4 What medications are useful in treating acute pain?

The medications useful in treating acute pain are similar to those used in treating other types of pain. The World Health Organization analgesic ladder developed for treating patients with cancer pain also provides a useful approach to treating acute pain (Figure 77-2). At the lowest level (mild pain), nonopioid analgesics such as nonsteroidal antiinflammatory drugs (NSAIDs) (e.g., ibuprofen or acetaminophen) are useful. Such drugs have an analgesic ceiling; above a certain dose no further analgesia is expected. For moderate pain compounds combining acetaminophen or aspirin with an opioid are useful. The inclusion of acetaminophen limits the amount of such agents that should be used within a 24-hour period because toxic accumulations can occur. The next step to consider would be adding an agent such as tramadol. Tramadol has a dual mechanism of action as a weak μ-opioid agonist and a weak inhibitor of reuptake of norepinephrine and serotonin. Care should be taken when concurrently prescribing with selective serotonin reuptake inhibitors since there is a potential increased incidence of serotonin syndrome (although there are very few reported cases). With severe levels of pain an opioid such as morphine or hydromorphone is a better choice; such opioids have no analgesic ceiling. Most postoperative or trauma patients initially respond better to morphine or other opioids. Intravenous agents are usually faster, and patients report more satisfaction with analgesia after surgery or trauma. By the time the patient is eating and ready for discharge, opioid-acetaminophen agents or NSAIDs are often adequate.

Figure 77-2 World Health Organization analgesic ladder.

5 Do all types of pain respond equally to medication containing opioids?

Not all types of pain respond equally to the same medication. Opioid analgesics are helpful in controlling somatic or visceral pain. Bone pain may be helped partially by opioids. However, NSAIDs and steroids are highly effective in treating bone pain. The combination of NSAIDs and opioids is synergistic in controlling pain. Neuropathic pain, often described as pain with a burning, hyperesthetic quality, responds to a diverse group of drugs, including antidepressants (amitriptyline), anticonvulsants (carbamazepine or gabapentin), antiarrhythmics (mexiletine), muscle relaxants (baclofen), and α-adrenergic agonists (clonidine). Opioids may also be helpful. Frequently pain control is improved after 1 to 2 days of using adjuvant drugs. Alternative medications may also help to control somatic or visceral pain. Drugs that control pain by different mechanisms may be synergistic when used together (such as NSAIDs and opioids). By using lower doses of two different agents, the patient may have good pain control with fewer side effects. Another option for mild to moderate pain is use of topical agents such as patches impregnated with lidocaine (Lidoderm) or diclofenac (Flector). In addition, topical gels or ointments can be considered, including 5% lidocaine ointment, 1% Voltaren gel, 1.3% diclofenac, or 4% ketamine compounded ointment. These patches and topical agents can also be used in conjunction with oral medications.

6 What is the risk of addiction with opioids?

Addiction (or psychologic dependence) needs to be differentiated from physical dependence. Physical dependence, a physiologic adaptation of the body to the presence of an opioid, develops in all patients maintained on opioids for a period of several weeks. If the opioid is stopped abruptly without tapering, the patient may show signs of withdrawal. The patient can stop opioids at any time and avoid withdrawal symptoms by tapering down. Tolerance is the need for a higher dose of opioid to produce the same pharmacologic effect. Neither physical dependence nor tolerance indicates addiction. The psychologic dependence seen with addiction is characterized by a compulsive behavior pattern involved in acquiring opioids for nonmedical purposes (psychic effects) as opposed to pain relief. The risk of iatrogenic addiction is very low; several studies have shown it to be less than 0.1%. Patients who are inadequately treated may seem to be drug seeking, because they repeatedly request opioids and are concerned with the timing of their next dose. Such pseudo addiction may mimic addictive behavior but is caused by inadequate pain treatment. This iatrogenic condition can be avoided by listening to the patient and carefully assessing his or her pain. With proper doses of pain medication, pseudo addiction disappears. Current studies report that patients with a past history of other substance abuse are at higher risk for opioid addiction. About 4% of patients treated for trauma had problems with opioids but showed other indications of addictive behavior that correlated with their increased use.

7 How should opioids be given? Are some opioids better than others?

Opioids can be given in various ways. Oral administration is usually the easiest and least expensive. Tablets should be provided on a schedule (e.g., oxycodone-acetaminophen tablets every 4 hours) rather than on an as needed (PRN) or as requested basis. Many studies have shown that PRN schedules usually provide only 25% of the maximal possible daily dose of opioids, despite the patient’s repeated requests. If a patient cannot take medication orally, opioids can be administered intramuscularly, intravenously (including patient-controlled analgesia [PCA] pumps), subcutaneously, rectally, transdermally, epidurally, intrathecally, through iontophoresis, and through buccal mucosa. Because PCA pumps are safe and effective, they are often used when the patient cannot take oral medication.

Meperidine has the highest incidence of allergic reactions; in addition, its first metabolite, normeperidine, can accumulate and cause central nervous system excitation, including seizures. Normeperidine accumulation is dose dependent and more common in patients with renal impairment. Consequently meperidine has been removed from many hospital formularies and replaced with better opioid alternatives. Morphine has an active metabolite (morphine-6-glucuronide) that is analgesic and has a longer half-life than morphine. This metabolite can be useful in many cases because it allows a slow, sustained increase in analgesia. However, in patients with decreased renal function, the accumulation of an active metabolite may lead to increased side effects, including increased risk of respiratory depression. Fentanyl acts more rapidly than morphine or hydromorphone and has no active metabolites. It is a safer choice for patients with impaired renal or liver function. Hydromorphone also has no active metabolites. It is five times as potent as morphine and less dysphoric; however, its onset of action and duration are more similar to morphine than to fentanyl. Methadone can be given intravenously. The intravenous dose is equivalent to the oral dose, unlike other opioids, which are more potent intravenously. Oxymorphone is a potent newer opioid that is only available orally. Tapendatol is a new oral opioid drug just approved by the Food and Drug Administration. It is approved for moderate to severe acute pain as a schedule II drug. Tapendatol is a combination of an opioid binding drug with a norepinephrine reuptake inhibitor. It is projected to be between tramadol and morphine in potency.

In a hospital setting the general guideline should be to schedule pain medications for the first 1 to 2 days after the surgery or injury. After that period of time the medication can be transitioned to an as needed status. As noted previously, assessment should continue by pain score and function to determine appropriate dosing. In an outpatient setting 1 day of scheduled pain medications is reasonable before transitioning to as needed.

8 When treating acute pain in a chronic pain patient, how should the approach differ?

When a chronic pain patient has suffered an injury or undergone surgery, the general rule is that the typical dose of oral opioids should be tripled for the first 1 to 2 days. In the preoperative preparation for a chronic pain patient, a one-time dose of gabapentin (900 to 1200 mg) or pregabalin (75 to 100 mg) coupled with a one-time dose of celecoxib (Celebrex) (200 mg) has been shown to improve pain control. After surgery gabapentin or pregabalin can be continued as a regular oral dose, and celecoxib should be continued at 100 mg bid for 5 days. Regional blocks should be used whenever possible and continued at least 24 hours after surgery if possible. A low-dose ketamine (0.05 to 0.2 mg/kg/hr) infusion during the operation helps with pain control and can be continued after surgery by combining ketamine with the opioid in a PCA infusion.

9 How should a patient-controlled analgesia pump be set?

Several decisions must be made in setting up a PCA pump. The first is what drug to use. As discussed previously, the most commonly used agents are morphine and hydromorphone. Meperidine has been removed from many hospital formularies and should only be used in rare circumstances. Fentanyl also can be used, particularly in patients with end-organ failure. Morphine comes prepackaged in a 1-mg/ml concentration; because hydromorphone is five times as potent, a 0.2-mg/ml concentration is equivalent to 1 mg of morphine. After choosing the drug, a decision should be made about the type of infusion: increment dosing only, basal (continuous) with incremental dosing, or incremental dosing with a basal dose only at night (between 10 pm and 6 am) to help the patient sleep. Studies have shown no significant benefit to a basal rate, although anecdotally patients prefer a basal rate at night to help them sleep. Finally, the duration of the lock-out period needs to be determined. Lock-out refers to the time between actual delivery of opioid doses (e.g., if a 6-minute lock-out period is selected, the patient cannot receive opioid doses closer than 6 minutes apart, regardless of how often he or she activates the PCA pump). The lock-out period should be short enough to allow the patient to titrate the opioid level but long enough to allow the patient to feel the effect of one dose before delivering another. The usual lock-out ranges are 6 to 10 minutes.

10 What are common side effects of opioids? How are they treated?

The common side effects of opioids are sedation, pruritus, nausea and vomiting, urinary retention, and respiratory depression. In patients who have taken opioids previously, the risk of respiratory depression and sedation is less. Pruritus is treated by applying lotion to the affected area, by intravenous or oral delivery of diphenhydramine (25 to 50 mg), and in severe cases by using an opioid antagonist or agonist–antagonist (e.g., nalbuphine, 5 mg every 6 hours). Propofol, 10 mg every 6 hours, is also effective. Urinary retention is treated by urinary catheter drainage or nalbuphine. Nausea and vomiting respond to a decrease in opioid dose (elimination of a basal rate), nalbuphine, and antiemetics. Ondansetron, 4 mg intravenously, has proved to be a much more effective antiemetic than droperidol. Respiratory depression is treated by using a pure antagonist (naloxone) or agonist–antagonist (nalbuphine).

11 How do neuraxial opioids work?

Opioid receptors are present in levels I and II of the substantia gelatinosa of the dorsal horn. Opioids given either intrathecally or epidurally bind to these receptors. The dose of morphine can be decreased to 10% of the usual intravenous dose when given epidurally and to 1% when given intrathecally. The clinical behavior of the opioid can be predicted by its lipid solubility. Highly lipid-soluble opioids such as fentanyl pass through membranes and bind quickly. Fentanyl has a rapid onset, short duration, and limited spread (five levels). Morphine, which is highly hydrophilic, moves through membranes more slowly and has a slower onset but longer duration because it stays suspended in solution and is released slowly to bind to the opioid receptors. Because of its poor lipid solubility, it spreads throughout the entire length of the spinal fluid and can help to control pain from several different anatomic sites. The termination of clinical activity of neuraxial opioids is caused by vascular absorption and breakdown. Local anesthetics such as lidocaine and bupivacaine can be used alone or in combination with opioids.

12 How do agonist-antagonists differ from opioids such as morphine?

μ-, δ-, and κ-opioid receptors have been identified in the central nervous system. Most morphine equivalent opioids are primarily μ-agonists, with some δ- and κ-effect. Agonist-antagonists are μ-antagonists and κ-agonists. Because κ-receptors provide weaker analgesia, agonist-antagonists are adequate for mild to moderate pain, whereas μ-agonists are adequate for moderate to severe pain. Suboxone is a newer oral combination of buprenorphine combined with naloxone. Patients using this agent can be given μ-acting opioids but will need higher doses.

13 How should patients with continuous infusions for analgesia or patient-controlled analgesia pumps be monitored?

Patients receiving analgesia do not need elaborate monitoring equipment. Pulse oximetry can be used if there is any concern for oxygen desaturation, but usually nurses are able to monitor patients safely by checking respiratory rate every hour and level of sedation every hour the patient is awake. Vital signs are taken as scheduled. The catheter site of the infusion should be checked daily for any signs of infection (redness, swelling) or leakage.

14 How is an oral agent chosen for a patient who previously received intravenous opioids?

Choice of an oral agent should be based on how much pain the patient still has and how much opioid was needed to control the pain. Opioid-acetaminophen compounds are adequate for patients whose pain requires 0 to 2 mg/hr of morphine. Hydrocodone-acetaminophen is a milder analgesic than oxycodone-acetaminophen and is useful for patients who require minimal opioids. An equal analgesic dosing chart (Table 77-1) can be used to select equivalent levels of analgesics.

15 Which nonsteroidal antiinflammatory drug should be used?

If the patient can take oral medication, an oral agent should be used. Most oral agents have the same degree of analgesia as antiinflammatory activity. The degree of potency of analgesia parallels the risk of gastric upset with oral agents. One or two specific agents may work better for a given patient, but their identification is usually a matter of trial and error. Price also may be a factor. Older, off-patent NSAIDs may be significantly cheaper and just as effective (e.g., naproxen, indomethacin, and ibuprofen).

For patients who cannot take oral medication, parenteral ketorolac is the available option. Ketorolac has a more potent analgesic than antiinflammatory effect. It may be given intravenously or intramuscularly. In patients over 65 years old who weigh less than 100 pounds or who are frail, half of the regular dose should be used. In patients with a serum creatinine above 1.3 ml/dl, alternatives to the use of ketorolac should be considered. The side effects of NSAIDs may be observed with either oral or parenteral use. Patients who have active gastric disease; are anticoagulated or hypovolemic; or have a history of asthma, congestive heart failure, or renal disease may have complications from NSAID use.

16 Are cyclooxygenase-2 agents any better for pain than cyclooxygenase-1 agents?

Cyclooxygenase-2 (COX-2) agents may have fewer gastrointestinal or platelet effects, but they are no better than COX-1 agents for pain control in most patients.

17 What other techniques can be used for acute pain management?

In addition to PCA pumps and epidurals, intrathecal opioids can be used, especially if spinal anesthesia is used for the procedure. Preservative-free morphine can be used for inpatients, and fentanyl for outpatients. Morphine doses of 0.1 to 0.3 mg are adequate for many lower extremity, urologic, and gynecologic procedures and have a minimal risk of respiratory depression. For thoracic procedures higher doses are needed (0.3 to 0.75 mg) and involve a risk of respiratory depression. Fentanyl can also be used intrathecally; 10 to 15 mcg of intrathecal fentanyl is equal to 0.1 to 0.3 mg of intrathecal morphine. Because fentanyl is more lipid soluble than morphine, it does not spread as far but still may be given through lumbar spinal injection.

Other types of blocks can be useful. Intercostal blocks decrease pain and improve ventilation in patients with rib fractures or flail chests. Continuous brachial plexus blocks increase blood flow in patients with collagen vascular diseases or arterial spasm (Burger’s disease) and those who have digital reattachment, improving healing and providing good pain control. Single injections in the brachial plexus are helpful for shoulder or upper arm procedures. Recently continuous sciatic and/or femoral blocks have been useful for patients with knee or lower leg procedures. The use of ultrasound has improved the success rate of these catheters and allows other nerves to be blocked with continuous catheters.

18 How does good acute pain management make a difference?

Pain is a form of stress and produces an elevation in stress hormones and catecholamines. Good pain management has been shown to result in shorter hospital stays, improved mortality rates (especially in patients with less physiologic reserve such as those in the intensive care unit), better immune function, fewer catabolism and endocrine derangements, and fewer thromboembolic complications. In addition, specific benefits have been shown for patients undergoing specific procedures. Patients who undergo amputation under a regional block with local anesthetic have a decreased incidence of phantom pain. Patients in whom a vascular graft is placed have a lower rate of thrombosis. A decreased mortality rate has been shown in patients with flail chests who have epidural analgesia.

Recent studies have shown the value of preemptive analgesia in some surgical situations. The blockade of the pathways involved in pain transmission before surgical stimulation may decrease the patient’s postoperative pain. Local infiltration along the site of skin incision in patients having inguinal hernia repairs with general anesthesia is beneficial if the infiltration is done before the skin incision. Similar results have been found for preoperative local infiltration along the laparoscopic port sites. Several studies using intravenous or epidural opiates in patients having thoracotomies and hysterectomies have also shown a preemptive effect. The use of local anesthetic with spinal and epidural anesthetics has not been shown to be preemptive. NSAIDs have not shown a preemptive effect. Further studies with larger patient groups are needed to provide definitive answers regarding preemptive analgesia.

Proper pain management not only keeps patients more comfortable but also may decrease the risk of morbidity and mortality, thus improving use of health resources.