Chapter 25: Analgesics

Pain

Definition of Pain

• Pain is described as an unpleasant sensory and emotional experience associated with tissue injury.

• Nurses must possess knowledge and skill in assessing and measuring pain effectively to achieve optimal pain management.

• Pain has been recognized as the “fifth vital sign.”

Pain Threshold

• Pain threshold: The minimal level of stimulus required to elicit a painful sensation.

  • It varies from person to person due to individual genetic makeup.

Pain Tolerance

• Pain tolerance: The maximum level of pain a person can withstand without having it influence normal functioning.

Types of Analgesics

• Analgesics can be classified into:

  • Opioid analgesics

  • Nonopioid analgesics

Nociceptors

• Nociceptors are sensory receptors that respond to potentially damaging stimuli by sending signals to the spinal cord and brain, leading to the sensation of pain.

Neuropathic Pain

• Neuropathic pain results from damage to the nervous system, often leading to chronic pain states.

Pain Classification

• The most common classification of pain is by duration:

  • Acute pain: Short-term pain typically following an injury or surgery.

  • Chronic pain: Long-lasting pain that persists beyond normal healing time.

  • Cancer pain: Pain caused by cancer or the treatment of cancer.

  • Somatic pain: Pain from skin, muscles, and joints.

  • Superficial pain: Pain that originates from the skin or mucous membranes.

  • Vascular pain: Pain related to blood vessel function or blood flow.

  • Visceral pain: Pain from internal organs.

Pathophysiology

Gate Theory of Pain

• Gate theory suggests that tissue injury activates nociceptors, leading to the release of chemical mediators that stimulate pain pathways.

Endorphins and Opioids

• Endorphins: Neurohormones that inhibit pain conduction, naturally produced by the body.

• Opioids: Pharmaceutical agents that activate the same receptors as endorphins to alleviate pain.

Pain Severity Measurement

• Patients are often asked to rate their pain severity on an 0 to 10 scale, where 10 indicates the most severe pain.

Undertreatment of Pain

• Unequal access to pain relief in patients leads to unrelieved pain in up to 80% of patients in the U.S..

Reasons for Undertreatment

• Sociocultural variables: Influences of culture on pain expression.

• Inability to describe pain: Patients may lack the vocabulary to articulate their pain.

• Fear of substance use disorder: Concerns about addiction to opioid medications.

• Nurse's ability to measure pain: Difficulty in accurately assessing pain intensity.

• Inaccurate analgesic dosing: Misjudgment of the correct medication dosage.

• Attitudes of healthcare team members: Misconceptions or biases against pain management.

Effects of Unrelieved Pain

• Unrelieved pain may lead to harmful effects affecting nearly all organ systems of the body.

Nonopioid Analgesics

• Nonopioid analgesics are less potent than opioids and are usually available over-the-counter (OTC).

Uses

• Effective for mild to moderate pain, particularly for:

  • Dull, throbbing pain from headaches, dysmenorrhea (menstrual pain), minor abrasions, inflammation, muscular aches, and mild arthritis.

NSAIDs (Nonsteroidal Anti-Inflammatory Drugs)

Types of NSAIDs

• Aspirin

• Ibuprofen

• Naproxen

Action

• Provide analgesic, antipyretic, and anti-inflammatory effects.

• Decrease platelet aggregation (i.e., reduce the clumping of platelets in blood, which can prevent clot formation).

Aspirin Specifics

• Aspirin is often the drug of choice for arthritic pain and inflammation.

• Side effects/adverse reactions:

  • Tinnitus: ringing in the ears.

  • Vertigo: dizziness.

  • Gastrointestinal distress.

  • Excessive bleeding.

  • Metabolic acidosis: increase in acidity of blood.

  • Anaphylaxis: severe allergic reaction.

  • Bronchospasm: narrowing of the airways.

  • Dyspnea: difficulty in breathing.

  • Urticaria: hives.

  • Reye syndrome: a rare but serious condition that causes swelling in the liver and brain in children and teenagers.

Acetaminophen (Tylenol)

Characteristics

• Acetaminophen is not an NSAID; it inhibits the synthesis of prostaglandins, which are chemicals in the brain that promote pain and inflammation.

Uses

• Effective for:

  • Muscular aches and pain.

  • Fever.

Dosage

• Maximum dose is 4 g/day. If frequently taken, the recommended maximum is 2 g/day.

Side Effects

• Includes anxiety, headache, insomnia, fatigue, constipation, peripheral edema, and a low incidence of gastrointestinal distress.

Toxic Effects/Excess Dosing

• Can lead to hepatic failure (liver failure) or renal failure (kidney failure).

• May cause blood dyscrasias (blood disorders) and hearing loss.

Clinical Judgment: Acetaminophen

Concept

• Recognize pain cues to assess severity and obtain history on liver dysfunction.

Analyze Cues and Prioritize

• Given hypotheses might include: acute pain, injury, discomfort, and decreased mobility.

Generate Solutions

• Target outcome: The patient will report that pain has decreased within one hour after acetaminophen administration.

Take Action

• Monitor liver enzyme tests for abnormalities to mitigate toxicity risks.

• Educate patients to keep acetaminophen out of children's reach and to avoid alcohol during use.

• Encourage reporting of side effects, and check serum levels if toxicity is suspected.

Opioid Analgesics

Uses

• Indicated for moderate to severe pain and have antitussive (cough suppressing) and antidiarrheal effects.

Mechanism of Action

• Act primarily on the central nervous system (CNS) to suppress pain impulses and may suppress respiration and coughing as secondary effects.

Side Effects/Adverse Effects

• Common side effects include:

  • Nausea and vomiting.

  • Constipation and urinary retention.

  • Orthostatic hypotension: drop in blood pressure upon standing.

  • Respiratory depression: slowed or inadequate breathing.

Morphine

Uses

• Commonly prescribed for acute pain, dyspnea, and to relieve preoperative anxiety.

Side Effects/Adverse Reactions

• Potential effects include drowsiness, dizziness, blurred vision, miosis (constricted pupils), orthostatic hypotension, dyspnea, and dependence.

Antidote

• The antidote for morphine overdose is Naloxone.

Clinical Judgment: Morphine

Concept

• Focus on pain recognition and patient assessment, including drug history and allergies.

Analyze Cues and Prioritize

• Hypotheses may include acute pain and decreased gas exchange as potential issues.

Generate Solutions

• Expected outcome: The patient will report a decrease in pain.

Take Action

• Administer morphine before the peak of pain for maximum effectiveness, monitor vital signs closely to detect any respiratory changes, check pupils, and keep naloxone on hand in case of overdose.

Meperidine

Uses

• Effective primarily for GI procedures and preferred over morphine for use during pregnancy.

Caution

• Use of larger doses in older adults and patients with advanced cancer may lead to neurotoxicity.

Side Effects

• Potential side effects include dizziness, drowsiness, euphoria, confusion, and constipation. Less constipation and urinary retention compared to morphine, but dependency may still occur.

Hydromorphone

Characteristics

• Its analgesic effect is approximately six times more potent than that of morphine.

Side Effects and Adverse Reactions

• Include dizziness, drowsiness, confusion, miosis, orthostatic hypotension, weakness, constipation, urinary retention, tolerance, dependence, and respiratory depression, noted to have fewer hypnotic effects and gastrointestinal disturbances compared to morphine.

Patient-Controlled Analgesia (PCA)

Medications Used

• Commonly involves morphine, fentanyl, or hydromorphone.

Mechanism

• PCA allows for a loading dose followed by administration under predetermined safety limits and a lockout mechanism, enabling near-constant levels of analgesia.

Transdermal Opioid Analgesics

Route

• The transdermal route is beneficial for continuous pain management, especially for chronic conditions.

• Fentanyl is notably more potent than morphine and is available in various strengths.

Titration

• Titration is handled in two ways:

  • Downward for postoperative pain relief.

  • Upward for managing cancer pain.

Opioid Use in Special Populations

• Special considerations include:

  • Children

  • Older adults

  • Cognitively impaired individuals

  • Oncology patients

  • Individuals with a substance abuse history/disorder.

Adjuvant Therapies

• Adjuvant therapy is defined as therapy used alongside nonopioid and opioid analgesics.

Types of Adjuvant Analgesics

• Anticonvulsants

• Antidepressants

• Corticosteroids

• Antidysrhythmics

• Local anesthetics

Opioid Agonist-Antagonists

Characteristics

• These are medications that include an opioid antagonist mixed with an opioid agonist. They may be utilized to reduce substance use disorders.

Usage Restrictions

• Not typically given for cancer pain and considered safe for use during labor; however, safety during early pregnancy has not been established.

Clinical Judgment: Nalbuphine

Concept

• Focus on pain recognition, assessing pain type, duration, location, and patient drug history while noting baseline vital signs for later comparison.

Analyze Cues and Prioritize

• Potential hypotheses include decreased gas exchange and hypotension.

Generate Solutions

• The anticipated outcome is that the patient will report pain relief.

Take Action

• Monitor vital signs; assess bowel sounds and last bowel movement; check urine output; warn against alcohol and CNS depressants while using nalbuphine; and encourage patients to report side effects.

Opioid Antagonists

Mechanism of Action

• Opioid antagonists displace opioids and block their receptors.

Use

• Primarily used as an antidote to reverse opioid overdose, counteracting respiratory depression, sedation, and hypotension.

Side Effects/Adverse Effects

• Possible effects include sweating, tachycardia, hypo/hypertension, nausea, vomiting, elevated prothrombin time (PTT), bleeding tendencies, and reversal of analgesia.

Nursing Interventions

• Continuously monitor vital signs and bleeding.

Headaches: Migraine and Cluster

Migraine Characteristics

• Typically characterized by unilateral throbbing pain accompanied by nausea, vomiting, and photophobia (sensitivity to light).

Triggers for Migraines

• Common triggers include cheese, chocolate, red wine, aspartame, fatigue, stress, monosodium glutamate, missed meals, strong odors, fluctuations in light, hormonal changes, medications, and weather changes.

Pathophysiology Theory

• Generally thought to result from neurovascular events occurring in the cerebral cortex.

Cluster Headache Characteristics

• Defined by severe unilateral nonthrobbing pain, often concentrated around the eye.

• Present in clusters and not associated with an aura or nausea/vomiting but more common in males.

Treatment and Prevention

• Potential preventive treatments may include beta-adrenergic blockers, anticonvulsants, and tricyclic antidepressants.

Migraine and Cluster Headache Management

Analgesics

• Commonly utilized analgesics include:

  • Aspirin with caffeine.

  • Acetaminophen.

  • NSAIDs such as ibuprofen and naproxen.

Opioid Analgesics

• May also involve meperidine, butorphanol (nasal spray), and ergot alkaloids like dihydroergotamine.

Selective Serotonin 1 Receptor Agonists

• Sumatriptan and zolmitriptan are used in management.

Practice Questions

Practice Question #1

• Scenario: Patient’s pain medication is changed from morphine sulfate to hydromorphone. Which statement is true?

• A. Hydromorphone must be administered intravenously.

• B. Hypertension is a common side effect.

• C. Physical dependence does not occur with hydromorphone therapy.

• D. Hydromorphone is more potent than morphine.

• Answer: D. Hydromorphone is more potent than morphine.

Practice Question #2

• Scenario: Nurse assesses a patient receiving morphine via a PCA pump with a respiratory rate of 6 breaths/min. The nurse anticipates administration of which drug?

• A. Naloxone

• B. Sumatriptan

• C. Nalbuphine

• D. Hydromorphone

• Answer: Naloxone

Practice Question #3

• Scenario: Identify a common side effect/adverse effect of morphine therapy.

• A. Diarrhea

• B. Hypertension

• C. Urinary retention

• D. Tachypnea

• Answer: C. Urinary retention

Practice Question #4

• Scenario: Patient received morphine sulfate for severe pain. What is the best indication that the medication has been effective?

• A. Patient verbalizes pain relief.

• B. Patient has an increase in heart rate.

• C. Patient is resting.

• D. Patient has an increase in blood pressure.

• Answer: A. Patient verbalizes pain relief.