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Pain management

Last updated: March 25, 2021

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Pain is an unpleasant sensory and emotional experience that arises from actual or potential tissue damage. There are a number of ways to differentiate pain, the most common of which is the distinction between acute and chronic pain. Acute pain is a warning signal for actual or potential tissue damage and is associated with trauma, surgery, and illness. Chronic pain is generally defined as pain lasting beyond the normal tissue healing time. Standardized pain intensity scales are used to evaluate pain in a clinical setting. Pain management involves a multimodal approach with analgesic drugs, physical therapy, behavioral therapy, as well as interventional and surgical methods. The management of chronic pain follows the WHO analgesic ladder, a three-step algorithm and set of guiding principles based on using pharmacologic agents sequentially, escalating from non-opioids for mild pain to strong opioids for severe pain, in accordance with the degree of pain as reported by the patient. Each step of the ladder consists of regular medication and PRN medication as needed. If the analgesic effect is not sufficient at a certain level of the WHO ladder, advancing to the next step must be considered. Independent of the step, additional adjuvant drugs may be administered to potentiate analgesia and manage side effects of the analgesic drugs.


  • Pain (according to the International Association for the Study of Pain; IASP): “Pain is an unpleasant sensory and emotional experience arising from actual or potential tissue damage, or described in terms of such damage. [...] Pain is always subjective.” [1]
  • Acute pain
    • A warning signal indicating actual or potential tissue damage that triggers a protective reaction.
    • Typically associated with trauma, surgery, and acute illness.
  • Chronic pain
    • Pain that lasts beyond the normal tissue healing time; (6 months according to the IASP )
    • Unlike acute pain, chronic pain has no protective role in preventing further tissue damage and can be considered a disease entity in its own right.

Types of pain [2]

  • Nociceptive pain: pain that is triggered by chemical, mechanical, or thermal stimuli (noxious stimuli)
    • Somatic pain (musculoskeletal pain): localized, sharp pain that varies in duration and quality (Aδ fibers)
    • Visceral pain: dull, diffuse, deep pain (C fibers)
  • Neuropathic pain: pain caused by abnormal neural activity that arises secondary to injury, disease, or dysfunction of the nervous system
  • For an overview of pain symptoms in patients with serious or life-threatening illnesses, see “Pain concepts in palliative care”.


Sensitization [4][5]

  • Abnormal pain perception due to increased neuronal sensitivity to noxious stimuli (hyperalgesia) and/or reduced neuronal threshold to otherwise normal stimuli (allodynia) in response to local injury, inflammation, and/or repetitive stimulation.
  • Plays a major role in the generation and maintenance of chronic pain and neuropathic pain (e.g., postherpetic neuralgia)
  • Although not completely understood, the pathophysiology is thought to involve the following two mechanisms:
    • Peripheral sensitization
      • Injury, inflammation, or repetitive stimulation of the peripheral nociceptive neurons local release of chemical mediators (e.g., cytokines, nerve growth factors, histamine)→ repeated or prolonged exposure to chemical mediators upregulates the ion channels in the nociceptors → increases sensitivity and/or reduces threshold to chemical mediators even further → increased action potentials → abnormal pain perception
      • Usually ceases once the tissue injury or inflammation heals
    • Central sensitization
Overview of referred pain
Organ Dermatome Projection
Diaphragm C4 Shoulders
Heart T3–4 Left chest
Esophagus T4–5 Retrosternal
Stomach T6–9 Epigastrium
Liver, gallbladder T10–L1 Right upper quadrant
Small bowel T10–L1 Periumbilical
Colon T11–L1 Lower abdomen
Bladder T11–L1 Suprapubic
Kidneys, testicles T10–L1 Groin



To optimize pain management, a thorough history and assessment of pain is required prior to initiating treatment.

  • Pain characteristics (location, quality, temporal aspects, triggers)
  • Associated symptoms (changes in mobility and strength)
  • Pain impact (on daily life, sleep, activities)
  • Previous pain assessments and/or treatment
  • Pain intensity scale: subjective grading of pain severity by the patient
    • Numeric rating scale (NRS): most common pain scale, evaluates pain on a scale from 0–10
    • Visual analog scale (VAS): visual equivalents suitable for children
    • Verbal descriptor scale
  • Pain diary: regular documentation of the pain intensity to identify peaks and triggers; enables treatment optimization

Pain is subjective! Pain scales are used to assess a patient's pain and response to pain management over time. They cannot be used to compare pain intensity between patients!


WHO analgesic ladder

The WHO analgesic ladder is a 3-step algorithm for the management of acute and chronic pain.

  • Principles
    • Regular analgesic (modified-release drugs, administered at fixed times and doses)
      • By the mouth: preferably, analgesics should be given orally.
      • By the clock: regular administration at fixed times, rather than on demand
      • By the ladder(symptom-orientated): if the patient is still in pain, it is necessary to go up a step
    • Appropriate PRN medication
      • Short-acting analgesics for peaks in pain
      • If PRN medication is required ≥ 3x/d → inadequate analgesia likely; review the regular medication
    • Additionally, concurrent treatment with adjuvant drugs
Pain severity Non-opioid analgesics Mild opioids Strong opioids Adjuvant drugs
Step I Mild pain - - If required
Step II Moderate pain - If required
Step III Severe pain - If required

Nonopioid analgesics are first-line agents for mild to moderate pain [11]
For both opioid and nonopioid analgesics, use the minimal effective dose for the shortest duration of time to minimize adverse effects. Pain intensity scales should be used in regular intervals to assess the success of pain management.

Oral analgesics

Oral analgesics
Drug class Drug Important considerations
Nonopioids Acetaminophen [12]
NSAIDs [12]
  • Ibuprofen and naproxen are the preferred first-line analgesics for mild to moderate pain. [12]
  • Use with caution in patients with PUD and renal disease.
  • Contraindicated in patients with a recent MI and in the perioperative period of CABG (exception: low-dose aspirin in the management of acute MI)
  • Avoid NSAIDs, if feasible, in patients with bleeding disorders and those who will soon undergo surgery or an invasive procedure.
  • See nonopioid analgesics for further information.

Selective COX-2 inhibitor

  • Preferred second-line analgesic for mild to moderate pain [12]
  • Preferred over NSAIDs in patients with PUD
  • Use with caution in patients with renal or cardiovascular disease. [13]
  • See nonopioid analgesics for further information.

Combination analgesics

  • Consider combination analgesics for the management of moderate to moderately severe pain.
  • Follow the same precautions and contraindications for opioids and NSAIDs when prescribing these combination analgesics.

Parenteral analgesics

Parenteral analgesics
Drug class Drug Important considerations

Analgesic suppositories

Topical analgesics

Topical analgesics
Drug Dose Indications

Adjuvant analgesics


Anticonvulsants are useful adjuncts in the management of neuropathic pain. They typically will not be helpful for acute pain, rather are more commonly used for chronic neuropathic pain.

Muscle relaxants

Consider muscle relaxants in patients with pain associated with muscle spasticity.


Tricyclic antidepressants and SNRIs can be helpful for chronic pain syndromes and neuropathic pain. Antidepressants for chronic or neuropathic pain are recommended by the American Society of Anesthesiologists in their 2010 guideline, but only duloxetine is FDA-approved for this indication. All others are off-label use. [23][24]

Intravenous patient-controlled analgesia

  • Infusion pump designed to release additional IV medication in response to patient's request
  • Indication: severe acute pain that is difficult to manage and is expected to be limited in duration

Management of side effects

There are a number of procedures available that complement the pharmacologic management of pain.

  • Regional anesthesia: infiltration with local anesthetics (e.g., lidocaine)
  • Physical therapy
    • Massage
    • Thermotherapy
      • Involves the application of heat to joints, muscle, and/or soft tissue (e.g., using hot cloths, ultrasound, heating pads, warm compresses).
      • Used to relieve pain and induce muscle relaxation.
    • Desensitization techniques
    • Osteopathic manipulative treatment (OMT): a technique used by osteopathic physicians to relieve pain through stretching, gentle pressure, and resistance
  • Acupuncture
  • Behavioral therapy


Assessment of pain in the ICU

  • Patients in ICU are typically unable to communicate and require a specialized pain scale [30]
  • Behavioral pain scale
  • Critical care pain observation tool (CCPOT)
    • Used to identify pain in critically ill patients.
    • Four items are evaluated and awarded points: facial expressions, body movements, ventilator compliance in intubated patients or vocalization in nonintubated patients, and muscle tension
    • ≥ 3 points indicates significant pain
  • For subjective grading of pain severity by the patient, see “Pain intensity scale
Pain intensity scales for critically ill patients
Behavioral pain scale score CCPOT score
Facial expression
  • 1 point for relaxed
  • 2 points for partially tightened
  • 3 points for fully tightened
  • 0 points for relaxed
  • 1 point for tense
  • 2 points for grimacing
  • Upper limbs
    • 1 point for no movement
    • 2 points for partially bent
    • 3 points for fully bent with finger flexion
    • 4 points for permanently retracted
  • Body
    • 0 points for no movement or normal
    • 1 point for protection
    • 2 points for restless or agitated
Muscle tension
  • N/A
  • 0 points for relaxed
  • 1 point for rigid or tense
  • 2 points for very rigid or tense
Mechanical ventilation compliance
  • 1 point for tolerating movement
  • 2 points for coughing, but tolerating most of the time
  • 3 points for fighting ventilator
  • 4 points for unable to control ventilation
  • Intubated patients
    • 0 points for tolerating normally
    • 1 point tolerating but coughing
    • 2 points for fighting the ventilator
Vocalization for extubated patients
  • N/A
  • 0 points normal tone or no sound
  • 1 point for moaning or sighing
  • 2 points for crying or sobbing

Pain Management [31]

Be aware of the adverse effects of opioids (e.g., delirium, CNS depression, tolerance) or NSAID therapy!

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