• Clinical science

Pain management

Abstract

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.

Types of pain

Definitions

  • Pain (according to the 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.”
  • 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 )

Types of pain

Type of nerve fiber Information carried Myelinated Diameter (in micrometers) Velocity (in m/s)
A-α Proprioception Yes 13–20 80–120
A-β Touch Yes 6–12 35–90
A-δ Pain (mechanical and thermal) Partially 1–5 5–30
C Pain (mechanical, thermal and chemical) No 0.5–1.5 0.5–2

Dysfunctional perception of pain

  • Hyperalgesia
  • Hypalgesia
  • Allodynia

References:[1][2][3][4][5][6]

Referred pain

  • Definition: : pain that is perceived at a location other than that of the causative stimulus; ; projection of pain usually onto a specific dermatome or myotome of the corresponding segment of the spinal cord
  • Common examples of referred pain:
  • Select treatments may reverse this pathway
Overview of referred pain
Organ Dermatome Projection
Diaphragm C4 Shoulders
Heart Th3–4 Left chest
Esophagus Th4–5 Retrosternal
Stomach Th6–9 Epigastrium
Liver, gallbladder Th10–L1 Right upper quadrant
Small bowel Th10–L1 Periumbilical
Colon Th11–L1 Lower abdomen
Bladder Th11–L1 Suprapubic
Kidneys, testicles Th10–L1 Groin

Referencs:[1][7][7][8]

Phantom limb pain

References:[9]

Evaluation of pain

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
  • 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!

References:[5]

Treatment of pain

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 (MR) 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
      • Modified-release (long-acting) analgesics are preferable
    • 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

A common mistake in pain management is the use of opioids as monotherapy. For effective and balanced pain relief, non-opioid analgesics, as well as co-analgesics if required, should be used in each step of the ladder!

Pain intensity scales should be used in regular intervals to assess the success of pain management!

Adjuvant drugs

Adjuvant drugs are administered to potentiate the analgesic effect or manage the side effects of analgesic drugs.

Neuropathic pain is primarily treated with tricyclic antidepressants or gabapentin/pregabalin!

References:[1][10][11][12]

Additional methods for pain management

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

References:[10][13]