Pain Management

• The International Association for the Study of Pain (IASP) published a definition of pain (2020): '“An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage”'
• Categories of pain


  • Acute pain
  • Chronic pain
• When managing pain, see local guidelines and seek advice from seniors and pain or palliative care specialists when in doubt
• There are two aspects to the experience of pain: Sensory and Affective
• Pain is supposed to indicate underlying or potential damage to tissues, but it can occur without tissue damage
• The physiology of pain is very complex and there is still a lot that is not fully understood about the experience of pain
• Pain is subjective, meaning that when someone indicates they are in pain, we need to accept their experience, even when there is no apparent underlying cause
• Pain threshold


  The point at which sensory input is reported as painful
• Allodynia refers to when pain is experienced with sensory inputs that do not normally cause pain (e.g., light touch)
• Pain tolerance


  Differs from pain threshold and generally refers to a person’s response to pain, influenced by biological, psychological, and social factors
• Each person may experience pain differently influenced by biological, psychological, and social factors
• Pain receptors


  Nociceptors at the ends of nerves detect damage or potential damage to tissues
• Afferent nerves


  Nerve signals are transmitted along these to the spinal cord
• Afferent sensory nerves


  Part of the peripheral nervous system, transmit pain signals, called primary afferent nociceptors
• Groups of nerve fibres transmitting pain

  • C fibres (unmyelinated and small diameter)
  • A-delta fibres (myelinated and larger diameter)
• Signal transmission in the central nervous system

  From the spinal cord to the brain, mainly in the thalamus and cortex
• Main sensory inputs generating a pain signal

  • Mechanical (e.g., pressure)
  • Heat
  • Chemical (e.g., prostaglandins)
• Pain can be experienced without activity in primary afferent nociceptors
• Activity in primary afferent nociceptors can be detected without the patient experiencing any pain
• Referred pain refers to pain experienced in a location away from the site of tissue damage
• Possible explanations for referred pain

  • Nerves sharing innervation of multiple body parts
  • Pain amplifying sensitivity in the spinal cord
  • Activation of the sympathetic nervous system
• Neuropathic pain


  Caused by abnormal functioning or damage of sensory nerves, resulting in pain signals being transmitted to the brain
• Typical features suggestive of neuropathic pain

  • Burning
  • Tingling
  • Pins and needles
  • Electric shocks
  • Loss of sensation to touch of the affected area
• There are no reliable ways to objectively measure pain, it is subjective and measured by asking the patient
• Commonly used ways to measure pain

  • Visual analogue scale (VAS)
  • Numerical rating scale (NRS)
  • Graphical rating scale
• The World Health Organisation (WHO) analgesic ladder is used to manage cancer-related pain and other painful conditions
• Steps of the analgesic ladder

  • Step 1: Non-opioid medications such as paracetamol and NSAIDs
  • Step 2: Weak opioids such as codeine and tramadol
  • Step 3: Strong opioids such as morphine, oxycodone, fentanyl, and buprenorphine
• Analgesic ladder


  1. Step 1: Paracetamol and NSAIDs

  2. Step 2: Weak opioids such as codeine and tramadol (tramadol has multiple mechanisms of action, including being an SNRI and agonist of opioid receptors)

  3. Step 3: Strong opioids such as morphine, oxycodone, fentanyl and buprenorphine
• Adjuvants for managing neuropathic pain

  • Amitriptyline - a tricyclic antidepressant
  • Duloxetine - an SNRI antidepressant
  • Gabapentin - an anticonvulsant
  • Pregabalin - an anticonvulsant
  • Capsaicin cream (topical) - from chilli peppers
• Medical overuse headache is a common side-effect of the long-term use of analgesic medication
• Key side effects of NSAIDs

  • Gastritis with dyspepsia (indigestion)
  • Stomach ulcers
  • Exacerbation of asthma
  • Hypertension
  • Renal impairment
  • Coronary artery disease, heart failure and strokes (rarely)
• Patients in whom NSAIDs may be inappropriate or contraindicated

  • Asthma
  • Renal impairment
  • Heart disease
  • Uncontrolled hypertension
  • Stomach ulcers
• Proton pump inhibitors (e.g., omeprazole or lansoprazole) are often co-prescribed with NSAIDs to reduce the risk of gastrointestinal side effects (e.g., acid reflux, gastritis and stomach ulcers)
• Key side effects of opioids

  • Constipation
  • Skin itching (pruritus)
  • Nausea
  • Altered mental state (sedation, cognitive impairment or confusion)
  • Respiratory depression (usually only with larger doses in opioid-naive patients)
• Naloxone is used to reverse the effects of opioids in life-threatening overdose (usually due to respiratory depression)
• Using opioids in Palliative Care

  Titrate and optimise doses over time using background opioids (e.g., 12-hourly modified-release oral morphine) and rescue doses for breakthrough pain (e.g., immediate-release oral morphine solution)
• The rescue dose is usually 1/6 of the background 24-hour dose
• If the patient requires regular rescue doses for breakthrough pain, the dose of the background opioid can be increased. The rescue doses will also need increasing so that they remain 1/6 of the background 24-hour dose
• Remember that each rescue dose is 1/6 of the 24-hour background dose. This is a very common exam question and something that seniors will commonly ask to test your knowledge
• Opioid Conversion: Equivalent doses to 10mg of oral morphine