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5th November 2024

Managing pain

Assessing pain and its causes

Key steps when assessing pain, whether or not in a palliative care context, include the following:

  • Characterise each individual pain (there may be more than one) to identify underlying causes
  • Identify reversible causes
  • Explore psychological, social, and spiritual factors
  • Consider using a validated structured pain assessment tool

Characterise each individual pain to identify cause

This involves the usual, familiar steps for assessing pain, including history (SOCRATES) and examination.

Below are some examples of features of different types of pain:

Type of pain Features in the history
Nerve pain Burning, shooting, tingling, hypersensitivity, changes in sensation
Increased intracranial pressure Worse in the mornings and when lying down; nausea
Bone pain Worse on weight bearing or with pressure on the bone
Intestinal colic Wavy/crampy pain
Incident pain For example, associated with moving
Muscle spasm In a specific muscle or over a trigger point

Identify reversible causes

Whilst there are many irreversible causes of pain related to a patient’s underlying conditions, palliative patients also get treatable illnesses that may cause pain. For example, nerve pain could be a manifestation of B12 deficiency and unilateral limb pain could be a deep vein thrombosis.

Principles of pharmacological pain management

Managing pain in palliative care patients is guided by the acuity and the likely cause.

Acute severe pain

  • Aim to relieve this immediately with subcutaneous or intravenous strong opioid medication
  • Give breakthrough dose of opioid (see section on opioid dose calculations)
  • In opioid-naïve patients, consider 5 mg subcutaneous or IV morphine (2.5 mg for elderly or frail patients)

Persistent pain in a non-emergency situation

The WHO (World Health Organisatin) pain ladder, initially developed in 1986, is a stepwise approach for uncontrolled pain. It has been the subject of much debate about its intended use, how effective it is, and whether it is still an appropriate tool. However, it remains widely used as a simple model for acute pain.

  • Step 1. Non-opioids, e.g. paracetamol, NSAIDs ± adjuvant therapies, e.g. tricyclic antidepressants for nerve pain
  • Step 2. Add weak opioids, e.g. codeine ± non-opioid ± adjuvant therapies
  • Step 3. Instead, try strong opioids, e.g. morphine sulphate ± non-opioid ± adjuvant therapies

Managing pain by cause

Below is a table summarising the common causes for pain and how to manage them:

Type of pain Management
Neuropathic pain Underlying cause: e.g. nerve compression – surgery or radiotherapy may be appropriate

Pain ladder – may be mixed pain

Adjuvant: tricyclic antidepressant (e.g. amitriptyline), pregabalin (or gabapentin)
Raised intracranial pressure Underlying cause: e.g. cerebral metastases – consider oncology assessment for radiotherapy

Pain ladder

Adjuvant: trial dexamethasone 8-16 mg and titrate to lowest dose, discontinue if no response
Intestinal colic Underlying cause: e.g. constipation (laxatives) or obstruction (surgical intervention)

Adjuvant: hyoscine butylbromide
Bone pain Underlying cause: e.g. bone metastases – consult oncologist for radiotherapy or bisphosphonates, fracture – consult orthopaedics, malignant hypercalcaemia – rehydration and bisphosphonates

Pain ladder

Adjuvant: hot or cold packs

Pain on movement – breakthrough analgesia 20-30 mins before moving
Muscle spasms Adjuvants: heat pad, massage, transcutaneous electric nerve stimulation, muscle relaxant (benzodiazepines, e.g. diazepam, baclofen)
Spinal cord compression Seek specialist help

16 mg dexamethasone

Use of opioids

Two key principles in opioid management of pain are:

  1. Consideration of the 24-hour total dose and calculation of PRN doses on the basis of this
  2. Conversion from one opioid to another, maintaining equivalent doses

Opioid dose calculations

When working with doses, the first step is to calculate total dose received over 24 h = total regular + total PRN

Opioid dose calculationsOpioid conversions

The following suggested conversion rates between opioids are taken from the Scottish Palliative Care Guidelines. Note that the BNF suggests a dose reduction of 25-50% when switching between opioids if there is a concern of opioid toxicity. The Scottish Palliative Care Guidelines suggest a dose reduction of up to 30% with re-titration when there is a risk of toxicity, in the frail or elderly, or just because the pharmacokinetics are different between drugs.
Regular doses of modified-release (long-acting) preparations should be: (regular + PRN) in 24h
(twice daily) 2
PRN or breakthrough doses should be: (regular + PRN) in 24h
(up to four hourly) 6

Patches can be difficult to remember, and the above equivalences are approximations. Here are two possible approaches:

  1. Remember how much is equivalent to the smallest patch and multiple up for bigger patches.
    For example:
    Remember, a buprenorphine 5 mcg patch is approximately equivalent to 12 mg morphine in 24 h
    Work out how much a buprenorphine 15 mcg patch is equivalent to by multiplying by 3
    3 x 12 mg = 36 mg morphine in 2 4h
  2. Ensure the time frame and units are consistent, i.e. mg over 24 hours, then use the conversion
    For example: buprenorphine 5 mcg/hr patch
    Total dose in 24 h = 5 mcg x 24 = 120 mcg = 0.12 mg
    Conversion factor to PO morphine (in 24h) = approx. x100
    0.12 mg x 100 = 12 mg/24h PO morphine
Worked example:

A patient is on 30 mg BD of PO modified-release morphine (e.g. MST) and has had 3 PRN doses of 10 mg immediate-release morphine (e.g. Oramorph) over the past 24 hours. He is not able to take anything orally and the decision is made to set up a syringe driver. What dose of morphine should be put in the syringe driver?

Total oral morphine dose over 24 h = total regular + total PRN

= 30 x 2 + 10 x 3

= 60 + 30 = 90 mg

Conversion from oral to subcutaneous route: ÷ 2, 90 ÷ 2 = 45 mg

Answer = 45 mg subcutaneous morphine over 24h

Pain management in renal impairment

Opioid accumulation is a potential reversible cause of deterioration (for example becoming drowsy or confused) in palliative patients. Morphine’s active metabolite accumulates in renal failure, and therefore renal function must be taken into account when prescribing. Different opioids are more or less appropriate for patients with renal failure, and when making dose adjustments a balance must be struck between adequate pain control and opioid toxicity.

Drug Notes Prescribing
Morphine To be avoided N/A
Oxycodone Limited accumulation of metabolites in renal failure Consider dose reduction if eGFR <10
Alfentanil Opioid of choice Dose as in normal renal function
Fentanyl Available as patch, sublingual or buccal for incident pain Dose reduction if eGFR <20, do not start in opioid-naïve patients
Buprenorphine Mainly used as a patch Dose reduction if eGFR <10

References

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