16.2 Pain Assessment, Opioid Titration & Breakthrough Pain Management

16.2 Pain Assessment, Opioid Titration & Breakthrough Pain Management

Comprehensive Pain Assessment in Palliative Patients

Pain is one of the most prevalent and feared symptoms in palliative nursing care. Effective pain management requires systematic, multidimensional assessment rather than relying solely on vital signs.

The Concept of "Total Pain"

Pioneer Dame Cicely Saunders established that palliative pain encompasses four interconnected domains:

1. Physical Pain: Tissue damage, tumor invasion, muscle spasms, visceral organ distension, bone metastases.
2. Psychological Pain: Anxiety, depression, fear of death, helplessness, loss of independence.
3. Social Pain: Financial stress, role strain within the family, isolation, worry over dependents.
4. Spiritual Pain: Search for meaning, guilt, spiritual distress, existential angst.

Addressing physical pain without managing psychological or spiritual distress results in refractory, unresolved pain.

Pain Assessment Tools & Classification

Nurses must assess pain location, intensity, quality, onset/duration, aggravating/relieving factors (PQRST framework), and underlying etiology:

• Cognitively Intact Patients: Numeric Rating Scale (NRS 0-10), Visual Analogue Scale (VAS), or Verbal Rating Scale (VRS).
• Cognitively Impaired / Dementia / Non-Verbal Patients: Validated behavioral pain tools such as the Abbey Pain Scale or PAINAD (Pain Assessment in Advanced Dementia), evaluating vocalizations, facial expressions, change in body language, behavioral changes, and physiological changes.

Pain Etiology Classification

• Nociceptive Somatic Pain: Well-localized, aching, throbbing, or stabbing pain arising from bone, skin, or musculoskeletal tissue (e.g., bone metastases). Responds well to NSAIDs and opioids.
• Nociceptive Visceral Pain: Poorly localized, cramping, deep aching, or pressure from capsule stretching or hollow organ distension (e.g., hepatic capsule stretch, bowel obstruction). Responds to opioids and antispasmodics.
• Neuropathic Pain: Burning, shooting, electric-shock, or lancinating pain caused by nerve compression or damage (e.g., post-herpetic neuralgia, brachial plexus invasion). Requires co-analgesics (adjuvants) such as gabapentinoids.

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The WHO Analgesic Ladder & Opioid Selection

The World Health Organization (WHO) Analgesic Ladder provides a structured stepwise approach to pain pharmacotherapy:

• Step 1 (Mild Pain, NRS 1-3): Non-opioid analgesics (Paracetamol 1g PO Q6H) +/- Adjuvant.
• Step 2 (Moderate Pain, NRS 4-6): Weak opioids (Codeine, Tramadol) + Non-opioid +/- Adjuvant. (Note: In modern palliative practice, low-dose strong opioids are increasingly preferred over Step 2 weak opioids due to unpredictable CYP2D6 metabolism of codeine and tramadol).
• Step 3 (Severe Pain, NRS 7-10): Strong opioids (Morphine, Oxycodone, Fentanyl, Methadone) + Non-opioid +/- Adjuvant.

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Opioid Titration & Breakthrough Pain Calculations

When initiating Step 3 strong opioids in opioid-naive patients, regular immediate-release (IR) oral morphine (e.g., 2.5 mg to 5 mg PO Q4H) is titrated daily until pain control is established.

Sustained-Release Baseline & Breakthrough Doses

Once pain is stabilized, the total 24-hour oral morphine equivalent dose (OMED) is converted into a regular long-acting, sustained-release (SR) formulation given every 12 hours (e.g., Morphine Sustained-Release / MST Continus PO BD), paired with immediate-release opioids for breakthrough pain.

• Breakthrough Pain Dose Calculation: The individual breakthrough pain dose is calculated as 10% to 15% of the total 24-hour baseline OMED. Breakthrough doses are prescribed every 1 to 2 hours PRN as immediate-release oral morphine syrup/tablets or subcutaneous morphine.

Clinical Calculation Scenario:

• Patient Prescribed: MST (Morphine Sustained Release) 60 mg PO twice daily (Q12H).
• Step 1: Calculate Total 24-Hour OMED: $60\text{ mg} \times 2 = 120\text{ mg oral morphine per 24 hours}$
• Step 2: Calculate Breakthrough Dose (10% - 15%): $10\% \text{ of } 120\text{ mg} = 12\text{ mg}$ $15\% \text{ of } 120\text{ mg} = 18\text{ mg}$
  • Prescribed breakthrough dose range: 12 mg to 15 mg PO IR Morphine Q1H-Q2H PRN.
• Step 3: Daily Dose Adjustment: If the patient requires 4 breakthrough doses in 24 hours (e.g., $4 \times 15\text{ mg} = 60\text{ mg}$ breakthrough morphine), the new total 24-hour OMED is $120\text{ mg (baseline)} + 60\text{ mg (breakthrough)} = 180\text{ mg/24h}$. The new regular dose becomes MST 90 mg PO BD.

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Equianalgesic Conversions & Opioid Rotation

Opioid rotation (switching from one opioid to another) is indicated when a patient experiences intolerable opioid side effects (e.g., severe hallucinations, uncontrollable nausea, opioid-induced neurotoxicity) or deteriorating renal function.

Standard Equianalgesic Ratios (Singapore Nursing Standards)

• Oral Morphine to Subcutaneous / Intravenous Morphine: Oral morphine undergoes significant first-pass hepatic metabolism. The equianalgesic conversion ratio of Oral Morphine to Subcutaneous Morphine is 2:1 (oral dose divided by 2).
  • Example: 30 mg Oral Morphine = 15 mg Subcutaneous Morphine.
• Oral Morphine to Oral Oxycodone: Oral Oxycodone is approximately 1.5 times more potent than oral morphine (Ratio 1.5:1 or 30 mg Oral Morphine = 20 mg Oral Oxycodone).
• Oral Morphine to Transdermal Fentanyl: Transdermal Fentanyl is reserved for stable pain in opioid-tolerant patients (contraindicated in acute unstable pain due to slow 12-24 hour onset).
  • Example: 60 mg 24-hour Oral OMED $\approx$ 25 mcg/hour Fentanyl Patch (applied every 72 hours).

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Equianalgesic Conversion Matrix

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Managing Neuropathic Pain & Co-Analgesics (Adjuvants)

Opioids have limited efficacy against pure neuropathic pain. Adjuvant medications must be co-prescribed:

• Gabapentinoids: Gabapentin (starting 100-300 mg PO ON/TDS, adjusted for renal function) or Pregabalin (25-75 mg PO BD). Inhibit presynaptic voltage-gated calcium channels.
• Tricyclic Antidepressants (TCAs): Amitriptyline (10-25 mg PO ON). Inhibits serotonin and norepinephrine reuptake; caution in elderly due to anticholinergic side effects (urinary retention, sedation, dry mouth).
• Corticosteroids: Dexamethasone (4 mg to 16 mg PO/IV daily in divided doses). Decreases peri-tumoral edema in spinal cord compression, brain metastases, capsular stretch pain, and malignant bowel obstruction.

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Opioid Toxicity & Side Effect Management

Nurses must proactively prevent and manage opioid-related adverse effects:

1. Opioid-Induced Constipation (OIC):
   • Crucial Rule: Patients NEVER develop tolerance to opioid-induced constipation.
   • Proactive Nursing Management: All patients starting Step 2 or Step 3 opioids MUST be co-prescribed a routine bowel regimen (stimulant laxative such as Senna + osmotic agent such as Lactulose or Macrogol). Bulk-forming laxatives (e.g., Psyllium/Metamucil) are contraindicated in weak palliative patients as they cause fecal impaction if fluid intake is low.
2. Nausea & Sedation:
   • Tolerance to nausea and sedation usually develops within 3 to 7 days. Prescribe short-term PRN Haloperidol 0.5-1 mg PO or Metoclopramide 10 mg PO.
3. Opioid Neurotoxicity & Overdose:
   • Manifestations: Severe sedation, confusion, vivid hallucinations, myoclonus (muscle twitching), hyperalgesia, pinpoint pupils, and respiratory depression (respiratory rate < 8-10 breaths/minute).
   • Emergency Management: Stop/hold opioid dose. Administer small, titrated doses of diluted intravenous Naloxone (e.g., 40 mcg to 80 mcg IV Q2-3 mins) aimed at restoring adequate ventilation (RR > 10/min) without precipitating severe withdrawal pain crisis.