5.3 Pain Assessment, Multimodal Analgesia & Epidural/PCA Care
Key Takeaways
- Acute pain is assessed with a structured OPQRST history - onset, provocation and palliation, quality, region and radiation, severity, and time - recorded in the patient's own words and scored both at rest and during functional movement (the '5th vital sign') using validated numerical, visual, or behavioural tools (Abbey / PAINAD scales).
- Multimodal analgesia combines synergistic agents acting on distinct anatomical nociceptive pathways (paracetamol, NSAIDs, weak opioids, strong opioids) to optimize dynamic analgesia while minimizing opioid-related toxicities.
- Patient-Controlled Analgesia (PCA) enforces an absolute 'patient-only' activation rule; proxy dosing by family members or clinicians bypasses safety lockout mechanisms and is a primary cause of fatal opioid overdoses.
- In opioid toxicity, excessive sedation invariably precedes respiratory depression; emergency naloxone must be administered via careful slow intravenous titration (40–80 mcg increments) rather than large boluses to avoid precipitating acute withdrawal crises.
- Continuous epidural analgesia requires bilateral dermatomal sensory mapping (cold test), motor block assessment using the Bromage scale, and immediate escalation for suspected epidural haematoma (triad of severe back pain, progressive motor block, and urinary incontinence).
Pain Assessment, Multimodal Analgesia & Epidural/PCA Care
Core Clinical Principle: Effective postoperative pain management is not merely a matter of patient comfort—it is a physiological imperative. Severe unrelieved surgical pain triggers neuroendocrine stress responses (hypertension, tachycardia, myocardial ischaemia), impairs respiratory mechanics (hypoventilation, splinting, atelectasis), delays ambulation, increases VTE risk, and contributes to chronic persistent postsurgical pain. Optimal management balances powerful dynamic analgesia with strict vigilance against drug toxicity.
1. Systematic Acute Pain Assessment: The "5th Vital Sign"
In acute Irish hospital settings, pain is routinely documented alongside temperature, pulse, blood pressure, and respirations as the fifth vital sign. Pain must be evaluated systematically:
- At Rest vs. On Movement (Dynamic Pain): A patient who reports a resting pain score of 1/10 may experience excruciating pain of 9/10 upon coughing, deep breathing, or attempting to mobilize. Dynamic pain scores govern whether respiratory physiotherapy and early ambulation are achievable.
- Timing of Re-Assessment: Pain must be re-evaluated 30 minutes after intravenous analgesia and 60 minutes after oral analgesia to gauge therapeutic efficacy.
Structured Pain History: OPQRST
RCSI lists the OPQRST mnemonic under its Pain reading group, and it is the structure to use whenever a patient can self-report:
| Letter | Element | What to ask |
|---|---|---|
| O | Onset | When did it start? What were you doing? Sudden or gradual? |
| P | Provocation / Palliation | What makes it worse? What makes it better? Does movement, coughing or breathing change it? |
| Q | Quality | Describe it in your own words - sharp, dull, aching, burning, stabbing, cramping, throbbing? Burning or shooting pain with altered sensation suggests a neuropathic component that will respond poorly to opioids alone |
| R | Region / Radiation | Where is it? Does it move or spread anywhere? |
| S | Severity | Score it now, at its worst and at its best, using a validated scale - and score it at rest and on movement |
| T | Time / Timing | Constant or intermittent? How long does it last? Is there a pattern? What analgesia has been taken, when, and did it help? |
Record the patient's own words, not your paraphrase. "It's like a band tightening round my chest" carries information that "chest pain, moderate" destroys.
Validated Assessment Tools
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| POSTOPERATIVE PAIN ASSESSMENT TOOLS |
+-------------------+---------------------------------------------------------+
| NRS (0–10) | - Numerical Rating Scale: 0 (No Pain) to 10 (Worst Pain)|
| | - Mild: 1–3 | Moderate: 4–6 | Severe: 7–10 |
| | - Standard self-report tool for cognitively intact pts |
+-------------------+---------------------------------------------------------+
| VAS / VRS | - Visual Analogue Scale: 10 cm horizontal line |
| | - Verbal Rating Scale: None, Mild, Moderate, Severe |
+-------------------+---------------------------------------------------------+
| Abbey Pain Scale | - For patients with severe cognitive impairment/dementia|
| | - Evaluates 6 behavioural categories: vocalisation, |
| | facial expressions, body language, behavioural change,|
| | physiological signs, and physical body changes |
+-------------------+---------------------------------------------------------+
| PAINAD Scale | - Pain Assessment in Advanced Dementia |
| | - Evaluates breathing, negative vocalisation, facial |
| | expression, body language, and consolability (0–10) |
+-------------------+---------------------------------------------------------+
2. The Philosophy of Multimodal Analgesia
Modern perioperative care utilizes multimodal (balanced) analgesia, which combines two or more analgesic agents or techniques with distinct mechanisms of action. By targeting pain pathways at multiple anatomical levels—peripheral nociceptors, peripheral nerves, the dorsal horn of the spinal cord, and cerebral sensory centers—multimodal regimens achieve additive or synergistic analgesia while significantly reducing individual drug dosages and their associated adverse effects (an opioid-sparing effect).
[ SURGICAL TISSUE TRAUMA ]
|
v
+---------------------------------------+ ==> Inhibited by NSAIDs, Paracetamol,
| PERIPHERAL NOCICEPTOR ACTIVATION | and Local Anaesthetic infiltration
+---------------------------------------+
|
v (Conduction via A-delta & C fibres)
+---------------------------------------+ ==> Blocked by Regional / Epidural
| PERIPHERAL NERVE CONDUCTION | Local Anaesthetics (Bupivacaine)
+---------------------------------------+
|
v (Modulation in Dorsal Horn)
+---------------------------------------+ ==> Inhibited by Opioids, Ketamine,
| SPINAL CORD TRANSMISSION | Alpha-2 Agonists, and Epidural Opioids
+---------------------------------------+
|
v (Spinothalamic Tract to Cortex)
+---------------------------------------+ ==> Modulated by Systemic Opioids,
| CENTRAL CORTICAL PERCEPTION | Paracetamol, and Tramadol
+---------------------------------------+
The Step-Down Surgical WHO Ladder
While the original WHO Analgesic Ladder was designed to step up for progressive cancer pain, acute postoperative pain follows a Step-Down trajectory: beginning with potent multimodal regimens (Step 3 strong opioids + non-opioids) immediately post-op, and de-escalating to Step 2 weak opioids and Step 1 simple analgesics as surgical healing progresses.
| Step & Class | Mechanism & Common Agents | Dosing & Regimen | Key Nursing Cautions & Contraindications |
|---|---|---|---|
| Step 1: Non-Opioid Baseline<br>(Paracetamol) | Central COX-3 / endocannabinoid prostaglandin inhibition. | 1 g IV/PO 6-hourly (Max 4 g / 24h). | Reduce max daily dose to 2–3 g/24h in patients with low body weight (< 50 kg), chronic hepatic impairment, malnutrition, or chronic alcoholism. |
| Step 1: Non-Opioid Baseline<br>(NSAIDs / COX-2 Inhibitors) | Peripheral inhibition of cyclooxygenase (COX-1/COX-2), halting inflammatory prostanoid synthesis. (Ibuprofen, Diclofenac, Ketorolac) | Ibuprofen 400 mg TDS PO; Diclofenac 50–75 mg BD PO; Ketorolac 10–30 mg IV (max 48h). | Contraindications: Renal impairment (eGFR < 30 mL/min or acute oliguria), active peptic ulcer disease, aspirin-sensitive asthma, severe heart failure, high surgical bleeding risk. |
| Step 2: Weak Opioids | Mild mu-opioid receptor agonism ± monoamine reuptake inhibition. (Codeine, Tramadol) | Co-codamol (30/500 mg) 2 tabs QDS; Tramadol 50–100 mg QDS PO/IV. | Tramadol lowers seizure threshold and carries risk of serotonin syndrome if combined with SSRIs/MAOIs. Codeine requires CYP2D6 bioactivation (variable efficacy). |
| Step 3: Strong Opioids | Potent pure mu-opioid receptor agonism in CNS and dorsal horn. (Morphine, Oxycodone, Fentanyl) | Morphine 2–5 mg IV titration; Oxycodone 2–5 mg PO/IV; Fentanyl 25–50 mcg IV boluses. | Causes sedation, respiratory depression, nausea, vomiting, constipation, urinary retention, and pruritus. Sedation score precedes respiratory depression! |
3. Patient-Controlled Analgesia (PCA): Mechanics & Safety
Patient-Controlled Analgesia (PCA) allows a patient to self-administer small, programmed intravenous boluses of a strong opioid (typically morphine, fentanyl, or oxycodone) at the press of a handheld electronic button.
Core Programmable Parameters
- Demand Bolus Dose: The exact quantity of opioid delivered when the patient presses the button (e.g., Morphine 1 mg IV).
- Lockout Interval: A pre-set electronic safety window (typically 5 to 10 minutes). During the lockout period, any button press by the patient is electronically recorded as an attempt but will not trigger drug delivery. This lockout allows the preceding bolus to reach peak circulation and effect, preventing drug stacking and accidental overdose.
- Continuous (Background / Basal) Infusion: A steady hourly infusion delivered alongside demand boluses. In opioid-naive acute surgical patients, continuous background infusions are STRONGLY DISCOURAGED because they dramatically increase the risk of fatal nocturnal respiratory depression. Basal infusions are reserved for opioid-tolerant chronic pain or palliative patients.
- Attempt-to-Delivery Ratio: The PCA pump logs both successful deliveries and unsuccessful attempts during lockout. If a patient records 40 attempts but only receives 8 deliveries, it indicates severe unrelieved pain requiring immediate clinical review of the bolus dose or multimodal strategy.
[!CAUTION] The Cardinal Rule of PCA: PATIENT-ONLY ACTIVATION Only the patient may press the PCA button. Proxy dosing by family members, visitors, or nursing staff is strictly prohibited. The intrinsic physiological safety mechanism of PCA relies on self-regulation: if a patient becomes overly sedated, they fall asleep and physically cannot press the button, naturally protecting themselves from overdose. When a well-meaning relative presses the button while the patient is sleeping ("PCA by proxy"), this protective mechanism is bypassed, leading directly to fatal opioid-induced respiratory depression.
4. Opioid Monitoring, Toxicity & Emergency Naloxone Reversal
Clinical Principle: Sedation Precedes Respiratory Depression
Nurses must recognize that excessive sedation is the earliest and most reliable clinical warning sign of impending opioid-induced respiratory depression. A falling respiratory rate (< 8–10 breaths/min) is a late, critical manifestation. Sedation must be evaluated and recorded using a validated scale, such as the Pasero Opioid-Induced Sedation Scale (POSS):
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| PASERO OPIOID-INDUCED SEDATION SCALE (POSS) |
+---+-------------------------------------------------------------------------+
| S | Sleep, easy to arouse | Acceptable; no action needed |
+---+----------------------------------+--------------------------------------+
| 1 | Awake and alert | Acceptable; no action needed |
+---+----------------------------------+--------------------------------------+
| 2 | Slightly drowsy, easily aroused | Acceptable; no action needed |
+---+----------------------------------+--------------------------------------+
| 3 | Frequently drowsy, arousable, | UNACCEPTABLE; decrease opioid dose |
| | drifts off during conversation | by 25–50%; notify prescriber |
+---+----------------------------------+--------------------------------------+
| 4 | Somnolent, minimal or no response| CRITICAL EMERGENCY; stop opioid, |
| | to verbal / physical stimuli | summon team, administer NALOXONE |
+---+----------------------------------+--------------------------------------+
The Triad of Opioid Toxicity
- Severe Central Nervous System Depression: Somnolence, stupor, or coma (POSS 4).
- Severe Respiratory Depression: Bradypnoea (respiratory rate < 8 breaths/min), shallow hypopnoea, cyanosis, and falling SpO2.
- Miosis: Pinpoint, constricted pupils.
Emergency Naloxone (Narcan) Titration Protocol
Naloxone is a pure competitive mu-opioid receptor antagonist that rapidly reverses opioid-induced respiratory depression.
[!WARNING] The Danger of Rapid Large-Dose Naloxone Boluses Administering an undiluted 400 mcg (0.4 mg) to 2 mg intravenous bolus of naloxone to an acute postoperative patient instantly strips every opioid receptor in the body. This precipitates a catastrophic acute withdrawal crisis: excruciating surgical pain, massive sympathetic catecholamine discharge, severe hypertension, tachycardia, ventricular arrhythmias, acute pulmonary oedema, and cardiac arrest.
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| EVIDENCE-BASED NALOXONE TITRATION PROTOCOL |
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| 1. IMMEDIATE RESUSCITATION & ESCALATION |
| - Stop all opioid infusions / PCA immediately. |
| - Call emergency medical team / resuscitation code. |
| - Support airway: chin lift / jaw thrust; apply high-flow oxygen. |
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v
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| 2. DILUTION PROTOCOL |
| - Draw up one 400 mcg (0.4 mg / 1 mL) ampoule of Naloxone. |
| - Dilute with 9 mL of Sterile Normal Saline (0.9% NaCl) in a 10 mL syringe|
| - Yields a concentration of: 40 mcg per mL. |
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v
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| 3. SLOW TITRATED ADMINISTRATION |
| - Administer 40 to 80 mcg (1 to 2 mL) slowly IV every 2 to 3 minutes. |
| - TITRATION ENDPOINT: Patient is arousable, breathing comfortably at |
| respiratory rate > 10–12 breaths/min, without triggering severe pain. |
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v
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| 4. RENARCOTISATION MONITORING |
| - Naloxone plasma half-life is short (30 to 60 minutes). |
| - Morphine and Oxycodone have longer half-lives (2 to 4 hours). |
| - As naloxone metabolises, the patient may relapse into coma and apnoea! |
| - Continue close INEWS monitoring; prepare repeat doses or IV infusion. |
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5. Epidural Analgesia: Dermatomes, Bromage Scale & Emergencies
Continuous epidural analgesia provides profound regional pain relief following major thoracic, abdominal, or pelvic surgery. It involves an indwelling catheter placed into the epidural space delivering a continuous infusion of a low-concentration local anaesthetic (e.g., Bupivacaine 0.1% or 0.125%) combined with a lipophilic opioid (e.g., Fentanyl 2 mcg/mL).
Systematic Nursing Monitoring Protocol
- Sensory Block Assessment (Cold Test): Ice or an ethyl chloride cold spray is applied bilaterally to dermatomes from C6 down to S1. The patient indicates where the sensation of cold changes from sharp cold to blunt or absent. The upper and lower sensory block levels must be documented every 4 hours. The block should match the surgical incision (e.g., T4–T10 for upper laparotomy; T10–L1 for lower abdominal surgery). A sensory block rising above T4 can block cardiac accelerator fibres (causing severe bradycardia and hypotension) and intercostal respiratory muscles.
- Motor Block Assessment (The Bromage Scale): Local anaesthetics can penetrate motor nerves, causing lower limb weakness. The nurse assesses lower extremity motor function using the standardized Bromage Scale:
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| THE BROMAGE SCALE |
+---+--------------------+----------------------------------------------------+
| 0 | No Motor Block | Full flexion of knees and feet (0% block) |
+---+--------------------+----------------------------------------------------+
| 1 | Partial Block | Just able to flex knees, full movement of feet |
| | | (approx 33% block) |
+---+--------------------+----------------------------------------------------+
| 2 | Almost Complete | Unable to flex knees, but able to move feet |
| | | (approx 66% block) |
+---+--------------------+----------------------------------------------------+
| 3 | Complete Block | Unable to move feet or knees (100% block) |
+---+--------------------+----------------------------------------------------+
[!NOTE] In thoracic epidural infusions, lower limb motor block should ideally be Bromage 0. Any sudden progression of motor block, or any asymmetric (unilateral) motor block, is an alarming clinical finding requiring immediate medical evaluation.
- Blood Pressure & Sympathetic Blockade: Local anaesthetics in the epidural space block sympathetic vasomotor fibres, causing profound arterial and venous vasodilation, venous pooling, and systemic hypotension. Patients require prescribed IV fluid boluses and vasopressor orders (e.g., ephedrine, metaraminol).
- Catheter Site & Dressing Care: The insertion site must be covered with a transparent occlusive dressing. Inspect every shift for: CSF leakage (clear watery fluid, which causes postural post-dural puncture headache), bleeding, localized erythema, or purulent exudate.
- Catheter Removal Safety & LMWH Timing: Check platelet count (> 80–100 × 10^9/L) and coagulation profile prior to removal. To prevent spinal/epidural haematoma:
- Withhold prophylactic LMWH for at least 12 hours prior to epidural catheter removal.
- After catheter removal, wait at least 4 hours before administering the next LMWH dose.
The Catastrophic Emergency: Epidural Haematoma / Abscess
An expanding epidural haematoma or abscess compresses the spinal cord or cauda equina within the rigid spinal canal, leading to permanent paraplegia if not surgically decompressed within 6 to 8 hours of onset.
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| CLASSIC TRIAD OF COMPRESSIVE EPIDURAL HAEMATOMA |
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| 1. SEVERE LOCALIZED BACK PAIN: New-onset, intense, sharp or throbbing pain |
| around the catheter site or radiating down the lower limbs. |
+-----------------------------------------------------------------------------+
| 2. PROGRESSIVE MOTOR & SENSORY DEFICIT: Rapidly increasing Bromage score |
| (advancing from 0 to 2 or 3 in hours) and ascending lower-limb numbness. |
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| 3. SPHINCTER DYSFUNCTION: Acute new-onset urinary retention or faecal |
| incontinence. |
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|
v
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| EMERGENCY NURSING ACTION: |
| - STOP THE EPIDURAL INFUSION IMMEDIATELY. |
| - Keep patient flat on bed rest. |
| - Immediately page anaesthetist and surgical/neurosurgical team. |
| - Arrange STAT EMERGENCY MRI OF THE SPINE. |
| - Prepare patient for emergency surgical decompression (laminectomy). |
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While conducting night rounds on a surgical ward, a nurse enters the room of a 48-year-old patient who underwent an open gastrectomy 12 hours ago and is receiving intravenous morphine via a Patient-Controlled Analgesia (PCA) device. The patient is sound asleep and snoring gently, but the patient's spouse is observed pressing the PCA demand button. When questioned, the spouse states: 'He was groaning in his sleep earlier, so I wanted to make sure his pain doesn't wake him up.' What is the nurse's priority response and action?
A 52-year-old post-laparotomy patient receiving intravenous oxycodone via a Patient-Controlled Analgesia (PCA) pump is found somnolent and unarousable to verbal or physical stimuli (sedation score 4). The nurse notes a respiratory rate of 6 breaths/min, pinpoint pupils, and an oxygen saturation of 84% on room air. The nurse stops the infusion, applies high-flow oxygen, and summons the emergency medical team. What is the evidence-based pharmacological method for administering naloxone in this acute postoperative setting?
A 60-year-old patient on the surgical ward is receiving a continuous thoracic epidural infusion of bupivacaine 0.125% and fentanyl 2 mcg/mL following an extensive low anterior resection. Two hours ago, the patient had no motor block (Bromage score 0). The patient now complains of a new, severe, sharp aching pain in their mid-back around the epidural catheter site, and the nurse observes that the patient is now completely unable to move their feet or bend their knees (Bromage score 3). What is the nurse's priority emergency action?