01Core principlesThe concepts and mechanisms needed to understand the subject.
Acute postoperative pain is a changing clinical state produced by tissue injury, inflammation, nerve injury and patient-specific vulnerability. Good management supports breathing, coughing, sleep, mobilisation and rehabilitation. Complete absence of pain is rarely a safe or realistic goal. Function-led assessment asks what the patient can do and whether analgesia improves recovery without unacceptable adverse effects.
The 2024 Association of Anaesthetists and British Pain Society consensus recommends multimodal, personalised and procedure-specific care. Paracetamol, an NSAID where appropriate, regional analgesia and selected adjuncts can reduce opioid requirement. Each component has limits: NSAIDs may be unsuitable with renal injury or bleeding risk; local anaesthetic techniques need trained follow-up; sedating adjuncts may compound respiratory depression.
Opioids remain useful for moderate to severe acute pain, but dose should be the lowest that achieves a functional purpose and oral immediate-release formulations are preferred when possible. Sedation, airway obstruction and reduced ventilation can occur before oxygen saturation falls, particularly with supplemental oxygen. Concurrent benzodiazepines, gabapentinoids or other sedatives increase risk and require careful justification and monitoring.
Pain that changes character or fails to follow the expected trajectory requires diagnosis. A larger analgesic dose cannot safely substitute for assessing bleeding, infection, ischaemia, compartment syndrome, nerve injury or an anastomotic problem. The acute pain team adds value when advanced techniques, opioid tolerance, complex comorbidity or persistent severe pain exceed the routine pathway.
Key points
- Assess what pain prevents the patient from doing, its site and trajectory, and whether the pattern fits the operation; a number alone cannot distinguish undertreatment from a complication.
- Use procedure-specific multimodal analgesia where suitable: combine non-opioid medicines, regional techniques and non-pharmacological measures, then reserve immediate-release opioid for defined functional goals.
- Sedation is an early warning of opioid-induced ventilatory impairment; check it with respiratory observations and escalate before profound hypoxaemia develops.
- Review renal, hepatic, respiratory and gastrointestinal risk, frailty, sleep apnoea, chronic pain, pre-existing opioid exposure and interacting sedatives before prescribing.
- Avoid routine modified-release opioids and compound opioid-paracetamol products for acute postoperative pain because titration and safe de-escalation are harder.
- Discharge opioid supply should be small, usually no more than seven days under the UK consensus, with written taper, storage, disposal and help-seeking advice.
02Mechanisms and patternsImportant relationships and how to distinguish them.
Ask whether pain limits deep breathing, coughing, movement, sleep, self-care or physiotherapy and reassess after intervention.
Compare location, quality and change over time with the operation, drains, dressings and examination rather than accepting a single score.
Increasing drowsiness, snoring obstruction, slow or shallow breathing and reduced responsiveness require immediate opioid review and airway support.
Burning, electric shocks, allodynia, sensory change or weakness suggests nerve involvement and may need targeted assessment.
Sudden escalation, instability, peritonism, tense swelling or pain on passive stretch demands urgent surgical review.
Chronic pain, high-dose preoperative opioids, anxiety, depression and frailty predict a harder recovery and need a prospective plan.
03Interpreting evidenceInformation, measurements and their limitations.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Bedside pain and function assessment - Why
- Define pain mechanism, severity, functional limitation and response to treatment.
- Interpretation and limitations
- A falling number without improved breathing or movement may not represent success; new focal findings or deterioration redirects assessment toward a complication.
- 02
Sedation and respiratory observations - Why
- Detect opioid-induced ventilatory impairment before cardiorespiratory arrest.
- Interpretation and limitations
- New sedation or reduced ventilation is actionable even when supplemental oxygen preserves saturation; stop further opioid, support the airway and escalate.
- 03
Renal and hepatic function - Why
- Guide selection and dosing of analgesics and identify organ injury contributing to adverse effects.
- Interpretation and limitations
- Acute kidney injury increases risk from NSAIDs and renally cleared opioids; hepatic disease changes paracetamol and opioid decisions and requires individual prescribing.
- 04
Focused surgical examination - Why
- Identify bleeding, infection, ischaemia, compartment syndrome, urinary retention or another postoperative cause.
- Interpretation and limitations
- Disproportionate pain plus new physical signs should trigger cause-specific imaging, laboratory tests or operative review without waiting for analgesic failure.
- 05
Analgesic administration record - Why
- Reconstruct drug, route, time, response and cumulative sedative burden.
- Interpretation and limitations
- Repeated doses without benefit suggest a wrong mechanism, failed delivery or complication; duplicate paracetamol and overlapping sedatives can create avoidable toxicity.
04Applied reasoningWorked examples connecting principles to decisions.
01Worked case: routine recoveryPain limiting breathing after abdominal surgeryA stable adult reports incisional pain that prevents deep breathing and mobilisation after major abdominal surgery.+
- 1Examine the patient and wound, review observations and operative events, confirm that the pattern is expected, and set functional goals for cough, deep breathing and mobilisation.
- 2Give regular non-opioid analgesia where suitable, check any regional technique and add a small titrated immediate-release opioid dose if function remains limited.
- 3Reassess function, pain, nausea, sedation and ventilation after treatment; involve the acute pain service if goals remain unmet or adverse effects limit titration.
- 4Reduce treatment as recovery progresses and prepare a discharge plan that names each medicine, duration, taper and safety advice.
02Opioid emergencyIncreasing sedation after repeated opioid dosesA postoperative patient becomes difficult to rouse with shallow breathing after several opioid doses.+
- 1Call for help, stop opioid administration, open and support the airway, give oxygen and assess breathing and circulation continuously.
- 2Provide ventilation if inadequate and use titrated naloxone under the local emergency protocol while preserving analgesia where possible.
- 3Seek the cause, account for all sedatives and organ impairment, and continue enhanced observation because toxicity may recur after naloxone wears off.
03Unexpected painEscalating limb pain beneath a regional blockPain increases rapidly after limb surgery despite an apparently working block and passive movement is very painful.+
- 1Remove restrictive external causes where appropriate, examine perfusion, swelling, motor and sensory function, and summon urgent surgical assessment.
- 2Do not delay compartment-pressure assessment or definitive surgical decision while repeatedly increasing analgesia or waiting for the block to regress.
- 3Continue safe analgesia and physiological support while documenting the onset, progression, examinations and time of escalation.
05Relevant medicines and safetySpecific regimens and precautions where medicines are relevant.
Paracetamol
Use the locally approved regular adult dose, reducing or avoiding it when low body weight, malnutrition or hepatic disease requires.Count every combination product and all routes toward the daily total; overdose may be occult and demands urgent toxicology management.
Non-steroidal anti-inflammatory drug
Use the lowest effective adult dose for the shortest suitable period when procedure and patient risks permit.Review renal function, hydration, ulcer and bleeding risk, asthma sensitivity and cardiovascular disease; avoid reflex continuation during acute kidney injury.
Immediate-release opioid
Give a small age-appropriate oral dose and titrate to a defined functional response with reassessment.Sedation, ventilatory impairment, nausea, constipation and persistent use are important harms; avoid routine modified-release dosing and minimise co-sedatives.
Naloxone rescue
Titrate intravenous naloxone in small increments under the emergency protocol when opioid-related ventilation is inadequate.Abrupt full reversal can cause severe pain and sympathetic stress; recurrence is possible because many opioids outlast naloxone, so monitoring must continue.
06Checking understandingVerify the reasoning, revisit uncertainties and apply feedback.
- Record pain at rest and on the movement needed for recovery, then document whether treatment improves function.
- When opioids are used, monitor sedation with respiratory rate, breathing quality, oxygenation and other observations appropriate to risk.
- Inspect epidural or peripheral catheter sites and reassess block distribution, motor function, pump settings and cumulative local-anaesthetic exposure.
- Trend nausea, vomiting, bowel function, urinary retention, pruritus, confusion and mobilisation because adverse effects can negate analgesic benefit.
- At every transition, reconcile the inpatient and discharge prescriptions, remove duplicate or modified-release opioids, and communicate a stop plan.
07Special situationsVariants, exceptions and circumstances that change the usual approach.
Movement reveals value
A treatment that lowers a score but leaves the patient too sedated to cough or mobilise has not met the recovery goal.
Trajectory carries diagnosis
The direction and character of pain over time often distinguishes expected tissue injury from bleeding, infection, ischaemia or nerve damage.
Oxygen can mask hypoventilation
Supplemental oxygen may preserve saturation while carbon dioxide rises, so sedation and ventilation still require direct assessment.
Discharge creates exposure
The quantity and formulation supplied after surgery influence persistent use, diversion and overdose risk beyond the hospital episode.
Regional care needs ownership
A catheter or dense block is safe only when ward staff can assess it, respond to complications and reach specialist help promptly.
08Common pitfallsFrequent interpretation and management errors.
- 01
Treating an unexpected new pain pattern with serial opioid boluses before examining for a surgical complication.
- 02
Using a pain score as the only outcome while coughing, mobility and sedation deteriorate.
- 03
Prescribing modified-release opioid routinely for short-lived acute pain in an opioid-naive adult.
- 04
Combining opioids with several sedatives without a clear indication and enhanced respiratory monitoring.
- 05
Sending excess opioid home without duration, taper, safe storage, disposal and support instructions.
- 06
Assuming a functioning block excludes compartment syndrome or postoperative nerve injury.