Postoperative pain

Postoperative pain is acute pain caused by surgical trauma, which is expected to settle within days to weeks. Poorly controlled pain delays mobilisation, impairs breathing and wound healing, raises the risk of delirium and thromboembolism, and predisposes to chronic postsurgical pain.

Clinical relevance. Moderate to severe pain affects over half of surgical patients, and chronic postsurgical pain develops in about 10 to 30% depending on the operation (thoracotomy, mastectomy, hernia repair, amputation, knee replacement). Opioid related harm after surgery includes respiratory depression, ileus, delirium, and persistent use.

Mechanisms. Tissue injury releases inflammatory mediators that sensitise nociceptors (peripheral sensitisation), and sustained input leads to central sensitisation. Visceral, somatic and neuropathic components often coexist.

Classification.

• By mechanism: nociceptive somatic (incisional), visceral (bowel, bladder), neuropathic (nerve injury, phantom limb).
• By tempo: early (first 72 hours), subacute (up to 3 months) and chronic postsurgical pain (over 3 months).
• By context: opioid naive, opioid tolerant (daily opioid use for over 1 week), and those with chronic pain, substance use or sleep apnoea.

Key distinctions. Pain that escalates after an initial improvement, or is out of proportion to the operation, needs a search for a complication rather than more analgesia.

History.

• Operation, anaesthetic and regional techniques, analgesia given so far, and time of last doses.
• Pain site, character, severity at rest and on movement (numeric scale 0 to 10), effect on breathing, coughing, sleep and mobilisation, and the trajectory since surgery.
• Previous pain and opioid use, long term medicines (opioids, gabapentinoids, antidepressants, benzodiazepines), alcohol and drug use, and previous response to analgesics.
• Allergies and adverse effects (nausea, itch, sedation, constipation).
• Comorbidities: kidney or liver disease, sleep apnoea, respiratory disease, peptic ulcer, heart failure, asthma, pregnancy, age and frailty.

Examination.

• Observations: sedation score, respiratory rate, oxygen saturation, blood pressure, heart rate, temperature.
• Wound, dressing, tight casts or bandages, drains and catheters. Abdomen (distension, tenderness, peritonism). Limbs (compartment tension, perfusion, neurological deficit).
• Regional block or epidural: sensory level, motor block, insertion site, signs of haematoma, infection or toxicity.
• Mental state (delirium, anxiety). In patients who cannot report pain (dementia, intubation), use a behavioural scale such as PAINAD or the Critical Care Pain Observation Tool.

Red flags.

• Pain increasing or changing in character after initial improvement, or severe pain with fever, tachycardia, hypotension, rigid abdomen or distension (leak, ischaemia, bleeding, perforation).
• Severe limb pain with tense swelling, pain on passive stretch, paraesthesia or pulselessness (compartment syndrome, arterial occlusion).
• New chest pain, breathlessness or calf pain (myocardial infarction, pulmonary embolism, deep vein thrombosis).
• Severe back pain with leg weakness, numbness or sphincter dysfunction after epidural or spinal anaesthesia (epidural haematoma or abscess, needing emergency MRI).
• Sedation, respiratory rate under 10 breaths/min or pinpoint pupils (opioid toxicity).
• Perioral numbness, tinnitus, seizure or arrhythmia after a local anaesthetic block (toxicity).
• Delirium or agitation.

Special groups. Older adults need lower doses and slower titration. Kidney impairment needs adjusted opioids and no NSAIDs when eGFR is under 30 mL/min. Obstructive sleep apnoea increases the risk of respiratory depression. Opioid tolerant patients need baseline opioids continued plus extra analgesia. Children need weight based dosing. Pregnancy limits NSAIDs.

Expected surgical pain. Incisional, visceral, muscle and positional pain, shoulder tip pain after laparoscopy (diaphragm irritation by carbon dioxide), pain from drains, catheters and tubes.

Surgical complications.

• Anastomotic leak and peritonitis, bowel obstruction or ileus, perforation, ischaemia (mesenteric, limb, graft).
• Haematoma, bleeding, wound infection, abscess, dehiscence, fascial closure too tight.
• Compartment syndrome (limb, abdominal), nerve injury, positioning injury, retained foreign body, pancreatitis, urinary retention, urinary tract injury.

Medical complications. Myocardial infarction, pulmonary embolism, pneumonia, pneumothorax, pleural effusion, deep vein thrombosis, gout, acute gastric stress ulcer, constipation, urinary retention. Regional anaesthesia related. Block failure, epidural haematoma or abscess, nerve injury, local anaesthetic systemic toxicity, high block, post dural puncture headache.

Neuropathic. Phantom limb pain, complex regional pain syndrome, intercostal neuralgia, postherpetic neuralgia, central sensitisation.

Drug related and other. Opioid induced hyperalgesia, opioid withdrawal, alcohol withdrawal, delirium and anxiety, drug seeking behaviour.

Step 1. Score pain at rest and on movement with a numeric scale (or behavioural scale), set functional goals (deep breathing, coughing, walking), and check sedation and respiratory rate before each opioid dose.

Step 2. Exclude a complication when pain is atypical, rising or associated with abnormal observations: repeat examination, full blood count, CRP, lactate, electrolytes, creatinine, ECG and troponin, and a blood gas. Add imaging directed by the findings (CT abdomen, duplex, CT pulmonary angiography, chest radiograph, ultrasound).

Step 3. Limb pain with tense compartments needs urgent surgical assessment, with compartment pressure measurement only if the diagnosis is doubtful (delta pressure, diastolic pressure minus compartment pressure, under 30 mmHg supports the diagnosis). Back pain with neurological signs after neuraxial block needs emergency MRI.

Step 4. Review analgesic plan for dose, route, timing and adverse effects. Check for renal and hepatic function and interactions.

Limitations. Pain scores vary between patients and are unreliable in delirium and dementia. Raised inflammatory markers after surgery are non-specific.

Principles. Use multimodal analgesia: scheduled non-opioid drugs, regional or local techniques where possible, and titrated opioids for breakthrough pain. Treat early, reassess every 30 to 60 minutes after changes, and aim for pain low enough to cough, breathe deeply and mobilise. Prescribe a laxative and an antiemetic with opioids.

Non-opioid foundation.

• Paracetamol 1 g orally or IV every 6 hours (maximum 4 g daily; 3 g daily if weight under 50 kg, malnutrition, alcohol excess or liver disease).
• IV paracetamol dose if weight under 50 kg: 15 mg/kg every 6 hours, maximum 60 mg/kg daily. Monitor liver tests with prolonged use.
• Ibuprofen 400 mg orally every 8 hours with food (maximum 1.2 g daily without specialist advice and 2.4 g daily under supervision), or diclofenac 50 mg orally every 8 hours (maximum 150 mg daily), or naproxen 250 to 500 mg orally every 12 hours (maximum 1 g daily), for up to 5 days.
• NSAID monitoring: blood pressure, creatinine, haemoglobin and bleeding.
• Avoid NSAIDs with eGFR under 30 mL/min, active peptic ulcer, heart failure, coronary artery bypass grafting, anticoagulation, aspirin sensitive asthma, third trimester and high bleeding risk.
• Add omeprazole 20 mg orally once daily in patients at risk of gastrointestinal bleeding.
• Ketorolac 15 mg IV every 6 hours (maximum 60 mg daily and 5 days). Use 10 mg every 6 hours with a maximum of 40 mg daily if over 65 years, weight under 50 kg or kidney impairment.
• Avoid ketorolac with eGFR under 30 mL/min, active peptic ulcer, heart failure, anticoagulation, bleeding risk and aspirin sensitive asthma.
• Dexamethasone 4 to 8 mg IV once at induction reduces pain, nausea and opioid use. Monitor glucose in diabetes.

Local and regional techniques.

• Local anaesthetic infiltration at the wound, and continuous wound catheters, reduce opioid use.
• Maximum doses for adults: lidocaine plain 4.5 mg/kg (maximum 300 mg), with adrenaline 7 mg/kg (maximum 500 mg), bupivacaine 2 mg/kg (maximum 150 mg), levobupivacaine or ropivacaine up to 3 mg/kg (ropivacaine maximum 225 mg for a single dose).
• Use peripheral nerve blocks and epidural or spinal analgesia for major abdominal, thoracic, orthopaedic and vascular surgery. Observe the insertion site, motor block, level, blood pressure, and neurological deficit every 4 hours.
• Time anticoagulant doses around neuraxial puncture and catheter removal. For prophylactic enoxaparin, remove the catheter at least 12 hours after the last dose and give the next dose at least 4 hours after removal.
• Local anaesthetic systemic toxicity: stop injection, call for help, give oxygen, and treat seizures with a benzodiazepine.
• Give lipid emulsion 20% 1.5 mL/kg IV over 1 minute then 15 mL/kg/hour. Repeat the bolus up to twice and double the infusion rate if needed, up to a maximum of 12 mL/kg.
• Avoid vasopressin and calcium channel blockers. Continue resuscitation, which may be prolonged.

Opioids (titrated, lowest effective dose, shortest duration).

• Intravenous morphine in recovery: 1 to 2 mg IV every 3 to 5 minutes until the patient is comfortable (reduce to 1 mg in older adults or frail patients). Monitor sedation and respiratory rate. Then move to oral or patient controlled administration.
• Patient controlled analgesia with morphine: bolus 1 mg, lockout 5 to 10 minutes, no background infusion in opioid naive adults, with a four hour limit set locally.
• Monitor sedation, respiratory rate, saturation and pain hourly for the first 4 hours and then every 4 hours.
• Reduce the dose in older adults, kidney impairment and sleep apnoea. Avoid morphine when eGFR is under 30 mL/min; use fentanyl or hydromorphone.
• Oral oxycodone immediate release 2.5 to 5 mg every 4 hours as needed. Start at 2.5 mg in patients over 65 or with kidney or liver impairment, and increase by 2.5 to 5 mg up to a single dose of 10 mg.
• Reassess oxycodone daily. Avoid more than 90 mg oral morphine equivalent daily without review.
• Tramadol 50 mg orally every 6 hours as needed (maximum 400 mg daily, or 300 mg daily over 75 years; maximum 200 mg daily if CrCl under 30 mL/min with a 12 hour interval).
• Avoid tramadol in epilepsy and with serotonergic drugs. Monitor for nausea, sedation and seizures.
• Opioid tolerant patients: continue the baseline opioid or its equivalent (convert and reduce by 25 to 30% when switching opioids), add multimodal agents, and expect higher breakthrough needs (10 to 20% of the total daily dose each time).
• Reversal of opioid toxicity: naloxone 40 to 100 micrograms IV every 2 minutes until respiratory rate is over 10 breaths/min. The maximum for a first response is 400 micrograms. Then give an infusion at 2 micrograms/kg/hour when long acting drugs are involved.
• Full reversal returns pain and may cause withdrawal. Observe for resedation for 2 hours or more.
• Antiemetic: ondansetron 4 mg IV every 8 hours (maximum 16 mg IV in a single dose and 24 mg daily; monitor QTc).
• Laxative: macrogol 1 sachet orally daily or senna 7.5 to 15 mg orally at night, adjusted to bowel function.
• Avoid opioid with benzodiazepines and sedatives when possible.

Adjuvants for neuropathic or severe pain.

Gabapentin 100 to 300 mg orally at night, increased every 1 to 3 days to 300 mg three times daily (maximum 3600 mg daily). Renal dosing: for CrCl 30 to 59 mL/min 400 to 1400 mg daily in two doses; for CrCl 15 to 29 mL/min 200 to 700 mg once daily; under 15 mL/min 100 to 300 mg once daily.

Monitor sedation, dizziness and respiratory depression, especially with opioids and in older adults. Do not use gabapentin routinely as a preoperative drug in older patients.

Ketamine 0.1 to 0.25 mg/kg IV bolus then infusion 0.1 to 0.25 mg/kg/hour for severe pain not controlled by opioids under specialist supervision, with monitoring for hallucinations, blood pressure and heart rate.

Children. Paracetamol 15 mg/kg orally every 4 to 6 hours (maximum 60 mg/kg daily and 4 g daily), ibuprofen 10 mg/kg orally every 6 to 8 hours (maximum 40 mg/kg daily), and morphine 0.05 to 0.1 mg/kg IV titrated. Avoid codeine and tramadol in children under 12 years and after tonsillectomy.

Non-drug measures. Early mobilisation, splinting the wound when coughing, positioning, cold packs, reassurance and information.

Monitoring. Pain score, sedation and respiratory rate every 1 to 4 hours (and after each dose change), bowel function daily, urine output, and regional block checks. Reduce analgesics step by step, stopping opioids first. Plan discharge analgesia with the shortest opioid course (for example 3 to 5 days), a written plan and a clear stop date.

Referral and escalation. Acute pain service for patients with complex pain, opioid tolerance, regional catheters, or pain not controlled in 24 hours. Surgeon for suspected complication. Anaesthetist urgently for suspected local anaesthetic toxicity or high block. Chronic pain service for persistent pain at 3 months.

Admission criteria. Uncontrolled pain after discharge, suspected complication, respiratory depression, sedation, epidural or block complications, and inability to take oral analgesia.

Discharge and safety netting. Discharge with simple scheduled analgesia, a limited opioid supply when needed, laxatives, driving and safety advice, and a taper plan. Patients return for worsening pain, fever, vomiting, abdominal distension, leg or chest pain, sedation, confusion or new neurological symptoms.