Postoperative pain and opioid analgesia

• Pain after surgery is expected, but it is not harmless. Poorly controlled pain slows recovery, increases complications, prolongs hospital stay and can evolve into chronic pain at the surgical site.
• The modern default is multimodal analgesia: two or more drugs or techniques with different mechanisms, combining regional blocks, non-opioid analgesics and, when needed, opioids rather than relying on a single drug.
• Paracetamol (acetaminophen) and non-steroidal anti-inflammatory drugs (NSAIDs) are the foundation of most regimens. Opioids are added for moderate to severe pain and are used at the lowest effective dose for the shortest time.
• Regional techniques (peripheral nerve blocks, epidural analgesia) are central to multimodal care and allow large reductions in opioid dose. Epidural analgesia is particularly useful after thoracic and abdominal surgery.
• Opioid-related adverse effects, especially respiratory depression and sedation, are prevented by risk assessment, dose reduction in older adults, close monitoring and ready access to naloxone.
• A proportion of patients develop chronic postsurgical pain, defined as pain at or near the surgical site that persists for more than three months. Better acute pain control is one of the few modifiable ways to reduce that risk.

By the end of this page you should be able to:

1. Explain why adequate postoperative analgesia is part of recovery after surgery, not a comfort measure alone.
2. Classify postoperative pain by mechanism and time course, and choose appropriate assessment tools.
3. Apply the World Health Organization (WHO) analgesic ladder and describe where modern multimodal analgesia modifies it.
4. Plan a multimodal regimen built on paracetamol and NSAIDs, with regional techniques, opioids and patient-controlled analgesia added at the right time.
5. Recognise and manage opioid-related adverse effects, including respiratory depression, and state the key cautions about opioid dose conversion.
6. Identify risk factors for progression from acute to chronic postsurgical pain and describe how transitional pain services aim to reduce it.

Postoperative pain is not a single experience. It is a group of physiological, psychological and behavioural responses that follow surgical injury. It typically peaks 24 to 72 hours after surgery and gradually resolves as tissues heal. ^[1] Surgical injury produces somatic pain from skin and deep tissue, visceral pain from traction and ischaemia of organs, inflammatory pain from the tissue repair response and sometimes neuropathic pain from nerve injury. Preoperative anxiety, depression and fear also amplify it. ^[1]

The need for management is not theoretical. A European study found that 72.8% of patients experienced acute postoperative pain, and 48.7% had moderate to severe pain. ^[1] In a survey of 26,193 surgical cases across 122 hospitals in China, 48.7% of patients had moderate to severe pain on the first day after surgery. ^[1] Acute pain does not merely hurt: it increases complications, delays recovery, prolongs hospital stay and raises costs. ^[1] Unresolved pain also feeds into sensitisation, and a proportion of patients develop pain at the surgical site that outlasts healing. Effective analgesia therefore sits at the centre of enhanced recovery after surgery (ERAS), with the aims of improving recovery, reducing opioid consumption and shortening stay. ^[1]

The different mechanisms of postoperative pain matter because they respond to different drugs.

• Somatic pain arises from incision of skin, muscle and fascia. It is well localised and usually responds to local infiltration, nerve block and NSAIDs.
• Visceral pain follows manipulation, distension or ischaemia of organs. It is diffuse, poorly localised and often accompanied by autonomic symptoms such as nausea and sweating.
• Inflammatory pain is driven by prostaglandins, bradykinin and other mediators released at the operative site. It responds to NSAIDs and regional techniques.
• Neuropathic pain follows injury to a peripheral nerve, for example intercostal or inguinal nerves during surgery, and presents with burning, shooting or electric qualities.

Postoperative pain also has a time course. In the first 24 to 72 hours it is dominated by nociceptive and inflammatory mechanisms. After that, as movement increases, musculoskeletal and neuropathic components become more apparent. The intensity and duration of this early pain are among the strongest predictors of who will develop persistent pain. ^[1]

Pain is subjective, so it must be measured rather than guessed. For rapid bedside assessment, unidimensional tools are used: the visual analogue scale (VAS), numeric rating scale (NRS) from 0 to 10, faces pain scale (FPS) and verbal descriptor scale (VDS). ^[1] For fuller evaluation, multidimensional tools such as the Brief Pain Inventory (BPI) or McGill Pain Questionnaire (MPQ) capture pain location, quality, affect and interference with sleep and function. ^[1] BPI is recommended in particular for assessing postoperative pain because it captures psychological features as well. ^[1]

A useful modern addition is function-based assessment: asking whether the patient can cough, deep breathe, sit, transfer and comply with physiotherapy, rather than treating a score in isolation. ^[1] Pain assessment should be repeated at rest and with movement, in the first hours after surgery and whenever analgesia is changed. Assessment tools have no single best choice; unidimensional scales suit rapid screening, while multidimensional scales suit comprehensive evaluation. ^[1]

The WHO analgesic ladder was proposed in 1986 as a framework for the stepwise treatment of cancer pain. ^[2] It has since been used much more widely, including for many types of acute and chronic pain. ^[2] It remains a good way to teach ordered thinking about analgesia.

The original three steps are: ^[2]

1. Mild pain: non-opioid analgesics such as a non-steroidal anti-inflammatory drug or paracetamol, with or without adjuvants. ^[2]
2. Mild to moderate pain: a weak opioid such as codeine or tramadol, with or without a non-opioid analgesic and adjuvants. ^[2]
3. Moderate to severe pain: a strong opioid such as morphine, oxycodone or hydromorphone, with or without a non-opioid analgesic and adjuvants.

A modified version later added interventional pain management as a fourth step. ^[2] The ladder's strengths are that it starts from the simplest effective medicine, adds rather than replaces analgesics and gives a logical order. Its limitation today is that it reads like a single-drug staircase. Modern postoperative care instead runs several steps at once: regional block, paracetamol, NSAID and a low dose of opioid together. The ladder is therefore better used as a scaffold for thinking than as a literal instruction to work upwards one drug at a time. Multi-society guidelines from 2016 onwards have reinforced multimodal analgesia as the default perioperative strategy, and the 2025 guideline discussed throughout this page gives 33 recommendations across 17 clinical questions for adult postoperative pain. ^[1]

Multimodal analgesia is the combination of two or more analgesic drugs or techniques with different mechanisms, acting at different points along the pain pathway from incision through spinal transmission to perception. ^[1] Combining paracetamol, NSAIDs, regional blockade and opioids in this way produces additive or synergistic effects, reduces the dose and adverse effects of any single drug, encourages early mobilisation and accelerates recovery. ^[1]

A systematic review of 110 randomised trials found that multimodal analgesia reduced postoperative pain scores relative to single-agent analgesia, reduced perioperative opioid use, lowered nausea and vomiting, reduced sedation scores, improved quality-of-recovery scores and shortened average hospital stay, though many of these analyses were heterogeneous. ^[1] On this basis, multimodal analgesia is recommended perioperatively to improve analgesia and reduce opioid consumption, reduce nausea and vomiting, reduce sedation, improve recovery quality and patient satisfaction and shorten hospital stay. ^[1]

Multimodal analgesia is not a fixed recipe. It is tailored to the operation, the patient and the available resources: peripheral block for shoulder arthroscopy, epidural for open thoracic surgery, simple infiltration for day-case procedures. Procedure-specific regimens are increasingly recommended, with non-opioid analgesics and regional techniques as the base and opioids reserved for rescue. ^[1]

Paracetamol (acetaminophen) and NSAIDs are the backbone of postoperative analgesia in adults without contraindications. ^[1] They are recommended to improve analgesia and reduce opioid use. ^[1] Paracetamol has central analgesic and antipyretic effects and a favourable adverse-effect profile at standard doses. NSAIDs reduce inflammation and hyperalgesia at the operative site by inhibiting cyclo-oxygenase. Used together, paracetamol and an NSAID are superior to either drug alone. ^[1]

This combination is worth stressing. Paracetamol and NSAIDs work by different mechanisms, so their combined effect can be synergistic: one review found that paracetamol plus an NSAID produced better analgesia and less rescue medication use than monotherapy. ^[1] NSAIDs have been shown in trials to reduce early postoperative resting and movement pain and 24-hour morphine use without a significant increase in adverse events. ^[1] For minor surgery, paracetamol or an NSAID alone is often sufficient. ^[1]

Safety matters as much as efficacy:

• NSAIDs should be used with particular caution, or avoided, in patients with a history of gastrointestinal bleeding or ulcer, bleeding disorders, significant renal or hepatic impairment, severe cardiac disease or after coronary artery bypass grafting. ^[1]
• Short-term perioperative NSAID use of up to about seven days has not been shown to increase the risk of serious renal, bleeding, healing, gastrointestinal or cardiac adverse events, but risk and benefit still need weighing in each patient. ^[1]
• Oral and intravenous paracetamol are considered to have equivalent analgesic effects. ^[1]
• In older adults, paracetamol and NSAIDs remain foundational analgesics, but clinicians must watch for cardiovascular, renal and gastrointestinal effects of NSAIDs. ^[1]

Opioids are potent full agonists at opioid receptors in the central and peripheral nervous systems and remain the mainstay for moderate to severe postoperative pain. ^[1] Their common adverse effects are respiratory depression, excessive sedation, nausea and vomiting, pruritus, dizziness, urinary retention, delirium, cognitive impairment and constipation. ^[1] For that reason they should be used when needed and discontinued as soon as possible, starting low, using the smallest effective amount and shortest duration and avoiding opioid-only regimens where a multimodal approach is possible. ^[1]

Strong opioids such as morphine, oxycodone, hydromorphone and fentanyl are appropriate for severe pain; weak opioids such as tramadol or codeine can be used, with many of the same cautions. Tapentadol, tramadol and methadone have additional pharmacological mechanisms and differ in their risk profiles. Opioid-naive adults should start at a low dose, often equivalent to about 5 to 10 morphine milligram equivalents for a single dose or 20 to 30 morphine milligram equivalents per day, with product labelling used as the starting point and calibration for severity of pain, renal function and hepatic function. ^[3] Older and frail patients, and those with renal or hepatic impairment, have a smaller therapeutic window and need doses started lower and increased more slowly. ^[1][3]

A single strong opioid should not be assumed to be safe simply because it is low dose. In the 2022 prescribing guidance, initiating or escalating opioids is tied to increased risk at higher total daily doses, and overdose risk is doubled across multiple studies for dosages of 50 to under 100 morphine milligram equivalents per day relative to under 20 per day. ^[3] Opioids may also prolong recovery for some acute pain conditions and are associated with an increased likelihood of long-term opioid use after short courses, with reported rates of new long-term use after short-term postoperative exposure ranging from under 1% to 13%. ^[3]

Patient-controlled analgesia (PCA) allows a patient to self-administer small bolus doses of an analgesic through a programmed pump, giving individualised control and rapid treatment of breakthrough pain. ^[1] It is a useful method for moderate to severe pain but it is not an opioid delivery system alone; it works best on top of a regional block or a paracetamol and NSAID foundation. ^[1]

A 2025 guideline based on a large network meta-analysis supports three principles for intravenous PCA: ^[1]

• Combine drugs with different mechanisms of action, because this improves analgesia and reduces adverse effects.
• Include a mu-opioid receptor agonist, because opioids remain central to the management of moderate to severe postoperative pain.
• Consider dexmedetomidine as an adjuvant, because its combination with opioids can reduce opioid dose, PCA demands and rescue use, lower pain scores and nausea and shorten recovery, with caution in bradycardia or conduction block.

PCA pumps are usually run with opioid plus an adjuvant such as dexmedetomidine, ketamine or an NSAID. In selected patients, ketamine or esketamine as an adjuvant may reduce opioid consumption and the risk of postoperative depression, but longer infusions can produce psychotomimetic effects and need close monitoring. ^[1]

Regional analgesia is a core part of multimodal care. Peripheral nerve blocks are recommended as an essential component of multimodal analgesia to improve pain control, reduce opioid consumption and lower the incidence of nausea and vomiting. ^[1] Ultrasound guidance has made these blocks safer, more precise and more widely used. Single-shot blocks give good early analgesia for roughly the first day; continuous techniques extend coverage when pain is expected to last longer. Single-injection blocks can be associated with rebound pain as they wear off, so planning continuation analgesia matters. ^[1]

The choice of block follows anatomy and procedure:

• Limb surgery benefits from brachial plexus blocks for shoulder and arm surgery, and femoral or adductor canal blocks for knee surgery. All common peripheral nerve block techniques reduce early pain and opioid use compared with placebo. ^[1]
• Thoracic surgery benefits from erector spinae plane blocks (ESPB) and thoracic epidural analgesia; ESPB can significantly reduce 24-hour opioid use and early pain scores after thoracic surgery. ^[1]
• Abdominal surgery benefits from transversus abdominis plane blocks, rectus sheath blocks, quadratus lumborum blocks and erector spinae blocks, which lower early resting and movement pain scores. ^[1]
• Spinal surgery can be supported with thoracolumbar fascial plane or erector spinae blocks, which reduce early pain scores and analgesic use. ^[1]

Epidural analgesia behaves differently from peripheral blocks. After thoracic and abdominal surgery, epidural analgesia gives superior postoperative analgesia compared with intravenous analgesia and is preferred within a multimodal plan, although catheter-related complications and adverse effects such as urinary retention and pruritus must be anticipated. ^[1] After lower limb surgery, epidural analgesia has no clear advantage over peripheral nerve blocks, while being associated with a higher incidence of urinary retention and a longer hospital stay, so it is not recommended first-line there. ^[1] Neuraxial analgesia produces better outcomes when local anaesthetic and opioid are combined, because of synergy and longer duration. ^[1]

Opioid-related adverse effects are predictable and preventable.

• Respiratory depression is defined as a respiratory rate of 8 breaths per minute or less, arterial oxygen saturation less than 90% on room air, or the onset of hypopnoea. ^[1] Management principles include suspending opioid delivery or reducing the PCA dose, maintaining a patent airway, maintaining close monitoring of respiratory rate and oxygen saturation, providing supplemental oxygen and, when depression is severe or due to overdose, giving intravenous naloxone at 5 to 10 micrograms per kilogram. ^[1] Nalmefene may have a longer duration and higher receptor affinity than naloxone in this setting, but whether it should replace naloxone remains debated. ^[1]
• Excessive sedation should be treated as an emergency. If a patient cannot be roused, or is comatose, airway obstruction and respiratory depression must be assumed. Older adults need particular care because age reduces drug metabolism and clearance; opioid doses should start low and be increased slowly to the minimum effective dose, with vigilance about mental state and respiratory rate. ^[1]
• Nausea and vomiting should be prevented rather than treated once established. Multimodal regimens that reduce opioid use already lower nausea and vomiting. ^[1] For low to moderate risk patients, prophylaxis with one or two antiemetics from different classes is recommended: a 5-HT3 antagonist, dexamethasone, a dopamine antagonist or an NK-1 antagonist. High-risk patients should receive combinations of two or three or more. ^[1]
• Opioid-sparing regimens themselves change outcomes. Compared with opioid-only intravenous analgesia, opioid-sparing strategies reduced resting pain in the first 24 hours, reduced 24-hour morphine consumption, lowered nausea and vomiting with an odds ratio of 0.64, lowered dizziness with an odds ratio of 0.58 and pruritus with an odds ratio of 0.51. ^[1]

Practical prevention therefore rests on multimodal design, dose restraint, individualised starting doses, slow titration in older or frail adults, close monitoring in the first 24 hours and ready availability of naloxone. ^[1][3]

Conversion between opioids is one of the most error-prone areas in pain medicine. The common method is to express a regimen as morphine milligram equivalents (MME), using published conversion factors. ^[3] Common approximate conversion factors are: codeine 0.15; transdermal fentanyl, measured in micrograms per hour, 2.4; hydrocodone 1.0; hydromorphone 5.0; methadone 4.7; morphine 1.0; oxycodone 1.5; oxymorphone 3.0; tapentadol 0.4; tramadol 0.2. ^[3] Multiplying a daily dose by the factor gives the daily dose in MME, for example 20 milligrams of hydrocodone daily giving 20 MME daily. ^[3]

These figures are for risk assessment and comparison, not for prescribing. Three rules matter most: ^[3]

1. Equianalgesic conversions are estimates only. They cannot account for individual variability in genetics and pharmacokinetics.
2. Do not use the calculated MME dose to determine the dose when converting from one opioid to another. When switching opioids, the new opioid is usually dosed at a substantially lower amount because of incomplete cross-tolerance and individual pharmacokinetic variability. Prescribing the full calculated equivalent risks overdose. ^[3]
3. Be especially cautious with methadone and transdermal fentanyl. Methadone has a long and variable half life, and its peak respiratory depressant effect occurs later and lasts longer than its peak analgesic effect. Fentanyl patches are dosed in micrograms per hour, their absorption is affected by heat and other factors, and small errors in patch handling cause large harm.

Additional cautions: if a patient receives concurrent opioid prescriptions, total MME across all sources should be considered when assessing overdose risk; buprenorphine products approved for pain are not included in standard MME tables because of their partial mu-receptor agonist activity and ceiling effects; and these factors apply to prescribing, not to the management of opioid use disorder. ^[3]

Breakthrough pain is a transient flare of pain on top of an otherwise stable baseline analgesic regimen. It can be spontaneous or triggered by predictable factors such as movement, breathing, coughing or physiotherapy. ^[1] It is common after open gynaecological surgery, where studies report that 66.8% of patients experience at least one episode of moderate breakthrough pain. ^[1] Short-acting opioids are usually used for these episodes, while paracetamol may help prevent them. ^[1]

Rebound pain is the abrupt return of pain when a single-dose peripheral nerve block wears off. It occurs in roughly 40 to 50% of patients after single-shot blocks, derails recovery and increases opioid use. ^[1] Orthopaedic surgery and preoperative pain are strong risk factors for it. ^[1] Prevention includes intraoperative intravenous dexamethasone or ketamine or esketamine, which both reduce rebound pain, continuous nerve block rather than a single shot, and a multimodal oral regimen in place before the block resolves. ^[1]

Chronic postsurgical pain is pain at or related to the surgical site that persists beyond the normal healing period, usually longer than three months. ^[1] It places a large burden on patients and on health systems. Its incidence is reported to range from approximately 10% to 40%, depending on operation and definition. ^[1]

Risk factors fall into two groups. ^[1]

• Patient factors: moderate to severe acute postoperative pain, younger age, female sex, smoking, anxiety, depression, preoperative pain, pain catastrophising. ^[1]
• Surgical factors: longer operative time and postoperative wound infection.

These risks are only partly modifiable, and that is where analgesia matters. Better acute pain control is one of the most credible ways to reduce long-term postoperative pain, which is why the same guidelines that treat acute pain also recommend transitional pain services: multidisciplinary teams that bridge the inpatient acute pain service with follow-up in the weeks after discharge, taper opioids, manage psychological contributors and aim to prevent pain from becoming chronic. ^[1] Early evidence supports small but clinically meaningful reductions in opioid use and pain interference with such services. ^[1]

Day-case surgery. In ambulatory surgery, postoperative pain is a leading cause of delayed discharge and unplanned readmission. For mild pain, paracetamol or an NSAID is recommended as foundational analgesia. For moderate to severe pain, paracetamol and NSAIDs combined with local infiltration or a peripheral nerve block are recommended, with opioids added only if required. ^[1] Neuraxial analgesia is not recommended in day case because of anticoagulation, thromboprophylaxis and catheter-management difficulties. ^[1]

Older adults. Older patients have reduced physiological reserve and drug tolerance, so analgesic plans should rest on non-opioids and regional techniques, opioid doses should start low and be titrated slowly under close monitoring, and peripheral nerve blocks should be considered first-line where available. ^[1]

Low-resource settings. The evidence-based principles do not depend on expensive drugs. A multimodal regimen of paracetamol, an NSAID when safe, local infiltration or a simple block and oral opioids for rescue can be delivered reliably in most hospitals. Where nerve block equipment, ultrasound or acute pain staffing is limited, prioritise: preoperative education, the simplest consistent regimen, attention to opioid safety, respiratory monitoring and escalation pathways to a referral centre. Epidural and advanced techniques should only be performed by staff with training and the ability to manage complications such as local anaesthetic systemic toxicity. ^[1]

• Postoperative pain peaks 24 to 72 hours after surgery, arises from somatic, visceral, inflammatory and sometimes neuropathic mechanisms and affects most patients. ^[1]
• Multimodal analgesia, combining regional techniques, paracetamol, NSAIDs and opioids when needed, is the standard approach for adult postoperative pain. ^[1]
• Paracetamol and NSAIDs form the foundation of most regimens and are superior in combination; NSAIDs require caution in renal, gastrointestinal, cardiac and bleeding risk. ^[1]
• Opioids are used for moderate to severe pain at the lowest effective dose for the shortest time, with dose reduction in older and frail adults. ^[1]
• PCA is an adjunct on top of a regional or non-opioid foundation and is not an opioid delivery system by itself. ^[1]
• Peripheral nerve blocks reduce pain and opioid use across most operations; epidural analgesia is preferred for thoracic and abdominal surgery but not first-line for lower limb surgery. ^[1]
• Respiratory depression, defined as a respiratory rate of 8 or less, oxygen saturation less than 90% on air or hypopnoea, is prevented by multimodal design, dose restraint and monitoring, and treated with airway care and naloxone 5 to 10 micrograms per kilogram intravenously. ^[1]
• Nausea and vomiting prevention and opioid-sparing strategies both reduce opioid-related adverse effects. ^[1]
• Morphine milligram equivalents are a risk-assessment tool: equianalgesic tables give estimates only and should not be used unchanged when switching opioids or managing opioid use disorder. ^[3]
• Chronic postsurgical pain occurs in 10 to 40% of patients and is associated with severe acute postoperative pain, preoperative pain, anxiety, depression and longer surgery. ^[1]
• Transitional pain services try to bridge acute and community care, reduce long-term opioid use and prevent persistent pain. ^[1]
• Procedure-specific regimens mirror the principle: match the technique to the operation, using opioids last. ^[1]

• Regional and local anaesthesia.
• General anaesthesia and airway management.
• Perioperative care and postoperative fever and complications.
• Neuroblastoma and other surgical topics are outside this scope but share the principles of multimodal care.