Postoperative pain

The goal for postoperative pain management is to reduce or eliminate pain and discomfort with a minimum of side effects as inexpensively as possible.

Pain relief should be achieved for humanitarian reasons, to obtain physiological benefit, provide a smoother postoperative course, earlier hospital discharge, and reduce the onset of chronic pain syndromes.

Adequacy of pain relief is determined by the individuals perception of pain.

The surgical site effects the degree of postoperative pain: Surgery on the thorax and upper abdomen are more painful than operations on the lower abdomen which, in turn, are more painful than operations on the limbs.

Surgery involving a body cavity, a large joint surface or deep tissues are associated with pain.

Postoperative pain associated with thoracic or upper abdominal surgery may produce changes in pulmonary function, increase abdominal muscle tone and decrease in diaphragmatic function.

Postoperative pain associated with thoracic or upper abdominal surgery maya decrease the ability to cough and clear secretions, resulting in atelectasis and pneumonia.

Postoperative pain increases the sympathetic response of the body with tachycardia, increased cardiac workload, and increased oxygen consumption.

Prolonged postoperative pain can reduce physical activity and increase the chances of venous stasis, deep vein thrombophlebitis and pulmonary embolism.

Persistence of postoperative pain can lead to postoperative ileus, nausea, vomiting, and urinary retention, by impairing gut and urinary tract motility.

Patient-controlled analgesia (PCA), is better than the intermittent delivery of intramuscular opioids, but it does not produce as much pain relief as epidural opioid analgesia.

The under-treatment of acute postoperative pain occurs because physicians overestimate the length of action and the strength of the drugs and that they have fears about respiratory depression, vomiting, sedation and dependency.

Patient fear and anxiety may lead to high levels of postoperative pain.

Pain rating scales are the most commonly used method of assessing acute pain and its relief.

Assessment of pain in infants or patients who cannot communicate can be assessed with picture scales using varied facial expressions or by clinical observation of sighing, groaning, sweating, ability to move.

Measurement of pain while the patient is at rest is inadequate to determine the need for analgesia, and the relief from treatment should be assessed when the patient is active

Sharp or stabbing pain is associated with surgery.

Assessment of pain in the early post-operative period must be made at regular intervals and should be part of the routine postoperative care

Frequent reassessment and delivery of analgesia for postoperative pain is required.

The World Health Organization Analgesic Ladder with three rungs is utilized for postoperative pain control.

In the first instance peripherally acting drugs such as aspirin, acetaminophen or non-steroidal anti-inflammatory drugs are utilized.

If pain control is not achieved, the second part of the ladder is to introduce weak opioid drugs such as codeine with appropriate agents to control and minimize side effects.

The final rung of the ladder is to introduce strong opioid drugs such as morphine.

Analgesia from peripherally acting drugs may be additive to that from centrally-acting opioids.

The World Federation of Societies of Anaesthesiologists (WFSA) Analgesic Ladder has been developed to treat acute pain. that is expected to be severe, and may need strong analgesics in combination with local anesthetic blocks and peripherally acting drugs.

Initial medications may be required to be given parenterally. and since postoperative pain should decrease with time and the need for drugs to be given by injection should cease.

Restoration of the use of the oral route to deliver analgesia is the second rung on the WFSA ladder where adequate analgesia can be obtained by using combinations of peripherally acting agents and weak opioids.

The final step on the WFSA ladder occurs when the pain can be controlled by peripherally acting agents alone.

Regional anaesthetic techniques used for surgery may have positive respiratory and cardiovascular effects associated with reduced blood loss and excellent pain relief which can improve convalescence.

Many local anaesthetic techniques which can be continued into the postoperative period to provide effective pain relief.

Many local anaesthetic techniques have minimal risk to the patient and include local infiltration of incisions with long-acting local anaesthetics, blockade of peripheral nerves or plexuses and continuous block techniques, peripherally or centrally.

Management should consist of a combination of approaches to achieve the best results.

Infiltration of a wound with a long-acting local anesthetic can provide effective analgesia for several hours, and further pain relief can be obtained with repeat injections or by infusion of local anesthetic via a thin catheter.

Blockade of plexuses or peripheral nerves can provide anesthesia for surgery or specifically for postoperative pain relief.

Either single shot or continuous infusion techniques can be used to block brachial plexus, lumbar plexus, intercostal, sciatic, femoral or any nerves supplying the specific area of the surgery.

Spinal anaesthesia provides analgesia for surgery in the lower half of the body and pain relief can last many hours after completion of the operation if long-acting drugs containing vasoconstrictors are used.

Epidural catheters can be placed in either the cervical, thoracic or lumbar regions but lumbar epidural blockade is the most commonly used.

Continuous infusions of local anaesthetic may produce effective analgesia.

Intravascular injection of local anaesthetic drugs can produce serious or life-threatening effects.

Local anaesthetic injections at any site can form part of balanced analgesia with a mixture of techniques to provide pain relief.

This has the advantage of decreasing the dosage of each drug needed and diminishing the likelihood of side effects.

Non-opioid analgesics are the most commonly used analgesic agents: aspirin, paracetamol and the non-steroidal anti-inflammatory drugs (NSAIDs).

Non-opioid analgesics are the main analgesic treatment for mild to moderate pain.

Nonopioids can provide surgical anaesthesia or as an additional technique when general anaesthesia is given.

Side effects are common with intrathecal and epidural analgesics, including: nausea, vomiting, itching, urinary retention, and respiratory depression.

Respiratory depression may be caused by systemic drug absorption, and spread in the cerebrospinal fluid.

The incidence of respiratory depression is increased by factors such as dose, age, posture, aqueous solubility of the drug administered, positive pressure ventilation and increased intra-abdominal pressure

All patients receiving intrathecal or epidural opioids whose level of consciousness drops must be assumed to have respiratory depression until proved otherwise.

It is dangerous to prescribe other opioids to patients receiving intrathecal or epidural opioids as this increases the likelihood of clinically significant respiratory depression.

Opioid analgesic drugs act at receptors within the central nervous system.

The major receptor groups are mu, kappa and sigma, on the basis of their binding characteristics.

Morphine and related compounds are known as mu agonists.

Morphine remains the gold standard by which other analgesics are judged. Morphine has a short half life and poor bioavailability. It is metabolised in the liver and clearance is reduced in patients with liver disease, in the elderly and the debilitated. Major side effects include nausea, vomiting, constipation and respiratory depression. Tolerance may occur with repeated dosage but this is highly unlikely to become apparent during the first week of continuous treatment.

Parenteral doses range from 2.5mg to a maximum of 20mg.

Morphine may need to be prescribed as frequently as 2 hourly.

Pethidine is a synthetic opioid which is structurally different from morphine but which has similar actions.

It has a short half life and similar bioavailability and clearance to morphine.

Pethidine has a short duration of action and may need to be given hourly.

Pethidine has a toxic metabolite (norpethidine) which is cleared by the kidney, but which accumulates in renal failure or following frequent and prolonged doses and may lead to muscle twitching and convulsions.

Extreme caution is advised if pethidine is used over a prolonged period or in patients with renal failure.

Parenteral doses range from 25mg to a maximum of 150mg.

Frequency of administration 1 to 4 hourly.

Methadone is different from morphine and pethidine but has the same actions.

It differs from the other agents in that it is well absorbed by mouth and undergoes little metabolism.

It is slowly metabolized in the liver and has a very long half life.

The resultant prolonged duration of action makes it more suitable for use in chronic pain rather than acute postoperative pain although it has been used successfully for this purpose.

Oral doses range from 2.5mg to 25mg given 6 to 12 hourly.

Fentanyl is used chiefly for intraoperative analgesia because of its relatively short duration of action.

It has similar actions and side effects to morphine and is metabolised in the liver.

Postoperatively it has been used intrathecally or epidurally as described earlier.

Buprenorphine is described as a partial agonist, which, in practical terms, means that it has different properties from drugs which work mainly at the mu receptor.

Buprenorphine appears to have some action at all the major opioid receptors.

Its most useful attribute is that it can be delivered by the sublingual route.

It is rapidly absorbed and has a prolonged duration of action (6 h) but is associated with a high incidence of nausea, vomiting and sedation.

Of the opioids, buprenorphine poses the least risk to patients with renal failure as the metabolites are virtually inactive and if accumulation does occur it is of no significance.

Sublingual doses range from 200-400mcg 8 hourly.

Nalbuphine and Butorphanol are known as agonist/antagonists as unlike conventional opioids, they act at the kappa receptor rather than the mu receptor.

Both have been used to provide postoperative analgesia by intermittent, continuous and PCA techniques.

They exhibit a ceiling effect for analgesic activity (which has limited their popularity) and also for respiratory depression which should make clinical use safer.

They are alleged to have a lower abuse potential than conventional opioid agents.

Side effects and toxicity

Opioid analgesics share many side effects though the degree may vary between agents.

The most common include nausea, vomiting, constipation and drowsiness.

Larger doses produce respiratory depression and hypotension.

The specific antidote naloxone is indicated if there is coma or very slow respiration.

Because of its short action, repeated injections of 200 – 400mcg intravenously may be necessary.

Alternatively, it may be given by continuous intravenous infusion, the rate of administration being adjusted according to response.

Pain relief in children

Management of pain in children is often inadequate and there is no evidence to support the idea that pain is less intense in neonates and young children due to their developing nervous system.

Children tend to receive less analgesia than adults and the drugs are often discontinued sooner.

Furthermore, it is simply not true that potent analgesics are dangerous when used in children because of the risks of side effects and addiction.

As with all pain, successful management depends upon the identification and treatment of all the factors which contribute, in particular fear and anxiety.

Children over four are better able to report pain and are able to use color scales, pictures of varying facial expression and often visual analogue scales.


Management of pain in children needs to be handled more actively than in adults. Greater effort should be made to anticipate pain as children cannot be relied upon to ask for analgesia as might an adult. It may be better to establish a schedule of regular analgesia. The route of administration will depend on the drug to be used, the severity of the pain and the likely side effects. Drugs are best given by mouth if possible but the rectal route may be tolerated better if vomiting is a problem. The parenteral route (by injection) should only be used if the drug selected can only be given by that method or where other methods have failed. Intramuscular injections should be avoided as they may be very painful themselves and subcutaneous or intravenous routes are to be pref2241ed.

Local anaesthetic creams are available that can be applied under an occlusive dressing to produce anaesthesia of the underlying skin for up to an hour. These may enable painless placement of venous catheters or allow infiltration of the area with local anaesthetic. These creams should not be used rectally, directly on the wound or on mucous membranes.

Many procedures associated with the relief of pain can themselves be painful. The performance of regional blockade, wound infiltration and the placement of intravenous or subcutaneous lines and catheters may be carried out without discomfort or resistance whilst the patient is anaesthetised.

Infiltration of local anaesthetic agent into the wound before wakening can reduce postoperative pain for long periods. Equally, regional anaesthesia undertaken while the child is under general anaesthesia can give prolonged control of pain and avoid the use of opioids. It is particularly suitable where early discharge from hospital is required. Extradural anaesthesia by the caudal route will provide excellent analgesia for any surgery below the waist such as herniorrhaphy, orchidopexy or circumcision. Children and their parents should be warned of the possibility of urinary retention and of transient weakness or numbness. Hypotension does not seem to be a problem in children under the age of six, but can be anticipated in older children and adults.

Dose schedule for caudal block with bupivacaine in children. 0.25% solution is satisfactory for blocks requiring a volume of 20ml or less. A more dilute solution (0.2% bupivacaine) should be used where volumes of 20ml or more are required.

For short cases 1% lignocaine will be effective and the required volume can be calculated in a similar fashion.

Type of block Volume (ml/kg) Lumbosacral 0.5 Thoracolumbar 1.0 Mid-thoracic 1.25

Maximum doses of bupivacaine in any four hour period are 2-3mg/kg and for lignocaine 3mg/kg (without adrenaline), 6mg/kg (with 1:200,000 adrenaline)

Non-opioid analgesics

Paracetamol is effective for mild to moderate pain. It can be given as an oral suspension in a dose of 15mg/kg to a maximum of 60mg/kg in 24 hours. Slightly higher doses (20mg/kg) are needed if this drug is used rectally as absorption is less reliable.


Aspirin should not be given to children under 12 years old because of the association with Reye’s syndrome. There is little experience with the use of NSAIDs in children except in the case of ibuprofen. This is available as a suspension or a syrup and should be given up to a dose of 20mg /kg/day. Diclofenac is available as a suppository (12.5mg or 25mg) for paediatric use and can be used as a premedicant or administered at induction of anaesthesia. Dosage can be up to 3mg/kg/day.


Opioids can be used in the same way for children as for adults. The chief concern is that of respiratory depression when larger doses are being used. Suggested dose guidelines given here will minimise the possibility of this and yet still give effective pain relief.

Codeine is effective by mouth for mild to moderate pain and is usually taken in combination with paracetamol. Caution is needed when using this drug with neonates who may be more liable to respiratory depression. Codeine can be given by subcutaneous or intramuscular injection to provide pain relief for babies or children who are outpatients. Doses are similar whichever route is chosen. Codeine is effective when given by suppository. However, children between the ages of 2 and 12 may not always appreciate the virtues of giving the drug by this method.

Codeine is not suitable for intravenous use as it can produce severe falls in blood pressure and apnoea.

Doses of codeine syrup range from 0.5-1mg/kg 4 hourly given orally or by intramuscular injection. Codeine given as a suppository: 1mg/kg 4 hourly.

Morphine is the drug of choice for children who are inpatients.

The pref2241ed route of injection of morphine is intravenous but other routes like subcutaneous route can be used.

Intrathecal and epidural opioids used in children is associated with a very high incidence of nausea and vomiting, itching, urinary retention and late respiratory depression.

The elderly report pain less frequently and require smaller doses of analgesic drugs to achieve adequate pain relief.

The most effective way to provide postoperative pain relief is with local anaesthetics.

Intercostal nerve block can aid pulmonary function after chest or upper abdominal surgery.

Epidural blockade can improve pain below the waist and aid the return of gastrointestinal function after surgery.

Epidural blockade can spread more widely in the elderly and there may compromise respiratory function due to intercostal paralysis.

Analgesic medications with a longer duration of action provide better pain relief.

Postsurgical pain may need to delayed hospital discharge, readmissions, delayed convalescence, and increased health care costs.

Pain management associated with postoperative pain can lead to opiate overdosage, adverse effects of medication, increase nursing care.

No opioid pain medications in postoperative pain may decrease morbidity, expedite discharge and contain costs.

Presently the cornerstone of postoperative pain management remains opioid based narcotics.

Unfortunately, opioid based narcotics have adverse effects of nausea, vomiting, pruritus, confusion, and respiratory depression.

Postop complication rate is about 34% and patient-reported risk for complications increased as pain levels rose.

Patients who report the lowest level of pain, and patients with moderate pain had about a two-fold greater risk for complications.

Patients reporting the highest level of pain have a nearly threefold greater risk for complications.

Pain control could shorten hospital length of stay.

Preoperative smoking cessation resulted in reduced pain after lung surgery compared with pain levels in patients who continued to smoke.

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