vatlogo7a

The Virtual Anaesthesia Textbook

Post-operative Pain

Last modified 9/11/2014. Comments to: Chris Thompson

Contents:


Introduction; rationale for post-operative pain relief

Recent years have witnessed with increasing interest in postoperative pain management. It wasn't always so! As a result an increasing number of patients have become more medically sophisticated and more likely to request specific modes of treatment.

The International Association for the Study of Pain and their journal "Pain" are the main international group with an interest in pain management. Their web site includes many useful clinical update sheets and technical information sheets. In their updates section is the 1993 classic "Pain Control - the new Hows and Whys" - explaining the logic behind attempting to manage pain better.

Most professional anaesthesia organisations have policy statements or guidelines on pain management. Some links include the US ASA Practice Guidelines for Perioperative Pain management, ANZCA Guidelines on Acute Pain Management, Acute Pain Management, Scientific Evidence, update Dec 2007, ASPAN's pain and comfort clinical guideline.

The American Pain Society provides abstracts from their meetings, and the American Pain Foundation provides a number of information sheets, mostly from a chronic pain perspective, in their library.

In recent years most major hospitals have implemented Acute Pain Services to provide pain care 24 hours a day. In its simplest form, an institution provides staff and facilities; in return the staff are responsible for optimising all aspects of peri-operative pain management. Typically, the process includes definition and effective implementation of policies, protocols and guidelines. These are particularly important for advanced pain management techniques such as PCA, Epidural, plexus infusions etc.

The aim of postoperative pain treatment is to provide subjective comfort in addition to inhibiting trauma-induced nocioceptive impulses in order to blunt autonomic and somatic reflex responses to pain and subsequently to enhance restoration of function by allowing the patient to breathe, cough and move more easily.

Peculiarity of postoperative pain:

  • Constant surgically-related pain, frequently described as aching in nature and ordinarily near the surgical site.
  • Acute exacerbation of pain added to the basal pain and due to activities such as coughing, getting out of bed, physiotherapy, and dressing changes.
  • Regularly it is a self limiting condition.
  • Usually there is a progressive improvement over a relatively short period.

Unrelieved pain after surgery is often unhealthy; fortunately, it is preventable or controllable in an overwhelming majority of cases.

Pain control may have a further benefit of improving clinical outcome by reducing the incidence of postoperative complications such as:

  • myocardial infarction or ischemia
  • risk of tachycardia and dysrhythmia
  • impaired wound healing
  • risk of atelectasis
  • thromboembolic events
  • peripheral vasoconstriction
  • metabolic acidosis.


Factors influencing analgesic requirements

Assessment of pain after surgery should be frequent and simple.

Elements that influence analgesic requirement and consumption include:

  • Age of the patient: elderly patients request smaller doses.
  • Sex.
  • Pre-operative analgesic use.
  • Past history of poor pain management.
  • Coexisting medical conditions such as substance abuse or withdrawal, hyperthyroidism, anxiety disorder, affective disorder, hepatic or renal impairments.
  • Cultural factors and personality. (e.g., patients vary from being intolerant of any discomfort to surprising self-control or patients consider pain to be a normal part of life).
  • Preoperative patient education. Appropriate pre-operative education can improve expectations, compliance and ability to effectively interact with pain management techniques.
  • Site of operation: thoracic and upper abdominal operations are associated with the most severe pain.
  • Individual variation in response and pain threshold.
  • Attitude of the ward staff.


Pain management techniques

Optimal application of pain control methods depends on Cupertino among different members of the health care team throughout the patient's course of treatment. To ensure that this process occurs effectively, formal means must be developed and used within each institution to assess pain management practices and to obtain patient feedback to calibrate the adequacy of pain control.

Pre-emptive Analgesic Therapy

There is a lot of interest in controlling the "wind-up" phenomenon as related to postoperative pain. To this end the application of opioids, local anaesthetic blocks and other analgesic modalities are being instituted and established before surgery to attempt to decrease the intensity and duration of postoperative pain.

Pharmacological Management

Treatment modalities that are now available for postoperative pain control include intramuscular, subcutaneous, intravenous, oral, rectal, transdermal or transmuscular analgesics; continuous infusions of opioids and/or NSAIDs; patient-controlled administration of opioids and/or NSAIDs; and intermittent boluses and/or continuous infusion of epidural or intrathecal opioids.


NSAIDs

Pharmacological management of mild to moderate postoperative pain should begin, unless there is a contraindication, with a NSAID. David Gotleib from South Africa has provided an recently revised and very comprehensive overview of NSAID's and how they work.

NSAIDs decrease levels of inflammatory mediators generated at the site of tissue injury, primarily inducible COX-2, while activity of COX-1 is no different from normal.

NSAIDs have several advantages over opioids. They do not have hemodynamic effects, do not cause respiratory depression, or slow gastric emptying or small-bowel transit time. The pharmacy cost of some of them, however, is significantly greater than that of morphine, even by the oral route. IV parecoxib is very expensive.

Risks include increased bleeding, GI damage, renal impairment, exacerbation of aspirin-induced asthma, poor bone or wound healing, etc. Bone healing issues may be a contraindication in spinal fusion procedures. Additionally, NSAIDS are inadequate analgesics alone for severe pain; they seem best utilised in conjunction with other agents.

NSAIDs may cause significant renal impairment, particularly in patients with renal disease or decreased circulating blood volume, and may induce fluid retention, oedema and hypertension. When systemic vasoconstriction occurs, local prostaglandin release causes renal vasodilatation, thus maintaining renal blood flow and glomerular filtration rate near normal. Usually these drugs are not prescribed for visceral pain.

Increased bleeding due to platelet inhibition is a risk when 'older' COX-1 inhibitors (indomethacin, etc.) are used perioperatively. The new highly-selective COX-2 inhibitors (e.g. rofecoxib, celecoxib) can inhibit prostaglandin synthesis without inhibition of platelet aggregation, and with reduced renal & GI toxicity. In some studies perioperative bloodloss was actually reduced when highly-selective COX-2 inhibitors were administered pre-operatively. The increased risk of arterial thrombosis and myocardial infarction with long-term use of these drugs has removed Rofecoxib, but Parecoxib is similar, and oral meloxicam can be used. Try a PubMed search for 'blood loss surgery rofecoxib' or see Acta Anaesthesiol Scand. 2005 May;49(5):601-13.

Meloxicam has greater COX-2 than COX-1 inhibition, but in clinically adequate doses COX-1 inhibition is probable so bleeding may be a problem in some patients. No-one has conclusively evaluated significance of bleeding with perioperative meloxicam in humans. The issue is complex. See these articles for more info: COX Selectivity in Monocytes (J Pharm Pharmacol. 2001 Dec;53(12):1679-85); effect on chondrocytes (J Rheumatol. 1999 Jun;26(6):1366-73); on gastric mucosa Aliment Pharmacol Ther. 2000 Jun;14(6):795-9; for perioperative use in total hysterectomy Clin Exp Obstet Gynecol. 2004;31(2):133-6; use in DOG cruciate repair - .Can Vet J. 2003 Aug;44(8):643-8.

This 'Thorax' review article evaluates nimesulide and meloxicam and their use in NSAID-induced asthma. Nimesulide is a little more COX-2 selective than Meloxicam. It can be successfully administered to most patients who could not tolerate other COX-1 inhibiting NSAIDS due to angio-odema or asthma. Meloxicam in low doses may be tolerable.

Ketorolac and parecoxib can be administered intravenously. Ketorolac is very potent and predominantly affects COX-1 and is associated with platelet dysfunction, whereas parecoxib is a precursor of valdecoxib, a highly-selective COX-2 inhibitor.

Acetaminophen or paracetamol is commonly used as a mild analgesic in the peri-operative setting. Sold as Tylenol® in USA, Efferalgan® in Europe, Panadol® in Australia. No COX1 or COX2 activity, so does not affect platelet aggregation, nor does it provide peripheral anti-inflammatory activity. Possibility of severe hepatic impairment in overdose (deliberate or accidental). Advice for medical practitioners is available in our poisonings & toxicology chapter. If the patient cannot tolerate oral medication, proparacetamol, an IV preparation, or alternative routes such as rectal administration can be used.

At present, one NSAIDs, ketorolac (overview), is approved in some countries for parenteral use and one acetaminophen-like drug: propacetamol (Prodafalgan® in France, Proefferalgan® in Italy). The introduction of parenteral NSAIDs has increased the number of patients who can benefit from non opioid analgesic - especially those who are to receive nothing by mouth. Ketorolac administration reduced morphine requirements by 49% in patients recovering from abdominal surgery.


Opioid drugs

Please see our chapter on opioids.

For post-operative pain, the most commonly used opioid drugs are morphine, papaveretum, pethidine, codeine and methadone. Some actions are due to metabolites.

Opioids may be administered by a variety of routes:

ORAL OPIOIDS - e.g. oxycodone, codeine, tramadol, morphine. Medicines given by mouth cause less discomfort than injections, but they can work just as well. They are inexpensive, simple to give, but there may be a delay in pain relief. Short and long-duration presentations are available. Codeine metabolism influences its effectiveness. Metabolism of codeine to morphine and especially codeine-6 glucuronide (also Chen 1991)are necessary for analgesia Lotsch 2006, Williams 2002, Vree 2000. This is subject to considerable inter-patient variability and it can be an unreliable analgesic in some patients.

Tramadol (Tramal® in Germany, Contramal® in Italy, Ultram® in USA, Adolonta® in Spain), a central analgesic with low affinity for opioid receptors, has been used extensively in postoperative management. It has proven to be a very weak opioid with an analgesic potency roughly similar to pethidine that is due primarily to non-opioid actions. At low doses it potentiates opioid actions. Dependency liability is low. Little respiratory depression occurs unless given in large doses. Serotoninergic side-effects (confusion, disorientation, even dementia) can occur, and physicians need to be alert for the development of the serotonin syndrome. Nausea is common after IV administration.

INTRAMUSCULAR ADMINISTRATION - Opioids, particularly morphine sulphate (info : Wikipedia) and meperidine hydrochloride (demerol, pethidine) (info: Wikipedia), administered by the intramuscular, subcutaneous or IV route, have been the mainstay of postoperative analgesia. Meperidine (pethidine) is shorter acting, but is metabolised to active agents (norpethidine) that can precipitate seizures and therefore is not recommended for prolonged administration.

Opioids given by intermittent injection generally are not able to maintain steady analgesic plasma levels for 2 to 4 hours. Opioids are often significantly underdosed because of a widespread, dominant fear for patient safety.

Disadvantages of this technique:

  • IM injections are painful.
  • a steady blood concentration is difficult to sustain
  • there are prolonged intervals where the patient experiences pain: a) the patient may be unaware that pain relief is available; b) there may be delays between request for relief and the actual time of administration; c) there is the risk of respiratory depression and overdose; d) further delay between the time of injection and the onset of pain relief.

SUBCUTANEOUS INJECTIONS - May provide a very effective method of pain relief. The onset of pain relief occurs at about the same time as with the intramuscular route. The injection is less painful and the effect lasts longer.

Unless the dose and the timing is judged appropriately, there are still periods of unrelieved pain.

INTRAVENOUS ROUTE - Continuous intravenous infusions provide pain control as long as steady state concentrations are maintained above the minimum effective analgesic blood concentrations. Steady state concentrations are dependent on systemic clearance and this is related to hepatic blood flow.

Both pethidine and morphine are suitable drugs for continuous intravenous infusions but unless a loading dose is used, a steady state is not achieved for about 24 hrs. To avoid the side effects of a large bolus, a loading dose given as an infusion is preferable, always remembering that there is drug elimination during loading.

PCA (Patient Controlled Analgesia) - Patient controlled analgesia allows a patient to receive drugs on demand. A PCA pump administers drugs, usually intravenously, when the patient pushes a button. The physician has the possibility of determining the intermittent injection dose (the dose received when the patient pushes the button), the lockout interval (the minimal length of time that must elapse between consecutive doses), a limit to how much drug may be injected in a limited time (1-4 hours), a bolus dose to be administered by a nurse through the machine, and a basal rate (continuous infusion rate without the need for patient or caregivers intervention).

The equipment is expensive and the technique may allow breakthrough pain on an intermittent basis because when the patient is asleep, the administration ceases. This can be overcome by a slow background infusion that is supplemented by a patient controlled additional dose. Patient information is mandatory.

EPIDURAL OPIOID DRUGS - Drugs administered by these routes can reduce the dosage of opioid required for adequate pain relief, especially if administered in association with local anaesthetics. There is no sensory loss, no muscle paresis and no autonomic blockade with opioid drugs administered by these routes.

With intrathecal injections there is a variation in the rate of onset of analgesia and its duration depending on whether the drug is lipophilic or hydrophilic and by transport within the cerebro-spinal fluid. Morphine is hydrophilic. When administered by the spinal routes it takes about 45 minutes to reach maximum effect and lasts for 8-12 hours. Pethidine, methadone and fentanyl being lipophilic act quickly, but the duration of action is short.

Of considerable concern is the risk of delayed respiratory depression which may occur up to 18 hrs after the opioid drug is injected. Very small intrathecal doses (less than 1mg of morphine, even less in the elderly) are safest, and post-administration monitoring must record respiratory rate at least hourly. Resuscitation facilities and trained staff must be available. The respiratory depression is reversed by naloxone. When epidural opioids are utilised in the postoperative time, the patient should be monitored carefully: postoperative orders after epidural morphine.

The dose of morphine by the epidural route is about 5-10 times that of the intrathecal route.


Regional and local analgesia

Direct injection of local analgesic drugs close to peripheral nerves, major nerve trunks or nerve roots produces analgesia by blocking conduction of afferent impulses.

Neural blockade with neuraxial administration of local anaesthetics and/or opioids has now been established as being an effective means postoperative pain treatment. In some situations, such as major abdominal, orthopaedic and thoracic surgery, it has been documented to provide superior pain relief to alternative techniques. Risks of epidural local anaesthetics include hypotension, epidural abscess or haematoma, paraplegia, etc. Overall morbidity and mortaility is no different.

A number of peripheral nerve blocks are very useful in the PACU for the transitional period immediately following general anaesthesia before the patient is fully awake and stable: intermittent or continuous paravertebral, intercostal, femoral nerve, brachial plexus block, and wound-infiltration.

The Virtual Anaesthesia Textbook includes chapters on local anaesthetics and local anaesthetic techniques.

Relatively few side effects occur ordinarily, providing that these techniques are carefully managed by highly qualified staff.

INTRATHECAL BLOCK - Intrathecal local anaesthesia provides analgesia during the postoperative period especially if long acting analgesic drugs such as bupivacaine are used. If opioid drugs are administered before the block wears off, very good pain relief is possible. Usually, to avoid PDPH, a small gauge pencil-point needle is used. Small diameter catheters have made it possible to use continuous spinal techniques but these have been associated with a high complication rates.

EPIDURAL ANALGESIA - Epidural analgesia is a more useful technique for the relief of postoperative pain because a catheter can be used to maintain analgesia in the postoperative period. "Top up" is done only by doctors and/or administered by programmed pump. Administration of drugs via a continuous infusion pump or via Infusor® Baxter (non-electric device) avoids fluctuations in the level of analgesia.

INTERCOSTAL BLOCK - This is performed at the angle of the rib where the intercostal nerves pass round the chest wall beneath the inferior border of the ribs. There is a risk of pneumothorax. Multiple blocks are necessary and the high blood levels are reached. This is a particularly useful technique for pain relief in patients with chest injuries.

INTERPLEURAL ANALGESIA - Interpleural analgesia is the percutaneous introduction of a catheter between the parietal and the visceral pleura placed at an interspace just below the level of the incision. Local anaesthetic is introduced through the catheter into the pleural space. Analgesia occurs due to diffusion of local anaesthetic to the intercostal nerves, sympathetic chain and direct action on pleural nerve endings. The results of several studies have varied from moderate to excellent analgesia to no analgesia and further work on defining the exact role of interpleural analgesia is currently underway.

NERVE BLOCKS - Of particular benefit are the "3 in 1" block, the femoral nerve block, the sciatic nerve block for postoperative analgesia after lower limbs orthopaedic procedures and the block of the dorsal nerve of the penis for pain relief following circumcision. Brachial plexus blocks are great for the upper limb - axillary, interscalene and infra-clavicular approaches from the excellent NYSORA site.


Physical Methods

Commonly used physical agents include applications of cold, massage, movement, TENS, and rest or immobilization. Transcutaneous electrical nerve stimulation (TENS) may be effective in reducing pain and improving physical function. This has been used with varying degrees of success in the management of postoperative pain. Evidence is accumulating that TENS acts by increasing CSF levels of beta-endorphins, together with activating of the "pain gate" by counter irritation.


Patient education

Preparing patients in order to understand their responsibilities in pain management is important. A number of pain scales are available. To ensure that postoperative pain measurement is both valid and reliable, the staff should review the selected pain measurement scale or tool with the patient before surgery (see also measurement of pain in children).

J. Oyston and A De Nicola have a useful page "What every patient should learn about anaesthesia" also translated in Italian, that contains related information. Patient information can be an adventure when there are language problems.

ANZCA provide a 1.2Mb PDF publication Managing Acute Pain - A Guide for Patients.

This chapter originally by Nello DiNicola


Link to VAT

visitors to this chapter since April 29th 2000.

Original concept for the Virtual Anaesthesia Textbook by:
Dr. Chris Thompson
Senior Staff Specialist Anaesthetist
Royal Prince Alfred Hospital
Sydney Australia