Opioids and acute pain management

Key Points
  • Opioids given by the parenteral (intravenous, intramuscular or subcutaneous) routes for acute pain have a more rapid onset of action than those given by the oral route.
  • Oral opioids may be as effective in the treatment of acute pain as opioids given by other more invasive routes if equi-analgesic doses are administered.
  • Intravenous opioid patient controlled analgesia (PCA) provides better analgesia than conventional (intramuscular and sub-cutaneous) opioid regimens, although the magnitude of the difference in analgesia is small.
  • The effectiveness of epidural opioid analgesia has been well demonstrated and provides better pain relief than parenteral opioid administration.
  • Direct comparisons between different opioids are limited, however indirect comparisons, where the individual drugs have been compared with a placebo, may be used to generate a ‘league table’ of analgesic efficacy (see below). This table is based on randomised, double-blind, single-dose studies in patients with moderate to severe pain and shows the number of patients that need to be given the active drug (NNT*) to achieve at least 50% pain relief in one patient compared with a placebo over a 4 to 6 hour treatment period. 
  • It should be noted that according to the league table opioids may be less effective for acute pain than medicines with other different mechanisms of action.

*NNT (number needed to treat). The number of patients needed to be treated for one to benefit compared with a control. A treatment that works for everyone, and where no patient has a response with control, would have a NNT of 1. The higher the NNT, the less effective the treatment.

 

Opioids and acute pain management

The treatment of acute pain is essential to facilitate recovery from surgery or trauma by enabling early mobilisation and avoiding complications, including the bed-bound risks of venous thromboembolism, pulmonary embolus, pressure sores and pneumonia. Severe untreated acute pain may also predispose to the development of chronic pain.

Opioids are very effective in treating acute pain and are best used as part of a multimodal analgesic approach in combination with paracetamol, non-steroidal anti-inflammatory drugs and local anaesthetics where appropriate. Initiating opioids in the acute setting requires a prescriber to ensure that the opioids are not continued beyond the expected period of tissue healing.

A Canadian study showed that, although the inflammatory response to injury normally resolves within three months, a significant proportion of patients given opioids for post-operative pain took opioids well beyond this time. Pressures for earlier discharge from acute hospitals result in the potential for patients leaving hospital after a short stay with a supply of strong opioids. Although it is essential to supply patients with appropriate analgesia on discharge, clear information for the patient regarding the importance of tapering and stopping these drugs, and good communication with the patient’s primary care team should reduce the unnecessary continuation of opioids in the community.

There are a small number of patients who repeatedly present to an acute hospital describing pain and requesting opioid analgesia. They are often difficult to assess and manage. Developing an individualised management plan for these complex patients is essential. This will reduce unnecessary tests and provide a clear analgesic strategy. A multidisciplinary approach involving social, primary and secondary care is most likely to produce a robust and appropriate outcome.  The Royal College of Emergency Medicine has produced best practice guidelines regarding the identification and management of frequent attenders in the Emergency Department.

 

Oxford Analgesic League Table

League table of analgesic efficacy

Single dose analgesics for moderate to severe acute pain: NNT* for at least 50% maximum pain relief over four to six hours.

* NNT (number needed to treat). The number of patients needed to be treated for one to benefit compared with a control. A treatment that works for everyone, and where no patient has a response with control would have a NNT of 1. The higher the NNT, the less effective the treatment.  Treatments with NNTs of 2-5 are considered effective for acute pain.

 

Further Reading

  • Clarke H, Soneji N, Ko DT, et al. Rates and risk factors for prolonged opioid use after major surgery: population based cohort study. British Medical Journal 2014; 348: g1251.
  • Dolin SJ, Cashman JN & Bland JM. Effectiveness of acute postoperative pain management: I. Evidence from published data. British Journal of Anaesthesia 2002; 89: 409-23.
  • Macintyre PE, Schug SA, Scott DA, Visser EJ, Walker SM. Acute Pain Management: Scientific Evidence (3rd edition). Australia and New Zealand College of Anaesthetists and Faculty of Pain Medicine 2010.
  • Marret E, Remy C & Bonnet F. Meta-analysis of epidural analgesia versus parenteral opioid analgesia after colorectal surgery. British Journal of Surgery 2007; 94: 665–73.
  • McNicol E, Quah C, Hudcova J. Patient controlled opioid analgesia versus non-patient controlled opioid analgesia for postoperative pain. Cochrane Database of Systematic Reviews 2015; 6: CD003348.
  • Moore A, Edwards J, Barden J et al. Bandolier’s Little Book of Pain. 2003 
  • Moore RA, Derry S, Aldington D, Wiffen PJ. Single dose oral analgesics for acute postoperative pain in adults - an overview of Cochrane reviews. Cochrane Database of Systematic Reviews 2015; 9: CD008659.
  • Royal College of Emergency Medicine. Care of frequent attenders at multiple Emergency Departments. 2014. 
  • Thorson D, Biewen P, Bonte B, et al. Institute for Clinical Systems Improvement. Acute Pain Assessment and Opioid Prescribing Protocol. 2014. 
  • Wu CL, Cohen SR, Richman JM et al. Efficacy of postoperative patient-controlled and continuous infusion epidural analgesia versus intravenous patient-controlled analgesia with opioids: a meta-analysis. Anesthesiology 2005;103:1079–88.
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