Opioids remain the mainstay for the treatment of moderate to severe acute pain. All full opioid agonists (eg morphine, oxycodone, hydromorphone, fentanyl), given in appropriate doses, produce the same level of analgesia and side effects. ANZCA, Section 4.1.1, p 55.

Opioid requirements vary considerably between individuals. Variability depends on factors such as patient age, gender, genetic differences, psychological factors and opioid tolerance. Doses of opioid should, therefore, be titrated based on the needs of individual patients. ANZCA, Section 4.1.3, p 61; French section 5.2, page 405.

Opioids can be administered by a variety of routes (oral, rectal, intravenous., subcutaneous., intramuscular, transdermal, epidural, intrathecal and intraartricular) ANZCA, chapter 6, p 150. Neuraxil regional, systemic and peripheral regional techniques should be preferred over opioids administered ‘as needed’ by the intramuscular route. ASA section IV, p 253

Treatment specific perioperative issues

In the immediate postoperative period i.v. titration is the best route for administration as it allows for the fastest onset of effect and individualized treatment. French section 5.1, p 405

In the postoperative care unit, giving 2 or 3 mg i.v. bolus doses of morphine at 5-minute dose intervals, until adequate pain score is reached, with no limitation on the number of doses given, was more effective and resulted in no more adverse effects compared to the same boluses given at 10 minute intervals or when a maximum of 5 boluses was allowed. ANZCA chapter 6.2.1, p 155.

Titrated doses should be reduced in patients over 85 years old French section 5.4, p 405 There is a 2 to 4 fold decrease in opioid requirements as patient age decreases. ANZCA Section 4.1.3. p 61.

Other than for treatment of severe acute pain, the oral route is the route of choice for administration of most opioids ANZCA chapter 6 p 150, and should be used as soon as the function of the gastrointestinal tract is restored after surgery French section 5.1, p 405

Oral immediate release (IR) preparations are effective for treatment of acute pain. Titration is rapid and safe. Analgesic effect is obtained in about 45-60 minutes. Controlled release preparations (CR, also referred to as ‘slow release’) are generally discouraged as sole agents but can be given at set time intervals with IR opioids given for titration of CR opioids and for acute, breakthrough pain. ANZCA section 6.1.1, p153.

PRN IM injections has traditionally been the main method for administering opioids after surgery despite that surveys show that this frequently produces ineffective analgesia. Placement of SC plastic cannula (=’butterfly’ needles) allows for intermittent injections without repeated skin punctures ANZCA section 6.3.1 p 157.

IV-PCA morphine can provide better analgesia compared to conventional IV or SC methods, though the difference was small. Opioid consumption and satisfaction were higher, there was no difference in adverse effects, other than pruritus ANZCA section 7.1.1., p 171; French 5.3, p 405. PCA can be used with older patients. ANZCA section 11.2.5, p 405.

Recommendations specific to the treatment

Analgesic efficacy of opioids. There are two methods by which this can be determined. (1) Equianalgesic dose tablesGerman table 6.2.2. where morphine serves as the ‘gold standard’ against which other opioids are compared to. These tables are based on single dose studies in opioid naïve patients and they do not take incomplete cross-tolerance into account. Thus, values might not be directly applicable for calculating opioid doses in patients who have been given repeated doses in the acute or chronic pain setting. These tables should be regarded as giving an approximation of the equivalent potency of drugs and should only be used as a guide. ANZCA section 4.1.1, p 55.

(2) The 2007 Oxford League table of analgesic efficacy comparison of opioids and non-opioids using the measure of ‘Number Needed to Treat’ (NNT). Low numbers indicate that the medication has a greater analgesic effect. 10 mg of IM morphine has an NNT of 2.9 (2.6 -3.6), similar to the NNT of IM100 mg pethidine (meperidine) which is 2.9 (2.3 – 3.9) Bandolier. See ANZCA Table 6.1. p 151-152, for further discussion about the Oxford League table

Opioid-induced hyperalgesia is a paradoxical effect when administration of an opioid results in sensitization of pro-nociceptive pathways. Morphine, in high doses, may lead to this more than other opioids. ANZCA chapter 4, ‘Tolerance and hyperalgesia’, p 68.

'Opioid rotation' can be a useful strategy to manage patients with acute pain who have intolerable opioid-related side effects that are non-responsive to treatment. It can be also used in opioid-tolerant patients.ANZCA chapter 4.1.1 p 55 and if opioid-induced hyperalgeisa is suspected ANZCA chapter 4, ‘Tolerance and hyperalgesia’, p 68.

Circumstances when the treatment is not recommended

See renal insufficiency, sleep apnoea, hepatic failure, opioid tolerant

Transdermal fentanyl patches are currently contraindicated for management of acute or postoperative pain in many countries. ANZCA section 6.5.1. p 159.

Treatment specific issues related to nursing/monitoring patients

The most common adverse effects related to opioids are nausea, vomiting, sedation, constipation and urinary retention. Not as common, but potentially life threatening, is respiratory depression, requiring careful monitoring of patients.

Many of the side effects will go undetected unless patients are specifically asked about them.

The following should be monitored in the post anaesthesia recovery unit when titrating opioids: (1) neurological (level of consciousness, pain score); (2) respiratory (respiratory rate and capillary oxygen saturation SpO2); (3) haemodynamic (blood pressure and heart rate). French section 5.2, p 405.

Titration should be interrupted if the patient becomes somnolent. Patients should be monitored during titration and up to one hour after titration as this corresponds to peak morphine activity and to the possible onset of respiratory depression. French section 5.2, p 405.

Assessment on the ward: Assessing level of sedation is a more sensitive measure for detecting respiratory depression than respiratory rate ANZCA chapter 4, ‘Respiratory depression’, p 63.

Summary

Opioids are the principle medication for treatment of moderate to severe acute pain after surgery. Their efficacy increases if given with a non-opioid. Titration is required to achieve effective analgesia. One opioid is not superior to another but some opioids can be better for some patients. The principle routes of administration after surgery are intraveneous and oral. The incidence of adverse effects is dose dependent. Patients receiving opioids should be monitored for related adverse effects. Opioids in high doses can induce hyperalgesia.

Recommended Reading:

1. Allen TK, Jones CA, Habib AS.Dexamethasone for the prophylaxis of postoperative nausea and vomiting associated with neuraxial morphine administration: a systematic review and meta-analysis. Anesth Analg. 2012 Apr;114(4):813-22.
2. Blaudszun G, Lysakowski C, Elia N, Tramèr MR. Effect of perioperative systemic α2 agonists on postoperative morphine consumption and pain intensity: systematic review and meta-analysis of randomized controlled trials. Anesthesiology. 2012 Jun;116(6):1312-22.
3. Kokki H, Kokki M, Sjövall S. Oxycodone for the treatment of postoperative pain. Expert Opin Pharmacother. 2012 May;13(7):1045-58.