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Postoperative pain management

In this article Dr Morell-Ducos discusses current best practice recommendations in the use of opioids in the postoperative setting.
Patient arm with IV morphine PCA administration
© UCL

In this step, Dr Fausto Morell-Ducos, Consultant in Anaesthesia and Pain Medicine at UCLH, discusses current postoperative pain management recommendations which aim to reduce the incidence of opioid-related averse drug events and persistent postoperative opioid use.

Intravenous (IV) opioid use in the post-anaesthesia care unit

Administration of opioids for severe acute pain in the immediate postoperative period (in the ‘recovery’ or post-anaesthesia care area) is best achieved using intermittent IV bolus doses as this allows rapid titration to effect. The oral route is also usually not available during this phase of recovery.

This is usually carried out using a treatment algorithm to guide management with bolus doses of opioid given at 3- or 5-min intervals as required [1].

Patient-controlled analgesia

Intravenous patient-controlled analgesia (IV PCA) should be used for post-operative systemic analgesia when the enteral route is not available (for example, due to ileus). IV PCA use is associated with improved patient satisfaction, at the expense of slightly higher cumulative opioid use [1].

The routine use of background infusions with IV PCA increases the risk of opioid-induced ventilatory impairment (OIVI) and is not associated with improved analgesia, and should be avoided in opioid-naïve patients [2]. There is an argument for their use in the opioid-tolerant patient or in those on long-term opioid therapy, and we will cover this in Step 3.19.

The use of the intramuscular route is not advised as it is often associated with significant pain and unreliable absorption, resulting in inconsistent analgesia. Although previously routine and considered safer, there is no evidence of reduced incidence of opioid-related adverse drug events (ORADEs) compared to other routes [2].

What is the best way to administer immediate-release (IR) oral opioids?

Once on the ward, the oral route should be used as soon as possible for all medications [2-3] as most evidence suggests that IV administration of opioids does not provide substantially superior analgesia compared with oral administration, and can lead to higher opioid use.
As explored in the previous step, the use of modified-release (MR) preparations is no longer recommended. Similarly, compound analgesics (fixed-ratio combinations of two or more medications, such as co-codamol and co-dydramol) are not recommended as they do not allow titration according to need or weaning of the opioid alone as pain decreases [4].
There are unfortunately few studies which allow evidence-based recommendations on optimum dosing or dose intervals of IR opioids to be made [5].
The use of fixed doses and intervals, not tailored to individual patient characteristics (e.g. IR morphine 10-20 mg as required every 4-6 hrs for all patients), or of regular IR opioid doses, raises similar concerns regarding safety as well as poor analgesia as the routine use of MR opioids.
There is some evidence to back recent recommendations that the initial prescribed dose of IR opioids should be age-related (rather than weight-related) and that both the dose and agent choice should take into account renal function [5]. Patient age is a better predictor of postoperative opioid requirements than weight. This is due to increased central nervous system (CNS) sensitivity to opioid effects rather than changes in metabolism.
Post-operative IR opioids should be prescribed on an as required (pro re nata – PRN) basis, and the dose titrated to effect. The timing of assessments after administration of a medication depends on its time to achieve peak effects, typically 1 hour after administration of an oral IR opioid.
A PRN dose interval of 2 hours, instead of the 4-6 hours which is more customary in the UK, allows titration to effect as well as pre-emptive administration before activities which are expected to elicit pain, like physiotherapy.
This clearly requires effective and frequent communication with the patient to assess response to analgesia, and is probably the reason regimes with regular MR preparations as the mainstay of analgesia are preferred, since they are perceived to require less nursing input (although there is little evidence to support this) and to be safer (which the evidence shows not to be the case, as the concurrent administration of MR and IR opioids is associated with greater incidence of ORADEs).
The preoperative administration of opioids (a practice historically known as ‘opioid loading’) has not been shown to decrease postoperative pain or opioid consumption and is not recommended.

Multimodal analgesia

Randomised trials have shown that multimodal analgesia, the simultaneous use of more than one medication acting at different receptors, or of a single medication administered through more than one technique, eg systemically and neuraxially (via spinal [intrathecal] or epidural injection), is associated with superior pain relief and decreased opioid consumption than unimodal analgesia [2].

An example of this is the use of local anaesthetic-based regional (peripheral and neuraxial) analgesic techniques in combination with non-opioid analgesics administered regularly, with systemic opioids as rescue analgesia. Systemic opioids may not be required at all in some patients when this approach is used.

The addition of non-pharmacological interventions may also be of additional benefit.

The specific combination of appropriate multimodal interventions possible will vary depending on the specific surgery, individual clinical factors and patient choice.

Resources such as PROSPECT, the Australia and New Zealand Faculty of Pain Medicine’s Acute Pain Management: Scientific Evidence [1] or the American Pain Society’s Guidelines on the Management of Postoperative Pain [2] can be used as a guide.

The reverse pain ladder

As acute postoperative pain gets better with healing, we give most analgesia after surgery, then go down the analgesic steps as the pain settles. As we saw in Step 1.19, this concept is referred to as the ‘reverse pain ladder’.

Reverse pain ladder diagram demonstrating the three step approach to weaning analgesia over time as pain decreases. In the course of normal recovery, and as pain improves, patients would be expected to 'step down' the ladder from left (opioids) to right (no opioids), stopping opioids first.

The diagram above shows a three-step approach to weaning analgesia over time as pain decreases. In the course of normal recovery, and as pain improves, patients would be expected to ‘step down’ the ladder from left to right, stopping opioids first. Depending on the severity of postoperative pain, on discharge from hospital a patient may be started on the top step, step 3. They should be prescribed a higher potency IR opioid (eg morphine or oxycodone) for a limited period, along with regular simple analgesics (paracetamol and if not contra-indicated, a non-steroidal anti-inflammatory drug [NSAID]). The next step down, step 2, utilises lower potency opioids (e.g. codeine, dihydrocodeine or tramadol). Again, these should be in combination with simple analgesics. As pain improves, opioids can be weaned off completely on step 1 with the patient continuing with paracetamol (plus NSAID) until no longer required.

References

1. Schug SA, Palmer GM, Scott DA, et al. Acute Pain Management: Scientific Evidence (5th edition). APM:SE Working Group of the Australian and New Zealand College of Anaesthetists and Faculty of Pain Medicine, Melbourne (2020).

2. Chou R, Gordon DB, De Leon-Casasola OA, et al. Management of postoperative pain: A clinical practice guideline. J Pain 2016;17:131–57.

3. Wilkinson P, Srivastava D. Surgery and Opioids: Best Practice Guidelines 2021. Faculty of Pain Medicine. Faculty of Pain Medicine, London (2021).

4. Levy N, Quinlan J, El-Boghdadly K, et al. An international multidisciplinary consensus statement on the prevention of opioid-related harm in adult surgical patients. Anaesthesia 2021;76:520–36.

5. Quinlan J, Levy N, Lobo DN, et al. No place for routine use of modified-release opioids in postoperative pain management. Br J Anaesth 2022;129:290–3.

© UCL
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Opioids and Surgery

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