Case 15.5

Managing chronic pain patients for elective surgery

Background

With every patient, there are different issues surrounding pain management, and the patient with chronic pain presenting acutely can be a particular challenge.

Recent data suggest that chronic pain is as prevalent as one in six of the population. Only a small proportion of those are referred to specialist pain services, and yet many are seen by virtually all other medical specialties and allied professions. Chronic pain results in changes to the nervous system, producing hyperaesthesia, allodynia, and central sensitization. Unfortunately, due to these factors, the chronic pain patient’s acute pain experience is usually worse than that of the rest of the surgical population. Chronic pain patients often have a fear of increased pain and worry their pain will be severe and uncontrolled. They may display hypervigilance, fear, and anxiety.

Learning outcomes

1  Recognize the difficulties in managing patients with chronic pain through the perioperative period

2  Understand the need for additional analgesia whilst still meeting background analgesic requirements

3  Have a familiarity with dose conversions between differing routes of administration and opioid agents.

CPD matrix matches

2E01; 2E02

Case history

You have been referred an anxious 46-year-old female who is scheduled for major lower bowel resection for surgical management of inflammatory bowel disease. She has had several procedures before and suffers from chronic abdominal pain. She has attended the chronic pain clinic in the past and is on several analgesic medications. She has been in hospital for a few weeks, with an inadequate response to medical management, and has become increasingly more frail and in more pain. It is anticipated that she will be undergoing a prolonged open procedure.

What needs to be considered when managing this patient’s pain?

Pain is an unpleasant sensory and emotional experience, and pain perception is affected by biological, psychological, and social influences—the biopsychosocial model of pain. How a person experiences pain is modified not only by specific receptors in the body (the usual target for pharmacological treatment), but also by many processes within the brain and nervous system which, in turn, are affected by emotions, beliefs, and circumstances. These powerful influences are more challenging to treat and, in chronic pain, often require time and perseverance.

Chronic pain patients are likely to have consulted a number of health professionals, seeking either relief of their pain or investigation into its cause. They may be on a number of analgesic medications, and some patients will be on strong opioids.

Pre-assessment

As with any surgical patient, a thorough history and assessment is required. In addition to your pre-assessment questions, ask about the patient’s pain. Where is it? How often do they have it? What does it feel like? Does it affect sleep, mood, working life, daily activities? What makes it worse or better? Any information about their pain can be valuable.

Information should be obtained about previous pain management, acute and chronic. Ask about treatments tried, including medications, how effective they were, and why they were stopped or changed. A lot of people with problematic pain have tried several strategies before, and the treatment was either ineffective or intolerable. Look through medical notes—anaesthetic charts, medicine prescription charts, and clinic letters—and establish how post-operative pain was managed previously. Ask how the patient felt about these past experiences. You may find she had a wonderful experience with one operation, but a dreadful time with another which will help you plan your own management.

Case update

Your patient describes her abdominal pain as a deep, almost constant, ache with intermittent episodes of sharp, stabbing pain in her lower abdomen. She also complains of sharp, burning pain across her abdomen, worse around previous surgical scars. The pain can wake her at night, is often related to food, but it can come on at any time. Before this episode, her pain, although present, was controlled. It interfered less with her day-to-day life than previously, and she had recently returned to studying for her university degree. She scores her usual pain level as 4/10 on a verbal rating scale (VRS).

Since her admission, her pain has been much worse and more continuous. Her usual medications include paracetamol, slow-release morphine 50 mg, short-acting oral morphine 15 mg, as required (taken twice on normal days, sometimes more, up to six times per day), gabapentin 600 mg three times daily, sulfasalazine, and lactulose. During this admission, she has had IV antibiotics and steroids. She has been intermittently nil by mouth and has been mainly receiving subcutaneous morphine 10 mg for analgesia.

In the past, she has tried amitriptyline which did not help her pain significantly but did leave her feeling drowsy and with a terribly dry mouth. Prior to starting morphine, she took tramadol and codeine which did not work well for her pain and worsened her inflammatory bowel symptoms. She completed a pain management programme a year ago where she learned relaxation skills to help her cope with her pain symptoms. She practises this 2–3 times a week.

She had a laparotomy with bowel resection 3 years ago, following a severe flare-up, requiring high dependency care. Her anaesthetic management at that time was general anaesthesia with opiates and a ketamine bolus, followed by morphine PCA. She had a lot of pain post-operatively, and the acute pain team were involved. She is currently 62 kg.

A letter from the chronic pain clinic suggests, in addition to the pain from her inflammatory bowel disease, she suffers from CPSP with hyperalgesia and allodynia around the area of her abdominal scars.

Who may be able to assist you with planning this patient’s analgesia?

It is important to make the acute pain team aware of any patients with potentially complicated analgesia and to discuss your plan with them. It may also be useful to inform the chronic pain consultant involved with the patient, particularly if they are still seeing the patient regularly or if you have any questions about their treatment.

How would you manage this patient’s opioid therapy through the perioperative period?

Patients on chronic opioid therapy may include chronic pain patients, cancer patients, and patients with substance misuse disorders. For many of these patients, a dose reduction is part of their long-term treatment plan. Patients can be anxious about increasing their opioid, which may be perceived as a failure or setback, and also fearful of anticipated pain. The acute situation is not the time to be focussed on reducing the background opioid dosage, and the patient, and staff involved in their care, should be aware of this. A more realistic aim would be to discharge the patient with a regime similar to what they were prescribed prior to admission, or a clear plan with that goal in mind. Occasionally, an operation does reduce, or remove, the cause of pain, such as in some cases of cancer surgery or neurosurgery, and the dosage of opioid should be decreased cautiously, bearing in mind that an abrupt cessation may result in withdrawal symptoms.

The selection of opioid and the route of administration depends on the individual patient’s situation. The aim is to administer a suitable dose that provides satisfactory pain relief and to avoid detrimental effects, including opioid toxicity. Ideally, the background opioid dose should be maintained, and the acute pain treated in addition.

In this patient’s circumstance, where she has been acutely unwell and has not been able to take oral medications, opioids must be provided by another route. An appropriate solution would be a background IV morphine infusion, combined with PCA. This approach would usually require high dependency care to ensure appropriate monitoring is provided.

Discuss the oral to intravenous opioid conversion equivalences

Your patient takes morphine sulphate, slow-release tablets, totalling 100 mg/24 hours and equalling 33 mg/24 hours intravenously. This dose would be provided by an infusion with concentrations of morphine sulphate of 2 mg/mL at 0.5–1 mL/hour. Her daily requirements in hospital are likely to be higher and should be calculated from her medicine chart. It is likely the 10 mg morphine subcutaneous injections she has been receiving are inadequate, and she may require an initial loading dose of morphine to control her pain. Once the morphine PCA is in place, the patient should be reviewed after a few hours to ensure optimal pain control. Direct comparison of opioids and consequent equianalgesic doses can be difficult to ascertain. Local guidance should be consulted. Table 15.4 provides a guide with information drawn from personal knowledge and corroborated by several sources such as the British National Formulary’s Prescribing in Palliative Care, MIMS online, and the Scottish Intercollegiate Guidelines Network guideline (see Further reading at the end of this case).

Table 15.4 Opioid equivalence table

	Dose equivalent
Morphine PO	10 mg
Morphine IM/SC	5 mg
Morphine IV	3.3 mg
Morphine epidural	1 mg
Diamorphine SC/IV	3 mg
Tramadol PO	50–100 mg
Dihydrocodeine PO	100 mg
Codeine PO	80–100 mg
Oxycodone PO	5—6.6 mg
Oxycodone IV	3—5 mg
Fentanyl IV	100 micrograms

PO, oral; IM, intramuscular; SC, subcutaneous; IV, intravenous.

Note: this is a guide only. Any change in opioids should be done with caution, due to interindividual variations of cross-tolerance and metabolism.

If opioid switching is necessary, an opioid conversion tool should be consulted to calculate equivalent doses (see also Table 15.5). Some physicians, when switching opioids, e.g. from fentanyl to morphine, advocate reducing the 24-hour dose by up to 50%, as patients genetically differ in cross-tolerance to opioids, and there is a risk of inducing opiate toxicity. This is less of an issue in the hospital setting where the patient can be monitored closely, and, during a dose reduction, the patient can be given additional opioid at any time, if required. Close monitoring is particularly desirable for the patient on high-dose opioids (>200mg of oral morphine equivalent/24hours).

Table 15.5 Transdermal opioid conversion tables

Based on the recommendations by the manufacturers and British National Formulary.

What are the general guidelines for dealing with any patient requiring opioids?

◆  Minimize the number of routes of administration and of the different types of opioids. For example, if a patient’s background opioid is a fentanyl patch and this is to continue, a fentanyl PCA would be an appropriate option. The more complicated things are, the higher the risk of drug error and opioid toxicity

◆  Write clear prescriptions, and document your plan in the medical notes. You may have formulated a perfect strategy, but unless it is communicated effectively, it will be lost when the out-of-hours team are dealing with the patient.

What non-opiate analgesia may be of use for this patient?

◆  Paracetamol reduces opioid requirements significantly. Some patients do not perceive it has benefits, but an explanation of its usefulness in increasing the efficacy of opiate medications usually helps with compliance

◆  NSAIDs are very effective analgesics. Of course, there are important contraindications (renal impairment, coagulopathy, and atopic asthma, to name a few), but ask at the pre-assessment visit if the patient is able to take them without side effects. Check with the surgeon if there are concerns about perioperative effects, e.g. in some orthopaedic surgery. Surgeons may be happy for NSAIDs to be prescribed as required or as a once-only medication. If the oral route is unavailable, IV and PR formulations can be used. Consider prescribing a PPI if concerned about gastric irritation (and continue for 2–3 days post-treatment)

◆  Local anaesthetics are used extensively to treat pain in the hospital setting. Where possible, use it. Consider it for every procedure—local infiltration, peripheral nerve blocks and catheters, neuraxial blockade, wound catheters or intravenous infusion. Local anaesthetics are particularly useful for wound pain and can be given in the recovery area, if necessary; ask the surgeon to do this if any concerns about injecting the wound area

◆  Ketamine, an NMDA antagonist, is a useful opioid-sparing analgesic, particularly for neuropathic pain (and it is increasingly recognized that acute surgical pain will often have a neuropathic element). Advise patients about side effects, as they are likely to be better tolerated if forewarned, e.g. hallucinations and dark dreams. It can be given as a bolus intraoperatively and/or a subcutaneous or IV infusion perioperatively. Many hospital wards are now comfortable managing subcutaneous ketamine infusions, alleviating the need for HDU care

◆  Clonidine, a centrally acting α2-agonist, is also a good opioid-sparing analgesic. Most often used perioperatively via the IV or epidural route, it can also come in immediate and slow-release tablets and patches. It is used in many conditions such as hypertension, restless legs, and opioid withdrawal. If administered intravenously, it can be given as a titrated bolus, with close monitoring for hypotension and bradycardia, or by infusion. As this is not used routinely for many cases, a patient on a clonidine infusion will require care in a high dependency area, with instructions clearly documented, including common adverse effects—as mentioned previously, plus drowsiness, dry mouth, headache, postural hypotension, and anxiety.

Is intravenous or oral opioid analgesia optimal?

◆  Oral opioids should be used whenever enteral fluids are well tolerated. This general principle applies to many medications. It removes the need for repeated IV or subcutaneous cannula insertions; it saves on resources and time for staff and is one move closer to the patient getting back to normal.

Whatever treatment you administer, it will be more effective if it is discussed beforehand with the patient. Explain how it will work, and reassure them that there is something that can be done for their pain. Remember that pain perception, and therefore pain relief, is about much more than just a few receptors in the CNS. The brain is a powerful tool; it can create pain when there is no physical stimulus and hide it where there is obvious tissue damage. Be empathetic, and your treatment will be more successful.

Case update

Your patient has her operation under general anaesthesia with a thoracic epidural. Post-operatively, she returns to the HDU where her background morphine infusion and PCA are continued, with a plain local anaesthetic epidural infusion. She is also prescribed regular paracetamol. On day 2, she is allowed sips of water; her oral morphine and gabapentin are restarted, and her background morphine infusion discontinued. You go to see her on day 3 when her epidural has been removed, and she is comfortable with her PCA and oral medication. She is hoping to be discharged to the ward today and expects her PCA to stop soon. Overall, she is pleased with the analgesia she received and thanks you for taking care of her.

Summary

Patients with chronic pain can be challenging to manage in the acute setting. The mainstay of acute perioperative analgesia is opioid medications, and there are many useful adjuncts such as local anaesthesia. Patients who are already established on opioid therapy need careful management at this time to avoid withdrawal syndrome, opioid toxicity, and uncontrolled pain. As with all pain management, communication is the key—including with the patient.

Further reading

British National Formulary. Prescribing in palliative care, March 2013.

British Pain Society (2010). Opioids for persistent pain: good practice. Available at: <http://www.britishpainsociety.org/book_opioid_main.pdf>.

Chou R, Fanciullo GJ, Fine PG, et al. (2009). Clinical guidelines for the use of chronic opioid therapy in chronic noncancer pain. Journal of Pain, 10, 113–230.

Kehlet H, Jensen TS, and Woolf CJ (2006). Persistent postsurgical pain: risk factors and prevention. Lancet, 367, 1618–25.

Lewis N and Williams J (2005). Acute pain management in patients receiving opioids for chronic and cancer pain. Continuing Education in Anaesthesia, Critical Care & Pain, 5, 127–9.

Macintyre PE, Schug SA, Scott DA, Visser EJ, and Walker SM; APM:SE Working Group of the Australian and New Zealand College of Anaesthetists and Faculty of Pain Medicine (2010). Acute pain management: scientific evidence, 3rd edn. Australian and New Zealand College of Anaesthetists and Faculty of Pain Medicine, Melbourne.

Macrae WA (2008). Chronic post-surgical pain: 10 years on. British Journal of Anaesthesia, 101, 77–86.

MIMS Online. Opioid analgesics: approximate potency equivalence with oral morphine. Available at:<http://www.mims.co.uk/Guidelines/1146201/Opioid-Analgesics-Approximate-Potency-Equivalence-Oral-Morphine/>.

Scottish Intercollegiate Guidelines Network (2008). Control of pain in adults with cancer, SIGN guideline 106. Available at: <http://www.sign.ac.uk/pdf/qrg106.pdf>.