Poorly controlled post-operative pain is one of the most frequently cited fears in patients about to undergo surgery. Even now, with a variety of drugs and modalities available for managing acute post-operative pain, improvements are still needed.
An increasing amount of surgery is now carried out on a day-case basis, with the length of stay for other procedures also reducing. Effective post-operative pain management is pivotal in minimising length of stay and facilitating prompt mobilisation. Initiatives such as the Enhanced Recovery Programme driven by the Quality, Innovation, Productivity Prevention (QIPP) agenda in the NHS have explored effective analgesic strategies that reduce overall recovery times, such as minimising opioid use to optimise the return of normal gut function.(1) Equally, it has also been recognised that even uncomplicated surgical procedures can result in chronic pain syndromes.
Increasingly complex surgical procedures are now being undertaken, and surgery is being carried performed on an increasingly ageing population. Multiple comorbidities and associated polypharmacy are common, adding to the considerations when selecting an effective and safe post-operative analgesic regimen.
A number of factors are associated with an increased level of post-operative pain. These are summarised in Table 1.
Some of these factors can be modified to potentially reduce the intensity of post-operative pain, such as utilising the laparoscopic approach, which requires only small surgical incisions. Other factors cannot be modified, but should instead be proactively identified pre-operatively to plan an effective post-operative pain management strategy. Guidelines that take into account the clinical factors associated with different surgical procedures should optimise analgesic regimens.(2) The provision of patient information pre-operatively regarding post-operative pain can manage unrealistic patient expectations and minimise associated fear and anxiety.
Assessment of pain severity
Pain is a subjective experience, so accurate assessment of the patient’s perceived level of pain is essential before appropriate analgesia can be administered. Validated pain assessment tools are essential to minimise variation in practice and documentation. Pain should be assessed at rest and on movement and re-assessed at regular intervals, including after analgesia has been administered. These assessments should be accurately documented. A number of different validated pain assessment tools are available:
- The Numerical Rating Scale (NRS): The patient is asked to rate their pain on a scale of 0–3, 0–5 or 0–10, with 0 being no pain and the largest number being the most pain imaginable.
- The Visual Analogue Scale (VAS): The patient is asked to rate their pain by marking a cross on a line marked at one end with “no pain” and at the other end with ‘worst possible pain’.
- The Verbal Rating Scale (VRS): The patient is asked to rate their pain verbally according to descriptions of ‘none’, ‘mild’, ‘moderate’, ‘severe’ or ‘very severe’.
- Faces pain scales: The patient is asked to point to a pictogram of a face that describes their pain level. These range from a smiling face through to a tearful face. Most centres will agree on one scale to be utilised on the majority of their patients, to facilitate consistency and familiarity amongst staff. However, the Faces pain scale is particularly useful for those patients otherwise unable to communicate their pain, such as children, the elderly and those with communication difficulties.
Multi-modal analgesia, or utilising a combination of two or more analgesics from different classes, is accepted as the optimal approach to managing post-operative pain. Regimens that avoid or minimise the use of opioids are preferred in those undergoing day-case or short-stay surgical procedures. By utilising drugs with different modes of action there should be a synergistic effect, hence enabling individual drug doses to be kept to a minimum and to minimise associated side effects, particularly those of the opioids. The use of regular paracetamol has been shown to reduce morphine doses by less than 20%, compared with 40% when morphine and regular non-steroidal anti-inflammatory drugs (NSAIDs) are used together.(3) Regimens should be increased and decreased in a step-wise manner.
Paracetamol is an effective analgesic and should be the cornerstone to all post-operative analgesic regimens. An intravenous preparation is available for those unable to tolerate oral medication.
NSAIDs are effective post-operative analgesics. However, concerns regarding their side effects and contraindications limit their use. In appropriate patients, NSAIDs used during the first three-to-four days post-operatively improve pain management and may reduce opioid usage, thereby reducing the incidence of opioid-related side-effects, such as nausea, vomiting and sedation.(3)
Opioids are still a key component of analgesic regimens for moderate-to-severe post-operative pain. Codeine and tramadol are frequently used weak opioids, either as rescue analgesia to supplement regular non-opioids or on a regular basis if rescue doses are insufficient. Patient-controlled analgesia (PCA), utilising intravenous strong opioids such as morphine, is widely recognised as the preferred method for administering strong opioids post-operatively. Studies show that this method provides more effective analgesia compared to intramuscular administration and that patient satisfaction is high.(4) For PCA to be an effective method of delivery, however, effective staff training, appropriate patient selection and subsequent education and monitoring are essential. Alternative methods of delivery of PCA are also being developed, such as intranasal administration.
Regional and local anaesthesia
The use of local anaesthetic agents is now an essential component of multi-modal analgesia regimens. Localised wound infiltration of local anaesthetics at the end of surgery can effectively improve post-operative pain relief. Local anaesthetics can also be infused into the wound on a continuous basis over a fixed period of time. Methods of delivery include a standard infusion pump device or an implantable disposable device, such as the On-Q Painbuster device®. The On-Q Painbuster is an elastomeric pump that delivers local anaesthetics at a pre-set flow rate. The advantages of using such a system include:
- Simplicity of use
- Shorter duration of hospital stay
- Reduced treatment costs
- Decreased complications associated with anaesthetics.
- The advantages of using such a system in long-term wound infiltration include:
- Reduced side effects
- Faster resumption of full body functions and range of motions
- Quicker recovery and faster healing
- Improved the patient comfort
- Cost effectiveness.
Continuous infusions into abdominal wounds have been found to promote early mobilisation and reduce post-operative opioid requirements.(5) Local anaesthetics have also been peri-operatively infused into the leg stumps of amputees with some success. Local anaesthetics plus or minus local anaesthetics can also be administered via the epidural route and are suitable for many patients undergoing major procedures, such as thoracotomy or upper gastrointestinal surgery. Some systems enable the patient to deliver bolus doses themselves (patient-controlled epidural analgesia). The delivery of opioids via the epidural route minimises the overall opioid consumption; it is essential that these patients are managed by an experienced multi-disciplinary team because the potential risks associated with epidural analgesia are high. Nerve blocks, for example transversus abdominis plane (TAP) blocks, can also reduce pain post-operatively, although data to support other benefits, such as reducing opioid usage or reducing nausea and vomiting, are lacking.(6)
More commonly utilised for the management of patients with chronic neuropathic pain, gabapentin is now being utilised for its potential benefits in treating post-operative pain and reducing opioid consumption. Side-effects such as sedation and dizziness might limit its use. Gabapentin has also been utilised peri-operatively, with doses being commenced pre-emptively at the pre-operative stage to minimise the incidence of developing chronic pain after procedures such as hysterectomy and herniorraphy.(7) Pregabalin has been used in a similar way, although there is less evidence to support its overall benefits.
Non-pharmacological methods may have some benefits in managing post-operative pain in conjunction with drug therapy. These include the application of cold, acupuncture, TENS and the use of distraction and relaxation techniques.
Some elderly patients might have difficulty in communicating their pain and in utilising standard pain assessment scales. Their expectations regarding acceptable levels of pain can be different, and many adopt a stoical attitude and are reluctant to accept regular analgesia. Age-related pharmacokinetic and pharmacodynamic changes might result in a higher incidence of side-effects, in addition to comorbidities and concurrent medication.
The main issue in appropriately managing post-operative pain in children is in identifying and assessing their pain. Some children may be able to utilise the Faces pain scales, but in the very young it might be necessary to rely on visual signs such as facial expressions and behaviour. Similar drugs can be utilised as used in adults but it is essential to utilise child-friendly formulations to facilitate compliance. It must be remembered that children cannot be relied upon to request analgesia, so regular administration, or at least regular prompting, is preferable.(8)
Chronic pain patients
Many patients take long-acting opioids to manage chronic pain problems. These patients present an additional challenge because they are more likely to suffer from higher levels of post-operative pain and to require larger doses of opioids post-operatively.(9) Potential reasons for this observation are complex, possibly including chronic opioid tolerance or opioid-induced hyperalgesia. These patients need to be identified at the earliest opportunity and an analgesic plan formulated for the entire peri-operative period. This should ensure the continued control of their chronic pain issue with supplementary analgesia to manage their acute post-operative pain, with a smooth transition back to their usual analgesia after the post-operative pain has abated.
Patients that misuse opioids present similar challenges. However, their usual opioid consumption may be comparatively high and in addition many may have complex psychological problems. Accurate pain assessment may be difficult, with some healthcare staff doubting the patients’ responses because of their history of misuse. Non-opioid analgesics should be maximised, but there should not be a reluctance to use opioids if required to control post-operative pain. A proactive strategy should be formulated to ensure that opioids are for an appropriate duration with a clear plan for the return to the patients’ usual heroin substitute, if appropriate.
Role of the pharmacist in the team
Pharmacists should be integral members of the multidisciplinary pain team, preparing guidelines and ensuring the safe and appropriate use of analgesics. Some epidural or PCA preparations are not available in a licensed, ready-to-use form, so it is essential to source or manufacture products of suitable quality that minimise the potential for wrong-route administration errors. A pharmacist’s input into the management of more complex patients is essential, such as those with polypharmacy or additional pharmacokinetic considerations. Newer formulations often have additional safety considerations, with the input of a specialist pharmacist being essential to ensure their safe and appropriate introduction into practice.
- Poorly-controlled post-operative pain is one of the most frequently cited fears in patients about to undergo surgery.
- Effective post-operative pain management is pivotal in minimising length of stay and facilitating prompt mobilisation.
- Accurate assessment of the patient’s perceived level of pain is essential before appropriate analgesia can be administered.
- Localised wound infiltration of local anaesthetics at the end of surgery can effectively improve post-operative pain relief.
- Pharmacists should be integral members of the multidisciplinary pain team, preparing guidelines and ensuring the safe and appropriate use of analgesics.
- Wilmore DW et al. Management of patients in fast track surgery. BMJ 2001;322:473.
- European Society of Regional Anaesthesia and Pain Therapy. PROSPECT: Procedure Specific Post-operative Pain Management. www.postoppain.org (accessed 9 July 2012).
- Elia N et al. Does multimodal analgesia with acetaminophen, nonsteroidal antiinflammatory drugs, or selective cyclooxygenase-2 inhibitors and patient-controlled analgesia morphine offer advantages over morphine alone? Meta-analyses of randomized trials. Anesthesiology 2005;103:1296–304.
- Werawatganon T, Charuluxanun S. Patient controlled intravenous opioid analgesia versus continuous epidural analgesia for pain after intra-abdominal surgery. Cochrane Database Syst Rev 2005 Jan 25;(1):CD004088.
- Wang LW et al. Wound infusion with local anaesthesia after laparotomy: a randomized controlled trial. ANZ J Surg 2010;80:794–801.
- Charlton S et al. TAP blocks (nerve blocks) for analgesia after abdominal surgery. Cochrane Database Sys Rev 2010;12:CD007705
- Sen H et al. The effects of gabapentin on acute and chronic pain after inguinal herniorrhaphy. Eur J Anes 2009;26:772–6.
- Morton NS. Management of postoperative pain in children. Arch Dis Child Educ Pract Ed 2007;92:14-19.
- Carroll IR, Angst MS, Clark JD. Management of perioperative pain in patients chronically consuming opioids. Reg Anesth Pain Med 2004;29:576–91.