This site is intended for health professionals only
BSc(Hons) MB ChB FRCA
Specialist Registrar in Anaesthesia
University College Hospitals NHS Trust
Department of Anesthesia
University of Toronto
Medical Director of Ambulatory Surgical Unit
Toronto Western Hospital
Ambulatory (day) surgery accounts for an estimated 70% of all surgical procedures in North America.(1) The UK has seen a dramatic increase in ambulatory surgery, from 34% in 1990 to 65% in 1997.(2) Rates are also increasing in the rest of Europe and Australia.(3) This is due to a combination of economic forces, improved anaesthetic and surgical techniques and better-coordinated preoperative planning. Successful ambulatory surgery is dependent on providing effective analgesia that produces minimal adverse effects (such as nausea and vomiting) and can be easily managed after the patient is discharged from the surgical centre.(4) The management of postoperative pain following ambulatory surgery has been noted to be inadequate in a number of studies.(5–9) Pain is the most common reason for delayed discharge(10) and for contacting the family physician after discharge from the hospital.(11) Inadequate pain control is the main reason for unanticipated hospital readmission following discharge.(12,13) The continuing success of ambulatory surgery will depend on the successful implementation of postoperative pain management strategies.
Incidence and severity of pain following ambulatory surgery
Recent studies have challenged the commonly held belief that patients merely experience mild pain after discharge following ambulatory surgery. The incidence of moderate- to-severe postoperative pain after discharge following ambulatory surgery has been reported as 21% in the UK(7) and ranging from 31%(14) to 40%(6) in North America. Most disturbing is that this moderate-to-severe pain can last for up to a week after surgery.(5,6) Despite this, patients in moderate-to-severe pain after discharge express satisfaction with their care.(15)
Patient satisfaction with pain management is a complex subject, often related to communication issues, reluctance of patients to report pain and the belief that pain is an inevitable consequence of surgery.(6) In the UK, a survey revealed that almost 50% of patients would tolerate pain after surgery rather than “complain” about it to their caregivers.(15) Interestingly, patients ranked pain in the top three most undesirable outcomes after ambulatory surgery.(16,17) Therefore, it is important for clinicians to realise that patients’ reports of satisfaction with their postoperative pain management after discharge do not necessarily mean that they are experiencing well-controlled pain during their recovery.
The problem with pain
Pain is a problem in that it is a distressing personal and subjective sensation that is difficult to quantify objectively. Pain has been informally defined as “whatever the experiencing person says it is, existing whenever he says it does”,(18) and as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”.(19,20) The American Pain Society (APS) recommendation that pain scores be documented on the patient’s record has resulted in pain being assessed as the fifth vital sign. In paediatric and adult populations, postoperative pain is associated with increased postoperative nausea and vomiting (PONV). (21,22) PONV results in delayed discharge after ambulatory surgery and unanticipated hospital admissions.(12,13) This has significant resource implications.
As the age of patients having ambulatory surgery increases, the potential for severe pathophysiological changes increases. Pain is particularly harmful in elderly patients with underlying chronic conditions, such as ischaemic heart disease and hypertension.(23) Persistent pain after discharge following ambulatory surgery has numerous adverse effects. Beyond discomfort and suffering, patients may experience sleep deprivation and delayed return to normal functioning.(23) Inadequately treated and persistent postoperative pain may also progress to debilitating chronic pain.(23,24) For example, this has been shown to occur following inguinal hernia repair, where the incidence of chronic pain has been reported to be as high as 12%.(24) Effective perioperative analgesia has also been shown to reduce the operative stress response and postoperative organ dysfunction.(25)
Identifying painful procedures
The visual analogue scale (VAS) and numerical pain rating scale have been validated for measuring pain intensity.(23) It is imperative that patients be taught how to use these self-report pain-rating tools before surgery, when they are awake and best able to understand instructions. In addition to proper assessment, an important first step in managing postoperative pain more effectively is to identify the procedures most likely to result in considerable pain. Being able to predict patients at risk of significant postoperative pain makes it possible to develop an effective preoperative, intraoperative and postoperative pain management strategy specifically tailored to age, physical condition of the patient and nature of the surgery. Recently, research by Chung and colleagues noted that 29% of ambulatory surgery patients were suffering moderate-to-severe pain 24 hours after surgery. The ambulatory procedures most likely to result in moderate-to-severe postoperative pain were identified and ranked according to severity of pain intensity (pain rated 3 or higher on the 0 to 10 VAS).(14) The most painful ambulatory procedures in descending order, from highest to lowest pain intensity score, were: lumbar microdiscectomy; laparoscopic cholecystectomy; shoulder; elbow and hand; knee; ankle; and inguinal hernia surgery.
General and regional anaesthesia
The choice of an anaesthetic technique depends on patient and surgical factors. All general and regional anaesthesia techniques have both advantages and disadvantages. The main disadvantages of general anaesthesia are the high incidence of PONV and moderate-to-severe postoperative pain, which may delay discharge.(9)
Regional anaesthesia utilises local anaesthetics that inhibit the transmission of neural impulses by reversibly inhibiting sodium channels in pain fibres. The main disadvantage of regional anaesthesia is that it is very time-sensitive. Planning is crucial as regional blocks take a longer time to take effect compared with general anaesthetics, although competitive discharge times and costs compared with general anaesthesia have been demonstrated.(26) Regional anaesthesia may be used as the sole anaesthetic technique or in combination with general anaesthesia to provide intraoperative and postoperative analgesia. The use of upper and lower limb peripheral nerve blocks provides excellent analgesia with minimal adverse effects such as PONV. Peripheral nerve blocks have enabled major shoulder and knee reconstructions to be performed on an ambulatory basis. However, when the local anaesthetic block wears off the pain experienced can be severe, and this must be anticipated and adequate rescue oral analgesia provided.(27) The postoperative analgesia from a peripheral block can be extended for up to 72 hours postoperatively using peripheral nerve catheters and local anaesthetic infusions from elastomeric pumps.(28)
Studies comparing patients having ambulatory arthroscopic shoulder surgery demonstrated that 8% of patients who received general anaesthesia without an interscalene block required unanticipated hospital admission overnight because of severe pain; none of the patients who received an interscalene block required an overnight stay.(29,30) Klein and colleagues demonstrated that, even with an insensate extremity after a block, patients could be safely discharged home.(31) It is important to recognise that approximately 20% of these patients may require oral opioid analgesia for up to seven days postoperatively, emphasising the need to anticipate and adequately prescribe analgesics for moderate-to-severe pain following discharge.(31)
Neuraxial techniques remain an alternative to general anaesthesia.(32) The advantages of neuraxial techniques are the avoidance of the risks of general anaesthesia, improved analgesia, a much-reduced requirement for postoperative opioids for pain relief and, thus, a reduced tendency for PONV.(33) The potential disadvantages of this technique include the time required to perform and await the onset of the block and neurological complications, including postdural puncture headaches and the rare but devastating risk of spinal haematoma or infection.
Pain is produced by several different mechanisms with many different mediators. These mechanisms are inducible and, once induced, the inflammatory process and sensation of pain are increased. The administration of analgesia before surgery (preemptively) may be effective in reducing the postoperative pain from surgery by preventing the peripheral and central sensitisation caused initially by surgical incision and later by inflammatory injury.
Some studies support the effectiveness of preemptive analgesia.(34) However, there is a lack of evidence for preemptive treatment with nonsteroidal anti-inflammatory drugs (NSAIDs), intravenous (IV) opioids, IV ketamine, peripheral local anaesthetics and caudal analgesia.(35) Despite this, the preoperative administration of nonopioid analgesia, such as paracetamol, NSAIDs and local anaesthesia, before surgical incision is an important component in reducing postoperative pain scores and analgesic requirements in the first 24 hours after discharge.(36)
Combinations of analgesics that act by different mechanisms result in additive or synergistic analgesia, allowing lower total doses of each of the drugs and thereby reducing adverse effects. A multimodal analgesic technique combines drugs, such as an opioid, NSAID, acetaminophen and a local anaesthetic, which act on different targets of nociceptive pain transmission. The combination of these drugs is superior to any modality alone, and the technique is highly recommended.(37) Clinical trials have demonstrated a reduction in postoperative opioid analgesic requirements by up to 40% when acetaminophen and NSAIDs are coadministered perioperatively.(38,39) Optimal postoperative pain management should strive to maximise analgesia while minimising opioid side-effects.
Paracetamol (also known as acetaminophen) is the most commonly used oral analgesic and antipyretic worldwide because it is cheap and effective for mild pain, and because it has a low adverse effect profile when the recommended daily dose is not exceeded. Paracetamol inhibits prostaglandin synthesis; however, unlike NSAIDS, it does not irritate the gastric mucosa, affect platelet function or cause renal insufficiency. Paracetamol has a significant opioid-sparing effect, which has been demonstrated in preoperative rectal doses of 40mg/kg in paediatric surgery.(39) The recommended rectal dose is higher than the recommended oral dose (from 15mg/kg every six hours to a maximum of 75mg/kg in a 24-hour period), because of unreliable absorption in the suppository form.(40) In children, the recommended rectal dose of paracetamol is 90mg/kg rectally in a 24-hour period.(41,42) The rectal route is preferred to avoid the problem of delayed gastric emptying or vomiting after opioid intake. The maximum adult oral dose is 4g over a 24-hour period. Paracetamol is also available in combination with opioids for postoperative analgesia. The ceiling on the recommended daily dose of nonopioid limits the usefulness of combination drugs to the treatment of short-term mild-to-moderate pain only.(23) In the UK, intravenous (IV) paracetamol (Perfalgan) has recently become available, and studies regarding its use in ambulatory surgery are awaited with interest.
NSAIDs are currently the drug of choice after daycase procedures. Traditional NSAIDs, called nonselective NSAIDs, have significant gastrointestinal (GI), haematological and renal adverse effects, mediated through inhibition of the isoenzyme cyclooxygenase-1 (cox-1). Examples of nonselective NSAIDs are aspirin, ibuprofen, diclofenac and ketorolac.
Relatively new to the family of NSAIDs are the cyclooxygenase-2 (cox-2)-selective NSAIDs, sometimes called cox-2-selective inhibitors. Under normal physiological conditions, minimal cox-2 is expressed; however, the inflammatory response induces cox-2 expression. This expression is partly responsible for the pain the patient experiences postoperatively after discharge.(43) Two oral forms of cox-2-selective NSAIDs are currently available, celecoxib (Celebrex) and valdecoxib (Bextra). Both appear to be as effective as nonselective NSAIDs in suppressing inflammation and providing analgesia for ambulatory surgery,(44) with less risk of GI toxicity. The incidence of endoscopy-verified ulcers with these drugs is reduced to levels similar to those seen with placebo.(45) Another significant advantage of the cox-2-selective NSAIDs over the nonselective NSAIDs in the perioperative patient is that they do not impair platelet function or increase bleeding time.(46)
A long-acting injectable IV formulation of a cox-2-selective NSAID, known as parecoxib, is available in the UK and Canada and is currently undergoing trials in the USA. Parecoxib is hydrolysed enzymatically to the active drug valdecoxib (which is available in tablet form). Both oral valdecoxib and IV parecoxib have been reviewed and concluded to be effective treatments for acute postoperative pain in ambulatory surgery.(47) The IV preparation is particularly useful in the immediate postoperative period when patients are unable to take oral medication or are suffering from PONV. Following the recent withdrawal of rofecoxib from the marketplace due to safety concerns, the spotlight has refocused on the cox-2-selective NSAIDS, and future prescribing will be guided by ongoing reviews and research.
Postoperative pain control is started intraoperatively by supplementing general anaesthesia with short-acting opioids such as fentanyl. In the postanaesthetic care unit (PACU), IV fentanyl or morphine can be used for moderate-to-severe pain. No difference in adverse effects was noted between IV morphine and IV fentanyl in the PACU setting. However, the incidence of nausea and vomiting in patients who received morphine increased significantly on the journey home.(48) It is prudent, therefore, to consider using fentanyl for severe postoperative pain in the PACU, in view of its ease of titration and rapid onset (three to five minutes) compared with morphine (eight to 30 minutes).
In addition to appropriate IV opioid titration, a long-acting oral opioid should be considered for surgery that is likely to result in moderate-to-severe postoperative pain after discharge. The operating room anaesthesiologist, who administers both intraoperative and immediate postoperative analgesia, can prescribe oral controlled- release oxycodone (OxyContin) for patients having surgery known to produce significant postoperative pain. Controlled-release oxycodone has been demonstrated to provide analgesia that takes effect in approximately 45 minutes and has a 12-hour duration of analgesic action. This allows a simple twice-daily dosing schedule, ensuring better compliance and improved sleep after discharge.(49) Controlled-release oxycodone has high bioavailability, as it does not undergo extensive first-pass metabolism and has a consistent absorption profile.(50,51) Comparison studies showed that controlled-release oxycodone has a better adverse effect profile for some patients than controlled-release morphine, with a tendency toward less nausea, vomiting and pruritus.(52) Unlike codeine, oxycodone does not depend on a patient’s genotype for its analgesic effect.
A study by Reuben and colleagues demonstrated that 20mg of controlled-release oxycodone given every 12 hours after ambulatory anterior cruciate ligament surgery provided superior analgesia with fewer adverse effects than “as required” immediate-release oxycodone in the first three postoperative days.(53) All patients in this study also received an intraoperative dose of a short-acting NSAID. In a later study, these authors randomised patients undergoing ambulatory laparoscopic tubal ligation to receive either 10mg controlled-release oxycodone or placebo preoperatively. Those who received the preoperative dose of controlled-release oxycodone were found to have lower postoperative pain scores, reduced PONV, shorter time to discharge and significantly reduced analgesic use after discharge home.(54)
Every effort should be made to ensure that patients leave the hospital or surgery centre with well-controlled pain and prescriptions for adequate and appropriate analgesics for the course of recovery. Patients should be told to take their opioid and nonopioid analgesics regularly “around the clock”, initially “as required”. As pain subsides, the analgesics may then be tapered as appropriate.
Adverse effects of opioids include constipation, urinary retention, vomiting and sedation. The patient must be informed of these adverse effects both verbally and in writing, and should also be told what to do if they occur. They should also be advised to prevent constipation by increasing their fluid, fruit and fibre intake and by taking a laxative plus stool softener daily during opioid therapy.
There has been a recent resurgence in interest in the use of single low-dose ketamine (0.1–0.15mg/kg) given towards the end of painful surgery. The use of this NMDA receptor antagonist results in significant opioid-sparing effects that can be long-lasting.(55–57)
Protocol-based analgesic management
Analgesic protocols can be useful tools for standardising pain management approaches and reducing variation in practice. Crews described the use of a multimodal analgesic ladder for postoperative ambulatory surgery based on whether the patient was expected to have mild, moderate or severe postoperative pain.(58) Crews proposes a standardised stepwise approach to pain management for ambulatory surgery that is based on the ubiquitous analgesic ladder of therapy for cancer pain developed by the World Health Organization. Lopez and colleagues demonstrated that a clinical guide for the treatment of postoperative pain based on Chung’s prediction of painful procedures could be used to improve pain management.(59) Eighty-six percent of patients who were cared for according to the guideline in this study rated their pain as less than 3 (VAS 0–10 scale) after discharge. Marquardt and colleagues reported that providing patients with discharge instructions that include protocols for ongoing maintenance analgesia and instructions on how to increase the analgesic dose for breakthrough pain resulted in improved pain control, mobilisation and sleep patterns for 72 hours postoperatively.(60) Postoperative pain may be present for at least one week after ambulatory surgery; therefore, an adequate supply of multimodal analgesics should be supplied in appropriate tapering doses.(61)
Ambulatory surgery departments should strive to standardise postdischarge analgesia regimens for all anticipated intensities of postoperative pain, and provide clear instructions on how to take additional analgesics for breakthrough pain. It has been noted that postoperative pain may be present up to one week following specific types of ambulatory surgery. Therefore, an adequate supply of appropriate analgesics must be prescribed at discharge.(5) Patient follow-up after discharge with a standardised telephone questionnaire to screen for patient understanding of postoperative instructions related to analgesia is essential, as it allows the patient to communicate concerns regarding their care and monitors the effectiveness of pain treatment.