Although the currently available armamentarium of analgesic and antiemetic drugs is impressive, management of acute postoperative pain, as well as nausea and vomiting, poses some unique challenges to ambulatory surgery. White (1995)indicated the increasing number and complexity of operations being performed on an outpatient basis present the practitioners of ambulatory anaesthesia with many unique challenges. Outpatients undergoing day-case procedures require an analgesic technique that is effective, has minimal side effects and can be easily managed away from the hospital.
Patient Controlled Analgesia is a pain control treatment developed in the late 1970s (48). Its advantage is that patients can self-administer opioids intravenously, according to their individual demands, by pressing a button. In 1982, Bennett's experimental results indicated that PCA is preferable to IM (intra-muscular injection) because it can meet individual pain requirements.
The disadvantage of PCA for postoperative pain relief is its related adverse effects. These include nausea, vomiting, dizziness, tiredness, respiratory depression, lack of concentration, and lethargy (White, 1988; Parker, Holtman and White, 1991).
With PCA, opioids can be administered by a nurse under the physician’s order at the patient’s request. Opioids have been used as an analgesic for most postoperative pain management (Barratt, 1997; Moote, 1994). Possible adverse effects are respiratory depression, constipation, vomiting, gastroparesis, and central nervous system depression including somnolence and conscious disturbance (Tortora, 1989; Follin, and Charland, 1997).
White (1995) also indicated that the control of postoperative pain and emesis is the most important factor in determining when a patient can be safely discharged from an outpatient facility. Since inadequately treated pain and emesis are among the most common problems after ambulatory surgery, the ability to provide adequate pain relief without exacerbating post-operative nausea and vomiting (PONV) remains one of the major challenges for providers of outpatient anaesthesia and surgery. Although peri-operative analgesia has traditionally been provided by opioid analgesics, aggressive use of opioids can be associated with sedation and an increased incidence of PONV, which, in turn, contributes to a delayed discharge from the day-care facility.
Non-Steroid Anti - Inflammatory Drug (NSAIDs) have shown a morphine-sparing effect when administered as postoperative pain control. Associated side effects include headache, drowsiness, vomiting, peptic ulcers, gastrointestinal irritation/bleeding, platelet dysfunction, and bronchospasm (d’Amours and Ferrante, 1996; Follin and Charland, 1997; Barratt, 1997; Tobias, 1997).
Local anesthetics can be administered by epidural, subarachnoid routes, or as a peripheral nerve block. Successful use of opioids can reduce side effects, such as vomiting and respiratory depression (Barratt, 1997; Follin and Charland, 1997).
Pharmacologically, the ideal analgesic would have quick onset of action, no unwanted effects, no ceiling effects and no tolerance. No drug meets all these requirements, but morphine and pethidine (meperidine) present the best compromise and are the most frequently used (Lubenow and Ivankovich, 1991).
In practice, the unwanted effects of opioid analgesics are varied. The extent and the type of unwanted effects which appear at various concentrations depend on each individual patient. A balance between analgesic effects and unwanted effects must be found for each individual. PCA is uniquely suited for this task, as it allows each patient to find his or her own balance between some of the unpleasant unwanted effects and analgesia. The following is a list of
common systemic effects of opioid agonists used in PCA (Mather and Owen, 1990, Eige 1992).
• Central nervous system effects usually consist of diminished responsiveness to nociceptive stimuli, mood elevation and sedation. In addition, further effects may include mental clouding, dizziness, dysphoria and hallucinations.
• Respiratory system effects are primarily reduced ventilatory response to CO2 (and to hypoxia) with the potential for respiratory depression. Unfortunately, potency of analgesia parallels the respiratory depressant action, so that as a patient receives more analgesic the risk of respiratory depression also increases. Respiratory depression is the most serious of the acute unwanted effects of opioids.
• Effects on the gastrointestinal system especially ileus include nausea and vomiting as well as uncoordinated gut activity, often resulting in constipation.
• Circulatory system effects are minimal at standard post-operative doses. Morphine and pethidine can sometimes cause hypotension.
• Other effects of morphine include generalized itching, disrupted sleep and nightmares (Fulton and Johnson, 1993).
It should be noted that the proposed PCA system features safety monitoring devices to monitor respiration rate, arterial oxygen saturation (SpO2) and end-tidal carbon dioxide concentration (ETCO2), primarily with the aim of detecting respiratory depression due to over sedation from analgesics. Respiratory depression resulting in apnoea is the most serious of the unwanted effects, although less severe effects are also of concern and may be the reason for discontinuation of PCA therapy (Rudolph, 1995).
The ratio of efficacy to toxicity is referred to as the therapeutic index and is traditionally defined in the literature as the ratio of the amount producing the adverse effect in 50 percent of the test population to the amount producing the desired effect in 50 percent of the test population. A high therapeutic index indicates a drug in which the unwanted effects are minor and the desired effects dominate. For PCA, a drug with a high therapeutic index would be particularly important because of the large differences, in between patients in amounts required for efficacy. However, the commonly used drugs in acute pain relief have a small therapeutic index relative to the range of effective dosages required by patients. This is one of
the reasons which makes a generalised approach to acute pain relief difficult, particularly as there are no suitably objective parameters of a patient’s analgesic requirements (Rudolph, 1995).
Adverse effects are associated with high systemic concentrations caused by over dose or accidental intravascular injection, resulting in central nervous system reactions like dizziness, visual and auditory disturbances. In extreme cases cardiovascular toxicity caused death (Follin and Charland, 1997). Other effects include hypotension, hypertension, numbness, motor block or loss of motor power and neurological injury (Gissen, Covino and Gregus, 1982; d'Amours, and Ferrante, 1996; Tobias and Thomas, 1995).
In order to minimize these opioid-related adverse effects, "balanced" analgesia techniques involving the use of opioid and non-opioid analgesic drugs (local anaesthetics and non- steroidal anti-inflammatory drugs (NSAIDs) are becoming increasingly popular. Local anaesthetic techniques, peripheral nerve blocks and wound infiltration with local anaesthetics are becoming increasingly popular adjuncts to general anaesthesia because they can provide considerable intra-operative and post-operative analgesia. These techniques decrease the incidence of pain and reduce the requirements for narcotic analgesics in the peri-operative period. Effective pain relief in the early post-operative period provides for rapid and smooth recovery, enabling earlier ambulation and discharge from the ambulatory surgery unit. The use of local anaesthetic techniques for postoperative pain control can also decrease the incidence of PONV and, thereby, potentially lower the incidence of unanticipated hospital admission after ambulatory surgery (White, 1988).
White (1988) also indicated that non-pharmacological techniques Transcutaneous electric nerve stimulation (TENS) or acupuncture-like transcutaneous electrical nerve stimulation (ALIENS), as well as peri-cutaneous electrical nerve stimulation (PENS), have been utilized in the treatment of both acute and chronic pain in the ambulatory setting. Given the inherent side effects produced by both opioid and non-opioid analgesics, as well as the local anaesthetics, it is not surprising that nonpharmacological approaches to managing acute postoperative pain are increasingly popular in the outpatient setting. The mechanisms by which TENS, ALIENS, and PENS exert their analgesic action have not been completely
elucidated. However, possible mechanisms include: (1) stimulation of descending pain inhibitory pathways, (2) an inhibition of substance-P release in central nervous system (CNS) structures, and (3) the release of endogenous opioid substances within the CNS.
Postoperative nausea, retching and vomiting are among the most common postoperative complaints which occur after general, regional and local anaesthesia. Although much less problematic in patients receiving local anaesthesia as part of a monitored anaesthetic care technique, the incidence of postoperative emesis in recent large studies has been reported to be in the 20-30% range, which is consistently lower than the 75-80% incidence reported during the "ether" era. Nevertheless, persistent nausea and vomiting may result in dehydration, electrolyte imbalance, and delayed discharge after outpatient surgery. Persistent retching or vomiting can cause tension on suture lines, venous hypertension and increased bleeding under skin flaps, as well as exposing the patient to an increased risk of pulmonary aspiration of vomitus (if the airway reflexes are depressed from the residual effects of anaesthetic and analgesic drugs). Although frequently described as a "minor" postoperative complication, the incidence of severe (intractable) nausea and vomiting has been reported to be 1 in 1000 (0.1%). Factors affecting post-operative nausea and emesis include the patient's demographic characteristics, the nature of the underlying disease for which the surgery is being performed, the type of operation, and the anaesthetic drugs and techniques (White, 1988).
In conclusion, White indicated that as a result of enhanced understanding of the mechanisms of acute pain and the physiological basis of nociception, the provision of "stress free" anaesthesia with minimal postoperative discomfort is now possible for most patients undergoing ambulatory surgical procedures. The aim of any analgesic technique should not only be to lower the pain scores but also to facilitate earlier mobilization and to reduce peri- operative complications, in particular PONV. In future, clinicians should be able to effectively treat postoperative pain using a combination of "balanced," "preemptive," and "peripheral" analgesia techniques without producing emetic sequelae.