Despite a growing trend in acute pain management, many deficiencies still account for the high incidence of moderate to severe postoperative pain to date. Patients nowadays continue to receive inadequate doses of analgesics, but additionally the identification and treatment of those patients with pain still remains a significant health care problem. Advanced techniques are available including epidural or intrathecal administration of local anaesthetics and opioids, various opioid administration techniques such as patient-controlled analgesia and infusions, or via sublingual, oral-transmucosal, nasal, intra-articular and rectal routes. Non-opioid analgesics such as non-steroidal anti-inflammatory drugs and newer non-opioid drugs such as alpha2-adrenergic agonists, calcium channel antagonists and various combinations of the above are possible. However, the solution to the problem of inadequate pain relief lies not so much in the development of new drugs and new techniques, but in the effective strategy of delivering these to patients.

The administration of opioids and local anaesthetics with patient controlled anaesthesia (PCA) is becoming ever more common in the treatment of acute postoperative pain [i] . This technique is used in several different ways of administration: aside from the widely known intravenous way, PCA is also performed in epidural analgesia [ii] , in peripheral plexus continuous blockade [iii] [iv] [v] and also by nasal [vi] [vii] or oral administration. The popularity of this technique is also accompanied by an increased concern over its safety, especially regarding the incidence of respiratory depression and its possible lethal consequences. Such scepticism is sometimes a result of a widespread “opiophobia” very common in Italy, where morphine usage is among the lowest in Europe.

 The theoretical advantages of patient-controlled administration are self-evident: if patients are enabled to press a button and receive their opioid dose only when they feel pain, the total amount of administered drug will be most likely reduced with respect to a continuous infusion. Such procedure allows patients to adjust their doses to suit their variable needs, as the demand for analgesics is only rarely constant throughout the day. For example, it’s quite evident how active or passive movement, or even cough may exacerbate perceived pain. There is also evidence that postoperative pain might function on a circadian rhythm characterised by a significant increase at night [viii] .

PCA technique has an intrinsic safety control, in that patients who start to develop respiratory depression are correspondingly sedated, thus usually unable to request any more (potentially dangerous) doses. Decreased consumption of drugs and a higher patient satisfaction rate have been demonstrated with this procedure [ix] . Clinical trials performed on over 10,000 patients have shown that the incidence of significant respiratory depression (such as to require medical intervention) is around 0.2%viii . This value is lower than that found with patients treated with intra-muscular opioids, which is 0.9% [x] [xi] . The incidence of respiratory depression was also considerably higher in studies performed in the 1980s on patients who were given continuous intravenous opioid infusionx . The usage of a basic continuous infusion in association with PCA seems to increase the risk of the dangerous complication to 1.65% of the cases [xii] [xiii] . In a study performed on 4,000 patients, only 9 of them had any respiratory complications, and in those cases the side-effects were always associated with pharmacological interactions, continuous opioid infusion or “nurse/physician-controlled analgesia” [xiv] . Also in childhood, the addition of a background continuous opioid infusion seems to increase the risk of adverse effects with no actual improvement of the pain score [xv] . Comparative studies show that continuous infusion does not reduce bolus demand, but instead increases the total amount of administered drug [xvi] [xvii] [xviii] . Continuous infusion may also reduce the safety of PCA, as it is administered independently of the patient’s sedation level (whereas a sedated patient cannot request additional boluses!). In the light of current knowledge, a continuous background opioid infusion in conjunction with PCA does not seem to have any advantages over PCA-only postoperative analgesia [xix] [xx] . As suggested in the American Society of Anesthesiologists guidelines, continuous infusion together with PCA is only indicated in patients who are already on an opioid therapy, or in addicted patients treated with methadone [xxi] . In such patients, continuous infusion dose should be around 50% of the estimated daily demand, the rest being administered through PCA [xxii] .

Because of all these considerations, PCA is now universally accepted as the safest technique for intravenous opioid administration in the treatment of acute postoperative pain.

The recommended bolus dose in adults under 70, derived from extensive experience conducted throughout most Western countries, is 1 mg morphine (or equivalent dosage of other drugs), with no background infusion and on a 5 minutes’ lockout. In patients of age 70 and over, these doses should be reduced by 30%.

PCA has recently been employed in epidural analgesia (PCEA), and although only limited data is available to date, several authors have confirmed its efficacy. In PCEA studies, a background infusion is often associated with the on-demand administration, in order to better adjust drug administration to the patients’ needs. It is thought that an intermittent opioid and/or local anaesthetic infusion would not allow the patient to rest comfortably during the first postoperative night. In one of the first studies on PCEA from Chrubasik [xxiii] , the administration of morphine in epidural PCA proved effective, and seemed to allow a reduction of drug usage and side-effects, but no control group had been included in that study.  In another work from Ferrante, PCEA was compared against a continuous epidural infusion (CEI), obtaining similar levels of analgesia, but also a reduction in bupivacaine and fentanyl hourly consumption in patients treated with PCEA [xxiv] . Owen studied the incidence of hypoxaemia (<90%) in abdominal surgery patients given epidural analgesia with continuous fentanyl infusion, PCEA and CEI + PCEA [xxv] . There was a significant reduction in hypoxaemic episodes and administered fentanyl doses in patients with PCEA. Other authors have found similar decrease in drug dosage, but also worse pain control during movement compared to CEI [xxvi] . More information is available regarding PCEA in obstetrics. Also in such patients, drug usage seems to be reduced by up to 40% in comparison with CEI [xxvii] . There are also indications of a decreased incidence of instrumental and cesarean deliveries, although more evidence is needed to confirm this data [xxviii] . Other authors have noticed similar patients’ satisfaction scores and decreased drug usage in PCEA patients.

PCEA is well accepted now in the treatment of postoperative pain. Besides the higher costs, some substantial differences are noticed in comparison with continuous infusion. Because pain scores alone, both at rest and during movement are not the sole parameter to evaluate an analgesic regimen, benefits may be assessed also in terms of dose sparing effects, reduced incidence of side-effects, thromboembolic prophylaxis, sympatholysis, earlier gastro-intestinal recovery and, consequently, discharge from the hospital. More studies are needed to understand the actual effects of PCEA. At present time PCEA with a basal rate is most probably the best compromise when using opioid/local anaesthetic combinations since the effect of deleting the concurrent infusion upon the above mentioned beneficial effects has not been established yet.

Although until now such a device is not available from a pharmacokinetic and dynamic point of view, it would be most inviting to give local anaesthetic at a constant rate while simultaneously administering additional opioids by PCEA [xxix] . Doing so, both the patient and the anaesthetist may participate in optimal tuning of pain relief.

PCA is used also in peripheral nerve blocks, particularly for open shoulder surgery and knee surgery. Continuous infusion of 0.125% bupivacaine or 0.2% ropivacaine at a rate of 8-10 ml/h is often considered the ‘gold standard’ [xxx] . However, this involves large volumes of local anaesthetic with potential risk of toxicity. Singelyn demonstrated that a lower basal infusion rate (5 ml/h) of bupivacaine associated with PCA boluses (2.5 ml, lockout 30 min) provided comparable pain relief, but significantly reduced the consumption of local anaesthetic [xxxi] . This technique reduced the incidence of side effects (Horner’s syndrome, clinical phrenic nerve palsy), and allowed reinforcement of the block shortly before physiotherapy. PCA boluses alone were unable to maintain adequate analgesia during continuous interscalene block. Sensory block decreased considerably below the analgesic threshold during sleep (pain appeared systematically during the first postoperative night) and PCA bolus size and/or lockout were inappropriate to restore it. Also continuous axillary plexus block, after major hand surgery gives an easy, safe and efficient analgesic technique. It provides lower postoperative pain scores and less side effects than i.v. PCA. Recently Iskandar [xxxii] demonstrated the efficacy of PCA technique alone (boluses of 0.25% bupivacaine: 0.1 mg/Kg – lockout 1 hour) after severe hand trauma surgery. When compared with a continuous infusion this technique provided comparable analgesia, but significantly reduced (by 69%) local anaesthetic consumption. Moreover in the PCA group, 94% of patients were satisfied or very satisfied with the technique instead of 43% in the other group. Similar results were obtained when a continuous infusion of a combination of bupivacaine, sufentanil and clonidine was compared with PCA boluses of the same mixture for postoperative analgesia by 3 in1 block after both knee and hip surgery. Again there was no difference between the groups as regards pain scores, rescue medication and satisfaction scores. However, total bupivacaine consumption was significantly lower in the PCA groups.

In conclusion, PCA alone or with a background infusion results in effective analgesia in all ways of administration with a high degree of patient satisfaction. With PCA, patients are in control of an important part of the therapy they receive, and this power in an otherwise extraneous environment might be the key to a successful treatment of postoperative pain.