Patient Controlled Analgesia

Patient-controlled analgesia (PCA) generally refers to a technique of parenteral drug administration in which the patient controls an infusion device that delivers a bolus of analgesic drug 'on demand' according to parameters set by the physician. Use of a PCA device allows the patient to overcome variations in both pharmacokinetic and pharmacodynamic fac tors by carefully titrating the rate of opioid administration to meet individual analgesic needs. Although is should be recognized that the use of oral 'rescue doses' is, in fact, a form of PCA, the term is not commonly applied to this situation. Long-term PCA in postoperative patients is most commonly accomplished via the intravenous route using an ambulatory infusion device. In most cases, PCA is added to a basal infusion rate and acts essentially as a rescue dose. Rare patients have benefited from PCA alone to manage episodic pain characterized by an onset so rapid that an oral dose could not provide sufficiently prompt relief. Long-term intravenous PCA can be used for patients who require doses that cannot be comfortably tolerated via the subcutaneous route or in those who develop local reactions to subcutaneous infusion. PCA has also been applied to spinally administered opioids and non-opioid approaches such as nitrous oxide. In pediatric age PCA is recommended for children of 8 years or more, without disabilities, in whom moderate to severe pain is anticipated for 24 hours or more. Most children over the age of 7 years understand the PCA concept, and sometimes even younger children can learn to use PCA, but some may not have the cognitive or emotional resources to use it. In children as young as 5 or 6 years PCA has also been used, however pain relief is not always satisfactory because of poor patient understanding. In these patients Nurse or Parent Controlled Analgesia (NCA/PCA) represent a more suitable modality of drug administration. As continuous infusion, PCA allows a steady analgesic serum concentrations with safety and efficacy in pain control (Fig. 7) [90]. The use of a background infusion of opioids in PCA therapy is controversial. It might provide better analgesic during sleep but this is not strongly supported by literature. However it may increase the occurrence of adverse effects such as nausea and respiratory depression [87, 88]. Morphine is the most common drug used in PCA, followed by Fentanyl and Hydromorphone [88-91]. The selection of opioid used in PCA is perhaps critical than the appropriate selection of parameters such as bolus dose, lockout and background infusion rate (Table 7) [91]. PCA dosage regimens must be individualized on the basis of pain intensity and monitoring pain parameters must be age appropriate. Monitoring involves measurements of respiratory rate, level of sedation and oxygen saturation. Efficacy of PCA therapy is assessed by self-reporting, visual analogue scales, faces pain scales and usage pattern. The effectiveness of analgesic techniques may be limited by the incidence and severity of adverse effects; potential adverse effects of PCA therapy, including respiratory depression, nausea, vomiting, and pruritus, can be prevented or controlled by the use of adjuvant drugs and by careful titration. The patient should be instructed in the use of PCA prior to coming to operating room or even in the anaesthetic room before induction. Clinicians must become aware on age-related and developmental differences in

Fig. 7. Opioids plasma concentration following bolus or PCA administration. (A) bolus infusion; (B) PCA administration

Table 7. PCA protocol with morphine

PCA protocol Purpose Initial dose recomandations

(Morphine)

Loading dose

Background infusion

(basal rate) Interval dose (PCA dose)

Lockout

4 hours maximum

Obtain immediate pain control To mantain pain control

A bolus interval dose to tritate pain control by the patient himself To prevent overdose To prevent overdose

6-15 minutes 0.25 to 0.35 mg/kg the pharmacokinetic, pharmacodynamic and monitoring parameters for the patients with PCA therapy. To date, safety and efficacy of PCA also in paediatric patients has been established and a role of this procedure has been proposed in postoperative pain management as well as burns, oncology and palliative care.

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