Patient Controlled Analgesia (PCA) and Postoperative Pain Management

Patient controlled analgesia is a safe method for postoperative pain management that many patients prefer to intermittent injections. Systemic PCA usually connotes intravenous drug administration, but it also can be subcutaneous or intramuscular. Few studies of the use of PCA drug delivery to the epidural space exist. A typical intravenous PCA prescription applicable to many contexts relies on a series of "loading" doses; for example, 3–5 mg of morphine, repeated every 5 minutes until the initial postoperative pain (if present) diminishes. A low–dose basal infusion (0.5–1 mg/hr) at night allows uninterrupted sleep. On–demand doses typically add I mg of morphine every 6 minutes, with a total hourly limit of 10 mg. Once the patient is able to take oral medications, an around–the–clock schedule of an oral opioid such as a codeine–acetaminophen combination is provided, and the basal infusion rate is discontinued. By observing the number of "on–demand" doses self–administered by the patient, the clinician can assess the adequacy of the oral medication and titrate it further, change to a stronger compound such as oxycodone with acetaminophen, or discontinue the PCA pump.

Intravenous administration is the preferred route for postoperative opioid therapy when the patient cannot take oral medications. When intravenous access is problematic, sublingual and rectal routes should be considered as alternatives to traditional intramuscular or subcutaneous injections. All routes other than intravenous require a lag time for absorption of the drug into the circulation. In addition, repeated injections with associated pain and trauma may deter some patients, especially children, from requesting pain medication. Continuous administration of low doses of opioids intravenously or transdermally and intermittent delivery across the buccal mucosa are relatively new but apparently effective methods to administer opioids postoperatively. Further experience is needed to define the clinical roles of these innovative methods in relation to more well–established methods.

"Patient controlled analgesia (PCA) is a safe method for postoperative pain management that many patients prefer to intermittent injections."

Opioids and local anesthetic agents interact favorably. Continuous administration into the epidural space of low concentrations of opioids in dilute solutions of local anesthetic provides excellent analgesia, while reducing the potential risks (e.g., respiratory depression or motor block) associated with equianalgesic concentrations of either agent administered singly. In a less technologically demanding approach, systemically administered opioids given pre–, intra–, or postoperatively augment the duration and effectiveness of local anesthetics given spinally or epidurally. Local anesthetics alone may be applied intermittently to specific nerves to interrupt pain pathways. For example, injecting local anesthetics around the intercostal nerves after thoracotomy significantly improves pulmonary function (Guideline Report, in press; Engberg, 1985b; Kaplan, Miller, and Gallagher, 1975; Toledo–Pereyra, and DeMeester, 1979). Catheters for continuous or repeated intermittent dosing of local anesthetic also have been employed postoperatively in the pleural space or adjacent to nerves such as the brachial plexus or cervical sympathetic ganglia. However, a clinical role for interpleural or perineural local anesthetics in the postoperative setting has not yet been defined.