New Techniques For Postoperative Pain Management

Patient-controlled modalities using intravenous or epidural routes have dramatically improved postoperative pain management. However, acute post-operative pain continues to be undermanaged. Intravenous patient-controlled analgesia (PCA), the current standard of care for acute postoperative pain management, requires the patient to be attached to a staff-programmed pump apparatus via an intravenous catheter and tubing, rendering it invasive and mobility limiting. An innovative, needle-free, iontophoretic, fentanyl-HCl patient-controlled, transdermal system (PCTS; Figure III-62) is being marketed for acute postoperative pain management. Fentanyl-HCl PCTS is a compact, self-contained system that is easily applied to the upper outer arm or chest. It provides pain relief therapeutically equivalent to that of a standard regimen of morphine intravenous PCA, with pharmacokinetics similar to those of intravenous fentanyl infusion. Fentanyl HCl PCTS may be an effective, non-invasive alternative to currently available PCA modalities

The E-TRANS Iontophoresis is a method of transdermal administration of drugs in which the ionized form of a drug is propelled through the skin by an externally applied electric field. Sweat gland ducts and hair follicles provide the pre-existing aqueous pathways that potentially allow the passage of water-soluble molecules across the skin upon the application of low voltages. The permeation flux achieved with low voltages, however, is often much smaller than is desirable. For transdermal drug delivery through human skin, the use of high voltage pulses, resulting in transdermal voltages greater than 50 volts, is sufficient to cause electroporation within the stratum corneum. This results in new aqueous pathways that facilitate ionic and molecular transport across the skin. E-TRANS (Alza Corporation and J&J company), an electrotransport transdermal system, uses low-level electrical energy to deliver drugs that would not normally diffuse across the skin. It has been used for the transdermal delivery of the analgesic fentanyl in a patient-controlled transdermal system. Compared to standard intravenous PCA, the patient-controlled transdermal system has the advantage of being needle-free, potentially reducing interruptions in pain relief stemming from I.V. problems, and without the cumbersome PCA pump (Figure III-63). This self-contained and disposable system adheres to the skin and is approximately the size of a credit card. Occasionally, a temporary minor skin discoloration may occur at the electrode surface.

In a study with 636 adults having major surgical procedures, three hundred and sixteen patients were titrated to comfort with incremental doses of the opioid and then randomized to treatment groups. The PCTS delivered 40 |g of fentanyl on demand over 10 min up to 6 times per hour, while the I.V.-PCA delivered 1 mg morphine bolus with a 5-min lockout, up to a maximum of 10 mg/h. Visual analogue scale (VAS) pain intensity scores were measured over 72 h. All efficacy end points had comparable outcomes between treatment groups. Patient global assessments for pain control of excellent or good were reported for 75.5% of the PCTS group versus 79.1% of the I.V.-PCA morphine group (p = 0.18). Similarly, physician global assessments of excellent or good were reported for 80.3% of the PCTS group versus 82.9% of the I.V.-PCA morphine group (p = 0.26). Outcome variables measured also included discontinuation of treatment after 3 h of inadequate pain relief, discontinuation for any reason, and last measured VAS pain score. No significant differences were noted between treatment groups for any of these variables. One serious episode of respiratory depression was reported in the I.V.-PCA group but none in the PCTS group [198].

Other adverse effects were as expected with systemic opiate therapy. Mild application site reactions occurred in 54% of patients in the PCTS group. The investigators considered PCTS and I.V.-PCA to be comparable for the treatment of acute postoperative pain.

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