Infraclavicular Perineural Local Anesthetic Infusion: A Comparison of Three Dosing Regimens for Postoperative Analgesia

Background: In this randomized, double-blind study, the authors investigated the efficacy of continuous and patient-controlled ropivacaine infusions via an infraclavicular perineural catheter in ambulatory patients undergoing moderately painful orthopedic surgery at or distal to the elbow.

Methods: Preoperatively, patients (n = 30) received an infraclavicular perineural catheter and nerve block. Postoperatively, patients were discharged home with both oral analgesics and a portable infusion pump delivering 0.2% ropivacaine (500-ml reservoir) in one of three dosing regimens: the basal group (12 ml/h basal, 0.05-ml patient-controlled bolus dose), the basal-bolus group (8 ml/h basal, 4 ml bolus), or the bolus group (0.3 ml/h basal, 9.9 ml bolus). Investigators and patients were blinded to random group assignment.

Results: The basal group (n = 10) required more oral analgesics than the basal-bolus group (P = 0.002) and had a shorter median infusion duration than the other two groups (P < 0.001 for both). The bolus group had the longest median infusion duration (P < 0.001 for both) but experienced an increase in breakthrough pain incidence (P = 0.004) and intensity (P = 0.04 vs. basal-bolus group) as well as sleep disturbances (P < 0.001 for both) compared with the other groups. Overall satisfaction was greatest in the basal-bolus group (9.7 +/- 0.5 vs. 7.9 +/- 1.7 and 8.1 +/- 1.5; P < 0.05 for both).     

Popliteal Sciatic Perineural Local Anesthetic Infusion: A Comparison of Three Dosing Regimens for Postoperative Analgesia

Background: This randomized, double-blind study investigated the efficacy of continuous and patient-controlled ropivacaine infusion via a popliteal sciatic perineural catheter in ambulatory patients undergoing moderately painful orthopedic surgery of the foot or ankle.

Methods: Preoperatively, patients (n = 30) received a posterior popliteal sciatic perineural catheter and nerve block. Postoperatively, patients were discharged home with a portable infusion pump delivering 0.2% ropivacaine (500 ml) in one of three dosing regimens: the basal group (12-ml/h basal rate, 0.05-ml patient-controlled bolus dose), the basal-bolus group (8-ml/h basal rate, 4-ml bolus dose), or the bolus group (0.3-ml/h basal rate, 9.9-ml bolus dose).

Results: The bolus group experienced an increase in baseline pain, breakthrough pain incidence and intensity, and sleep disturbances compared with the other two groups (P < 0.05 for all comparisons). Compared with the basal-bolus group, the basal group experienced an increase in these outcome measures only after local anesthetic reservoir exhaustion, which occurred earlier than in the other two groups (P < 0.05 for all comparisons). Satisfaction scores did not differ among the three groups.     

Application of Local Anesthetics in Dermatologic Surgery

BACKGROUND: Local anesthesia is an integral aspect of cutaneous surgery. Its effects provide a reversible loss of sensation in a limited area of skin, allowing dermatologists to perform diagnostic and therapeutic procedures safely, with minimal discomfort and risk to the patient. OBJECTIVE: This article discusses the application of local anesthetics in dermatologic surgery through a brief review of the mechanism of local anesthetic activity, classification of local anesthetics, and adverse effects. The discussion will focus on the different methods of administration and techniques that may make the administration less painful to patients. METHODS: An evaluation of the literature, as well as clinical experience in the administration of local anesthetics provide the basis for this review. CONCLUSION: Local anesthesia provides a safe and effective means of decreasing patient's sensitivity to pain. Because of its critical importance to the field of dermatology, a working knowledge of local anesthetics is necessary for optimal use of these agents.     

Possible Mechanism of Irreversible Nerve Injury Caused by Local Anesthetics: Detergent Properties of Local Anesthetics and Membrane Disruption

Background: Irreversible nerve injury may result from neural membrane lysis due to the detergent properties of local anesthetics. This study aimed to investigate whether local anesthetics display the same properties as detergents and whether they disrupt the model membrane at high concentrations.

Methods: Concentrations at which dodecyltrimethylammonium chloride and four local anesthetic (dibucaine, tetracaine, lidocaine, and procaine) molecules exhibit self-aggregation in aqueous solutions were measured using an anesthetic cation-sensitive electrode. Light-scattering measurements in a model membrane solution were also performed at increasing drug concentrations. The concentration at which drugs caused membrane disruption was determined as the point at which scattering intensity decreased. Osmotic pressures of anesthetic agents at these concentrations were also determined.

Results: Concentrations of dodecyltrimethylammonium chloride, dibucaine, tetracaine, lidocaine, and procaine at which aggregation occurred were 0.15, 0.6, 1.1, 5.3, and 7.6%, respectively. Drug concentrations causing membrane disruption were 0.09% (dodecyltrimethylammonium chloride), 0.5% (dibucaine), 1.0% (tetracaine), 5.0% (lidocaine), 10.2% (procaine), and 20% (glucose), and osmotic pressures at these concentrations were 278, 293, 329, 581, 728, and 1,868 mOsm/kg H2O, respectively.     

Inhibition of Mammalian Gq Protein Function by Local Anesthetics

Background: Local anesthetics have been shown to selectively inhibit functioning of Xenopus laevis Gq proteins. It is not known whether a similar interaction exists with mammalian G proteins. The goal of this study was to determine whether mammalian Gq protein is inhibited by local anesthetics.

Methods: In Xenopus oocytes, the authors replaced endogenous Gq protein with mouse Gq (expressed in Sf9 cells using baculovirus vectors). Cells endogenously expressing lysophosphatidic acid or recombinantly expressing muscarinic m3 receptors were injected with phosphorothioate DNA antisense (or sense as control) oligonucleotides against Xenopus Gq. Forty-eight hours later, oocytes were injected with purified mouse Gq (5 x 10-8 m) or solvent as control. Two hours later, the authors injected either lidocaine, its permanently charged analog QX314 (at IC50, 50 nl), or solvent (KCl 150 mm) as control and measured Ca-activated Cl currents in response to lysophosphatidic acid or methylcholine (one tenth of EC50).

Results: Injection of anti-Gq reduced the mean response size elicited by lysophosphatidic acid to 33 +/- 7% of the corresponding control response. In contrast, responses were unchanged (131 +/- 29% of control) in cells in addition injected with mouse Gq protein. Injection of mouse Gq protein "rescued" the inhibitory effect of intracellularly injected QX314: whereas QX314 was without effect on Gq-depleted oocytes, responses to lysophosphatidic acid after QX314 injection were inhibited to 44 +/- 10% of control response in cells in addition injected with mouse Gq protein (5 x 10-8 m). Similar results were obtained for m3 signaling and intracellularly injected lidocaine.