Effect of Acute Versus Continuous Glycemic Control on Duration of Local Anesthetic Sciatic Nerve Block in Diabetic Rats

Abstract

The duration of nerve block is longer in streptozotocin (STZ)-induced diabetic rats for all local anesthetics (with and without adjuvants) compared with normal rats. Perioperative glycemic control is currently practiced to reduce adverse events in many at-risk patients, especially in diabetic patients, to prevent neuropathy, poor wound healing, and greater incidence of infection. The aim of this study was to investigate in diabetic rats the importance of glycemic control before peripheral nerve block. To induce diabetes, rats were intravenously injected with a single dose of 50 mg/kg STZ to destroy pancreatic beta cells. Tactile allodynia in response to von Frey filament stimulation of the plantar hind paws was used as the criterion for diabetic neuropathy. Diabetic rats were randomly divided into experimental treatment groups. The continuous glycemic control experiment compared: 3 U/d insulin implant for 14 days, 1.5 U/d insulin implant for 14 days, and placebo treatment. The acute glycemic control experiment compared a single 6U Human Insulin Isophane Suspension (NPH) injection and placebo treatment. Nondiabetic rats received placebo implants or injections. Following treatment, 0.1 mL of 1% lidocaine hydrochloride with 5 μg/mL epinephrine hydrochloride was injected into the left sciatic notch. Animals were then reevaluated at 10-minute intervals for the absence or presence of sensory and motor response. All STZ-injected rats had blood glucose levels greater than 350 mg/dL and tactile allodynia. After insulin implants or injections, diabetic rats had much lower blood glucose levels than diabetic rats with placebo treatment. With both 3 and 1.5 U/d continuous glycemic control, the local anesthetic solution produced a shorter duration of sensory and motor nerve block in insulin-treated diabetic rats compared with placebo-treated diabetic rats, and shorter duration was similar to nondiabetic rats. With 6 U acute glycemic control in diabetic rats, there was no reduction in nerve block duration compared with placebo-treated diabetic rats. With continuous glycemic control in diabetic rats, the duration of sensory and motor nerve block was about 40 minutes shorter than that in the untreated diabetic rats and similar to that of normal rats. However, acute glycemic control did not affect nerve block duration, suggesting that this neuropathy cannot be rapidly reversed.