Comparison of subgluteal sciatic nerve block duration in type 2 diabetic and non-diabetic patients

Background. Although animal studies demonstrated delayed recovery after nerve block in laboratory models of diabetes, the duration of the action of sciatic nerve blocks clinically in patients with diabetes remains to be determined. We studied the duration of a sciatic nerve block in type 2 diabetic patients compared with non-diabetic patients. Methods. We prospectively included consecutive patients aged 50-80 yr, with type 2 diabetes with minor nerve injury (confirmed with 5.07 at 10 g monofilament test, n=23) and nondiabetic patients (n=49) scheduled for distal lower limb surgery. Before surgery, a subgluteal sciatic nerve block (20 ml of ropivacaine 4.75 mg ml(-1)) was performed with an ultrasound approach coupled with nerve stimulation. The primary endpoint was the sensory block duration. Results. There was no significant difference between groups for age, but haemoglobin A1c and creatinine values were significantly higher in the diabetic group. There was no difference in 5.07 (10 g) monofilament testing, but the diabetic group had lower scores for the 0.4 and 0.07 g tests (P<0.01). There was no significant difference in the median onset time for the sensory block (25 vs 25 min, NS), but the median duration of the sensory block (21 vs 17 h, P<0.01) and the motor block (16 vs 12 h, P<0.01) were higher in the diabetic group. No complication occurred in either group. Conclusions. These findings demonstrate that diabetic patients with pre-existing incipient neuropathy exhibit delayed recovery from the block with ropivacaine, confirming animal studies.