Intrathecal ropivacaine and clonidine for ambulatory knee arthroscopy - A dose-response study

Background: The aim of this study was to evaluate the association of a small dose of intrathecal ropivacaine with small doses of intrathecal clonidine for ambulatory surgery. Methods: One hundred twenty patients, classified as American Society of Anesthesiologists physical status I and scheduled for knee arthroscopy, were studied Patients were randomly assigned to receive 4 ml of one of the following double-blinded isobaric intrathecal solutions: 8 mg of ropivacaine (group 1; n = 30); 8 mg ropivacaine plus 15 mug clonidine (group 2; n = 30); 8 mg ropivacaine plus 45 mug clonidine (group 3; n = 30); and 8 mg ropivacaine plus 75 mug clonidine (group 4; n = 30). The level and duration of sensory anesthesia were recorded, along with the intensity and duration of motor block. Patient and surgeon were interviewed to evaluate the quality of anesthesia. Results: Intrathecal ropivacaine (8 mg alone) produced short sensory anesthesia and motor blockade (132 +/- 38 min and 110 +/- 35 min; mean +/- SD). However, the quality of anesthesia was significantly lower than in any other group (P < 0.05). Ropivacaine (8 mg) plus 75 <mu>g clonidine produced significantly longer sensory and motor anesthesia (195 +/- 40 min and 164 +/- 38 min; P < 0.05). However, this was associated with systemic effects, such as sedation and reduction of arterial blood pressure, Ropivacaine (8 mg) plus 15 <mu>g clonidine did not prolong sensory or motor blockade, afforded high quality anesthesia, and was not associated with detectable systemic effects. Conclusion: Small-dose intrathecal clonidine (15 mug) plus 8 mg intrathecal ropivacaine produces adequate and short-lasting anesthesia for knee arthroscopy.