The vascular effects of topical and intravenous alpha2-adrenoceptor agonist clonidine on canine pial microcirculation

Cerebral vascular effects of loading dose of dexmedetomidine: A Transcranial Color Doppler study

Background:

Dexmedetomidine has been widely used in critical care settings because of its property of maintaining stable hemodynamics and inducing conscious sedation. The use of dexmedetomidine is in increasing trend particularly in patients with neurological disorders. Very few studies have focused on the cerebral hemodynamic effects of dexmedetomidine. This study is aimed to address this issue.

Methods:

Thirty patients without any intracranial pathology were included in this study. Middle cerebral artery flow velocity obtained from transcranial color Doppler was used to assess the cerebral hemodynamic indices. Mean flow velocity (mFV), pulsatility index (PI), cerebral vascular resistant index (CVRi), estimated cerebral perfusion pressure (eCPP), and zero flow pressure (ZFP) were calculated bilaterally at baseline and after infusion of injection Dexmedetomidine 1 mcg/Kg over 10 min.

Results:

Twenty-six patients completed the study protocol. After administration of loading dose of dexmedetomidine, mFV and eCPP values were significantly decreased in both hemispheres (P < 0.05); PI, CVRi, and ZFP values showed significant increase (P < 0.05) after dexmedetomidine infusion.

Conclusion:

Increase in PI, CVRi, and ZFP suggests that there is a possibility of an increase in distal cerebral vascular resistance (CVR) with loading dose of dexmedetomidine. Decrease in mFV and eCPP along with an increase in CVR may lead to a decrease in cerebral perfusion. This effect can be exaggerated in patients with preexisting neurological illness. Further studies are needed to evaluate the effect of dexmedetomidine on various other pathological conditions involving brain like traumatic brain injury and vascular malformations.

Comparative evaluation of 0.75% ropivacaine with clonidine and 0.5% bupivacaine with clonidine in infraclavicular brachial plexus block

Background:

Infraclavicular brachial block with coracoids approach has gained popularity because of consistent bony landmarks and less chances of vascular puncture and pneumothorax.

Aim:

The aim of this study was to evaluate the effect of adding clonidine to bupivacaine or ropivacaine on the onset and duration of sensory and motor block and duration of analgesia in infraclavicular block.

Materials and Methods:

In a prospective randomized double-blind study, 60 patients of 18–65 years were randomly divided in to two groups of 30 each. Infraclavicular block was performed with 30 ml of 0.75% ropivacaine + 150 μg clonidine in group R and 30 ml of 0.5% bupivacaine + 150 μg clonidine in group B and were compared for onset and duration of sensory and motor block, postoperative analgesia, side-effects and complications.

Results:

Significant differences were observed in the time for onset of sensory block (5.80 ± 5.12 min in group R and 4.87 ± 1.46 min in group B, P < 0.05); onset of motor block (11.37 ± 2.66 min in group R and 9.60 ± 1.78 min in group B, P < 0.05); duration of sensory and motor block (10.07 ± 0.91 and 9.03 ± 0.89 h in group R and 12.50 ± 1.14 and 10.67 ± 1.18 h in group B respectively, P < 0.01) and duration of analgesia (15.30 ± 1.39 h in group R and 18.07 ± 1.66 h in group B). No significant difference was observed in hemodynamics, sedation, side-effects and complications.

Statistical Analysis:

Variables were compared using Chi-square test for nonparametric data and Student's t-test for parametric data.

Conclusion:

Addition of clonidine to bupivacaine lead to early onset and prolonged duration of sensory and motor block with prolonged analgesia as compared to the addition of clonidine to ropivacaine.

Addition of clonidine or lignocaine to ropivacaine for supraclavicular brachial plexus block: a comparative study

INTRODUCTION

Clonidine is used with local anaesthetics to improve analgesia. However, the improvement conferred when clonidine is used together with ropivacaine is controversial. Thus, the present study aimed to evaluate the improvement in analgesia when clonidine is used together with ropivacaine for supraclavicular brachial plexus block.

METHODS

This was a prospective, randomised, double-blind controlled study. A total of 75 patients who were scheduled to undergo supraclavicular block were randomly assigned into three groups (i.e. clonidine, lignocaine and control groups) of 25. Patients in all three groups received 20 mL of 0.75% ropivacaine. In addition to that, patients in the clonidine group received 1 mL of clonidine (150 μg) plus 9 mL of saline, patients in the lignocaine group received 10 mL of 2% lignocaine with adrenaline (1:200,000), and patients in the control group received 10 mL of saline. The characteristics of anaesthesia and analgesia for these three groups were assessed.

RESULTS

The addition of 2% lignocaine with adrenaline to ropivacaine led to earlier onset of the sensory block (by 4.88 mins), but no increase in the duration of analgesia when compared to analgesia using ropivacaine alone. The addition of clonidine to ropivacaine led to earlier onset of sensory and motor blocks (by 2.88 mins and 3.28 mins, respectively), as well as an increased duration of sensory and motor blocks (by 222.64 mins and 192.92 mins, respectively) when compared to analgesia using ropivacaine alone. The total duration of analgesia was increased by 208.24 mins with clonidine when compared to analgesia using ropivacaine alone. There were no significant differences in sedation score and no side effects in all three groups.

CONCLUSION

When compared to the use of ropivacaine alone, the addition of 150 μg clonidine to ropivacaine for brachial plexus block achieved earlier analgesic onset and improved duration of analgesia, without unwanted side effects.