Clonidine, an agonist for alfa2 pre-synaptic, has been shown to be an effective adjuvant therapy for acute postoperative pain and has been shown an effect in sedative, intra-ocular and blood pressure and arrhythmias.The objective of this study is evaluating the analgesic effect of clonidine and its repercussion on arterial and intraocular pressure and arrhythmias for cataract surgery.

After approved by the Ethical Committee and signed informed consent, 40 patients aged from 40 until 80 years undergoing cataract extraction will be randomized in two groups. Exclusion criteria will be myocardial ischemia, psychiatric disease, chronic pain, drugs dependency, chronic use of beta-blockage channel drugs. Group 2, patients will receive a single dose of 4mcg.kg-1 of clonidin2, 20 minutes before the surgical incision; group 1, patients will receive a sterile saline solution dose. Pain intensity will be assessed with the numeric rating scale. The antiarrythmic effect will be assessed with the continuous measure by Holter. The number of patients was calculated by Instat Graph® program. To detect difference in pain intensity of 3 between the groups by NRS, with 95% of power (estimated SD= 2.0), when the alpha level is set at 0.05, the sample should be of 20. Statistical analyses will be performed with parametric and nonparametric tests, considering the variety studied. The statistical program that will be utilized is Instat Graph®.

Inclusion Criteria:

• cataract surgery
• topical anesthesia

Exclusion Criteria:

• myocardial ischemia
• psychiatric disease
• chronic pain
• drugs dependency
• use of beta-blockage channel drugs