Dexmedetomidine, selective alfa2 receptors agonist produces sympatholysis. As a result heart rate decreases. With low doses blood pressure also decreases, with higher dosing - systematic vascular resistance increases. The indication for the drug is to produce sedation during surgical procedures and in ICU patients.

The aim of a study is to verify, whether the haemodynamic effect (heart rate, blood pressure and heart rate variability during drug infusion) depend on pre-drug autonomic system activity. Autonomic system activity is assessed using heart rate variability (HRV)measurement before drug injection and during drug infusion. Heart rate and blood pressure measured before and during drug infusion will be analysed.

HRV measurement analysis will be based on continuous Holter ECG recording, taken before drug injection and during its infusion. 5 minutes intervals will be analysed , using Frequency Domain Measures of HRV. Surgical procedure will start after measurement have been taken.

Inclusion Criteria:

• patients classified with American Society of Anesthesiologists Physical Status Classification System as 1 or 2 status
• planned eye surgery under sedation

Exclusion Criteria:

• patient's refusal
• contraindications to dexmedetomidine
• diseases/drugs that influence on autonomic nervous system activity