Background: The stress response to surgery is an unconscious response to tissue injury and refers to autonomic, hormonal and metabolic changes that follow injury or trauma. Excessive intraoperative stress evoked by surgical nociceptive stimulation may influence patient’s outcome, length of hospital stay and overall costs of hospital care. Traditionally, clinical signs like somatic or autonomic responses are used to evaluate whether analgesia is adequate. It has been proved to be unreliable demonstrating low specificity. In the present study hemodynamic changes are correlated with changes in surgical plethysmographic index (SPI) and entropy at the time of stress.