Materials and Methods: This double-blind clinical trial was performed during a 3-month period in 2016. A random sample of 84 patients with ASA (American Society of Anesthesiologists), class I, were enrolled in the study and the impact of ketamine on prevention of hypotension due to repositioning was investigated. After induction of anesthesia and intubation, ketamine 0.5 mg/kg of body weight as well as normal saline solution, with equal volumes, were injected to the intervention and control groups, respectively. Patients were repositioned though a similar method to prone position after peak of ketamine (after 1.5 minutes), and then, systolic, diastolic, and mean of the blood pressure were measured as a baseline, once before and 1 minute after the intubation, before repositioning, immediately after repositioning the patient from supine to prone position, and then every 2 minutes until 10 minutes after repositioning.

Results: There was significant differences in means (SDs) of systolic pressure and blood pressure in the first, second, and fourth minutes after repositioning, as systolic pressure and mean of the blood pressure in ketamine group was higher than those of control group. The changes of blood pressure in ketamine group was the least amount after repositioning.

Conclusions: Ketamine can increase blood pressure, especially systolic pressure of patients, on other hand changes of blood pressure in ketamine group after repositioning was least amount.