Tehran University Medical Journal

Background: Remifentanil is known to produce side-effects of hypotension and bradycardia. In this study, we examine the effect of low-dose ketamine infusion on the heart rate and blood pressure of patients anesthetized with remifentanil.

Methods: In a randomized clinical trial, 54 patients aged 20-50 years old, with ASA physical status Ι, were studied in two groups (n=27), Ketamine- Remifentanil (K-R group) and Placebo- Remifentanil (P-R group). Exclusion criteria were ASA physical status >1, gastroesophageal reflux, tachycardia, bradycardia, systemic diseases, use of antihypertensive drugs, difficult intubations, risk of aspiration and contraindications of ketamine. Remifentanil was started at a rate of 0.5 µg. kg^-1. min^-1 and anesthesia was induced with thiopental sodium 2 mg.kg^-1. Maintenance of anesthesia included halothane and nitrous oxide/oxygen mixture. Remifentanil infusion was continued in both groups at a rate of 0.5 µg.kg^-1.min^-1. In the K-R group, ketamine was started with an infusion rate of 10 µg.kg^-1. min^-1, 10 minutes after intubation, while in the P-R group, normal saline was started with the same dose of remifentanil. Heart rate, systolic, diastolic and mean arterial blood pressure were measured and compared at 1, 3, 5, 10, 15, 20, 25 and 30 minutes.

Results: No significant differences were found between basic patient characteristics of mean of age, sex, weight, systolic, diastolic and mean arterial blood pressure and heart rate (p>0.2) in the two groups. However, the rate of systolic, diastolic and mean arterial blood pressure changes in the P-R group was significantly greater than that of the K-R group (p<0.006). Heart rate changes were similar between the two groups (p=0.6). Incident of severe hypotension (a decrease of more than 25% of the basic value) was less in the K-R group than that of the P-R group (11% vs. 89% p=0.000).

Conclusion: Low-dose ketamine infusion modulates the effect of remifentanil-induced hypotension and provides better hemodynamic stability during general anesthesia.