Comparison of the Duration of Sensory Block and Side Effects of Adding Different Doses of Intrathecal fentanyl to Lidocaine 5% in Spinal Anesthesia

Background: Fentanyl has been used to improve the quality and duration of sensory block and analgesia in spinal anesthesia, but still the effects of different doses have not been appropriately specified. The aim of this study was to compare the duration of sensory block and side effects of adding different doses of intrathecal fentanyl to lidocaine 5% in spinal anesthesia. Materials and Methods: One hundred and forty adult patients undergoing elective surgery under spinal anesthesia were enrolled in a double blind placebo-controlled clinical trial. Patients were randomly assigned to four groups; control (2 ml distilled water), 2nd group (25 μg fentanyl), 3rd group (50 μg fentanyl), and 4th group (100 μg fentanyl). Duration of sensory block and the complications were recorded. Results: The duration of analgesia between the control group and the 3rd and 4th groups and between the second group and the 3rd and 4th groups was statistically different (P<0.001). The frequency of drowsiness and respiratory depression was significantly higher in third and fourth groups (P<0.01). The frequency of itching in the control group was lower than those of third and fourth groups (P<0.01). The frequency of nausea and vomiting and shivering in the control group was higher than the other groups (P<0.01). Conclusion: Adding 50 μg of fentanyl to 100 mg intrathecal lidocaine significantly increases the duration of analgesia, but it also is associated with the risk of respiratory depression.