Background: Spinal anesthesia is a well-established technique for lower limb surgeries, in the present study  intrathecal opioids were used in relatively high doses (nalbuphine 1.6 mg and fentanyl 50 μg) to prolong time of post-operative analgesia as an option of opioid free post-operative analgesia, to compare the effect of intrathecal nalbuphine versus intrathecal fentanyl as adjuvants to bupivacaine, as regard the post-operative analgesia, the hemodynamic stability, the onset and duration of sensory/motor block  in patients undergoing internal fixation of tibia.
Methods: The present study was carried out on 50 ASA I or II patients scheduled for internal fixation of tibia under spinal analgesia, categorized into two groups: Group F Patients received intrathecal injection of 2 ml of 0.5% hyperbaric bupivacaine plus 1 ml fentanyl (50μg) and Group N Patients received intrathecal injection of 2 ml of 0.5% hyperbaric bupivacaine plus 1ml nalbuphine hydrochloride (1.6 mg).
Results: There was no significant difference between the two groups as regard the heart rate and mean arterial blood pressure, onset, duration of sensory block and duration of motor block. Onset of motor block was significantly earlier in group F than group N (p=0.001*).  Duration of analgesia was significantly longer in group N when compared with group F (p=0.004*). There was no significant difference in time of the 1st request analgesia and total dose of diclofenac sodium between the two groups. In the two studied groups there was no cases experienced respiratory depression or bradycardia. As regard hypotension, shivering, pruritus, nausea and vomiting showed no significant difference between the two studied groups.
Conclusion: The addition of intrathecal Nalbuphine 1.6 mg to spinal bupivacaine prolonged the onset time of motor blockade and duration of analgesia compared with the fentanyl Intrathecal, fentanyl in a dose of 50 μg and Nalbuphine in a dose of 1.6 mg are safe adjunct to Bupivacaine.

THE EFFICACY OF NALBUPHINE VERSUS FENTANYL AS ADDITIVES TO BUPIVACAINE IN SPINAL ANAESTHESIA FOR INTERNAL FIXATION OF TIBIA-A DOUBLE BLINDED STUDY.