In caesarean section, sub arachnoid block using hyperbaric bupivacaine is the commonest anaesthetic technique. But this technique with conventional dose of hyperbaric bupivacaine (2.5ml-3ml) may be responsible for development of maternal and foetal side effects. So without hampering the quality of anaesthesia, the aim of the study was to compare the side effects between using low dose hyperbaric bupivacaine and fentanyl with conventional dose hyperbaric bupivacaine. It was a prospective, interventional, randomised, double-blinded and comparative study done in Jalalabad Ragib-Rabeya Medical College Hospital from April 2016 to December 2016.  Sixty patients undergoing caesarean section under sub arachnoid block were allocated into two groups. Group B received 12.5 mg (2.5 ml) 0.5% hyperbaric bupivacaine and group B+F received 10 mg (2 ml) 0.5% hyperbaric bupivacaine with 20 μg (0.4 ml) fentanyl. Mean timing for sensory block was significantly earlier in group B+F (p<0.001). But mean timing for motor block was significantly earlier in group B (p<0.00001). Maternal haemodynamics were significantly better at 5^th, 10^th, 15^th and 20^th minute of intra-operative periods in group B+F. Foetal outcome had no change and complications were comparatively less in group B+F. Post-operative analgesia was better in group B+F than group B. For that low dose hyperbaric bupivacaine with fentanyl may be safer and better option for parturient undergoing caesarean section.

Key word: Bupivacaine, Fentanyl, Caesarean section, Sub-arachnoid block.