We found that there is insu icient evidence to establish whether denser or normal bupivacaine is the more e ective in reducing the need for: a) switching to general anaesthesia; b) additional pain relief medication. Denser bupivacaine had a more rapid onset of pain relief. Quality of evidence: Due to the di erences among the included studies in doses given, variety of additional drugs used for pain relief, variation in regional anaesthesia techniques and the small numbers of participants, we rated the overall quality of evidence for di erent outcomes from very low to moderate, as very few women experienced untoward events in all trials. Hyperbaric versus isobaric bupivacaine for spinal anaesthesia for caesarean section (Review)