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Effect of spinal isobaric bupivacaine on opioid use after cesarean delivery
Abstract Number: F3A-235
Abstract Type: Original Research
During local anesthesia shortages in 2018, substitution of hyperbaric bupivacaine 0.75% (HBB) with isobaric bupivacaine (IBB) was proposed for non-urgent cesarean deliveries (CD).1 A recent systematic review (10 studies; N=614 subjects) reported a more rapid onset for HBB compared with IBB with no differences in conversion to GA or need for supplemental analgesia, but prolonged analgesic use was not mentioned.2 IBB with opioids results in a hypobaric solution spreading further cephalad than HBB with opioids,3 although the relevance of lower baricity on the duration of spinal morphine and fentanyl analgesia is unclear.4 We hypothesized that women receiving IBB rather than HBB have lower opioid use after CD and that time to 1st opioid dose will be delayed.
Between Feb-June 2018, IBB syringes were prepared daily by Pharmacy for non-urgent CD as a conservation measure due to HBB shortage. Anesthesia attending decided whether to use HBB (12mg) or IBB (12-15mg, with fentanyl 15mg & morphine 150mcg. Using electronic anesthesia records, all consecutive CDs under spinal anesthesia were identified and categorized into 2 groups (HBB vs IBB). Outcomes were non-use of oxycodone, cumulative dose of oxycodone and time to 1st oxycodone dose. Adjustment for the risk of receiving isobaric bupivacaine was applied.
There were 299 cases with IBB (30.5%) and 682 with HBB, with differences in patient and cesarean characteristics between groups (urgent cases received HBB). There were no differences in any measured outcomes; adjusting for the risk of receiving IBB did not modify these findings (Table).
Since we had no experience using IBB for CD but expected (1) prolonged duration of spinal block and (2) possible effect on the distribution/spread of spinal morphine due to lower baricity of spinal solution, we thought this may impact opioid use after CD. We found no differences between groups which is reassuring. Lack of observed difference may be due to many factors such as different clinical indication (although we performed risk adjustment), the fact that opioid use is relatively low now in our institution with 30% not using any oxycodone, or that the sample size is too small. We believe this is the 1st report examining in-hospital opioid use after spinal anesthesia with IBB.
2. Anaesthesia 2018;73;499-511
3. Can J Anaesth 1999;46;66-70
4. J Perianesth Nurs 2010;25:371-9