Does denser compared to normal bupivacaine, given as a lower back injection, give more effective and safer anaesthesia during caesarean section

Background: A pain-relieving drug, bupivacaine, is used during caesarean section through lower back injection. However, it is not clear that using hyperbaric bupivacaine (denser than the spinal fluid) is more or less effective in pain relief than isobaric bupivacaine (density equal to the spinal fluid). This Cochrane Review summarizes the best available evidence for the effectiveness and safety of the denser form of bupivacaine compared to the isobaric form when spinal anaesthesia (injection of medications into the lower back) is used for delivery of a baby by caesarean section.

Study characteristics: The evidence is current to March 2016. We found 10 clinical trials evaluating these two types of bupivacaine, involving 614 women. The studies assessed the following effects of the two types of medicine: women needing to switch to general anaesthesia, additional drugs for pain relief or low blood pressure, experiencing nausea and vomiting, headache and excessive numbness. We found that all the studies had been done properly. None of them reported their source of funding. We await responses from the authors of two more studies, and will cover these when we next update the review.

Key results: We found that there is insufficient evidence to establish whether denser or normal bupivacaine is the more effective 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 differences 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 different outcomes from very low to moderate, as very few women experienced untoward events in all trials.

Conclusion: We conclude that the denser form provides faster pain relief than the normal one. More research is required to be certain about the effectiveness of the denser form for other outcomes.

Authors' conclusions: 

Data are limited for some of the outcomes. Reporting of the included trials is less than optimal. For these reasons the overall quality of evidence is low or very low for most of the outcomes, based on the GRADE method of assessment. This review found that intrathecal hyperbaric bupivacaine had a more rapid onset of sensory blockade at the 4th thoracic vertebra (T4) level than isobaric bupivacaine. Hower, despite incorporating more data in the analysis, we found little evidence that the need for conversion to general anaesthesia and supplemental analgesia differed between the hyperbaric or isobaric bupivacaine groups. This is mainly due to the rarity of these outcomes, variability in the dose, use of adjuvant drugs and differences in the technique used for regional anaesthesia. There were no differences in the adverse effects studied. Any possible advantage of hyperbaric bupivacaine needs to be confirmed in larger randomized trials. In future research, criteria for conversion to general anaesthesia need to be defined objectively and applied uniformly.

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Background: 

Bupivacaine is an amide local anaesthetic used in hyperbaric and isobaric forms. These are administered intrathecally into the spine to provide regional anaesthesia for caesarean section. Several trials have compared hyperbaric and isobaric bupivacaine but none have conclusively shown the benefit of either. This review was first published in 2013 and updated in 2016.

Objectives: 

Our objectives were to:

1. Determine the effectiveness of hyperbaric bupivacaine compared to isobaric bupivacaine for spinal anaesthesia in women undergoing caesarean section;

2. Determine the safety of hyperbaric bupivacaine compared to isobaric bupivacaine for spinal anaesthesia in women undergoing caesarean section.

Search strategy: 

We originally searched the following databases to January 2011: CENTRAL, MEDLINE and Embase.

For this update, we reran our search in the above databases from January 2011 to March 2016; two studies are awaiting a response from authors for assessment and will be dealt with when we next update the review.

We imposed no language restriction.

Selection criteria: 

We included all randomized controlled trials (RCTs) involving parturients undergoing spinal anaesthesia for elective caesarean section that compared the use of hyperbaric with isobaric bupivacaine.

Data collection and analysis: 

Two authors independently extracted the data. The data that were extracted included the number of events and the sample sizes in both the intervention and control groups. For continuous outcomes, we extracted mean and standard deviation.

We reported odds ratios (ORs) and risk ratios (RRs) for binary outcomes, and mean differences (MDs) for continuous outcomes.

Main results: 

We included three new RCTs in this update, which now comprises 10 studies with a total of 614 participants. We judged most trials as having uncertain risk of bias regarding randomization. Other than this, the overall risk of bias was low. Most included trials had small sample sizes. All of the trials assessed the primary outcome of conversion to general anaesthesia. Ten trials comparing anaesthesia performed with hyperbaric and isobaric bupivacaine failed to show any difference in need for conversion to general anaesthesia (RR 0.33, 95% CI 0.09 to 1.17, 614 participants, very low quality of evidence). Nine trials also failed to show a difference in the need for supplemental analgesics (RR 0.61, 95% CI 0.26 to 1.41, 554 participants, very low quality of evidence). Four trials comparing requirement for ephedrine did not show any difference (RR 0.89, 95% CI 0.57 to 1.38, 256 participants, very low quality of evidence). Seven trials did not provide convincing evidence of difference in nausea and vomiting (RR 0.99, 95% CI 0.57 to 1.72, 433 participants, low quality of evidence). Three trials failed to show a difference in headache (OR 1.82, 95% CI 0.47 to 6.99, 234 participants, low quality of evidence). Two trials showed that the time until sensory block to the thoracic 4th (T4) spinal level was shorter with hyperbaric bupivacaine (MD -1.06 minutes, 95% CI -1.80 to -0.31, 128 participants, moderate quality of evidence). Six trials showed no difference in the amount of ephedrine used (RR 0.23, 95% CI -1.65 to 2.12, 386 participants, moderate quality of evidence). Three trials failed to show any difference in high block (RR 0.88, 95% CI 0.16 to 4.90, 205 participants).

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