Prevention of hypotension after spinal anaesthesia for caesarean section: a systematic review and network meta-analysis of randomised controlled trials

Fitzgerald JP, Fedoruk KA, Jadin SM, Carvalho B and Halpern SH

Anaesthesia 2019. Early View (Online version of record before inclusion in an issue)
First Published 18 September 2019

Aim of Study

Compare methods of preventing hypotension in women having spinal anaesthesia for caesarean section.

Design and Location

Systematic review and network meta-analysis (worldwide).

Methodology

Two reviewers independently searched MEDLINE, Embase, Web of Science, and the Cochrane Library. They also searched the bibliographies of relevant systematic reviews and clinical practice guidelines. Only randomised controlled trials were included, and the final list of eligible trials was determined by consensus, with a third adjudicator to resolve disagreements.

Primary Outcome

Rate of intra-operative hypotension, as defined by the individual study investigators.

Secondary Outcomes

Rates of nausea and vomiting, maternal tachycardia, maternal bradycardia, reactive hypertension, neonatal Apgar scores one and five minutes after delivery, and umbilical artery pH.

Statistics

Random effects modelling to calculate odds ratio (95% CI) and standardised mean differences (95% CI).
The Tau² statistic was used to estimate heterogeneity between trials.
Inconsistency within the network was evaluated using the “sidesplit” function in Stata. Treatments were ranked using the surface under the cumulative ranking curve.

Results

All vasopressors, except mephentermine, reduced the rate of intra-operative hypotension compared with control, whereas crystalloid before induction of anaesthesia did not.  Vasopressors reduced the rate of intra-operative hypotension more than fluid infusion before or after induction of anaesthesia. There were no statistical differences in the rates of hypotension with phenylephrine, noradrenaline or metaraminol, but hypotension was more common with ephedrine.

Results for preventing nausea and vomiting were similar to those for hypotension.

Reactive hypertension was reported least for mephentermine and most for metaraminol. There were no significant differences in rates of reactive hypertension between ephedrine, phenylephrine and noradrenaline.

The rate of bradycardia after phenylephrine was higher than after ephedrine, mephentermine, noradrenaline and fluid. The rates of tachycardia after fluid infusion before anaesthesia and after ephedrine were greater than after metaraminol and phenylephrine.

Low rates of abnormal neonatal Apgar scores one minute and five minutes after delivery
precluded ranking of interventions. Umbilical artery pH was significantly higher after vasopressors than after fluid infusion, except after ephedrine, following which umbilical artery pH was significantly lower than after mephentermine, phenylephrine, metaraminol or angiotensin 2.

Conclusions/Discussions

Maternal hypotension and nausea/vomiting were less common after vasopressors than control, fluids, or leg compression. Vasopressors do have complications of reactive hypertension and maternal brady- and tachycardia. The findings were generally consistent with an international consensus statement which recommended alpha agonist drugs but cautioned bradycardia when using Phenylephrine.

Stated Limitations from the Study

  • Limited to women with low risk of morbidity, and having elective caesarean section.
  • Fluid infusion and leg compression could not be blinded studies.
  • Inconsistencies for rates of nausea/vomiting and also for umbilical artery pH within network when comparing interventions.
  • Protocol comparing vasopressors also included giving fluids.
  • Small number of trials involving Mephentermine and Metaraminol.
  • Equipotent doses of interventions were not assumed.

Discussion from Journal Club Meeting

  • Most people use Phenylephrine infusions, some use Metaraminol boluses.
  • Most experienced anaesthetists have used most interventions at some point in their career but now largely use that which is more prevalent within the department.
  • Noradrenaline appears to have a favourable therapeutic and side effect profile but would require delivery in extremely diluted concentrations.

Summary by Dr B Goodman. Journal Club Meeting 03 October 2019.

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