Techniques for preventing hypotension during spinal anaesthesia for caesarean section.

BACKGROUND

Maternal hypotension is the most frequent complication of spinal anaesthesia for caesarean section. Most workers define hypotension as a maternal systolic blood pressure below 70-80% of baseline recordings and/or an absolute value of < 90 - 100mmHg. Hypotension is often associated with nausea and vomiting and, if severe, poses serious risks to mother (unconsciousness, pulmonary aspiration) and baby (hypoxia, acidosis and neurological injury). Several strategies are currently used to prevent or minimise hypotension but there is no established ideal technique.

OBJECTIVES

To assess the relative efficacy and side effects of prophylactic interventions for hypotension following spinal anaesthesia for caesarean section.

SEARCH STRATEGY

The Cochrane Pregnancy and Childbirth Group Trials Register (January 2002) and the Cochrane Controlled Trials Register (Cochrane Library, Issue 4, 2001).

SELECTION CRITERIA

All published or unpublished randomised controlled trials comparing interventions to prevent hypotension with placebo or alternative treatment in women having spinal anaesthesia for caesarean section.

DATA COLLECTION AND ANALYSIS

Trials identified from searching are assessed for inclusion by the same two reviewers independently. Studies are excluded from review where: hypotension is not an outcome measure or clearly defined prior to administering a rescue treatment; randomisation is unsatisfactory; the spinal anaesthetic technique or dose of local anaesthetic is not controlled-for; and the intervention is implemented in response to a fall in blood pressure rather than for prevention. Review Manager software is used for calculation of the treatment effect, represented by relative risks and proportional and absolute risk reductions.

MAIN RESULTS

Twenty-five trials (1477 women) meet our inclusion criteria. Four of fifteen interventions reviewed reduce the incidence of hypotension under spinal anaesthesia for caesarean section: (1) crystalloid versus control, relative risk (RR) 0.78 (95% confidence interval (CI) 0.63, 0.98); (2) pre-emptive colloid administration versus crystalloid, RR 0.54 (95% CI 0.37, 0.78); (3) ephedrine versus control, RR 0.69 (95% CI 0.57, 0.84); and (4) lower limb compression versus control, RR 0.70 (95% CI 0.59, 0.83). Ephedrine is associated with dose-related maternal hypertension and tachycardia, and fetal acidosis of uncertain clinical significance.

REVIEWER'S CONCLUSIONS: No intervention reliably prevents hypotension during spinal anaesthesia for caesarean section. No conclusions are drawn regarding rare adverse effects of interventions due to their probable low incidence and the small numbers of women studied. Further trials are recommended, in particular assessing a combination of the beneficial interventions, ie colloid or crystalloid preloading, ephedrine administration and leg compression with bandages, stockings or inflatable boots.