Techniques for preventing hypotension during spinal anaesthesia for caesarean section.

BACKGROUND: Maternal hypotension is the most frequent complication of a spinal anaesthetic for caesarean section with an incidence approaching 100%. Most workers define hypotension as a maternal systolic blood pressure below 70-80% of baseline recordings and/or an absolute value of < 90 -100mmHg. The frequent occurrence and rapid onset of hypotension during spinal anaesthesia has encouraged anaesthetists to try and prevent or minimise the associated maternal symptoms of nausea and vomiting during the establishment of the block. Untreated, severe hypotension can also pose serious risks to both mother (unconsciousness, pulmonary aspiration, apnoea or even cardiac arrest) and baby (impaired placental perfusion leading to hypoxia, fetal acidosis and neurological injury). A range of strategies is 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, the Cochrane Controlled Trials Register, other databases and bibliographies of relevant papers are searched according to the strategy developed for the Pregnancy and Childbirth Group as a whole. Date of last search: May 2001. SELECTION CRITERIA: All published or unpublished randomised controlled trials that compare use of an intervention to prevent hypotension with placebo or alternative treatment in patients having spinal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 for the following reasons: 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. Statistical analyses use the Review Manager software for calculation of the treatment effect as represented by the relative risks and proportional and absolute risk reductions. MAIN
RESULTS: Twenty trials meet the criteria for inclusion. Four of the twelve interventions reviewed are shown to reduce the incidence of hypotension under spinal anaesthesia for caesarean section: (1) crystalloid 20ml/kg vs control, Relative Risk (RR) 0.78 (95% confidence interval (CI) 0.6, 1.0); (2) pre-emptive colloid administration vs crystalloid, (RR) 0.54 (95% CI 0.37, 0.78); (3) ephedrine vs control, RR 0.70 (95% CI 0.57, 0.85); and (4) lower limb compression vs control, RR 0.75 (95% CI 0.59, 0.94). There are no significant differences in maternal or neonatal side effects in any of the comparisons studied. REVIEWER'S
CONCLUSIONS: No studied intervention has been shown to eliminate the need to treat maternal hypotension during spinal anaesthesia for caesarean section. We are unable to draw any conclusions regarding adverse effects of the studied interventions, due to their probable low incidence and the small number of women studied. Further randomised controlled trials are recommended, in particular assessing a combination of the beneficial interventions, i.e. colloid or crystalloid preloading, parenteral ephedrine administration and leg compression with bandages, stockings or inflatable boots.