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Supplemental oxygen for caesarean section during regional anaesthesia.

BACKGROUND
Supplementary oxygen is routinely administered to low-risk pregnant women during an elective caesarean section under regional anaesthesia; however, maternal and foetal outcomes have not been well established.


OBJECTIVES
The primary objective was to determine whether supplementary oxygen given to low-risk term pregnant women undergoing elective caesarean section under regional anaesthesia can prevent maternal and neonatal desaturation. The secondary objective was to compare the mean values of maternal and neonatal blood gas levels between mothers who received supplementary oxygen and those who did not (control group).


SEARCH METHODS
We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, Issue 2, 2012), MEDLINE (1948 to February 2012) and EMBASE (1980 to February 2012). We did not apply language restrictions.


SELECTION CRITERIA
We included randomized controlled trials of low-risk pregnant women undergoing an elective caesarean section under regional anaesthesia and compared outcomes with, and without, oxygen supplementation.


DATA COLLECTION AND ANALYSIS
Two review authors independently extracted data, assessed methodological quality and performed subgroup and sensitivity analyses.


MAIN RESULTS
We included 10 trials with a total of 683 participants. Supplementary oxygen administration varied widely in dose and duration between trials. No cases of maternal desaturation were reported, although none of the 10 trials focused on maternal desaturation. Significant differences were noted in maternal oxygen saturation (higher with oxygen, N = three trials; mean difference (MD) 1.6%, 95% confidence interval (CI) 0.8 to 2.3, P < 0.0001), maternal PaO2 (oxygen pressure in the blood; higher with oxygen, N = six trials; MD 141.8 mm Hg, 95% CI 109.3 to 174.3, P < 0.00001), neonatal UaPO2 (foetal umbilical arterial blood; higher with oxygen, N = eight trials; MD 3.3 mm Hg, 95% CI 1.8 to 4.9, P < 0.0001) and UvPO2 (foetal umbilical venous blood; higher with oxygen, N = 10 trials; MD 5.9 mm Hg, 95% CI 3.2 to 8.5, P < 0.0001). No significant differences were reported in neonatal UapH (N = eight trials; MD 0.00, 95% CI -0.01 to 0.00, P = 0.26) and in average Apgar scores at one minute (N = five trials; MD 0.07, 95% CI -0.20 to 0.34, P = 0.6) and at five minutes (N = five trials; MD 0.00, 95% CI -0.06 to 0.05, P = 0.91).Only two out of 10 trials had a low risk of bias in all categories. When we separated the studies into low risk and high risk for bias, we found substantial statistical heterogeneity. None of the low-risk studies showed a significant difference in neonatal UaPO2 between the two intervention groups, whereas the high-risk studies showed a benefit for the neonatal oxygen group.The level of oxygen free radicals (malondialdehyde (MDA) and 8-isoprostane) was higher in participants who received supplementary oxygen (N = two trials; MD 0.2 µmol/L, 95% CI 0.1 to 0.4, P = 0.0002; MD 64.3 pg/mL, 95% CI 51.7 to 76.8, P < 0.00001, respectively).


AUTHORS' CONCLUSIONS
Current evidence suggests that supplementary oxygen given to healthy term pregnant women during elective caesarean section under regional anaesthesia is associated with higher maternal and neonatal oxygen levels (maternal SpO2, PaO2, UaPO2 and UvPO2) and higher levels of oxygen free radicals. However, the intervention was neither beneficial nor harmful to the neonate's short-term clinical outcome as assessed by Apgar scores.