Cerebral oximetry assessed by near-infrared spectrometry during preeclampsia: an observational study: impact of magnesium sulfate administration.

OBJECTIVES: To determine the regional cerebral oxygen saturation of hemoglobin (rcSO2) in severe preeclamptic parturients exhibiting neurologic symptoms compared with healthy pregnant women (control) and to describe the effects of MgSO4 infusion on rcSO2 and cerebral and systemic hemodynamic variables.

DESIGN: Prospective, observational study.

SETTING: Obstetric critical care unit in a university-affiliated hospital.

PATIENTS: Twenty severe preeclamptic parturients presenting with neurologic signs before any administration of MgSO4, and 20 control parturients.

INTERVENTION: Infusion of MgSO4 in severe preeclamptic patients.

MEASUREMENTS AND MAIN RESULTS: We measured rcSO2 using near-infrared spectroscopy, blood flow velocities of the middle cerebral artery, and cardiac output at baseline, 5 minutes, 1 hour, and 6 hours after the MgSO4 bolus (4 g), followed by continuous MgSO4 infusion (1 g/h). These measurements were also obtained in 20 control parturients at baseline and 6 hours. Baseline rcSO2 was significantly lower in the severe preeclamptic group: 61% (56-69) vs 66% (63-71) (p = 0.037). At inclusion, blood pressures were significantly higher in the severe preeclamptic group compared with the control group, whereas cardiac output and transcranial Doppler readings were similar. Five minutes after the MgSO4 bolus infusion, a median increase of 8.6% (3.2-18.1) in rcSO2 was observed (p = 0.007), reaching values of the control group that were maintained up to 6 hours. Blood pressures and systolic velocities of the middle cerebral artery significantly decreased (p < 0.01) after the MgSO4 bolus, whereas cardiac output did not change. The percentage increase in rcSO2 was negatively correlated to the mean blood pressure (r = 0.60, p < 0.0001).

CONCLUSION: Cerebral oxygenation impairment can be detected by near-infrared spectroscopy monitoring in severe preeclamptic parturients. These results suggested the presence of disorders in cerebral microcirculation and/or changes in cerebral oxygenation. MgSO4 infusion in patients with severe preeclampsia restored rcSO2 to control levels with no systemic side effects. Further studies are needed to confirm the usefulness of near-infrared spectroscopy monitoring in patients with preeclampsia and to assess the action of other antihypertensive therapies on rcSO2.