Cerebrospinal Acid-base in Pregnant and Non-pregnant Fertile Women

Effects of Pregnancy on the Physico-chemical Characteristics of Cerebrospinal Acid-base Equilibrium

The third trimester of pregnancy is typically characterized by the development of a marked respiratory alkalosis. The possible role of pregnancy-induced variations of cerebrospinal fluid (CSF) acid-base characteristics on the development of hypocapnic alkalosis is still unknown.

Aim of this study is to characterize, according to Stewart's approach, the acid-base equilibrium of CSF and arterial plasma of pregnant women and compare the results with data obtained from fertile, non-pregnant women.

The reduction in plasma PCO2 correlates with gestational age and was shown to be associated to plasma progesterone concentrations. We hypothesize that pregnancy-related haemodilution, inducing a reduction in CSF Strong Ion Difference (SID), might have a role in the development of pregnancy-related hypocapnic alkalosis.

Samples of CSF and arterial plasma of pregnant women with gestational age > 35 weeks undergoing spinal anesthesia for elective caesarean section will be analyzed for blood gases, pH, electrolytes, osmolality, albumin and haemoglobin concentration. In addition plasma copeptin levels will be analyzed. The same measurements will be performed in fertile, non-pregnant women undergoing spinal anesthesia for elective surgery.

Inclusion Criteria:

• Pregnancy with gestational age > 35 weeks
• Scheduled elective cesarean section under spinal anesthesia

Exclusion Criteria:

• known respiratory or neurologic disease
• multiple pregnancies