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

Study Overview
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Brief Summary
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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.

Detailed Description
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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.

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

Conditions
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Acid-Base Imbalance, Respiratory Alkalosis, Cerebrospinal Fluid, Pregnancy

Intervention / Treatment
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* Diagnostic Test: Acid - Base characterization


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Pregnancy with gestational age > 35 weeks Scheduled elective cesarean section under spinal anesthesia Exclusion Criteria: known respiratory or neurologic disease multiple pregnancies

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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Female

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Pregnant Women<br>Pregnant women with gestational age > 35 weeks undergoing spinal anesthesia for elective cesarean section. | Diagnostic Test: Acid - Base characterization<br>* Samples of cerebrospinal fluid and arterial blood will be collected anaerobically to measure acid-base variables, electrolytes, albumin, progesterone and copeptin levels<br>|
| Control Group<br>Fertile, non-pregnant women undergoing spinal anesthesia for elective surgery. | Diagnostic Test: Acid - Base characterization<br>* Samples of cerebrospinal fluid and arterial blood will be collected anaerobically to measure acid-base variables, electrolytes, albumin, progesterone and copeptin levels<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Strong Ion Difference | Strong Ion Difference (expressed in milliequivalents per Liter [mEq/L]) of cerebrospinal fluid and arterial plasma | 1 day | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Partial pressure of carbon dioxide (PCO2) | PCO2 (expressed in millimeters of Mercury [mmHg]) of cerebrospinal fluid and arterial plasma | 1 day | 
| Sum of albumin (expressed in mmol/L) and Phosphates (expressed in mmol/L) | The total amount of weak non carbonic acids, i.e. the sum of albumin and phosphates (both expressed in mmol/L) of cerebrospinal fluid and arterial plasma | 1 day | 
| Difference between cerebrospinal fluid and arterial plasma Strong Ion Difference (Delta SID) | The difference between plasma and cerebrospinal fluid SID (expressed in mEq/L) will be calculated as marker of electrolyte inbalance between these two extracellular fluid compartments. Delta SID = SIDcsf - SIDplasma | 1 day | 
| Difference between cerebrospinal fluid and arterial plasma partial pressure of CO2 (Delta PCO2) | The difference between cerebrospinal fluid and arterial plasma PCO2 (expressed in mmHg) will be calculated as a marker of acid-base equilibrium between these two extracellular fluid compartments. Delta PCO2 = SIDplasma - SIDcsf | 1 day | 
| Progesterone levels | Plasma and CSF Progesterone levels (expressed in ng/mL) will be measured | 1 day | 
| Copeptin levels | Plasma copeptin levels (expressed in pmol/L) will be measured as a marker of antidiuretic hormone activity | 1 day |