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.
Study Type
OBSERVATIONAL
Enrollment
40
Samples of cerebrospinal fluid and arterial blood will be collected anaerobically to measure acid-base variables, electrolytes, albumin, progesterone and copeptin levels
Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico
Milan, Italy
RECRUITINGStrong Ion Difference
Strong Ion Difference (expressed in milliequivalents per Liter \[mEq/L\]) of cerebrospinal fluid and arterial plasma
Time frame: 1 day
Partial pressure of carbon dioxide (PCO2)
PCO2 (expressed in millimeters of Mercury \[mmHg\]) of cerebrospinal fluid and arterial plasma
Time frame: 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
Time frame: 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
Time frame: 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
Time frame: 1 day
Progesterone levels
Plasma and CSF Progesterone levels (expressed in ng/mL) will be measured
Time frame: 1 day
Copeptin levels
Plasma copeptin levels (expressed in pmol/L) will be measured as a marker of antidiuretic hormone activity
Time frame: 1 day
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