Cerebrospinal fluid and arterial acid–base equilibria in spontaneously breathing third-trimester pregnant women. (November 2022)

• Record Type: Journal Article
• Authors: Zadek, Francesco; Giudici, Giorgio; Ferraris Fusarini, Chiara; Ambrosini, Maria T.; di Modugno, Adriana; Scaravilli, Vittorio; Zanella, Alberto; Fumagalli, Roberto; Stocchetti, Nino; Calderini, Edoardo; Langer, Thomas
• Is Part Of: British journal of anaesthesia. Volume 129:Number 5(2022)
• Page Start: 726
• Page End: 733
• Publication Date: 2022-11
• Subjects: acid–base imbalance -- cerebrospinal fluid -- hyperventilation -- hypocapnic alkalosis -- metabolic acidosis -- pregnancy -- respiratory alkalosis -- respiratory physiology -- water–electrolyte imbalance; Anesthesiology -- Periodicals; Anesthesia -- Periodicals; 617.9605
• DOI: 10.1016/j.bja.2022.07.048
• Languages: English
• ISSNs: 0007-0912

Abstract

Abstract: Background: Acid–base status in full-term pregnant women is characterised by hypocapnic alkalosis. Whether this respiratory alkalosis is primary or consequent to changes in CSF electrolytes is not clear. Methods: We enrolled third-trimester pregnant women (pregnant group) and healthy, non-pregnant women of childbearing age (controls) undergoing spinal anaesthesia for Caesarean delivery and elective surgery, respectively. Electrolytes, strong ion difference (SID), partial pressure of carbon dioxide ( P a CO 2 ), and pH were measured in simultaneously collected CSF and arterial blood samples. Results: All pregnant women (20) were hypocapnic, whilst only four (30%) of the controls (13) had an arterial P a CO 2 <4.7 kPa ( P <0.001). The incidence of hypocapnic alkalosis was higher in the pregnant group (65% vs 8%; P =0.001). The CSF-to-plasma Pco 2 difference was significantly higher in pregnant women (1.5 [0.3] vs 1.0 [0.4] kPa; P <0.001), mainly because of a decrease in arterial P co 2 (3.9 [0.3] vs 4.9 [0.5] kPa; P <0.001). Similarly, the CSF-to-plasma difference in SID was less negative in pregnant women (–7.8 [1.4] vs –11.4 [2.3] mM; P <0.001), mainly because of a decreased arterial SID (31.5 [1.2] vs 36.1 [1.9] mM; P <0.001). The major determinant of the reduced plasma SID of pregnant women was a relative increase in plasma chloride compared with sodium. Conclusions: Primary hypocapnic alkalosis characterises third-trimester pregnant women leading to chronic acid–base adaptations of CSF and plasma. The compensatory SID reduction, mainly sustained by an increase in chloride concentration, is more pronounced in plasma than in CSF, as the decrease in P co 2 is more marked in this compartment. Clinical trial registration: NCT03496311 .