Acid-Base Status and Cerebral Oxygenation in Neonates: A Systematic Qualitative Review of the Literature

Blood gas analysis is utilized to assess parameters of oxygenation and ventilation, including acid-base status [pH value, base excess (BE) or base deficit (BD), and bicarbonate (HCO₃)], to evaluate systemic metabolism status. Acid-base imbalances can have complex effects on the organism, potentially impacting oxygen delivery to tissue. Cerebral oximetry is a non-invasive monitoring technique using near-infrared spectroscopy (NIRS) for the continuous measurement of cerebral tissue oxygenation. The relationship between the acid-base status and cerebral tissue oxygenation in neonates remains unclear. This systematic qualitative review aims to analyze current knowledge of the potential correlations between different acid-base status parameters and cerebral tissue oxygenation measured via NIRS in neonates.

A systematic search of PubMed and Ovid Embase was performed, focusing on cerebral oxygenation, neonates, and acid-base status. Risk of bias was assessed using the ''Risk of Bias for Non-randomized Studies of Exposures'' (ROBINS-E) instrument.

Fifty studies that measured parameters of the acid-base status and cerebral tissue oxygenation in the neonatal period were identified. Seven studies demonstrated a correlation between pH and cerebral tissue oxygenation, while eleven studies found no such correlation. Five studies demonstrated a correlation between the BE/BD and cerebral tissue oxygenation, while six studies found no such correlation. Three studies demonstrated a correlation between HCO₃ and cerebral tissue oxygenation, while five studies found no such correlation.

Associations between acid-base status parameters and cerebral tissue oxygenation remain controversial. However, studies with the lowest risk of bias mainly demonstrated no significant correlation between any of the acid-base status parameters and cerebral tissue oxygenation.