Acid–base imbalances in critically ill obstetric patients: A multicentre retrospective cohort study

Abstract Background Acid–base imbalances are critical indicators of clinical outcomes in intensive care settings, yet their specific impact on critically ill pregnant obstetric patients remains underexplored. This lack of knowledge is particularly concerning given the potential for severe outcomes in this vulnerable population. Aim/objective The aim of this study was to assess acid–base abnormalities and their association with severe outcomes, including mortality. Methods We conducted a retrospective multicentre cohort study between 2006 and 2019 across six high-complexity hospitals in Colombia (two obstetric centres and four general hospitals with intensive care units that admit obstetric patients). Arterial blood gas was evaluated for acid–base balance at admission, and its association with clinical outcomes, including maternal death, mechanical ventilation, and vasopressor use, was assessed. Results The study included 798 patients: 768 survivors and 30 nonsurvivors. Our findings revealed that respiratory alkalosis was the most common imbalance (491/798 [61.5%]). Its presence is linked to better survival rates. Conversely, mixed metabolic and respiratory acidosis significantly increased the risk of mortality (18/768 [2.3%] in survivors vs. 7/30 [23.3%] in nonsurvivors, p < 0.001). After adjusting for confounders, lower potential hydrogen (pH) and bicarbonate (HCO₃) levels were associated with higher in-hospital mortality. Conclusions Most critically ill obstetric patients presented with baseline respiratory alkalosis, and the inability to maintain it was strongly associated with increased mortality. Further controlled studies are needed to confirm these findings and explore the impact of interventions to sustain respiratory alkalosis on outcomes.