Systematic review and meta-analysis of acute hypoxia and cognition: Domain-specific effects and the role of barometric pressure and carbon dioxide

This systematic review and meta-analysis examined the effects of acute hypoxia, barometric pressure and supplemental carbon dioxide on cognition. Five databases were searched, yielding 137 eligible records and 458 effect sizes. Risk of bias was assessed using the Rosendal score; mean (SD) score was 48 (15) %, indicating moderate study quality. Random effects meta-analyses assessed the effect of hypoxia on all effect sizes, on the speed and accuracy components of attention, memory, information processing, crystallised intelligence (learned knowledge and skills), executive function and reaction time, and the effect of supplemental carbon dioxide on performance. Effects of hypoxia on response speed and accuracy and of barometric pressure on cognition were investigated by meta-regression. When combining all effect sizes, cognition was impaired by hypoxia (Hedges' g: -0.48, 95 % confidence interval [CI]: -0.62 to -0.33) and was worse under normobaric than hypobaric conditions (Hedges' g difference: -0.58, 95 % CI: -0.87 to -0.30). Response accuracy was impaired more than response speed (Hedges' g difference: -0.38, 95 % CI: -0.09 to -0.67). Accuracy was impaired in the attention, crystallised intelligence, executive function and memory domains. Speed was impaired in the attention domain only. Seventeen effect sizes investigated the effect of supplemental carbon dioxide. Cognition was worse under poikilocapnic than isocapnic or hypercapnic hypoxia (Hedges' g: -1.55, 95 % CI: -2.59 to -0.53). These findings are important for groups at risk of low oxygen exposure, as they enhance understanding of how hypoxia impairs cognition and can improve hypoxia recognition and recovery training in operational settings.