The effect of end-tidal carbon dioxide levels on dynamic cerebral autoregulation and clinical outcome in acute ischemic stroke: An INFOMATAS study

Introduction Carbon dioxide is a key determinant of cerebral blood flow and its regulatory mechanisms. Previous work has shown patients with acute ischemic stroke (AIS), including lacunar stroke syndromes (LSS), are more likely to be spontaneously hypocapnic. We aimed to estimate the prevalence of hypocapnia in AIS and determine the association between end-tidal CO 2 (EtCO 2 ) and patient characteristics, dynamic cerebral autoregulation (dCA) parameters, and modified Rankin Score (mRS). Methods Participating centers were identified through systematic literature search and direct invitation. Data on dCA measures were derived from transfer function analysis at low frequency (LF) and very low frequency (VLF). Bivariate analyses were conducted at each time point separately using mixed effects models, with the participating center as a random effect. Results Prevalence of hypocapnia (EtCO 2 < 35 mmHg) was highest at <24 h (43%), decreasing at 24–72 h (31%), and 3 months (27%). Non-lacunar stroke had lower EtCO 2 compared to LSS ( t = 2.16,df = 62.2, p = 0.035) and higher prevalence of hypocapnia (FET, p = 0.029) at <24 h. At <24 h, reduced EtCO 2 was associated with higher phase at LF (β = −0.01,SE = 0.006, p = 0.029) but was not present at 24–72 h or 3 months. Lower EtCO 2 was associated with greater likelihood of poor mRS [3–6] at 24–72 h. Conclusion Hypocapnia at <24 h post-stroke is associated with improved dCA (through higher phase). Beyond 24 h this association is lost and hypocapnia becomes predictive of poorer clinical outcome. Hypocapnia was prevalent in LSS but to a lesser extent than non-lacunar AIS. Future work should affirm the value of capnography in acute stroke care.