Histological Analysis of the Effects of Rapid and Slow CO₂Removal on Neuronal Viability During Extracorporeal Cardiopulmonary Resuscitation

Background: Extracorporeal cardiopulmonary resuscitation (ECPR) is a specialized extracorporeal membrane oxygenation (ECMO) that provides temporary cardiopulmonary support during cardiac arrest when conventional resuscitation is unsuccessful. While ECPR is lifesaving, it carries a high risk of acute brain injury (ABI). Arterial carbon dioxide (PaCO 2 ) plays a critical role in regulating cerebral blood flow through its effects on vascular tone. PaCO 2 levels are often rapidly normalized immediately after ECMO cannulation. However, the impact of CO 2 removal rate on ABI remains poorly understood. This study aimed to investigate the impact of the rate of CO 2 removal on neuronal viability in a porcine model of ECPR. Hypothesis: Rapid CO 2 removal causes more neuronal injury vs slow CO 2 removal, particularly in brain regions that are vulnerable to ischemia. Methods: Six piglets (weight: 50.75±1.89 kg) were randomized into three groups: (1) a control group with no CO 2 removal, (2) a rapid CO 2 removal group achieved with a high sweep gas flow rate (200% relative to ECMO blood flow), and (3) a slow CO 2 removal group achieved with a low sweep gas flow rate (25% relative to ECMO blood flow). After the intervention, brain tissue was harvested, and coronal sections (10-μm) were stained with hematoxylin and eosin (H&E) for histopathological analysis. Hypoxia-vulnerable regions—including the oculomotor (CN3) nucleus, Purkinje cells, hypothalamus, caudate, putamen, entorhinal cortex, and hippocampal subfields (CA1–CA4)—were examined under light microscopy. Neuronal viability was assessed by established morphological criteria to quantify healthy versus injured neurons. Results: Rapid CO 2 removal significantly increased neuronal injury (injured neurons %) vs the control group in hypoxia-vulnerable brain regions: caudate (43±11 vs 11±2, p =0.041), putamen (67±6 vs 24±2, p =0.003), and cortex (35±7 vs 9±3, p =0.013). Conversely, slow CO 2 removal significantly reduced neuronal injury in the cerebellum vs control group (7±3 vs 46±11, p =0.037) and there was a significant difference between rapid and slow removal of CO 2 in the putamen (67±6 vs 30±4, p =0.004). No significant difference was observed in the midbrain, hypothalamus-4, CA-2 and CA-1 for any intervention. Conclusions: Rapid CO 2 removal during ECPR is associated with increased neuronal injury in vulnerable brain regions, while slow CO 2 removal mitigates this risk. Dr. Cho is funded by NIH (1K23HL157610; 1R21NS135045). This study is funded by Johns Hopkins Magic That Matters foundation grant. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.