Analysis of End-Tidal CO2 Variability During Plateau Waves Episodes: An Information Theoretic Approach

Plateau waves (PWs), commonly observed in traumatic brain injury (TBI), are abrupt increases in intracranial pressure (ICP) above 40 mmHg, often reducing cerebral perfusion pressure (CPP) and impairing cerebral blood flow. Monitoring and managing these fluctuations is critical to improve patients outcome. The partial pressure of carbon dioxide in arterial blood (PaCO2), measures the amount of CO2 dissolved in the blood and reflects the balance between CO2 production and elimination through respiration. It plays a critical role in regulating cerebral vasoreactivity and intracranial pressure. Moreover, the end-tidal carbon dioxide (etCO2), the level of CO2 measured at the end of an exhaled breath, can serve as a continuous non-invasive surrogate of PaCO2. Therefore, etCO2 analysis is a valuable tool for assessing cerebral hemodynamics and variations in etCO2 reflect changes in cerebral blood flow and metabolism. This study investigates etCO2 dynamics during PWs using entropy-based measures, including entropy, information storage (IS), and complexity (conditional entropy). Our findings reveal that etCO2 presents a slight increase just before the PW phase, that may trigger the increase of ICP. During PW, the median etCO2 continues to increase potentially amplifying the vasodilatory cascade. Additionally, increases in entropy and complexity during PWs suggest higher cerebral hemodynamic irregularity, reflecting reduced perfusion and compensatory vasodilation. The activation of the PW recovery mechanisms is also marked by elevated etCO2 IS during the baseline phase after the PW episode.Clinical relevance - Incorporating end-tidal CO2 analysis into the study of Plateau Wave episodes offers critical insights into the relationship between CO2 dynamics and intracranial pressure, deepening our understanding of these complex pathophysiological events.