Evaluation of Intracranial (Cerebral) Compliance in Myocardial Revascularization: Prospective Pilot Study

Author(s): Eduardo Costa Duarte Barbosa, Pedro Augusto Modinger Rohr, Ricardo Pilz Hegele, Sérgio Kakuta Kato, Gustavo Frigieri, Eraldo de Azevedo Lucio, Monica Luisa de Souza, Fernando Lucchese, Bruna Eibel

Background: Coronary Artery Bypass Grafting (CABG) is a critical treatment for coronary artery disease, but it carries a risk of neurological complications. The relationship between cardiac surgery and Intracranial Compliance (ICC) is not fully established, particularly whether improved coronary perfusion leads to improved ICC. This study utilized the non-invasive B4C device to monitor ICC, aiming to identify perioperative changes.

Methods: This was an observational, prospective pilot study of repeated measures, including 16 adult patients undergoing elective on-pump CABG at a single center in Porto Alegre, Brazil. Patients with pre-existing structural neurological disease were excluded. Non-invasive ICC was monitored using the B4C device, which analyzes the waveform of the intracranial pressure (ICP) pulse. The P2/P1 ratio (the ratio of the second to the first peak of the ICP waveform) was used as the primary indirect marker of compliance, with a P2/P1 ratio >1.2-1.4 indicating reduced compliance. Monitoring was performed at three time points:
• T0: Preoperatively (baseline)
• T1: Immediately post-surgery, with continuous sedation and initial stabilization in the Intensive Care Unit (ICU)
• T2: Immediately post-extubation, without sedation, in the ICU

Repeated measures ANOVA with Bonferroni post hoc correction was used for statistical analysis, with p< 0.05 considered significant.

Results: The sample was predominantly male (75%), with common comorbidities including systemic arterial hypertension (62.5%) and diabetes mellitus type II (31.3%). A statistically significant variation over time was observed for both the P2/P1 ratio ($p=0.003$) and Time to Peak (TTP) ($p=0.019$). The analysis revealed a biphasic pattern: T0 (Baseline): The mean P2/P1 ratio was 1.28 \ TTP 0.37, suggesting a state of reduced or abnormal ICC. T1 (Post-Surgery/Sedation): A significant improvement in compliance was noted, with the mean P2/P1 ratio dropping to 0.85 \ TTP 0.28 (significantly different from T0 and T2, p < 0.05), moving into the normal range. All patients were under continuous sedation at this point. T2 (Post-Extubation/No Sedation): The ventilatory and hemodynamic variables, though recorded, did not show significant differences that would interfere with the ICC assessment.

Conclusion: Non-invasive evaluation of cerebral compliance using the B4C device proved to be a viable and safe method in the perioperative period of complex cardiac procedures. The study demonstrates that ICC is compromised preoperatively (T0) and returns to a normal state post CAGB (T1,T2). The most robust finding was the significant, temporary improvement in ICC immediately post-surgery under continuous sedation (T1), which may be due to the surgery itself, post-aggression self-regulation, or a protective effect of the continuous sedation on cerebral autoregulation. Further studies with larger samples are recommended to clarify the causes of the observed dysfunction and the physiological mechanism responsible for the transient improvement.