gms | German Medical Science

Objective: The linear correlation coefficient of P_tiO₂ / CPP or ICP / CPP serves as a quantitative index for the status of cerebral autoregulation, yet it is merely a surrogate marker for the true hemodynamic situation best characterized by invasive CBF measurement. Furthermore, the delay of P_tiO₂ change in the context of CPP change may hamper interpretation of autoregulation. To further improve the diagnostic value of an autoregulation index (AI) we compared AI P_tiO₂ and AI CBF before and after temporal correction to P_tiO₂ and CBF latency after CPP alterations.

Methods: In five Patients suffering from severe aneurysmal SAH we performed continuous multimodal neuromonitoring (MAP, ICP, CPP, P_tiO₂, CBF) over a period of 7–10 days after SAH. From each of these data sets we selected two one-hour intervals during which cerebral autoregulation was evidently disturbed (defined by comparison of P_tiO₂, CBF, and CPP with the precondition of a change in CPP>10mmHg), and calculated the time delay of P_tiO₂ and CBF change in the context of CPP alterations. Thereafter, the corrected and uncorrected AI P_tiO₂ and AI CBF were calculated as correlation coefficients.

Results: Calculation of time delay resulted in a mean P_tiO₂ latency of 50 seconds and CBF latency of 10 seconds. The uncorrected mean AI P_tiO₂ and AI CBF revealed an AI of 0.39±0.3 and 0.57±0.2, respectively. By correcting these factors by the time delay we obtained significantly higher correlations of 0.53±0.3 (AI P_tiO₂) and 0.62±0.2 (AI CBF). These differences were statistically significant within and between all groups.

Conclusions: We have confirmed AI P_tiO₂ and AI CBF as valid assessment tools for the functional status of cerebral autoregulation, and demonstrated that adjustment to the temporal latency of P_tiO₂ and CBF response significantly increases the correlation index. Regarding its predictive value, we believe this enhancement to be essential for further improvement of test sensitivity and specificity. By comparing both indices we demonstrated that the AI CBF should be considered as the index of choice, possibly due to its direct interrelationship with the cerebrovascular perfusion status.