Regulation of cerebrovascular resistance below the lower limit of cerebral autoregulation during induced hypotension: an observational study.

Summary

In 50 patients undergoing aortic root surgery, the LLCA averaged 58 mm Hg. Cerebrovascular resistance continued to decrease below the LLCA, indicating residual reactivity and suggesting the LLCA is a transitional zone rather than a fixed threshold.

Key Findings

• Intraoperative LLCA was identified at a mean of 58 (SD 12) mm Hg in aortic root surgery patients.
• Cerebrovascular resistance declined continuously even below LLCA, indicating persistent reactivity.
• LLCA should be viewed as a transitional zone between exhausted and functioning autoregulation rather than a fixed point.

Clinical Implications

Blood pressure management during hypotension should consider individualized, dynamic cerebrovascular responsiveness rather than a single rigid LLCA value; continuous cerebral monitoring (e.g., MCA velocity) may better guide targets.

Limitations

• MCA velocity used as a surrogate for CBF; potential limitations under anesthesia
• Single-procedure context (aortic root surgery) may limit generalizability

Future Directions

Link autoregulatory zones to neurological outcomes, validate with multimodal monitoring (e.g., NIRS, TCD) across diverse surgeries, and develop individualized BP targeting algorithms.