Intracranial Pressure Variation Associated with Changes in End-Tidal CO2

Maintaining intracranial pressure (ICP) below 20-25 mmHg is an important clinical goal in the treatment of patients with traumatic brain injury (TBI). It is well known that the partial pressure of arterial CO₂ (PaCO₂) can affect cerebral blood flow, cerebral blood volume, and therefore ICP. The end-tidal CO₂ (ETCO₂) is usually monitored by clinicians as a proxy for PaCO₂. We show examples where subclinical fluctuations in ETCO₂ are associated with clinically significant fluctuations in ICR We estimated ICP from past and present values of ETCO₂ with a linear estimator. The variance of the ICP residuals was 37 percent of the variance of the ICP signal at frequencies above 0.33 mHz. We suggest that a large proportion of clinically significant ICP fluctuations could be eliminated or reduced if the patients ventilation and CO₂ levels were more tightly regulated