Comparison Between Continuous Brain Tissue pO 2,pCO 2,pH,and Temperature and Simultaneous Cerebrovenous Measurement Using a Multisensor Probe in a Porcine Intracranial Pressure Model

Abstract

Local brain tissue oxygenation (p_tiO₂) and global cerebrovenous hemoglobin saturation (S_JO₂) are increasingly used to continuously monitor patients after severe head injury (SHI). In patients, simultaneous local and global oxygen measurements of these types have shown different results regarding the comparability of the findings during changes in CPP and ICP. This is in contrast to theoretical expectations. The aim of this study was to compare P_tiO₂ measurement with cerebrovenous oxygen partial pressure measurement (p_cvO₂) in an animal intracranial pressure model. To this end, a multisensor probe was placed in the left frontoparietal white matter to measure p_tiO₂, pCO₂ (p_tiCO₂), pH (pH_ti), and temperature (t_ti) while simultaneously measuring these same parameters (p_cvO₂, p_cvCO₂, pH_cv, t_cv) in the sagittal sinus of 9 pigs under general anesthesia. By stepwise inflating a balloon catheter, placed in supracerebellar infratentorial compartment, ICP was increased and CPP was decreased. The baseline levels of p_tiO₂, p_tiCO₂, and pH_ti in the noninjured brain tissue showed more heterogeneity compared to the findings in cerebrovenous blood. Both, p_tiO₂ and p_cvO₂ were significantly correlated to the induced CPP decrease. PCO₂ was inversely correlated to the course of CPP in both measurement compartments. Temperature measurement showed a positive correlation with CPP in both compartments. These findings demonstrate that brain tissue oximetry and cerebrovenous pO₂ measurement are sensitive to CPP changes. The newly available continuous parameters in multisensor probes could be helpful in interpreting findings of cerebral oxygen measurement in man by analyzing the interrelationship of these parameters.