Correlation of end - tidal CO2 measurement to arterial PaCO2 during CO2 inhalation for cerebrovascular reactivity (CVR) test

Abstract

Background: The CO₂ inhalation was used for evaluating the cerebrovascular reactivity in the patients with cerebrovascular disorders. There were different methods to perform CO₂ inhalation. In our study, we designed the CO₂ inhalation method, using the Bain circuit and the previously known concept of the correlation between the end - tidal CO₂ (EtCO₂) and partial pressure of carbon dioxide (PaCO₂) in normal ventilation.

Objective: To study the correlation between the EtCO₂ and the PaCO₂ during CO₂ inhalation in the patients with cerebrovascular disorders using the Bain circuit.

Methods: A cross - sectional prospective study was performed in 14 patients. The patients with cerebrovascular disorders who were sent for computed tomography angiography (CTA) of the brain received the CO₂ inhalation (5% carbon dioxide in 95% oxygen) via the anesthetic mask using the Bain circuit for approximately 4 - 6 minutes until EtCO₂ was 20% higher than baseline value. The EtCO₂ and the PaCO₂ were measured before (pre -EtCO₂, PaCO2) and after the CO₂ (post - EtCO2, PaCO2) inhalation.

Results: There were 14 patients who had brain CTA scans and CO₂ inhalation. The mean of pre - EtCO₂ was 35.29 mm Hg and post - EtCO₂ was 42.64 mm Hg. The difference values of EtCO₂ and PaCO₂ was 2 -7.5 mm Hg. EtCO₂ values did correlate with PaCO2 values significantly both in pre - CO₂ inhalation (p = 0.024, r = 0.6) and post - CO₂ inhalation (p < 0.001, r = 0.9). Four patients had abnormal cerebrovascular reactivity when received CO₂ inhalation. Two of four patients had cerebral revascularization subsequently and the other two patients had clinical observation by a neurosurgeon.

Conclusions: There was a correlation of EtCO₂ and PaCO₂ during CO₂ inhalation for cerebrovascular reactivity test in the patients who had cerebrovascular disorders.