Discrimination of hemoglobin-effects on arterial-to-jugular bulb oxygen content differences according to arterial carbon dioxide tension

ABSTRACT

BACKGROUND: Arterial jugular bulb oxygen content differences (AJVDO2) can be related to cerebral blood flow and oxygen consumption. Plasma Hb has been reported to have both-sided effect on AJVDO2. Increased Hb increases oxygen content in artery and jugular bulb, and the net effect is to reduce AJVDO2. Moreover, increasing Hb raises blood viscosity, and could increase AJVDO2. This study was designed to discriminate the Hb-effects on AJVDO2 mathematically. METHODS: Sixty adults were enrolled in this study. General anesthesia and mechanical ventilation were administered. A normocapnic and a subsequent hypocapnic state were achieved. Paired data including 1/AJVDO2, PaCO2, Hb, mean arterial pressure, temperature and anesthetic concentration were recorded during each state. Nonlinear mixed-effects model was applied to fit 1/AJVDO2 using PaCO2 and Hb as covariates. RESULTS: The 1/AJVDO2 was well modeled by PaCO2 and Hb using a three-parameter logistic function: predicted 1/AJv DO2 = 0.38713 / 1+e(31.20981-PaCO2)/25.94210-1.45162xHb The increase in PaCO2 raised the 1/AJVDO2 sigmoidally (P < 0.0001) and its slope was affected by Hb (P = 0.0022). The transition point of the Hb-effect was PaCO2 = 31.20981 (SEM 1.519201). Intraclass correlation coefficient was estimated at 0.9973. CONCLUSIONS: Our finding suggests that the Hb-effect on 1/AJVDO2 is both-sided; the viscosity-effect is dominant at low levels of PaCO2 and effect of oxygen content is dominant at high levels of PaCO2