Differential effects of propofol on cerebrovascular carbon dioxide reactivity in elderly versus young subjects

Abstract

Study Objective To examine the age-related difference between elderly and young patients in the effect of propofol on cerebrovascular carbon dioxide (CO 2) reactivity. Design Prospective controlled study. Setting University hospital. Patients Elderly (older than 70 years, n = 13) and young patients (younger than 25 years, n = 13) scheduled for elective orthopedic surgery. Interventions After induction of anesthesia, a 2.5-MHz pulsed transcranial Doppler probe was attached to the patient's head at the right temporal window, from which mean blood flow velocity of the middle cerebral artery was measured continuously. Measurements After obtaining baseline values of velocity of the middle cerebral artery, arterial blood gases, and cardiovascular hemodynamics, end-tidal CO 2 was decreased by increasing the ventilatory frequency by 2 to 5 breaths per minute. Measurements were repeated when end-tidal CO 2 decreased and remained stable for 5 to 10 minutes. Cerebrovascular CO 2 reactivity, at propofol doses of 5 and 10 mg/kg/h, was measured. Main Results No significant differences were observed between the 2 groups in baseline absolute and relative CO 2 reactivity. However, there were significant differences between the 2 groups in absolute or relative CO 2 reactivity at a propofol dosage of 5 mg/kg/h. (Absolute CO 2 reactivity in young patients: 2.1 ± 0.8 cm/s/mm Hg; elderly: 1.6 ± 0.4* cm/s/mm Hg. Relative CO 2 reactivity in young patients: 7.4% ± 1.6%/mm Hg; in the elderly: 6.5% ± 0.9%*/mm Hg; unpaired t test, * P < .05). In contrast, there were no significant differences between the 2 groups in terms of absolute or relative CO 2 reactivity at a propofol dosage of 10 mg/kg/h. Conclusions Cerebrovascular CO 2 reactivity in elderly patients was lower than that in young patients at a propofol dosage of 5 mg/kg/h.