Effects of theophylline on human cerebral blood flow velocity during halothane and isoflurane anaesthesia

The acute influence of therapeutic doses of theophylline on cerebral blood flow velocities during general anaesthesia induced either by halothane or i soflurane has not been elucidated previously. The aim of this study, was th erefore to investigate these effects during steady state anaesthetic condit ions in anaesthetized patients using transcranial Doppler sonography. Thirt y-four Patients were investigated. Anaesthesia was maintained either with 1 MAC (mini-mum alveolar concentration) halothane (n=16) or 1 MAC isoflurane (n=18); FiO(2): 40%; end-expiratory pCO(2): normocapnia. Theophylline admi nistration was performed before surgery by infusing 6 mg kg(-1) over a peri od of 7.5 min. Measurements were recorded prior to theophylline administrat ion, and immediately after 2 mg kg(-1) (2.5 min), 4 mg kg(-1) (5 min) and 6 mg kg(-1) (7.5 min), as well as 5, 10, 15, 20, 30 and 45 min after theophy lline administration. Recorded variables included blood pressure, heart rat e, arterial oxygen saturation, end-expiratory pCO(2), body temperatures, mi ddle cerebral artery blood flow velocity and pulsatility index. Theophyllin e administration was well tolerated by all study subjects. Heart rate, bloo d pressure, body temperatures, arterial oxygen saturation and end-expirator y pCO(2) remained constant during the whole examination period. Following t heophylline, mean blood flow velocity decreased by 25% in the halothane and by 30% in the isoflurane group (P < 0.05). By the end of the examination p eriod, mean blood flow velocity had not yet recovered to the initial values whereby in both groups the mean blood flow velocity was 26% below the init ial values. In the isoflurane group, the pulsatility index increased by abo ut 20% (P < 0.05) and remained high until the end of the examination. In th e halothane group, however, there were no changes in the pulsatility index. Our results show a remarkable, significant and simultaneous decrease in bl ood flow velocity in the middle cerebral artery associated with theophyllin e administration during halothane and isoflurane anaesthesia in man.