British journal of anaesthesia
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The influence of aging on the pharmacodynamics of anaesthetic agents in the central nervous system remains poorly understood. As alpha-aminobutyric acid (GABA)-mediated neurotransmission appears to be an important target for anaesthetics in the brain, we hypothesized that aging could alter the sensitivity of the GABA carrier to anaesthetics. We have examined the effects of etomidate and propofol on the uptake of [3H]-GABA (5 min, 37 degrees C) into striatal synaptosomes of rats aged 2, 18 and 24 months. ⋯ Aging increased IC50 values for these anaesthetics. Nipecotic acid was unaffected. These data suggest that aging selectively alters the action of etomidate and propofol in the mammalian CNS.
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Randomized Controlled Trial Multicenter Study Comparative Study Clinical Trial
Comparison of ropivacaine with bupivacaine for paediatric caudal block.
In a double-blind, multicentre study 245 children aged 1-10 yr undergoing elective minor surgery as inpatients were randomly allocated to receive a single caudal extradural injection of 1 ml kg-1 of either 0.25% bupivacaine or 0.2% ropivacaine after induction of light general anaesthesia. The groups were comparable for age, weight, vital signs and duration of surgery. The onset time was similar for ropivacaine and bupivacaine (9.7 vs 10.4 min). ⋯ The mean time to first analgesia in the remainder was 233 min in the bupivacaine group and 271 min in the ropivacaine group. No motor block was measurable in either group. Ropivacaine 2 mg kg-1 was as effective as bupivacaine 2.5 mg kg-1 for caudal analgesia in children.
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The ratio of effective arterial elastance (Ea) to left ventricular elastance (Ees) is an indicator of the coupling between ventricular properties and arterial load properties. Another criterion for the coupling between an energy source and its load is the principle of economical fuel consumption, or mechanical efficiency, which is defined as the ratio of stroke work (SW) to myocardial oxygen consumption per beat (MVO2). It has been revealed that SW of ventricular contraction is maximized when Ea/Ees = 1, while mechanical efficiency is maximized when Ea/Ees = 0.5. ⋯ Before nicardipine (during hypertension), Ea was almost equal to Ees, whereas Ea/Ees was significantly reduced to about 0.5-0.6 at 3, 10, and 20 min after nicardipine. SWI/PVAI was maximized and significantly greater than the baseline value at 3 min after nicardipine. These results suggest that, during hypertension, ventricular and arterial properties were so matched as to maximize SW at the expense of the work efficiency, whereas mechanical efficiency of ventricular contraction was maximized after nicardipine.
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We investigated the cerebral haemodynamic effects of 1 MAC desflurane anaesthesia in nine male patients scheduled for elective coronary bypass grafting. For the measurement of cerebral blood flow (CBF) a modified Kety-Schmidt saturation technique with argon as inert tracer gas was used. Measurements of CBF were made before induction of anaesthesia and 30 min after induction under normocapnic, hypocapnic and hypercapnic conditions in sequence. ⋯ Hypo- and hypercapnia caused a 22% decrease and a 178% increase in CBF, respectively. These findings may be interpreted as the result of two opposing mechanisms: cerebral vasoconstriction induced by a reduction of cerebral metabolism and a direct vasodilator effect of desflurane. CBF alterations under variation of PaCO2 indicate that cerebrovascular carbon dioxide reactivity is not impaired by application of 1 MAC desflurane.