Transcranial Doppler ultrasound study of the effects of nitrous oxide on cerebral autoregulation during neurosurgical anesthesia: a randomized controlled trial

Abstract

The increase in CBF and the reduction in autoregulatory indices suggest caution in using N2O during sevoflurane anesthesia, especially in patients with reduced autoregulatory reserve and during neurosurgical interventions. Transcranial Doppler ultrasonography is an efficacious method to evaluate the effects of anesthetic agents on CBF.

Cerebral haemodynamic changes during propofol–remifentanil or sevoflurane anaesthesia: transcranial Doppler study under bispectral index monitoring

“…Nevertheless, the values of the hyperaemic response recorded during sevoflurane anaesthesia were lower than those recorded in normocapnic awake patients. 11 In this study, it was recorded that when approximately 2 MAC sevoflurane concentrations were used, the hyperaemic response showed a tendency to reduce. Conversely, during propofol-remifentanil anaesthesia, the autoregulatory index increased significantly.…”

Is nitrous oxide necessary in the future?

“…At a concentration of 70% nitrous oxide alone does not effect a change in cerebral blood flow ; however, when used with isoflurane of halothane, both cerebral blood flow and cerebral metabolic rate increase. When added to sevoflurane, cerebral autoregulation is impaired .…”

Transcranial Doppler and anesthetics

“…It is defined as the ratio between the systolic flow velocity (FV1) – calculated using the mean value of systolic peaks from five heart cycles, ending with the one preceding compression – and the hyperemic response (FV3), calculated using the mean systolic value of two heart cycles after compression, with exception of the very first cycle (Fig. 3A,B) (12, 13).…”

“…In common with other volatile anesthetics, but in a less evident manner, sevoflurane shows an intrinsic dose‐dependent cerebral vasodilatory effect (14, 16). Several studies, in fact, have demonstrated how it increases the cerebral blood flow velocity (CBFV) and decreases the cerebrovascular resistance (CVR) in a dose‐dependent manner (13, 17, 18). The reduction of CVR could cause an impairment of cerebrovascular autoregulation mechanisms but different transient hyperemic response tests, carried out on adults and children, showed that cerebral autoregulation is well preserved during anesthesia, with up to 2.0 MAC sevoflurane (19, 20).…”

“…A great number of studies, however, have now demonstrated adverse effects on cerebrovascular hemodynamics, both in humans and animals. When used alone, at concentrations of 30–60%, nitrous oxide significantly increases the CBFV, the intracranial pressure (ICP) and the CMRO 2 , while it reduces cerebral autoregulation and leaves cerebrovascular reactivity to acute arterial carbon dioxide (CO 2 ) changes unaltered (13, 58–60). Nevertheless, these effects can change if N 2 O is used, as often happens, together with other anesthetic agents.…”