Nitrous oxide is a potent cerebrovasodilator in humans when added to isoflurane. A transcranial Doppler study

Abstract

Nitrous oxide during neurosurgical procedures is almost always given in combination with either volatile or intravenous anesthetics. The modifying influence of such interventions has been studied clinically and in experimental settings; the reported findings, however, are inconsistent. The present study compares the cerebrovascular effects of MAC equivalent concentrations of isoflurane alone and isoflurane plus nitrous oxide. Twenty lumbar laminectomy patients randomized either to receive isoflurane or isoflurane plus nitrous oxide were investigated over a dose range from 0.5 to 1.5 MAC. A transcranial Doppler (TCD) ultrasonography device was used to measure cerebral blood flow velocity (CBFV) in the right middle cerebral artery (MCA) as an index of anesthetic-induced alterations in cerebral blood flow (CBF). A small but marginally significant decrease in CBFV at 1 MAC and no change at 1.5 MAC occurred in the isoflurane anesthetized patients. In contrast, a small but significant increase in CBFV at 1 MAC and a very significant increase at 1.5 MAC occurred in the isoflurane plus nitrous oxide anesthetized patients. Nitrous oxide added to an isoflurane anesthetic regimen is concluded to be a potent vasodilator. In addition, the vasodilating effects of nitrous oxide were not uniform; they progressively increased with an increasing isoflurane concentration.

Effect of acute exposure to hypergravity (GX vs. GZ) on dynamic cerebral autoregulation

“…In another study involving direct stimulation of the stellate ganglion during surgery, CFV increased possibly due to a vasoconstriction at the MCA (40). However, patients in that study were anaesthetized both with isoflurane, which is known to ablate autoregulation (37), and with nitrous oxide, which is a potent vasodilator when combined with isoflurane (36). Therefore, the increases in CFV during stellate ganglion stimulation were likely the result of increased mean BP augmenting CFV through vessels with impaired autoregulation.…”

Relationship Between Regional Cerebral Blood Flow and Electrocorticographic Activities Under Sevoflurane and Isoflurane Anesthesia

“…It is generally accepted that inhalational anesthetic agents have been shown to produce dose-dependent dilation in cerebral vessels and increase in CBF (Matta et al, 1999;Strebel et al, 1995), but its reported effects on rCBF are often contradictory depending on the condition of material or patients, and the huge variety of methods and techniques in both anesthesia and CBF evaluation.…”

MRI Measures of Middle Cerebral Artery Diameter in Conscious Humans During Simulated Orthostasis

“…28 Stimulation of T 2 and T 3 sympathetic ganglia during surgery caused marked increases in CFV, 29 which could have been due to vasoconstriction at the vessel of insonation or increases in CBF. Concurrent increases in MAP during stimulation may have augmented CBF through vessels with impaired autoregulation secondary to anesthetic effects on cerebrovascular control, 30,31 resulting in increased CBF and CFV. Direct infusions of norepinephrine in both anesthetized 32 and conscious 33 patients have not affected CFV, but cerebral vascular resistance was increased, possibly because of the myogenic constriction after the increase in systemic MAP.…”