Effect of Nitrous Oxide on Neurologic and Neuropsychological Function after Intracranial Aneurysm Surgery

Abstract

In a population of patients at risk for ischemic brain injury, nitrous oxide use had no overall beneficial or detrimental impact on neurologic or neuropsychological outcomes.

Nitrous Oxide in Neuroanesthesia

“…Nitrous oxide increases cerebral metabolic rate, blood flow, and intracranial pressure and, in animals, exacerbates ischemic neurologic injury, all theoretically undesirable effects in the setting of intracranial neurosurgery. Fueled by this information, the debate simmers, albeit largely uninformed by data on how nitrous oxide affects neurologic outcomes in humans-which brings us to the work of McGregor et al 3 in this issue of the Journal. These investigators studied short-and long-term gross neurologic and subtle neuropsychological outcomes in 1,000 subarachnoid hemorrhage patients as a function of whether they received nitrous oxide intraoperatively during craniotomy for intracranial aneurysm clipping.…”

“…Patients that received nitrous oxide also had lesser neurologic impairment at baseline but more often had a temporary clip placed and received putatively neuroprotective agents (in addition to hypothermia) intraoperatively. 3 These are potentially significant confounders that cloud some of the outcome trends, a point the authors recognize and discuss candidly. But no study, especially one of this magnitude, is perfect, and these imperfections do not undermine the validity of the study's principal conclusion: Nitrous oxide is unlikely to cause adverse neurologic or neuropsychological outcomes in neurosurgical patients at high risk for cerebral ischemia.…”

“…This is important because the groups are unevenly distributed, with only 373 patients (37%) receiving nitrous oxide. 3 Moreover, use of nitrous oxide was uneven across participating centers; the majority used it in less than 25% or greater than 75% of the cases, suggesting strong institutional preferences and biases about nitrous oxide in this high-risk patient population. 3 Besides introducing potential bias, nonrandom allocation of patients may have rendered the study somewhat underpowered to detect small differences between the groups.…”

“…3 Moreover, use of nitrous oxide was uneven across participating centers; the majority used it in less than 25% or greater than 75% of the cases, suggesting strong institutional preferences and biases about nitrous oxide in this high-risk patient population. 3 Besides introducing potential bias, nonrandom allocation of patients may have rendered the study somewhat underpowered to detect small differences between the groups. Patients that received nitrous oxide also had lesser neurologic impairment at baseline but more often had a temporary clip placed and received putatively neuroprotective agents (in addition to hypothermia) intraoperatively.…”

“…McGregor et al 3 capitalized on the wealth of information collected as part of the Intraoperative Hypothermia for Aneurysm Surgery Trial (IHAST). The details of IHAST are presented elsewhere, 4 but a few things are important to mention here.…”