Discussion
delirium, hyperactive delirium, postoperative pain, seizures
EVENT
Intraoperative systemic magnesium of target total 60 mg•kgFirst, an administered magnesium target total of 60 mg•kgThe optimal target level of ionized magnesium is unclear. In the field of obstetric intensive care, magnesium represents the first-choice medication in treatment and prevention of eclamptic seizures at a therapeutic level of 2.0 to 3.5 mmol•lSecond, we suspect that one of the reasons for our negative outcome is the rare incidence of RASS score >0 and delirium. Before the study we calculated the sample size from our previous data, which showed that we had RASS scores of 0.25±0.5 and 58 cases (24.5%) of hyperactive delirium in 237 patients (not published). However, in the current study we had only six occurrences of RASS score >0 out of 315 observations, six cases of positive CAM-ICU out of 315 observations, and a total of only four (6.3%) patients with positive CAM-ICU. We chose EVAR surgeries for this study because of the high incidence (24.5%) of delirium in our previous study. As a consequence, we encountered very low incidence. Therefore, we might not be able to detect positive neurological effects in this study and the sample size might be small to detect statistical significance. We were unable to clearly explain this change of incidence. In any event, in our setting we did not record sufficient incidence to detect a significant effect of magnesium on RASS scores and delirium.We chose RASS scores as primary outcomes. RASS score was a surrogate for reducing delirium incidence, not a clinical outcome goal in itself. The modified RASS has good sensitivity and specificity for incident delirium [Our study was performed in a strict, randomized, double-blind controlled fashion, which was one of the strengths of the study, although magnesium infusion did not show a neurological effect in this setting. However, this does not mean that there was no neurological effect on sedated condition and delirium, because these two factors should affect the outcome. We should gather data in a setting where substantial incidence of delirium can be obtained. In addition, a sufficiently high level of ionized magnesium should be allocated to the magnesium group. One study showed the dose–response effect of magnesium on postoperative pain relief [There are some limitations to the current study. First, the limited sample size from a single center may limit the generalizability of our findings. In addition, our small simple size was calculated with our previous data that had showed many cases of delirium and in the interim analysis our study could have shown the statistical significance, however, finally, we could not show the statistical significance. We should have more careful calculation in sample size and should have taken more numbers in the sample size. Second, the incidence of delirium decreased dramatically in this study compared with our previous observational data. We could not find precise reasons for this, and a reasonable explanation remains lacking. In any event, in this study the incidence was too low for a neurological effect of magnesium to be detected. Third, we did not analyze the dose–response relationship between amount of magnesium infused and the concentration. In fact, the ionized magnesium of administered magnesium did vary; however, we did not have sufficient samples in this setting from which to estimate the dose–response relationship. Future study should investigate further the dose–response issue.In conclusion, our results did not show that intra-operative magnesium to a target total of 60 mg•kg