To study the effect of non-invasive brain electromagnetic disturbance in detecting the degree of cerebral edema after subarachnoid hemorrhage (SAH) and the guidance on the use of dehydrating drugs.

A total of 56 patients with SAH underwent surgical treatment in Neurosurgery Department of the General Hospital Northern Theater Command from June 2019 to June 2020 were analyzed. The electromagnetic disturbance detection was performed every day before and 2 h after mannitol administration, and the DC value was recorded. The difference in the DC value was compared before and after the mannitol administration 1-7 d after the operation. The predictive efficacy of the DC value on the premature mannitol reduction/withdraw on the fifth day after the operation was assessed by receiver operating characteristic (ROC) curve.

From 1 to 7 days after operation, the DC value decreased gradually with the increase of time before the application of mannitol, and the DC value 2 h after mannitol administration was lower than that before mannitol administration, and the difference was statistically significant (P<0.05). Spearman analysis showed that the DC value was negatively correlated with time (r=-0.720, P<0.001). There was no statistically significant difference in DC values before and after mannitol administration 1-7 d after surgery (F=0.948, P=0.422). DC value was positively correlated with intracranial pressure before daily mannitol administration (P<0.05). Premature mannitol reduction/withdraw was determined by DC value on day 5 after operation, the area under the curve was 0.79 (95%CI: 0.59-0.99), the optimal cut-off point of the DC value was 131, the sensitivity was 87.5%, and the specificity was 50%.

Non-invasive electromagnetic perturbation technique can observe the changes of cerebral edema after SAH and the treatment of dehydration, and can provide evidence for the treatment of dehydration. DC value may be an evaluation method to evaluate the therapeutic effect of dehydration after SAH and bring benefits to patients.