Ethical Statements
This study was approved by the Institutional Review Board of Shimane Prefectural Central Hospital (number [no.]: R18-067). All study data were anonymous, and the requirement for informed consent was replaced by the opt-out method. This study was registered in clinical trial registry of university hospital medical information network in Japan (ID: UMIN000035160; no. R000040074; RL: https://upload.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000040074).
The sponsors had no role in the study design, data collection, data analysis, data interpretation, or writing of the manuscript. The corresponding author had full access to all the data in the study and had the final responsibility of deciding to submit this work for publication.
Patient selection and data collection
In total, 860 patients with a primary diagnosis of aSAH were reviewed retrospectively from our observational database between January 2000 and December 2017. aSAH was diagnosed based on computed tomography (CT) or magnetic resonance imaging findings. Figure 1 shows this study’s inclusion and exclusion criteria. Patients at initial admission and those who underwent definitive aneurysm treatment within 4 days after aSAH onset were included. Exclusion criteria were as follows: unknown ruptured aneurysm location, pre-event modified Rankin Scale (mRS) score >2, arterial dissection, infectious aneurysms other than saccular aneurysms, only drainage or conservative treatments, both surgical clipping and endovascular treatment, and absence of BMI data. Consequently, 393 patients with aSAH were enrolled in the final retrospective analysis (Figure 1).
The patients were treated with surgical clipping or endovascular coiling based on the judgment of several specialized neurosurgeons and endovascular specialists. The following data were collected from patients’ medical records: age, sex, the BMI at admission, medical history (the presence of hypertension and stroke), data of the aneurysm (size and location), World Federation of Neurosurgical Societies (WFNS) grade, Fisher CT group, symptomatic vasospasm, treatment (surgical clipping or endovascular coiling), and mRS score at discharge. The BMI was classified into three groups as follows: underweight (<18.5 kg/m2), normal (18.5–24.9 kg/m2), and overweight (³25 kg/m2) based on the World Health Organization BMI classification [23]. Additionally, blood samples were obtained to measure serum albumin levels based on the existing literature [2]. The definition of symptomatic vasospasm was judged according to the consensus of 2009, which is as follows: (1) the presence of neurological worsening including focal deficit, decline in the consciousness level, and motor paresis; (2) no other identifiable cause (intracranial disorders or systemic complications) of neurological worsening; and (3) confirmation of vasospasm by medical examination including evidence of vasospasm [20]. We defined vasospasm as >30% constriction of vessels according to digital subtraction or CT angiography and symptoms unlikely to be the result of other causes. Poor outcomes were defined as mRS score >2 at discharge after onset of aSAH.
Literature review
We conducted a literature review of references mentioning the relationship between the BMI and aSAH in English language published from January 2000 to April 2022 in PubMed. The date of the final search was April 30, 2022. The following terms were used when searching for the articles: [subarachnoid hemorrhage, BMI, poor outcome]. Cited references within the articles were also researched for relevancy to this study. We compared the data of those articles with the data of our study.
Statistical analysis
Categorical variables were compared using the Fisher exact test or chi-square test. Continuous variables were compared using the t-test or Mann–Whitney U test. Multivariable logistic regression analyses of poor outcomes (mRS score >2) at discharge were conducted for all patients. The odds ratio (OR) and 95% confidence interval (CI) were calculated for all BMI groups. For multivariable logistic regression analyses, independent variables were selected based on those in the existing literature [7], and no variable selection method was applied.
P-values <0.05 were considered to indicate statistical significance. All statistical analyses were performed using JMP proV15 software (SAS Institute Inc., Cary, NC).