Administering remimazolam to severely obese patients based on TBW may result in excessively high doses, complicating its use in clinical practice. In our case, the maintenance dose was calculated based on the ABW [5]. The ABW was calculated using the following formula: The patient's IBW was 46.8 kg and ABW was 69.7 kg.

\(\text=45.4+0.89\times\left(\text-152.4\right)+4.5\times\left(1-\text\right)\)  

\(\text=\text+0.4\times \left(\text-\text\right)\)

IBW, ideal body weight; ABW, adjusted body weight (kg); TBW, total body weight (kg); TBW, total body weight (kg); Height (cm); Gender, 0 for males, 1 for females.

Continuous infusion of remimazolam 6 mg/kg/h was used for induction of general anesthesia in a morbidly obese patient [4]. In a previous study involving patients aged 60–80 years, the induction dose ranged from 0.14 to 0.19 mg/kg [6]. Based on that report, the attending anesthesiologist administered remimazolam for induction at approximately 0.2 mg/kg of ABW. In our case, the BIS rapidly decreased with a bolus dose of 15 mg during anesthesia induction. To maintain general anesthesia, the patient received remimazolam at 0.5 mg/kg/h of ABW. In a previous report, remimazolam was maintained at 0.56 mg/kg/h of TBW for general anesthesia in ASA-PS3 patients [5, 7]. Notably, female patients may require a higher remimazolam infusion rate than male patients. Patients with a higher ASA-PS classification generally need a lower infusion rate than those with lower classifications. Additionally, patients with increased weight exhibit higher drug concentrations than those with lower weight when administered the same dose per kg [5]. Compared with previous reports, we used a lower maintenance dose of remimazolam. Another report indicated that the maintenance dose of remimazolam ranged from 0.3 to 0.5 mg/kg/h when used with remifentanil [8]. In severely obese patients, there is a risk of overdosing remimazolam based on TBW. Thus, at the discretion of the attending anesthesiologist, the maintenance dose of remimazolam in this case was set at 0.5 mg/kg/h based on ABW.

In our case, increased blood pressure after aortic valve implantation necessitated prompt blood pressure reduction using sevoflurane. Given that remimazolam has a lesser impact on circulatory suppression, it is imperative to contemplate strategies for managing elevated blood pressure, especially in instances of substantial improvement in circulation or during procedures involving severe surgical invasiveness.

In our case, flumazenil was used to achieve effective antagonism after the pharyngeal reflex, and spontaneous breathing was observed. Using a high dose of remimazolam and antagonizing it with a high dose of flumazenil may result in inadequate antagonism. Another risk associated with using high doses of flumazenil is the potential for seizures following flumazenil administration [9, 10]. However, the appropriate dose of flumazenil used as an antagonist remains unclear. In addition, the metabolism of remimazolam under conditions of low cardiac output or in the presence of valve disease remains uncertain. Accumulation should also be considered with long-term (> 24 h) use of remimazolam (ONO-2745–04) [11].

We determined the depth of anesthesia based on BIS values in this case. Previous research has indicated that BIS values during administration of remimazolam at appropriate doses are generally higher than those observed with other anesthetics, with some patients exhibiting BIS values greater than 60 [12, 13]. Due to individual differences in remimazolam use, it is necessary to quantitatively assess sedation, including electroencephalogram (EEG) monitoring.

In future cases with severely obese patients, remimazolam dosing based on ABW could help prevent excessive dosing. EEG monitoring, such as BIS, is a useful tool for assessing sedation levels during general anesthesia with remimazolam. Appropriate pain management for surgery is essential. We recommend the use of antagonist agents for remimazolam; however, the optimal timing and dosage remain undefined. In this case, the administration of the antagonist was initiated after signs of awakening were observed. Additionally, strategies for managing hemodynamic changes are necessary; these should include the use of inhaled anesthesia or calcium channel blockers to manage sudden blood pressure increases.

We managed anesthesia with remimazolam for TAVI in a severely obese patient with a BMI > 40. Owing to its pharmacological advantages, remimazolam may be an option for anesthesia induction and maintenance in severely obese patients with unstable circulation.