Studies have shown that excessive systemic inflammatory response and concomitant immunosuppression are the main cause of early death in patients with sepsis. Therefore, it is very important to reduce excessive inflammation and improve immunosuppression in the acute phase of sepsis. Clinical studies have shown that esketamine combined with propofol for sedation has been proven to be safe and effective for septic patients in the ICU due to its cardiovascular stability. Previous studies have demonstrated that esketamine has anti-inflammatory effects against depression and surgical stress. Our preliminary experimental studies have found that esketamine had strong anti-inflammatory effects in the acute phase of sepsis. However, it is not clear whether esketamine could reduce excessive inflammation and improve immunosuppression in septic patients primarily sedated with a continuous infusion of propofol. This intervention study is to investigate whether three consecutive days of intravenous esketamine infusions via infusion pump (0.07 mg/kg/h) could reduce excessive inflammation and improve immunosuppression in septic patients requiring mechanical ventilation in the ICU under sedation primarily with propofol.