Flow diagram of the study, ∗Data: arterial systolic, diastolic, and mean blood pressure, heart rate, and SpO2, T0 = pre-induction baseline, T3 = at second tidal volume, under mechanical ventilation after intubation, ABGA = arterial blood gas analysis, SpO2 = oxygen saturation, T1 = 2 minutes after preoxygenation, T2 = 5 minutes after preoxygenation.