Shifting patient from assisted ventilation to voluntary ventilation which of the following shows failure?

Ans is 'a' i.e. O2 saturation < 80% * O2 saturation of >90% is one of the criteria for successful weaning from mechanical ventilation.Numerical indices used to predict successful weaningIndicesValueMinute ventilation<10L /minuteVital capacity/body weight>10ml /kgRespiratory frequency<35bpmTidal volume /body weight>5ml /kgPEEP<5cm H2ORespiratory rate /tidal volume< 100/litreSpO2>90%Heart rate> 140bpm or change by >20%Systolic BP>180 or <90 mm/Hg