You are ventilating a fullterm baby with meconium aspiration syndrome

(B). All the given options are true causes for sudden drop of O2. The possible causes of desaturating baby on ventilator are; Oxygen supply, machine and it is connections, settings, tube block, self extubation and the patient himself. In the given scenario, the most likely cause is B because of meconium aspiration. The best action to such scenario is to disconnect the baby from the machine and use Ambu bagging gently to check the air entry and rise of Ozsaturation. if no rise you need to change the tube. In case of unequal air entry, pneumothorax is another possibility.