What size (internal diameter) endotracheal tube should be used to intubate a newborn with an estimated gestational age of 26 weeks (estimated birth weight of 800 g)?

The size of endotracheal tube that should be used to intubate a new born with an estimated gestational age of 26 weeks is 2.5 mm (internal diameter).  An endotracheal tube serves as open passage through the upper airway. The purpose of endotracheal intubation is to permit air to pass freely to and from the lungs inorder to ventrate the lungs.