Not subtle. Typically a birth complicated by significant birth asphyxia, which is where the baby is not getting enough blood and oxygen to the brain, is followed by a floppy baby, often with little crying or breathing without help from the doctors and nurses, seizures may also be a complication. Baby's may need to be on a breathing machine. Mild birth asphyxia may only have low tone that goes away.
Lack of respiratory. At delivery, a lack of spontaneous respiratory effort, depressed heart rate and no tone are the clear indicators of a probable lack of oxygen prior to or at the time of delivery. Primary asphyxia recovers quickly with stimulation. However secondary asphyxia required mask/bag ventilation and sometimes intubation and cardiac resucitation.