How can a doctor tell how many minutes a patient had been without breath?

A doctor can estimate how long a patient has been without breath by assessing the patient's clinical signs and symptoms, such as the absence of a pulse or the presence of cyanosis (bluish discoloration of the skin). They may also use medical devices like a pulse oximeter to check oxygen saturation levels, which can drop significantly after a few minutes without breathing. In emergency situations, the timing of the incident and patient history provided by witnesses can also help in making this determination. However, precise timing is often difficult to ascertain in practice.