• Grade 0: No blood detected in the pharynx, larynx, trachea, or mainstem bronchi.
• Grade 1: Presence of one or more flecks of blood or two or fewer short (less than one-quarter the length of the trachea) and narrow (less than 10% of the tracheal surface area) streams of blood in the trachea or mainstem bronchi (the two airways the trachea splits into; these carry air to and from the right and left lungs) visible from the tracheal bifurcation.
• Grade 2: One long stream of blood (more than one-half the length of the trachea) or more than two short streams of blood occupying less than one-third of the tracheal circumference.
• Grade 3: Multiple, distinct streams of blood, covering more than one-third of the tracheal circumference, with no blood pooling at the thoracic inlet.
• Grade 4: Multiple, coalescing streams of blood covering more than 90% of the tracheal surface with blood pooling at the thoracic inlet.
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