Hypoxemia is:

A. Inability to breathe without dyspnea unless sitting upright refers to a postural issue that might be seen in certain respiratory conditions but does not describe Cheyne-Stokes respirations.
B. Shallow breathing alternating with periods of apnea is not characteristic of Cheyne-Stokes respirations. While apnea does occur, the breathing pattern is more varied in depth.
C. Cheyne-Stokes respirations are characterized by a periodic pattern where the depth of breathing alternates between very deep and very shallow breaths, followed by periods of apnea. This is often seen in end-of-life care and is associated with respiratory distress or certain neurological conditions.
D. Rapid respirations that are unusually deep and regular are more consistent with Kussmaul respirations, which are typically seen in conditions like metabolic acidosis, not Cheyne-Stokes.

A. Hypercapnia refers to elevated levels of carbon dioxide (CO₂) in the blood, which can occur due to respiratory problems or insufficient ventilation.
B. Hypoxemia is a condition where there is low oxygen in the blood, not related to carbon dioxide levels.
C. Hypocapnia refers to low levels of carbon dioxide in the blood, often caused by hyperventilation.
D. Hypoxia refers to low oxygen levels in the tissues, not the blood levels of carbon dioxide.