Arterial blood gas (ABG): A sample of arterial blood that measures the oxygen, carbon dioxide, and bicarbonate levels.

Clubbing: A gradual enlargement of the fingertips in patients with respiratory conditions that cause chronic hypoxia.

Cyanosis: A bluish discoloration of the skin and mucous membranes caused by lack of oxygenation to the tissues.

Dyspnea: A subjective feeling of not being able to get enough air; also called shortness of breath.

FiO2: Fraction of inspired oxygen (i.e., the concentration of oxygen inhaled). Room air contains 21% oxygen levels, and oxygenation devices can increase the inhaled concentration of oxygen up to 100%. However, FiO2 levels should be decreased as soon as feasible to do so to prevent lung injury.

HCO3: Bicarbonate level reflected in arterial blood gas results. Normal range is 22-26 mEq/L.

Hypercapnia: Elevated carbon dioxide levels in the blood, indicated by PaCO2 level greater than 45 in an ABG test.

Hypoxemia: Decreased dissolved oxygen in the arterial blood, indicated by a PaO2 level less than 80 mmHg in an ABG test.

Hypoxia: A reduced level of tissue oxygenation.

Obstructive sleep apnea (OSA): Characterized by repeated occurrences of complete or partial obstructions of the upper airway during sleep, resulting in apneic episodes.

PaCO2: The partial pressure of dissolved carbon dioxide in the blood measured by an arterial blood gas sample.

PaO2: The partial pressure of dissolved oxygen in the blood measured by arterial blood gas sample.

SaO2: Calculated arterial oxygen saturation level.

SpO2: An estimated oxygenation level based on the saturation level of hemoglobin measured by a pulse oximeter.

Ventilation: The mechanical movement of air into and out of the lungs.