Patient assessment

A normal PaCO2 range of 35 to 45 mmHg represents the standard physiological balance between metabolic carbon dioxide production and alveolar ventilation. Higher ranges, such as 55 to 65 mmHg, are incorrect because they indicate hypercapnia and respiratory acidosis, which are abnormal in healthy individuals.

The PaO2/FiO2 (P/F) ratio is calculated by dividing the arterial oxygen tension by the fractional inspired oxygen concentration, which is 60 divided by 0.35, yielding approximately 171. Distractors like 300 or 400 are mathematically incorrect and would indicate much milder impairment or normal oxygenation.

A normal arterial PaO2 range on room air at sea level is 80 to 100 mmHg, indicating adequate oxygenation of the blood. A diagram for this topic isn't available yet — the worked example below walks the same reasoning step by step.

• !Distractors like 300 or 400 are mathematically incorrect and would indicate much milder impairment or normal oxygenation.
• !Higher ranges, such as 55 to 65 mmHg, are incorrect because they indicate hypercapnia and respiratory acidosis, which are abnormal in healthy individuals.

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