I've previously written about the alveolar gas equation and oxygen delivery equation, both of which deal with the physiologic process of oxygenation. Now I want to discuss the important relationship between alveolar ventilation (VA), carbon dioxide production (VCO2), and the alveolar carbon dioxide tension (PACO2). For the purposes of this explanation, PACO2 roughly approximates arterial carbon dioxide tension (PaCO2) if ventilation/perfusion mismatch is minimal.

Hypercarbia and hypocarbia have significant physiologic implications ranging from vascular auto regulation to acid-base status, so it’s important to keep the PaCO2 equation in mind when thinking about a patient’s ventilation.

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