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To the Editor.—
I was exceedingly pleased with the attempt of Sinha et al to deal with the importance of arterial blood gases in neurological problems (224:1258, 1973). However, a few points disturb me; they are perhaps detailed, but necessary for understanding.An arterial oxygen pressure (Pao2) is not really interpretable without knowing the arterial carbon dioxide pressure (PaCO2) that goes with it. If one is to assume that the Paco2 was 40 in all cases, then we're left with impossible combinations of PaO2-PaCO2 in their normals. Without breathing oxygen-enriched air, it is not physically possible to have a PaO2 greater than about 110 mm Hg if the Paco, is 40. We're left wondering how "normals" could then range to above 120 mm Hg, not to mention patients with neurological difficulties.Second, they redefined an important word in terms of pressures rather than content. Hypoxemia
Mohler JG. Arterial Oxygenation. JAMA. 1973;225(6):636. doi:10.1001/jama.1973.03220330048021