Final answer:
A normal central venous oxygen saturation (ScvO₂) reading can be deceptive in cases of severe sepsis and certain poisonings, where tissue hypoxia might still be present despite a 'normal' reading, thus requiring further evaluations such as lactate concentration and organ function to ensure accurate assessment of oxygen balance.
Step-by-step explanation:
ScvO₂ (central venous oxygen saturation) is a clinical measure representing the percentage of hemoglobin binding sites occupied by oxygen in the blood. While a normal ScvO₂ may indicate adequate oxygen delivery, it can be misleading in cases where the body's tissues are still not receiving enough oxygen. Conditions such as severe sepsis and certain poisonings illustrate instances where ScvO₂ values might not reflect tissue hypoxia, necessitating further assessments like lactate concentration and organ function tests to determine true oxygen balance and tissue oxygenation.