An oximetric pulmonary artery catheter shows a mixed venous O2 saturation decrease from 75% to 60%. Which could account for the decrease EXCEPT?

An oximetric pulmonary artery catheter shows a mixed venous O2 saturation decrease from 75% to 60%. Which could account for the decrease EXCEPT?

• A. Hypovolemia
• B. Bleeding
• C. Hypoxia
• D. Sepsis

Answer: (D)

Mixed venous oxygen saturation shows the balance between oxygen delivery (DO2) and oxygen consumption (VO2). A fall from 75% to 60% means tissues are extracting more oxygen or receiving less delivery. Decreased DO2 can come from reduced preload and cardiac output, as seen with hypovolemia or bleeding. Reduced arterial oxygen content, i.e., hypoxia, also lowers DO2 and drives a lower SvO2. Sepsis, however, does not reliably produce a lower SvO2. In sepsis, cardiac output is often increased and there can be peripheral maldistribution of blood flow; oxygen extraction may be impaired or mitochondria may be dysfunctional, leading to variable SvO2 values, which can be normal or even elevated in some septic patients. Thus sepsis is not a predictable cause of a drop in mixed venous O2 saturation, making it the exception in this scenario.

Mixed venous oxygen saturation shows the balance between oxygen delivery (DO2) and oxygen consumption (VO2). A fall from 75% to 60% means tissues are extracting more oxygen or receiving less delivery. Decreased DO2 can come from reduced preload and cardiac output, as seen with hypovolemia or bleeding. Reduced arterial oxygen content, i.e., hypoxia, also lowers DO2 and drives a lower SvO2.

Sepsis, however, does not reliably produce a lower SvO2. In sepsis, cardiac output is often increased and there can be peripheral maldistribution of blood flow; oxygen extraction may be impaired or mitochondria may be dysfunctional, leading to variable SvO2 values, which can be normal or even elevated in some septic patients. Thus sepsis is not a predictable cause of a drop in mixed venous O2 saturation, making it the exception in this scenario.