Pulmonary artery catheter (PAC) derived mixed venous oxygen saturation (SvO2) decreases in all of the following conditions EXCEPT:

• A Low cardiac output states (cardiogenic shock)
• B Severe anaemia with intact cardiac reserve
• C Septic shock with distributive physiology ✓
• D Carbon monoxide poisoning

Explanation

SvO2 reflects the balance between oxygen delivery (DO2) and consumption (VO2): SvO2 decreases when tissues extract more oxygen. In distributive septic shock (high cardiac output, maldistributed flow, and mitochondrial dysfunction), SvO2 is typically normal or elevated because peripheral oxygen cannot be utilised despite delivery. CO poisoning yields falsely normal or high pulse oximetry and also reduces effective DO2 without increasing SvO2 measurement. Low CO and anaemia reduce SvO2 by reducing DO2.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.