Anaesthesia Coffee Break What is the lowest oxygen saturation YOU would tolerate?
Jan 18, 2021
Explore the crucial question of the lowest acceptable SpO2 in a healthy ASA1 male under general anaesthesia. Discover the oxygen–hemoglobin dissociation curve and its implications for safe oxygen levels. Learn about common causes of intraoperative hypoxemia and immediate management strategies. The hosts break down physiological responses to hypoxemia, emphasizing the importance of maintaining a buffer above 91%. They also discuss practical scenarios and the urgency of escalating care when oxygen saturation drops below critical thresholds.
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Use 94% As Your Early Action Threshold
- Accept a SpO2 threshold of around 94% as your early action point and use 91% (PaO2 ≈ 60 mmHg) as the physiological danger threshold.
- Start troubleshooting before 94% becomes 91% by increasing FiO2 and checking ventilation, tube/circuit and haemodynamics.
Immediate Steps To Correct Hypoxemia
- Manage falling saturations by increasing FiO2, ensuring adequate alveolar ventilation and checking tidal volume or dead space.
- Also check and treat blood pressure because improving perfusion often improves oxygenation.
CO2 Changes Reflect Ventilation, Not Direct O2 Cause
- A rise in PaCO2 often reflects falling alveolar ventilation, not a direct cause of reduced PaO2 in isolation.
- Conserving mass links O2 consumption, respiratory quotient and CO2 to alveolar ventilation and PaO2 changes.