REBEL Core Cast 135.0: A Simple Approach to Hypoxemia (vs. Hypoxia)
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Jun 16, 2025
The podcast delves into the crucial differences between hypoxemia and hypoxia, emphasizing their significance in clinical settings. It outlines five causes of hypoxemia, including shunt and dead space, along with management techniques for each. Practical insights are shared on maximizing oxygen delivery and recognizing when to escalate care with positive pressure. The hosts also discuss the importance of rapid assessment in critical care, ensuring healthcare professionals can act swiftly in urgent situations.
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insights INSIGHT
Difference Between Hypoxemia and Hypoxia
Hypoxemia is low oxygen in the blood, while hypoxia is low oxygen at the tissue level.
Hypoxia has multiple types with different causes, important to differentiate at the bedside.
volunteer_activism ADVICE
Recognize Hypopnea or Apnea Quickly
Patients not breathing well (hypopnea or apnea) will have hypoxemia that is easy to recognize.
Look for decreased respiratory effort when assessing for hypoxemia at the bedside.
volunteer_activism ADVICE
Exclude High Altitude in Hospitals
Exclude high altitude as a cause of hypoxemia in hospitalized patients unless practicing at very high elevations.
High altitude is rarely relevant inside hospitals for hypoxemia cases.
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In this episode, we break down a practical bedside approach to hypoxemia. We clarify the difference between hypoxemia (low oxygen in the blood) and hypoxia (low oxygen at the tissue level), and walk through the major causes of hypoxemia that you need to recognize quickly at the bedside.
🔑 Key Concepts
Hypoxemia vs. Hypoxia: Know the Difference
Hypoxemia = Low oxygen in the blood.
Measured indirectly by SpO₂ (pulse oximeter) or directly by PaO₂ (arterial oxygen tension) or SaO₂ (oxygen saturation).
Hypoxia = Low oxygen at the tissue level.
Can happen with or without hypoxemia.
Four Types of Hypoxia
Hypoxemic Hypoxia: Blood oxygen is low, so tissues get less oxygen. (e.g., severe pneumonia)
Anemic Hypoxia: Low hemoglobin levels mean less oxygen-carrying capacity, even if oxygen levels are normal. (e.g., hemorrhage, hemolysis)
Ischemic Hypoxia: Blood flow to tissues is blocked or reduced. (e.g., MI, stroke, severe shock)
Histotoxic Hypoxia: Oxygen delivery is normal, but tissues can’t use it. (e.g., carbon monoxide or cyanide poisoning)
Five Major Causes of Hypoxemia
Hypopnea/Apnea (Decreased Respiratory Drive)
Inadequate breaths (or no breaths) means lower oxygen intake.
Seen in cardiac arrest, drug overdose, severe brain injury.
Easy to recognize as patients are encephalopathic or apneic.
High Altitude
Lower barometric pressure = less available oxygen, despite 21% FiO₂.
Rarely relevant inside hospitals, but important to know.
Diffusion Defect
Impaired oxygen transfer across alveoli, often due to chronic lung disease.
Key Move: High FiO₂ (non-rebreather mask) → if still hypoxemic, they need positive pressure (NIV or intubation).
🛌 Practical Bedside Approach
Give as much FiO₂ as possible (non-rebreather mask).
Watch SpO₂ response:
If it improves → V/Q mismatch or dead space more likely.
If it doesn’t improve → think shunt physiology.
If refractory hypoxemia persists → Start positive pressure ventilation (HFNC, CPAP, BiPAP, or intubation depending on the situation).
🚨 Clinical Bottom Line
Mastering the basics of hypoxemia helps you recognize dangerous physiology early — before your patient crashes. Keep in mind the four types of hypoxia and the five major causes of hypoxemia.
Post Peer Reviewed By: Marco Propersi, DO (Twitter/X: @Marco_propersi), and Mark Ramzy, DO (X: @MRamzyDO)
👤 Guest Contributor
Eric Acker
MD
Internal Medicine Resident,
Rising Chief Resident,
Cape Fear Valley Medical Center,
Fayetteville NC