Pulse oximetry as time machine: Lag times confuse doctors, complicate intubations (EMCrit)
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image: wikimedia Pulse Oximetry: The 30-Second Time Machine Why does it seem to take so long to re-oxygenate your crashing patient? Because your pulse oximeter is lying to you, no matter how good it is. Telescopes show us how a star looked millions or billions of years ago; pulse oximeters create a similar, though tiny time warp, revealing the patient's blood oxygenation was about 30 seconds ago, or more. (It can easily take that long for newly oxygenated blood to get out to the skin where you have the probe, especially if cardiac output is low.) In the steady state, the lag is irrelevant, but in crashing or unstable patients, it can mean a lot. For example, many patients have been unsafely extubated pre-hospital for "failed" intubations that were in fact correctly done, with an ET tube in proper position -- just because the
Pulse oximetry as time machine: Lag times confuse doctors, complicate intubations (EMCrit)
Pulse oximetry as time machine: Lag times…
Pulse oximetry as time machine: Lag times confuse doctors, complicate intubations (EMCrit)
image: wikimedia Pulse Oximetry: The 30-Second Time Machine Why does it seem to take so long to re-oxygenate your crashing patient? Because your pulse oximeter is lying to you, no matter how good it is. Telescopes show us how a star looked millions or billions of years ago; pulse oximeters create a similar, though tiny time warp, revealing the patient's blood oxygenation was about 30 seconds ago, or more. (It can easily take that long for newly oxygenated blood to get out to the skin where you have the probe, especially if cardiac output is low.) In the steady state, the lag is irrelevant, but in crashing or unstable patients, it can mean a lot. For example, many patients have been unsafely extubated pre-hospital for "failed" intubations that were in fact correctly done, with an ET tube in proper position -- just because the