ETCO2 & Dead-Space

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Steve Haywood
Steve Haywood
Former Respiratory Therapist working to de-mystify the ventilator through hands-on workshops and online education. Additional interests include HFNC in CHF and COPD, Medical Education, and Tupperware.

The Pre-brief

By combining an ABG with end-tidal CO2 measurements. We can accurately predict our patient’s fraction of dead space and monitor for changes in dead space.

PaCO2-PECO2/PaCO2 = Fraction of dead space. 

When your patient’s PECO2 is significantly lower than the PaCO2, think about increasing dead space. 

The Debrief

  • Dead space is gas in the pulmonary system that does not participate in gas exchange.
  • We have normal anatomic dead space made up of the trachea and bronchial tree.
  • Patients also have physiologic dead space composed of alveoli that are not participating in gas exchange.
  • When the fraction of dead space exceeds 0.3, we must have a concern that our patient’s physiologic dead space is increasing.


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