Capnogram waveform: obstruction


Capnography directly reflects the elimination of CO2 by the lungs to the anesthesia device. It indirectly reflects the production of CO2 by tissues and the circulatory transport of CO2 to the lungs

Capnography Waveform (image needed)

  • Phase 0 – Inspiration
  • Phase 1 – Represents the CO2-free gas from the airways (anatomical and apparatus dead space)
  • Phase 2 – Mixture of anatomical and alveolar dead space
  • Phase 3 – Consists of an alveolar plateau representing CO2-rich gas from the alveoli
  • Alpha Angle – Angle between phase II and III
  • Beta Angle – Angle between phase III and descending limb of inspiratory segment

Airway Obstruction (Asthma, Bronchospasm, COPD, Pregnancy, Kinked ET Tube)

  • Prolongation or slanting of the expiratory upstroke phase II
  • Prolongation of phase III
  • Alpha angle is increased


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