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Capnography for the intensivist

Capnography for the intensivist. Sarah Philipson. THE END. THE END. Questions?. Questions?. What is capnography ?. CO 2 physiology. Questions?. What is capnography ?. CO 2 physiology. Questions?. What is capnography ?. CO 2 physiology. How is it used?. Questions?.

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Capnography for the intensivist

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  1. Capnography for the intensivist Sarah Philipson

  2. THE END.

  3. THE END. Questions?

  4. Questions? What is capnography? CO2 physiology

  5. Questions? What is capnography? CO2 physiology

  6. Questions? What is capnography? CO2 physiology How is it used?

  7. Questions? What is capnography? CO2 physiology How is it used? Do I care? What are the problems with it?

  8. Capnography • Measurement of CO2vs time • Infrared spectroscopy measures the fraction of energy absorbed and converts this to a percentage of CO2 exhaled • Normal capnogram I – inspiratory baseline II – expiratory upstroke III – alveolar plateau IV – inspiratory downstroke

  9. Capnography • Measurement of CO2vs time • Infrared spectroscopy measures the fraction of energy absorbed and converts this to a percentage of CO2 exhaled • Normal capnogram I – inspiratory baseline II – expiratory upstroke III – alveolar plateau IV – inspiratory downstroke

  10. Capnography • Measurement of CO2vs time • Infrared spectroscopy measures the fraction of energy absorbed and converts this to a percentage of CO2 exhaled • Normal capnogram I – inspiratory baseline II – expiratory upstroke III – alveolar plateau IV – inspiratory downstroke Normal EtCO2 = 38-40mmHg

  11. A-B: Dead space B-C: Dead space + alveoli C-D: Alveoli D: ETCO2 D-E: Inspiration

  12. How we measure CO2

  13. Physiology – “ICU is easy!”

  14. Carbon Dioxide PRODUCTION AT TISSUES

  15. Carbon Dioxide PRODUCTION AT TISSUES TRANSPORT IN BLOOD

  16. Carbon Dioxide PRODUCTION AT TISSUES REMOVAL VIA VENTILATION TRANSPORT IN BLOOD

  17. Carbon Dioxide PRODUCTION AT TISSUES REMOVAL VIA VENTILATION TRANSPORT IN BLOOD

  18. Carbon Dioxide PRODUCTION AT TISSUES REMOVAL VIA VENTILATION TRANSPORT IN BLOOD

  19. Carbon Dioxide PRODUCTION AT TISSUES REMOVAL VIA VENTILATION TRANSPORT IN BLOOD

  20. CO2 production • Produced in tissues through cellular respiration – glycolysis, Krebs cycle, phosphorylation

  21. CO2 production

  22. CO2 transport • Diffuses across capillary membranes and is transported to lungs through the venous system • ~7% transported dissolved in blood • ~20% as carbaminohaemoglobin (reaction between carbon dioxide and the amine radicals of the haemoglobin molecule) • ~70% as bicarbonate and hydrogen ions from dissociation of carbonic acid

  23. CO2 transport i.e. cardiac output • Diffuses across capillary membranes and is transported to lungs through the venous system • ~7% transported dissolved in blood • ~20% as carbaminohaemoglobin (reaction between carbon dioxide and the amine radicals of the haemoglobin molecule) • ~70% as bicarbonate and hydrogen ions from dissociation of carbonic acid CO = SV x HR

  24. CO2 transport

  25. CO2 removal i.e. ventilation • Ventilation = rate, volume, diffusion

  26. CO2 removal i.e. ventilation

  27. ETCO2 - Why is it useful? Reflects changes in: • Ventilation • Can predict impending respiratory failure • Provides early warning of airway compromise • Transport • Can be used as a predictor of fluid responsiveness – found to be proportional to CI in measuring response to passive leg raise in patients with stable metabolic and respiratory conditions • Production • Metabolism

  28. Have I convinced you?

  29. Problems with capnography • Only reliable(?) in patients with stable metabolic and respiratory states • Abnormal Aa gradients make EtCO2 not a good predictor of PaCO2, but can still use trend • Needs to be a trend, not a one-off measure • Detects, does not diagnose – more tests! • Difficulty with equipment – easily clogged with water droplets • Normal capnogram can occur with glottic intubation – still need an XR

  30. Convinced? • Capnography • CO2 physiology • Production • Transport • Ventilation • The capnography curve and what it can tell us • Problems with capnography

  31. KEEP CALM AND WATCH THE CO2

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