Lecture Notes: Waveform Capnography

Introduction

• Presenter: Zack Fulkerson, Pulmonary and Critical Care Fellow
• Case Study: Patient transferred to ICU for altered mental status and respiratory failure
  • Emergency intubation
  • Hypotension and shock upon ICU arrival
  • Central access obtained; issue with pulse oximeter and end-tidal CO2
• Key Question: Is a change in the end-tidal CO2 significant?

Overview of Talk

• Discuss the physiology behind waveform capnography
• Application of physiological concepts to capnography examples

Physiology of Capnography

• Diagram Components:
  • Pulmonary circulation, alveoli, airways, mechanical tubing
  • Carbon dioxide (CO2) detector
• CO2 Registration Requirements:
  1. CO2 production in peripheral tissues via aerobic metabolism
  2. Pulmonary perfusion to circulate CO2 to the lungs
  3. Ventilation for CO2 diffusion into alveoli and transport to the detector
• Graphical Representation:
  • Plateau during expiration; end-tidal CO2 recorded here
  • Inspiration shows zero CO2
• Arterial vs. End-tidal CO2:
  • Metabolism and ventilation affect both similarly
  • Circulation can cause discrepancies

Patterns in Capnograms

• Normal Capnogram:
  • Zero CO2 during inspiration
  • Plateau during expiration; end-tidal measured here
• Decreasing End-Tidal CO2:
  • Causes: hyperventilation, decreased metabolism, increased dead space
• Increasing End-Tidal CO2:
  • Causes: hypoventilation, increased metabolism, exogenous bicarbonate
• Rebreathing Indicator:
  • Elevated baseline; issues with mechanical dead space or circuit
• Shark Fin Waveform:
  • Airway obstruction, e.g., COPD, asthma, mucus plug
• Loss of Plateau:
  • Leak in the circuit (e.g., tracheostomy cuff issue)
• Curare Cleft:
  • Patient attempting to breathe without full ventilatory trigger
• Zero End-Tidal CO2:
  • Potential cardiac arrest, apnea, or ventilator disconnection

Capnography in Cardiac Arrest

• CPR and Capnography:
  • Increase in end-tidal CO2 indicates restoration of perfusion
  • Target: end-tidal CO2 > 10-15
  • Decrease signals need for CPR provider change
  • Sudden increase suggests pulse return

Conclusion

• Importance of waveform capnography in critical care
• Provides valuable insights into patient status and management
• Note: Measure capnography carefully in real-time settings
• Presenter’s Note: Gratitude for audience engagement

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Remember to review these key points to better understand waveform capnography and its application in critical care scenarios.