9 - Capnography

capnography

continuous measurement and display of CO₂ concentration over time

capnometry

numerical value of E_TCO₂ without waveform

types of capnography

• mainstream

  • sensor placed directly in the airway

• sidestream

  • sample continuously drawn from airway into external sensor

physiology of CO₂

metabolism → transportation via bloodstream → elimination through lungs

factors affecting E_TCO₂

• ventilation

  • hypoventilation (↑__)

  • hyperventilation (↓__)

• perfusion

  • shock

  • pulmonary embolism

  • C.O. changes

• metabolism

  • fever

  • sepsis

  • metabolic acidosis

phases of capnogram

• phase 0 (baseline)

no CO₂ during inhalation

phases of capnogram

• phase 1 (dead space ventilation)

CO₂-free air from V_Danat

phases of capnogram

• phase 2 (ascending)

rapid rise as alveolar gas mixes with dead space gas

phases of capnogram

• phase 3 (alveolar plateau)

CO₂-rich alveolar gas exhaled; indicates effective ventilation

phases of capnogram

• phase 4 (E_TCO₂)

highest CO₂ concentration at end of exhalation (normal: 35-45 mmHg)

clinical application of capnography

• ET intubation verification (gold standard)

  • no waveform = tube in esophagus

• MV monitoring

  • titrating ventilator settings (PCV vs VCV)

  • detecting hypo-/hyperventilation and auto-PEEP

• sedation and procedural monitoring

  • conscious endoscopy

  • early detection of respiratory depression

• cardiac arrest and CPR

  • low E_TCO₂ (<10 mmHg) = poor compressions or no perfusion

  • sudden increase in E_TCO₂ = ROSC

• PE detection

  • sudden E_TCO₂ drop with maintained oxygenation

• assessment of readiness for extubation

capnography waveforms

• normal

capnography waveforms

• hyperventilation

capnography waveforms

• hypoventilation

capnography waveforms

• emphysema

capnography waveforms

• curare (spontaneous breathing during mechanical ventilation)

capnography waveforms

• hyperventilation / decreased pulmonary blood flow

capnography waveforms

• rebreathing CO₂

capnography waveforms

• obstruction

capnography waveforms

• pneumothorax

capnography waveforms

• poor compliance