Basics of Waveform Capnography
Waveform capnography assesses ventilation by monitoring exhaled carbon dioxide
Can use measurement and morphology during different phases of respiratory cycle to uncover pathophysiology
OVERVIEW
 • Capnography measures ventilation through exhaled C02 (PECO2)
 • Abnormal morphology can provide important data regarding pulmonary pathophysiology
CLINICAL APPLICATIONS
 • Confirmation of endotracheal intubation
 • Monitoring airway integrity
 • Monitoring cardiac output
 • Monitoring spontaneous respiration
 • Assessing for CO2 retention
 • Assessing ROSC during CPR by observing a sudden increase in waveform amplitude
ETC02 WAVEFORM
 • α-Angle
    - Between II and Ill
    - >900 = bronchospasm or V/Q mismatch
 • ß-AngIe
    - Between Ill and IV/0
    - >90° = rebreathing or mechanical obstruction
 • PHASE I
    - Inspiratory baseline
    - PECO2 = zero
 • PHASE II
    - Beginning of expiration
    - Transition as CO2 rises when anatomical dead space, then alveolar gas, is exhaled
 • PHASE Ill
    - Alveolar plateau
    - ETCO2: Peak CO2 at end of phase Ill, Correlates with PaCO2
 • PHASE IV/0
    - Start of inspiration
    - PECO2 rapidly falls to zero
WAVEFORM PATTERNS:
 • BRONCHOSPASM AND REBREATHING/AIR TRAPPING
    - Increase or loss of a-angle (aka "shark fin")
    - Dead space has not finished emptying before next inspiration
    - Increasing level of baseline PECO2 due to air trapping
 • EMPHYSEMA
    - Arterial CO2 represented by early peak, not end-tidal, due to hypercompliance and poor gas exchange surface
    - Pattern can also be seen with pneumothorax with air leak
 • SUDDEN LOSS OF WAVEFORM
    - Critical event needing emergency intervention
    - ET tube disconnected, dislodged, kinked, or obstructed
 • MECHANICAL AIRWAY OBSTRUCTION
    - Fixed mechanical obstruction affects both inspiration (phase IV/0) & expiration (phase II)
    - α-angle and ß-angle both >900
 • CARDIOGENIC OSCILLATIONS
    - Pulsation transmitted from the heart to the lung parenchyma produces small volume changes that manifest as oscillations
    - Sign of cardiomegaly
 • DOWNTRENDING ETCO2 - Decreasing waveform size can indicate:
    - Shock/low cardiac output state
    - Pulmonary embolism
    - Hyperventilation

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