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 #Waveform #Capnography #interpretation #patterns #diagnosis #pulmonary