In this episode, we explore the science, history, and frontline application of End-Tidal CO₂ (ETCO₂) — a tool that offers real-time insight into ventilation, perfusion, and metabolism. Danny and Rance from DnR explain how paramedics can use ETCO₂ to assess and guide care across multiple patient presentations. Key Takeaways: ETCO₂ is the sixth vital sign — reflecting ventilation, perfusion, and metabolism in real time. Capnography vs. Oximetry: SpO₂ shows what was happening; ETCO₂ shows what's happening now. Waveform interpretation: Alpha and beta angles reveal underlying pathology like bronchospasm, obstruction, or air trapping. Clinical uses: Tube confirmation: Real-time verification in 6 breaths or less. CPR: Values Ventilation: Real-time feedback for rate and volume. Head injuries: Maintain normocapnia; hyperventilate only during herniation. Sepsis, trauma, PE, and DKA: Trending ETCO₂ helps identify metabolic and perfusion problems. Practical tips: "Filter first, end-tidal to the sky." Inline sensors outperform sidestream for accuracy. End-tidal is not just for intubated patients — use it with nasal prongs for sedation and respiratory monitoring.