Airway, Respiration, and Ventilation
Three processes, not one
Ventilation is moving air (judged by chest rise, rate, and ETCO2). Oxygenation is loading hemoglobin (judged by SpO2). Respiration is alveolar gas exchange. A patient can look pink and still be ventilating terribly: a COPD patient on high-flow oxygen with an SpO2 of 99% and an ETCO2 of 70 is in trouble.
The ladder
Positioning and suction, then OPA/NPA, then supraglottic airway, then endotracheal intubation, then surgical airway. Oxygen devices: nasal cannula 1-6 L/min, simple mask 6-10, non-rebreather 10-15, BVM roughly 15, CPAP/PEEP for pulmonary edema and obstructive disease. For RSI/DSI, preoxygenate, have suction and a backup device at the bedside, and plan for failure before you push anything.
Traps
Pulse oximetry lags, reads falsely normal in carbon monoxide poisoning and severe anemia, and says nothing about ventilation. Capnography is the standard for confirming and continuously monitoring tube placement: a waveform sustained over at least six breaths, reassessed after every move. A sudden fall toward zero means dislodgement or esophageal placement. A rising ETCO2 with a falling rate means hypoventilation. A shark-fin waveform suggests bronchospasm. Over-ventilating an intubated patient drops CO2, reduces venous return, and can cause hypotension.
Rule of thumb
An intubated patient who suddenly desaturates gets a DOPE check before anything else: Displacement, Obstruction, Pneumothorax, Equipment.