Scenario; 54-year-old male is intubated in ICU after he failed a trial of BiPAP from community-acquired pneumonia. Due to patient's long stature, nerdy resident calculated the length of endotracheal tube (ETT) depth to be at 26 cm at lips. After ten minutes of intubation, the nurse informed you about frequent ventricular arrhythmia on the monitor which appears to be mostly Premature Ventricular Contractions (PVCs).
Explanation: PVCs is a frequent manifestation if ETT is touching carina and call for adjustment. A plethora of literature has been written and various formulas have been developed to calculate the exact depth of ETT but none of them have done well in real life. Rule of thumb so far has worked satisfactorily with 21 cm for females or 23 cm for males at lips. Adjustment with physical exam (auscultation of bilateral breath sounds) and CXR verification is still a standard of care.
Burman SO, Gibson TC, Chir B. Bronchoscopy and cardiorespiratory reflexes. Ann Surg. 1963;157:134–41