Endotracheal intubation involves placing a flexible tube through the mouth or nose into the trachea (windpipe) to secure the airway for mechanical breathing assistance. The depth of this endotracheal (ET) tube is a specific measurement. Precise placement is fundamental to the procedure’s success, ensuring air effectively reaches the lungs while avoiding serious complications.
Anatomical Considerations for Placement
The path of an endotracheal tube begins in the mouth, passes the tongue, and is guided through the larynx, which houses the vocal cords. The tube must advance past the vocal cords to sit securely within the trachea. This placement prevents the tube from being easily dislodged.
The ideal final position for the tip of the ET tube is in the mid-trachea. This location is a few centimeters above the carina, the point where the trachea divides into the two main bronchial tubes. This position ensures that delivered air is distributed evenly to both lungs.
Positioning the tube too high risks it slipping out of the trachea, while advancing it too far can lead to it entering one of the main bronchi. Because of the angle at which the bronchi split, the tube is more likely to enter the right mainstem bronchus. This event, a right mainstem intubation, would cause only the right lung to be ventilated.
Formulas and Techniques for Depth Estimation
Before final confirmation, healthcare providers use established guidelines to estimate the proper insertion depth. These initial calculations are based on patient characteristics and direct visualization, providing a starting point.
For adults, a widely used rule of thumb is to secure the tube at 23 centimeters for men and 21 for women, measured at the lips. Since these are averages, height-based formulas can provide a more personalized estimation, such as dividing the patient’s height in centimeters by 7 and then subtracting 2.5.
In pediatric patients, depth estimation is more sensitive due to their smaller airways. Simple age-based formulas are frequently used, such as taking the child’s age in years, dividing it by two, and adding 12. Another common method for children involves multiplying the internal diameter of the chosen ET tube by three. These formulas provide a starting point, but careful confirmation is always required.
Beyond formulas, direct visualization during intubation offers another guide. Many ET tubes have a black depth marker above the inflatable cuff. The clinician can aim to align this marker with the patient’s vocal cords to help place the tube’s tip appropriately.
Bedside Confirmation Methods
Immediately after the tube is inserted, a series of checks are performed at the bedside to confirm it is in the trachea. The most reliable of these rapid methods is capnography, which measures the concentration of carbon dioxide (CO2) in exhaled air. A consistent level of end-tidal CO2 (EtCO2) provides strong evidence of correct placement, as the esophagus does not contain a continuous source of CO2.
Alongside capnography, clinicians perform a physical examination. This includes watching for equal rise and fall of both sides of the chest with each delivered breath. Using a stethoscope, the provider listens for clear and equal breath sounds over both lungs. They also listen over the stomach, where the absence of gurgling sounds helps rule out esophageal placement. Observing condensation inside the tube is another sign of correct placement.
Radiographic and Advanced Verification
While bedside checks are important for immediate confirmation, the definitive verification of the tube’s depth is achieved through imaging. A portable chest X-ray is considered the gold standard for this purpose. The X-ray provides a clear image of the tube’s position, allowing for precise measurement of the distance between the tube’s tip and the carina.
On a chest X-ray, the ideal placement of the ET tube tip is between 5 and 7 centimeters above the carina in an adult with their neck in a neutral position. This distance provides a safe margin, making it unlikely for the tube to be pushed past the carina or pulled up toward the vocal cords with patient movement. If the X-ray reveals the tube is too deep or shallow, it can be adjusted and its new position confirmed.
Point-of-care ultrasound (POCUS) has emerged as a rapid and reliable method for confirming tube placement. An ultrasound probe on the neck can directly visualize the tube passing through the trachea in real-time. This technique can distinguish between tracheal and esophageal intubation and can also assess for bilateral lung sliding, which confirms both lungs are being ventilated.