Tidal Volume Calculator - Endotracheal Tube (ETT) Depth

Estimating ideal ETT position

This calculator determines the optimal endotracheal tube placement (based on patient height) to avoid right mainstem intubation, hypoxemia, and pneumothorax (when ETT is placed too deeply) or injury to vocal cords or accidental extubation (when ETT placed too shallowly).

ETT depth from front teeth (cm) (Chula formula) = 0.1 x Height in cm + 4

Whilst the height-based calculation does not exclude the need for chest x-ray, auscultation or ultrasound in determining ETT depth, it can assist with getting the ETT into a safe position from the start.

In cases with critical hypoxemia, delivering the ETT into the mid-trachea immediately may prevent desaturation.

In the original study, the Chula formula was tested on 100 patients of equal genders, who underwent general anesthesia with orotracheal intubation

With the help of a fiberoptic bronchoscope (inserted into the ETT after intubation) the distance from the tip of ETT to the carina and the distance from the upper border of the cuff of ETT to the vocal cords were measured.

Target tidal volume

Tidal volume is the measure of the amount of air inhaled during a normal breath. Safe tidal volumes can be determined based on patient’s height and gender and the rule of thumb, when lung-protective ventilation is required, is setting the tidal volume at 6-8 mL/kg ideal body weight.

Target tidal volume ranges from 6 to 8 mL/kg IBW, where:

• IBW male = 50kg + 2.3 x (Height in inches – 60)
• IBW female = 45.5kg + 2.3 x (Height in inches – 60)

Traditional pre-set tidal volumes higher than 10 ml/kg have been proved to be associated with increased risk of pulmonary barotrauma, decreased venous return and reduced cardiac output.

In patients with acute lung disease, recent studies have shown correlation between use of lower tidal volume and decreased mortality.

Tidal volumes between 6 and 6 mL/kg IBW are advised in ventilating patients with acute lung disease such as:

• Pneumonia;
• Fibrotic lung disease;
• Acute respiratory distress syndrome (ARDS);
• Chronic obstructive pulmonary disease (COPD).

References

Techanivate A, Kumwilaisak K, Samranrean S. Estimation of the proper length of orotracheal intubation by Chula formula. J Med Assoc Thai. 2005; 88(12):1838-46.

Warner MA, Patel B. Chapter 48 - Mechanical Ventilation; Benumof and Hagberg's Airway Management (Third Edition) 2013, Pages 981-997.e3.

Fuller BM, Ferguson IT, Mohr NM, Drewry AM, Palmer C, Wessman BT, Ablordeppey E, Keeperman J, Stephens RJ, Briscoe CC, Kolomiets AA, Hotchkiss RS, Kollef MH. Lung-Protective Ventilation Initiated in the Emergency Department (LOV-ED): A Quasi-Experimental, Before-After Trial. Ann Emerg Med. 2017; 70(3):406-418.e4.