The typical depth of the endotracheal tube is 23 cm for men and 21 cm for women, measured at the central incisors. The average size of the tube for an adult male is 8.0, and an adult female is 7.0, though this is somewhat an institution dependent practice.
A tube with a larger outer diameter will also be more difficult to pass through the stoma. A 10-mm outer diameter tube is usually appropriate for adult women, and an 11-mm outer diameter tube is usually ap- propriate for adult men as an initial tracheostomy tube size.
The size of an ETT signifies the inner diameter of its lumen in millimeters. Available sizes range from 2.0 to 12.0 mm in 0.5 mm increments. For oral intubations, a 7.0-7.5 ETT is generally appropriate for an average woman and a 7.5-8.5 ETT for an average man.
Typically, females require a 7.0- to 8.0-mm tube and males require a 7.5- to 9.5-mm tube with a 15-mm connector. The tube should be large enough to facilitate airflow and small enough to pass the vocal cords without damaging them. ET intubation can be done via the nasal or oral routes.
Ventilation with large volumes using small tracheal tubes results in high ventilator pressures. However, tracheal pressures are only marginally greater than those obtained with larger tubes. Small endotracheal tubes and high ventilation volumes result in a positive tracheal pressure at the end of expiration.
 The typical depth of the endotracheal tube is 23 cm for men and 21 cm for women, measured at the central incisors. The average size of the tube for an adult male is 8.0, and an adult female is 7.0, though this is somewhat an institution dependent practice.
For adult patients, the appropriate level the suction vacuum should be set at is 80 to 120 mmHG. For pediatric patients, suction vacuums should be between 60 and 80 mm HG. Setting levels too high should be avoided and can lead to tissue damage.
A tube should not be wider than 10 mm in adult females and 11 mm in adult males, to minimize the trauma to the tracheal wall and avoid long term complications . The ID influences the physiology of breathing and course of weaning off from the ventilator.
The endotracheal tube (ETT) size formula, (age/4) + 3.5, with a cuffed tube makes more sense anatomically. Classic teaching is that we should use the formula (16+age)/4 or (age/4) + 4 to calculate the uncuffed pediatric ETT size.
Types of endotracheal tubes include oral or nasal, cuffed or uncuffed, preformed (e.g. RAE (Ring, Adair, and Elwyn) tube), reinforced tubes, and double-lumen endobronchial tubes. For human use, tubes range in size from 2 to 10.5 mm in internal diameter (ID).
Please note ETT = endotracheal tube size.
Endotracheal tubes are commonly referred to by their internal diameter size (e.g., a 7.0 endotracheal tube has an inner diameter of 7 mm ).
Most of the anaesthesia textbooks recommend depth of placement of ET to be 21 cm and 23 cm in adult females and males, respectively, from central incisors. [5,6] It is suggested that the tip of ET should be at least 4 cm from the carina, or the proximal part of the cuff should be 1.5 to 2.5 cm from the vocal cords.
Always maintain a high index of suspicion of esophageal intubation, particularly if the intubation was difficult. If in doubt, pull out the tube and do the following: Bag-mask ventilation with an oropharyngeal or nasopharyngel or both.
A patient with an oral endotracheal tube may have an oral airway or bite block in place that should be changed at least every 24 hours. A ventilator, T-tube, or trach collar will provide constant humidification. Corrugated tubing should be emptied by disconnecting the tubing and draining into an appropriate receptacle.
Circuit tubing — The ventilator circuit tubing is generally corrugated plastic (22 mm inside diameter for adults), which has universal connectors (22 mm outside diameter, 15 mm inside diameter) that connect the ventilator to the endotracheal tube (ETT), tracheostomy tube, or noninvasive interface (figure 1).