Types of Endotracheal Tubes

Introduction
The endotracheal tube (ETT) is an essential and well-known element of anesthesiology practice. The presence of an ETT maintains a patent airway, allows for oxygenation and ventilation, permits suction of secretions, reduces the risk of aspiration of gastric contents or oropharyngeal secretions, and facilitates the use of inhaled anesthetics.

Materials
The most commonly used ETT material in the United States is polyvinyl chloride (PVC), a clear plastic that allows for visualization of exhaled breath condensation ("breath aerosol"), secretions, and other foreign matter within the tube. PVC is a semirigid material at room temperature but becomes relatively more pliable when warmed after placement in the trachea, allowing for easy manipulation of the tube tip during intubation while reducing the risk of mucosal ischemia after placement. Although less commonly used, ETTs made of other materials are available in the United States, including nylon, silicone, and Teflon.

Sizes
The size of an ETT indicates 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 intubation, a 7.0-7.5 ETT is usually appropriate for the average female and a 7.5-8.5 ETT is appropriate for the average male. However, the appropriate tube size is a multifactorial clinical decision that depends on the patient's height and weight, the type of surgery, and the presence of lung or airway disease. For nasal intubation, a size down 0.5-1.0 mm is appropriate. The length is proportional to the ETT size. Nasotracheal tubes are approximately 2 cm shorter than oral tracheal tubes. Because the anatomical variation of the trachea is difficult to predict, several sizes of ETTs should be available before intubation.

The appropriate pediatric tube size can be calculated using the formula ID = age (in years)/4) + 4. For example, a 6.0 ETT is usually appropriate for an 8-year-old patient.

Anatomy
The patient end, also called the distal or tracheal end, is placed in the trachea and typically has an inflatable cuff that provides a seal to prevent aspiration of gastric contents and reduce air leaks during positive pressure ventilation. The cuff is inflated by a balloon located at the machine (or proximal) end of the ETT. The balloon is connected to the cuff by a tube that runs the length of the ETT and contains a one-way valve that keeps the cuff inflated once the inflation syringe is removed. In general, cuffed tubes are used in patients older than 6 years of age.

Endotracheal tubes can be beveled or non-beveled. The bevel allows for better visualization of the glottis in front of the tube tip and makes it easier to pass the tube through the vocal cords. In orotracheal intubation, the bevel faces left at a 45-degree angle.