Endotracheal tube (ETT) is a flexible plastic tube, usually made of polyvinyl chloride (PVC), that is passed into trachea through the mouth (oral) or nose (nasal) to establish a patent airway and ensure adequate gaseous exchange or ventilation. It is also used to deliver or administer anaesthetic gases to patients during surgery.
DIAMETER AND LENGTH/DEPTH OF ENDOTRACHEAL TUBE.
Endotracheal tube has inner and outer diameter. The inner diameter (ID) is the diameter of the tube lumen while the outer diameter (OD) measures the diameter of the lumen and the thickness of the tube. The size of the tube is determined by the inner diameter. For instance, if the inner diameter of a tube is 7.5mm, the tube is size 7.5.
The length/depth of the tube is how far the tube goes into the patient during intubation. The normal length for adult male is 21-22cm while that of adult female is 20-21cm. The landmark for setting the the tube at the appropriate length is the incisor or the lips. It is important to document the length used for the intubated patient. This helps to know if the tube is coming outwards or going inside, and appropriate actions taken.
PARTS OF ENDOTRACHEAL TUBE.
BEVEL: This is slant portion found at the tip/edge of the tube. The bevel is usually LEFT-FACING instead of RIGHT-FACING. This helps easy visualization of the vocal cords during intubation and easy access into the trachea.
MURPHY’S EYE: This is an extra opening at the tip of the tube that sustains ventilation or gaseous exchange peradventure the bevel becomes obstructed by secretions or tracheal wall.
CUFF: Endotracheal tube can either be cuffed or uncuffed. Paediatrics tubes are usually uncuffed because their tracheal is easily damaged by pressure. However, children above 6years can cope with cuffed ETT. The cuff (located proximal to the tip of the tube inside the patient) is inflated by injecting pressurized air in a syringe into the PILOT BALLOON. The air will not leak even after the inflating syringe has been removed because of the ONE-WAY VALVE in the the pilot balloon. The pilot balloon, which remains outside after patient has been intubated, shows the true condition/status of the cuff (inside the patient)- whether it is inflated or deflated or leaking.
TYPES OF CUFF.
High volume – low pressure cuff and Low volume – high pressure cuff.
IMPORTANCE OF INFLATING THE CUFF.
1. To ensure good positive pressure ventilation, especially for patients on mechanical ventilator. The inflated cuff forms a seal on the tracheal wall, thus preventing leakage of air during ventilation.
2. To prevent aspiration of regurgitated gastric content.
However, care must be taken to avoid too much or too little pressurized air. The tracheal cuff pressure must be maintained between 20-25cm of water. If the pressure exceeds 30cm of water, the cuff may burst! A MANUAL MANOMETER can be used to measure cuff pressure. In facilities where this instrument is not available, 5-10ml of air is usually injected into the pilot balloon to inflate cuff.
NOTE: “Centimetres of water” as used here, is the unit of measurement of PRESSURE. It doesn’t mean water will be used for inflation. ONLY AIR MUST BE USED TO INFLATE CUFF!
WHAT HAPPENS WHEN THE TRACHEAL CUFF PRESSURE IS TOO HIGH?
A very high tracheal cuff pressure impedes blood flow to the tracheal wall and causes tracheal ischemia or necrosis.
AND IF THE TRACHEAL CUFF PRESSURE IS TOO LOW?
Risk for aspiration is high and positive pressure ventilation will not be effective as there may be leakage of air.
The endotracheal tube is a colourless plastic tube which cannot be visible on X-ray. However, for this purpose, a radio-opaque blue line runs longitudinally throughout the length of the tube to make it visible or seen on chest X-ray.
OTHER TYPES OF ENDOTRACHEAL TUBE INCLUDE:
Armoured or reinforced endotracheal tube.
Laser-resistant endotracheal tube.
Double lumen endotracheal tube.
Preformed endotracheal tube e.g. RAE – Ring, Adair, and Elwyn.