The trachea is a membrano-cartilaginous tube creating the start of lower respiratory passage and is non-collapsible.
Trachea stretches from the lower border of cricoid cartilage at the lower border of the C6 vertebra to the lower border of T4 vertebra in supine position, where it ends by dividing into left and right main bronchi.
The upper half of trachea can be found in the neck (cervical part) on the other hand the lower half is located in the superior mediastinum of the thoracic cavity (thoracic part).The trachea is a 4-6 inch (10-11 cm) long tube.
The external diameter of trachea is 2 cm in men and 1.5 cm in females.
The lumen is smaller in living human than that in cadavers. It’s about 3 millimeters in newborns and remains so up to the third year of life; afterward the lumen grows by 1 millimeter every year up to 12 years, after which it stays reasonably steady. This knowledge is really essential for the anesthetists to choose the correct size of tracheal tube to be inserted into the trachea in children during general anesthesia.
The trachea consists of about 16-20 C-shaped rings of hyaline cartilage being located one above the other the cartilages are deficient posteriorly where the gap is filled up by connective tissue and involuntary muscle termed trachealis the absence of cartilages on the posterior aspect enables growth of esophagus during deglutition in cross section the trachea seems d-shaped or horseshoe-shaped.
Cervical Part of Trachea
The cervical part of the trachea is all about 7 cm in length and stretches from the lower border of cricoid cartilage to the upper border of manubrium sterni. It goes downwards and somewhat backwards in front of the esophagus following curvature of the cervical spine and enters the thoracic cavity in the median plane with small deviation on the right side.
Relationships of the Cervical Parts of Trachea
In the neck, the trachea is comparatively superficial and has subsequent relationships:
Anteriorly, from superficial to deep it’s related to:
- superficial fascia including anterior jugular veins and jugular venous arch (crossing in the suprasternal space of Burns)
- investing layer of deep cervical fascia
- sternothyroid and sternohyoid muscles
- isthmus of thyroid gland in front of the second, third and 4th tracheal rings
- inferior thyroid veins and arteria thyroidea ima (occasional)
- left brachiocephalic vein in kids may rise in the neck
- thymus gland (in kids) and
- brachiocephalic artery (occasionally) in kids
Posteriorly it’s related to:
- esophagus and
- recurrent laryngeal nerve in the tracheoesophageal groove (on every side)
On every side it’s related to:
- lobe of thyroid gland going to the 5th or 6th tracheal ring andcommon carotid artery in the carotid sheath
Blood Supply and Lymphatic Drainage
- The arterial supply of the cervical part of trachea is derived primarily from branches of the inferior thyroid arteries.
- The veins from trachea drain into the left brachiocephalic vein.
- The lymph from trachea drains into pre and paratracheal nodes.
This is by sympathetic and parasympathetic fibres.
The parasympathetic fibres are originated from vagus via the recurrent laryngeal nerve. They’re secretomotor and sensory to the mucus membrane and motor to the trachealis muscle.
The sympathetic fibres are originated from the middle cervical sympathetic ganglion. They’re vasomotor in nature.
It’s a life saving surgical procedure done in cases of laryngeal obstruction. The tracheostomy is usually done in the retrothyroid region after displacing the isthmus of the thyroid gland upwards or downwards.
After displacing the isthmus the trachea is opened by a vertical incision in the region of the third and 4th or second and third tracheal rings. This is subsequently converted into circular opening and tracheostomy tube is added.
If the tracheostomy is done above the isthmus it’s named high tracheostomy and if it’s performed below the isthmus it’s named low tracheostomy.
The low tracheostomy is dangerous in children owing to shortness of the neck and presence of thymus and left brachiocephalic vein and occasionally brachiocephalic artery. These structures, if injured, will cause dismay hemorrhage.