Page 34 - Clinical Anatomy

ECA1 7/18/06 6:31 PM Page 19

The lower respiratory tract 19

2◊◊Fluid can be drained from the pleural cavity by inserting a wide-bore
needle through an intercostal space (usually the 7th posteriorly). The
needle is passed along the superior border of the lower rib, thus avoiding
the intercostal nerves and vessels (Fig. 8). Below the 7th intercostal space
there is danger of penetrating the diaphragm.
3◊◊For emergency chest drainage—for example traumatic haemothorax or
haemopneumothorax—the site of election is the 5 th intercostal space in the
mid-axillary line. An incision is made through skin and fat and blunt dis-
section carried out over the upper border of the 6th rib. The pleura is
opened, a finger inserted to clear any adhesions and ensure the safety of the
adjacent diaphragm before inserting a tube into the pleural space and con-
necting it to an under-water drain.
4◊◊Since the parietal pleura is segmentally innervated by the intercostal
nerves, inflammation of the pleura results in pain referred to the cutaneous
distribution of these nerves (i.e. to the thoracic wall or, in the case of the
lower nerves, to the anterior abdominal wall, which may mimic an acute
abdominal emergency).

The lower respiratory tract

The trachea (Figs 14, 15)
The trachea is about 4.5in (11.5cm) in length and nearly 1 in (2.5cm) in
diameter. It commences at the lower border of the cricoid cartilage (C6) and
terminates by bifurcating at the level of the sternal angle of Louis (T4/5) to
form the right and left main bronchi. (In the living subject, the level of bifur-
cation varies slightly with the phase of respiration; in deep inspiration is
descends to T6 and in expiration it rises to T4.)

Relations
Lying partly in the neck and partly in the thorax, its relations are:

Cervical
•◊◊anteriorly — the isthmus of thyroid gland, inferior thyroid veins, ster-
nohyoid and sternothyroid muscles;
•◊◊laterally—the lobes of thyroid gland and the common carotid artery;
•◊◊posteriorly—the oesophagus with the recurrent laryngeal nerve lying in
the groove between oesophagus and trachea (Fig. 16).

Thoracic
In the superior mediastinum its relations are:
•◊◊anteriorly—commencement of the brachiocephalic (innominate) artery