Remember the blood vessels!
The reasons for knowing the anatomy and hence the positions of the blood vessels and nerves which could be damaged by thoracentesis are numerous. By knowing their positions it is possible to avoid damaging them when inserting the needle and hence avoid many clinical conditions which would result from their damage. These include:
- 1) Haematoma - due to rupture of blood vessels.
- 2) Ischaemia - of muscles supplied by the intercostal blood vessels.
- 3) Neuritis - due to slight damage of the nerves.
- 4) Paralysis of the intercostal muscles- because of serious damage to the intercostal nerves which supply them. Since the external intercostal muscles are involved in inspiration, their paralysis could lead to breathing difficulty.
The muscles you should consider...
INTERCOSTAL MUSCLES
- The external intercostal - Its fibres run in a caudoventral direction, originating on one rib and inserting on the following rib. The muscle layers extent is from the upper ends of the ribs to the costochondral junctions and do not extend ventrally as far as the sternum. They assist inspiration by increasing the volume of the thorax by moving the ribcage cranially and ventrally.
- The internal intercostal - Its fibres run cranioventrally and are approximately perpendicular to the external intercostal muscles. Unlike the external intercostal muscles they do not extend to the dorsal region of the intercostal spaces, but instead they cover the ventral region around the sternum. They assist to a minor extent in expiration by pulling the the ribcage caudally and dorsally decreasing the volume of the thorax. This is only really used in forced expiration since during normal expiration the decrease in volume is primarily due to the passive recoil of the lungs.
- Transversus thoracis - This muscle originates from the dorsal aspect of the sternum. It is a triangular sheet whose apex points cranially. Slips of muscle split from the main body and run in a caudolateral direction to insert on the sternal ribs close to the costochondrial junctions. Morphologically it is the equivalent of the ventral part of the transversus abdominus. Since it is within the ribcage it lies over the internal thoracic vessels. It is involved in expiration.
You should know about the following muscles already:
- Cutaneous trunci
- Latissimus dorsi
- Pectoralis ascendens
- External abdominal oblique
- Serratus ventralis
- Serratus dorsalis
CLINICAL NOTE:
Although thoracocentesis is a fairly non-traumatic procedure, a knowledge of the muscles of the thoracic wall is necessary for several reasons.
LENGTH OF NEEDLE- An idea of the thickness of the muscle ( a consequence of the number of layers ) will decide the hypodermic needle length . If too short no fluid will be aspirated, and if too long , it risks puncture or laceration of structures more medial than the pleural space.
IATROGENIC INJURIES- (caused by the clinician) Although unlikely, if damage to the muscle occurred post-thoracentesis , it would be useful for the clinician to know which muscles were involved and so decide on therapy.
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