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Ischaemia results from an acute interruption of flow
of blood to a limb or organ. Oxygen supply is inadequate
to meet demand and anaerobic metabolism takes over,
producing lactic acidosis and activating cellular and
humoural inflammatory pathways. If the arterial supply
is not re-established in time, cell death occurs.
Skeletal muscle can be rendered ischaemic for 3-6 hours
and still recover function. Peripheral nerves are more
sensitive to ischaemia, and prolonged neurological deficit
may result from relatively short periods of tissue ischaemia.
If arterial supply is restored to ischaemia tissue,
the sudden release of inflammatory mediators, lactic
acid, potassium and other intracellular material into
the circulation can cause profound myocardial depression,
generalised vasodilatation and initiate a systemic inflammatory
response.
Laceration, with either complete or incomplete transection
of the vessel, is the most common form of vascular injury.
Haemorrhage tends to be more severe in partially transected
vessels, as complete transection results in retraction
and vasoconstriction of the vessel, limiting or even
arresting arterial haemorrhage.
Gunshot internal iliac artery.
Blunt trauma injures vessels by crushing, distraction
or shearing. This results in contusion to the vessel,
which may extend for some distance along its length.
An intimal flap may be formed which will lead to thrombosis
or dissection and subsequent rupture. Thrombosis may
propagate for some distance down the vessel, or embolise
to produce more distal effects.
Arterial haemorrhage may continue within a contained
haematoma, leading to a pulsatile mass of clot - a pseudoaneurysm.
Commonly, distal flow is preserved with false aneurysm
formation, and diagnosis may be difficult. These are
at risk of rupture if undiagnosed - and often present
late after the initial injury is forgotten.
Pseudoaneurysm, tibioperoneal
trunk.
If there is an injury to an adjacent vein as well as
to the artery, an arterio-venous fistula may form, which
may subsequently lead to rupture or cardiovascular compromise.
Arteriovenous fistulae also commonly present some time
after the initial injury.
Spasm as a unique entity is never the result of trauma,
and should not be assumed to be the cause of limb ischaemia.
Spasm is spelled C-L-O-T!
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