Thromboembolism (blood clots)
Embolism (foreign bodies in the circulation, e.g. amniotic fluid embolism)

Trauma
Traumatic injury to an extremity may produce partial or total occlusion of a vessel from compression, shearing, or laceration. Acute arterial occlusion may develop as a result of arterial dissection in the carotid artery or aorta or as a result of iatrogenic arterial injury (e.g., after angiography). Other
An inadequate flow of blood to a part of the body may be caused by any of the following:

Thoracic outlet syndrome (compression of the brachial plexus)
Atherosclerosis (lipid-laden plaques obstructing the lumen of arteries)
Hypoglycemia (lower than normal level of glucose)
Tachycardia (abnormally rapid beating of the heart)
Radiotherapy
Hypotension (low blood pressure, e.g. in septic shock, heart failure)
Outside compression of a blood vessel, e.g. by a tumor or in the case of superior mesenteric artery syndrome
Sickle cell disease (abnormally shaped red blood cells)
Induced g-forces which restrict the blood flow and force the blood to the extremities of the body, as in acrobatics and military flying
Localized extreme cold, such as by frostbite or improper cold compression therapy
Tourniquet application
An increased level of glutamate receptor stimulation 
Arteriovenous malformations and peripheral artery occlusive disease
rupture of significant blood vessels supplying a tissue or organ. Anemia vasoconstricts the periphery so that red blood cells can work internally on vital organs such as the heart, brain, etc., thus causing lack of oxygen to the periphery. Premature discontinuation of any oral anticoagulant.
Limb
Inadequate blood supply to a limb may results in acute limb ischemia or chronic limb threatening ischemia. Cutaneous
Reduced blood flow to the skin layers may result in mottling or uneven, patchy discoloration of the skin. Kidney Ischemia
Kidney Ischemia is a loss of blood flow to the kidney cells. Several physical symptoms include shrinkage of one or both kidneys, renovascular hypertension, acute renal failure, progressive azotemia, and acute pulmonary edema. It is a disease with high mortality rate and high morbidity. Failure to treat could cause chronic kidney disease and a need for renal surgery. Causes
Ischemia is a vascular disease involving an interruption in the arterial blood supply to a tissue, organ, or extremity that, if untreated, can lead to tissue death. It can be caused by embolism, thrombosis of an atherosclerotic artery, or trauma. Venous problems like venous outflow obstruction and low-flow states can cause acute arterial ischemia. An aneurysm is one of the most frequent causes of acute arterial ischemia. Other causes are heart conditions including myocardial infarction, mitral valve disease, chronic atrial fibrillation, cardiomyopathies, and prosthesis, in all of which thrombi are prone to develop. Occlusion
The thrombi may dislodge and may travel anywhere in the circulatory system, where they may lead to pulmonary embolus, an acute arterial occlusion causing the oxygen and blood supply distal to the embolus to decrease suddenly. The degree and extent of symptoms depend on the size and location of the obstruction, the occurrence of clot fragmentation with embolism to smaller vessels, and the degree of peripheral arterial disease (PAD).