Upper Limb Ischemia, Acute

Cold Hand
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Diagnosis and reasoning

This middle aged lady has presented with sudden pain and numbness of her left hand, while examination reveals the affected extremity to be cold and pulseless; this is acute upper limb ischemia (AULI) until proven otherwise. The explosive onset of symptoms favors an embolism, with the history of recurrent palpitations suspicious of a cardiac origin. CT arteriography is the gold standard diagnostic study in suspected AULI; here, it reveals an obstructive lesion at the bifurcation of the brachial artery. Note that this is suggestive of an embolism, as emboli often lodge at the branching points of an artery. The otherwise pristine vasculature also favors an embolism, as thrombosis mainly occurs in diseased vessels. An ECG and Echocardiogram should also be performed, both for preoperative preparation, and to look for a cardiac origin of emboli; these reveal (previously undiagnosed) atrial fibrillation, the most common individual etiology implicated in AULI. As there are no clinical findings suggestive of an inherited thrombophilia, screening in this regard cannot be justified. Anticoagulation with heparin should commence immediately; in addition, an embolectomy should be performed as early as possible. While she will subsequently require long-term anticoagulation with Warfarin, this is best postponed until she has been on heparin for 48 hours. This is because Warfarin therapy can induce a transient procoagulant state, due to inhibition of the vitamin K dependent anticoagulant proteins C and S. Although systemic thrombolysis is another option for the management of AULI, it is associated with a high rate of hemorrhagic complications, and is best avoided in facilities where an embolectomy can be performed.


Discussion

Acute upper limb ischemia (AULI) is much less common than ischemia of the lower limb, with correspondingly lower rates of loss of function and amputation. However, where these complications occur, the resultant disability is far more devastating. The incidence has been reported as 0.86 to 1.3 cases per 100000 individuals per year; patients tend to be older, with a mean age of 74 years. The most common etiologies underlying AULI are embolism (accounting for nearly three-quarters of episodes), thrombosis, and trauma; less common causes include vasculitis, thoracic outlet obstruction, and iatrogenic events. Emboli are often cardiac in origin, and may occlude arteries which are pristine; this is as opposed to thrombosis, where the affected arteries are usually diseased, with patients often having other vascular comorbidities such as ischemic heart disease or cerebrovascular disease. The most common sites of obstruction are the brachial (61%), axillary (23%), radial (23%), and subclavian (11.7%) arteries respectively. Note that the upper limb possesses a network of well-developed collaterals around the shoulder and elbow; this may be why AULI is often tolerated better than ischemia of the lower limbs. However, where complete ischemia occurs, irreversible changes are usually seen in peripheral nerves and skeletal muscle by 6 hours. It should also be appreciated that reintroduction of oxygenated blood after a period of ischemia often causes more damage than the ischemia alone. Reperfusion injury and compartment syndrome may occur acutely, while in the long term, chronic pain syndromes due to peripheral nerve injury have been reported. Clinically, limb ischemia is diagnosed by the presence of one or more of the six "P" findings: pain, pallor, polar (for cold), pulselessness, paresthesia, and paralysis. That said, pain alone is often the earliest symptom, and pulselessness perhaps the most important sign. Paresthesia and paralysis are late features, and indicate ischemic neuropathy and myonecrosis, which are harbingers of an unsalvageable limb. Certain salient points in the history and examination may also help determine the likely causative etiology. In particular, a sudden and severe onset of symptoms favors embolism; these patients may also have a history of atrial fibrillation, valvular heart disease, bacterial endocarditis, transient ischemic attacks or acute ischemia of the lower limbs. It should be noted that thoracic outlet obstruction and aneurysms may also give rise to emboli. Thrombosis tends to present in a more sub-acute manner. These patients often have risk factors such as diabetes, hypertension and dyslipidemia, and may have a history of ischemic heart disease or peripheral vascular disease. There may also be absent or decreased pulses in the contralateral limb and lower limbs. Patients with thoracic outlet syndrome or a cervical rib may give a history of similar episodes, especially following exercise; individuals with vasculitis may have symptoms and signs suggestive of a connective tissue disease, buerger's disease or giant cell arteritis. Where AULI is clinically suspected, the diagnosis can be confirmed via imaging studies. CT arteriography is the current gold standard, as it allows determination of the extent of obstruction, assessment of anatomical relationships of the arteries, and detection of collaterals, and congenital variations; the latter information is of use in planning the management. Digital Subtraction Angiography (DSA) and Magnetic Resonance Angiography (MRA) are other modalities which may be used for diagnosis. While Duplex Ultrasound is non-invasive and can also confirm the diagnosis, it does not provide the additional anatomical information yielded by the preceding investigations. Laboratory studies may reveal hyperkalemia, metabolic acidosis, and elevated levels of creatinine kinase, myoglobin, lactic acid, and inflammatory markers, depending on the size of the injured area. The overall goals of management are restoration of blood flow, preservation of life and limb, and prevention of recurrent thrombosis or embolism; coordination between the treating emergency physician, radiologist, and vascular surgeon is essential. Pain relief is an initial priority, and may require opioid analgesics; most authorities recommend that anticoagulation with intravenous heparin should be commenced immediately as well, so as to reduce propagation of thrombus. Options for definitive treatment include endovascular interventions such as percutaneous embolectomy and intra-arterial catheter-directed thrombolysis; medical thrombolysis; and surgical interventions such as open embolectomy and bypass grafting. Note that the exact technique employed depends on both the underlying etiology (e.g. embolism or thrombosis), state of the arteries, presence of comorbidities, and facilities available. Percutaneous embolectomy with Fogarty's balloon catheter is the most frequent procedure performed, and may be done under local anesthesia. Some authorities recommend that this should be preceded by a formal fasciotomy of the forearm to decompress the vasculature and assess viability; however, others assert that this may not be necessary, as the arm has loose fascial compartments, and compartment syndrome is rare. Intra-arterial catheter-directed thrombolysis involves embedding a cannula into the distal extent of the thrombus, followed by infusion of a thrombolytic agent; 5% of patients thus treated may experience serious hemorrhagic complications Medical thrombolysis is performed with tissue plasminogen activator (tPA) or similar agents, and should be followed by endovascular or open surgical revision of any lesion unmasked after thrombus dissolution. Hemorrhage and stroke may occur in up to 10% of patients. Note that following treatment of the acute condition, long term anticoagulation is required, typically with Warfarin. Where embolism is suspected, the likely source should be sought for; if a cardiac or vascular lesion cannot be identified, screening for connective tissue diseases and pro-coagulant states may need to be considered. Overall, the prognosis of AULI depends on multiple factors; indicators of a poor outcome include a late presentation, inappropriate embolectomy or thrombectomy, and failure to restore the radial pulse. Note also that most studies show a worse outcome in atherosclerotic occlusion, as opposed to embolization.


Take home messages

  1. Acute Upper Limb Ischemia (AULI) is a clinical diagnosis; pain is the earliest symptom, and pulselessness the most important sign.
  2. Almost three-quarters of cases of AULI are due to embolism.
  3. CT arteriography is the gold standard investigation in patients with suspected AULI.
  4. Following treatment of the acute condition, long term anticoagulation is essential.

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