Acute and critical limb ischemia: When time is limb
ABSTRACTAcute and critical limb ischemia post significant rates of morbidity and death, and need to be promptly recognized and treated to avoid amputation. Perfusion should be thoroughly assessed using multiple methods, and patients should be considered for revascularization (angioplasty or bypass surgery) to restore blood perfusion. Underlying conditions that need to be assessed and treated include cardiovascular disease, diabetes, and infection.
KEY POINTS
- In assessing peripheral artery disease, perform a thorough history and physical examination, paying close attention to the onset and characteristics of pain, activity level, history, and pulses, and the condition of the feet.
- Acute limb ischemia is a sudden decrease in limb perfusion, potentially threatening limb viability. Patients who have acute cessation of blood flow, sensation, or motor function need immediate revascularization to avoid amputation.
- Critical limb ischemia ranges from rest pain to gangrene and must be addressed with a multidisciplinary approach.
- The ankle-brachial index is a noninvasive, inexpensive test that can be done in the office with a hand-held Doppler device to assess the presence and severity of peripheral artery disease.
In many ways, vascular disease in the leg is similar to that in the heart. The risk factors, underlying conditions, and pathogenetic processes are the same, and in many cases, patients have both conditions. And just as cardiologists and emergency physicians have learned that in acute myocardial infarction “time is muscle,” we are coming to appreciate that in many cases of limb ischemia, “time is limb.”
Most physicians well understand the clinical spectrum of coronary artery disease, which ranges from stable angina to ST-elevation myocardial infarction. In the leg, the same situation exists: at the more benign end of the spectrum, patients experience no symptoms, but often that is because they lead a sedentary lifestyle, modifying their activity level to avoid pain. As the disease worsens, they can develop claudication and critical leg ischemia, comparable to non-ST-elevation myocardial infarction. The most severe condition is acute limb ischemia, analagous to ST-elevation myocardial infarction.
Distinguishing acute from critical limb ischemia is essential in patients who present with leg problems, whether it be leg pain or ulcers. The farther along the clinical spectrum the patient’s condition is, the more important it is to be aggressive in diagnosis and treatment. The history and physical examination are the most important first steps, focusing on the onset of symptoms, history, risk factors, and past interventions.
Peripheral artery disease is increasingly becoming a worldwide problem that is now being emphasized by the World Health Organization. Unfortunately, not enough attention is paid to the problem, not only in less-developed countries but also in the United States. Patients with peripheral artery disease tend to be elderly, in the lowest economic classes, and uninsured, and they often do not understand the impact of the disease on their health.
LEG ULCERS: CAUSES AND COSTS
Finding the underlying cause of leg ulcers is important, and the differential diagnosis is large (Table 1). However, knowing the cause does not necessarily lead to healing; it is still essential to assess perfusion, infection, and wound care, and to arrest edema.
Causes of leg and foot ulcers include venous insufficiency (with an estimated 2.5 million cases annually),1,2 diabetes (nearly 1 million cases),3 and pressure (ie, bedsores, occurring in up to 28% of patients in extended care),4 all at a cost in the billions of dollars.5–7
In general, peripheral artery disease itself does not cause ulcers; it is an inciting factor. It is important to find what started the process. Ill-fitting shoes, poor sensation because of diabetes, or a cut when trimming toenails can all contribute to a wound, and peripheral artery disease makes it unable to heal. The healing process requires more nutrients and oxygen than poor circulation can provide.
ACUTE LIMB ISCHEMIA
Acute limb ischemia is defined as any sudden decrease in limb perfusion causing a potential threat to limb viability.8 Although it comes on suddenly, it does not imply that the patient has not had long-standing peripheral artery disease. It is important to determine what suddenly changed to cause the onset of symptoms.
History and physical examination: The six Ps
A good history includes a thorough evaluation of the present illness, including the pain’s time of onset, abruptness, location, intensity, and change over time, and whether it is present at rest. The medical history should focus on claudication, diabetes, smoking, heart disease, palpitations, atrial fibrillation, and previous ischemic symptoms.8
The physical examination should focus on the “six Ps”:
- Pain
- Pulselessness
- Paresthesia (numbness occurs in about half of patients)
- Pallor (obstruction is typically one joint above the level of demarcation of pallor)
- Paralysis (a bad sign, particularly if the calf is tight)
- Poikilothermia (inability to regulate temperature).
A good pulse examination includes measuring the ankle-brachial index and a Doppler examination of both legs. A neurologic examination focusing on sensory and motor function is critical for determining the level of ischemia and the urgency of intervention.
Classification of acute limb ischemia
If it is determined that a patient has acute leg ischemia, it is important to categorize the condition using the classification system devised by the Society of Vascular Surgery and International Society of Cardiovascular Surgery (Table 2).9 The category establishes the type and urgency of treatment. This classification system is simple and depends on factors that can be assessed easily by nonspecialists:
- Pulses—arterial and venous pulses assessed by Doppler ultrasonography
- Sensation—the patient closes the eyes and answers if he or she can feel the examiner’s touch
- Motor function—can the patient move his or her toes?
Venous pulses can be difficult to assess. However, if the arterial pulse is present, the venous pulse should be next to it. Knowing the other criteria can determine the category, so not being certain of the venous pulse should not deter a clinician from assessing the other factors.
Category I is “viable.” Patients have intact sensory and motor functions and audible pulses. Patients in this category should be admitted and possibly started on anticoagulation therapy and referred to a vascular specialist within hours.
Category IIa is “threatened.” Sensation is starting to be lost but motor function is still present. These patients are considered to have reversible ischemia, analogous to myocardial infarction of the leg, and they require immediate attention.
Category IIb is similar and it also requires immediate attention.
Category III is usually irreversible, with loss of motor function and sensation.
