Ischemia

Ischemia is a medical condition in which tissue experiences an inadequate blood supply to meet its metabolic needs. It results from reduced arterial inflow or impaired venous drainage, leading to diminished oxygen and nutrient delivery (hypoxia) and the buildup of metabolic waste. If perfusion is not restored, cells may progress from reversible injury to irreversible injury and tissue necrosis.

Causes include blockage of a blood vessel by a thrombus or embolus, external compression, vasospasm, or systemic factors such as severe hypotension or microvascular dysfunction. Ischemia can be arterial, venous, or mixed; however arterial insufficiency is most clinically significant and common in acute presentations.

Common clinical contexts include myocardial ischemia (reduced blood flow to the heart) that can present as angina or myocardial infarction, cerebral ischemia that may cause stroke or transient ischemic attack, and mesenteric or peripheral ischemia that can lead to abdominal pain, bowel necrosis, or limb-threatening ischemia. The brain and heart are particularly sensitive to brief periods of reduced perfusion.

Pathophysiology involves energy failure and ion pump dysfunction during low oxygen availability, leading to cell swelling, lactic acidosis, and, with prolonged deprivation, membrane damage and cell death. Reperfusion after ischemia can trigger additional injury through oxidative stress and inflammation, although timely restoration of blood flow is essential to salvage tissue.

Diagnosis relies on clinical presentation supported by tissue-specific testing, such as ECG and cardiac biomarkers for myocardial ischemia, vascular imaging or Doppler studies, and brain imaging for cerebral ischemia. Treatment aims to restore perfusion, address the underlying cause, and prevent complications, using medical therapy, endovascular revascularization, or surgical intervention as appropriate.

Prognosis depends on tissue type, duration and severity of ischemia, and success of reperfusion. Chronic ischemia may cause progressive tissue decline, ulcers, or organ dysfunction and increases risk of adverse events.