n.
State in which the circulatory system fails to supply enough blood to peripheral tissues to meet basic requirements.
Symptoms
weak, rapid pulse ; low blood pressure ; and cold, sweaty skin
are not all present in every case. Causes include low blood volume, caused by bleeding or fluid loss from burn s or dehydration ; inability of the heart to pump enough blood, due to heart attack , pulmonary embolism , or cardiac tamponade (compression of the heart by fluid in the membrane around it); and blood-vessel dilation as a result of septicemia , allergy (including anaphylaxis ), or drugs. All result in reduced capillary blood flow; reflexes increase heart rate and constrict small blood vessels to protect the blood supply to essential organs. Without treatment of the underlying cause, these mechanisms fail; since the cause is not always clear, cases tend to require different and occasionally contradictory treatment (e.g., intravenous fluids can save the life of a patient with massive blood loss but can overload a weakened heart).