Hypotension is generally considered as systolic blood pressure less than 90 millimeters of mercury (mm Hg) or diastolic less than 60 mm Hg. However in practice, blood
Low blood pressure causes can be due to hormonal changes, widening of blood vessels, medicine side effects, anemia, heart & endocrine problems. Reduced blood volume, called hypovolemia, is the most common mechanism producing hypotension. This can result from hemorrhage, or blood loss; insufficient fluid intake, as in starvation; or excessive fluid losses from diarrhea or vomiting. Hypovolemia is often induced by excessive use of diuretics. Other medications can produce hypotension by different mechanisms. Decreased cardiac output despite normal blood volume, due to severe congestive heart failure, large myocardial infarction, or bradycardia, often produces hypotension and can rapidly progress to cardiogenic shock. Arrhythmias often result in hypotension by this mechanism. Beta blockers can cause hypotension both by slowing the heart rate and by decreasing the pumping ability of the heart muscle. Varieties of meditation and/or other mental-physiological disciplines can create temporary hypotension effects, as well, and should not be considered unusual. Excessive vasodilation, or insufficient constriction of the resistance blood vessels (mostly arterioles), causes hypotension. This can be due to decreased sympathetic nervous system output or to increased parasympathetic activity occurring as a consequence of injury to the brain or spinal cord or of dysautonomia, an intrinsic abnormality in autonomic system functioning. Excessive vasodilation can also result from sepsis, acidosis, or medications, such as nitrate preparations, calcium channel blockers, angiotensin II receptor blockers ACE inhibitors. Many anesthetic agents and techniques, including spinal anesthesia and most inhalational agents, produce significant vasodilation.
The cardinal symptom of hypotension is lightheadedness or dizziness. If the blood pressure is sufficiently low, fainting and often seizures will occur. Low blood pressure is sometimes associated with certain symptoms, many of which are related to causes rather than effects of hypotension: Chest pain Shortness of breath Irregular heartbeat Fever higher than 101 °F (38.3 °C) Headache Stiff neck Severe upper back pain Cough with phlegm Prolonged diarrhea or vomiting Dyspepsia Dysuria Foul-smelling urine Adverse effect of medications Acute, life-threatening allergic reaction Seizures Loss of consciousness Profound fatigue Temporary blurring or loss of vision In some cases loss of hair Ehlers-Danlos Syndrome