Hypotension means abnormally low blood pressure. It is generally defined as a systolic blood pressure below 90 mmHg, though what is considered clinically significant depends on the individual’s baseline and the clinical context. Some people have naturally low blood pressure and are asymptomatic; in others, the same reading causes significant symptoms or indicates a dangerous state.
In the acute setting following cardiac arrest, hypotension is a common and serious complication of post-cardiac arrest syndrome. The heart may be stunned and temporarily unable to generate adequate output (myocardial stunning), the systemic vasculature may be abnormally dilated (vasodilatory shock from the systemic inflammatory response), and intravascular fluid volume may be depleted. Persistent hypotension in the post-arrest period reduces perfusion of the brain and other vital organs, worsening the outcome from any brain injury sustained during the arrest. Management in the intensive care unit involves fluid resuscitation, vasopressor drugs to maintain blood pressure, and, where cardiac output is severely impaired, inotropic agents or mechanical circulatory support.
Hypotension also occurs in the context of specific arrhythmias: ventricular tachycardia that is rapid or prolonged can cause haemodynamic collapse, and any arrhythmia that dramatically slows or speeds the heart rate can reduce cardiac output. Antiarrhythmic drugs and some heart failure medications (ACE inhibitors, beta-blockers) can cause hypotension as a side effect, particularly when doses are being increased.
On discharge from hospital, some cardiac arrest survivors experience episodes of dizziness or lightheadedness, particularly on standing (orthostatic hypotension), related to autonomic nervous system changes, deconditioning or medication effects. Standing slowly, ensuring adequate hydration and salt intake, and wearing compression stockings can help. Blood pressure should be monitored regularly, and the GP or cardiac team should be informed of any persistent symptomatic episodes.
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