Hypotension is any blood pressure (BP) that is below the normal expected for an individual in a given environment.
There is no single numerical cut-off universally accepted as representing hypotension. For example, while systolic BP <90 mmHg may be considered hypotensive for someone with 'normal BP' of 120 mmHg, many healthy young adults will have a resting BP at or potentially below this level and will not be considered hypotensive. As a result, it is difficult to estimate the prevalence.
Background history and accompanying clinical findings should be considered, bearing in mind that many common illnesses present atypically in older adults, without characteristic symptoms such as pain.
Hypotension can be the first sign of a serious acute illness (such as myocardial infarction, sepsis, or gastrointestinal haemorrhage).
Once acute causes have been excluded, other chronic or recurring causes should then be investigated.
Blood pressure measurement
It is essential to use an appropriate cuff size for BP measurements. Using a cuff that is too small (under-cuffing) may cause overestimation of BP and may further mask a period of hypotension; while use of a cuff that is too large (over-cuffing) can lead to falsely low BP readings with subsequent unwarranted investigation.
If the patient is not hypotensive at the time of assessment, lying and standing BP recordings should be carried out in order to determine if orthostatic hypotension is present. The patient should rest supine for 5 minutes before lying BP measurement. A systolic BP drop of 20 mmHg or a diastolic BP drop of 10 mmHg occurring within 3 minutes of orthostasis is considered significant.
Most automatic sphygmomanometers overestimate BP in patients with atrial fibrillation, because they record the highest systolic pressure rather than an average over several cardiac cycles. Palpate the patient’s pulse to exclude arrhythmia before using an automatic sphygmomanometer.
BP is determined by cardiac output (the product of heart rate and stroke volume) and total systemic vascular resistance. Hypotension occurs when the cardiac output decreases and/or the systemic vascular resistance decreases. Hypotension is usually due to:
Decreased effective circulating volume (hypovolaemia)
Impaired cardiac output due to heart pump dysfunction (cardiogenic)
Impaired cardiac output due to obstruction to cardiac filling (obstructive)
Impaired peripheral vasoconstriction/distributive change.
In many cases, more than one mechanism is present (e.g., a patient with chronic heart failure who presents with a gastrointestinal bleed may have evidence of both hypovolaemia and reduced cardiac output).
Persistent hypotension can lead to shock, a state of reduced end-organ oxygenation owing to an imbalance between tissue oxygen demand and delivery.
Initial management considerations
Liaison with nursing staff, with regard to maintenance of patient safety while investigations are underway, is prudent. In particular, patients who are hypotensive in the setting of sepsis may have an accompanying delirium increasing their risk of falls and injury. It is often difficult to exclude or confirm the presence of shock without close monitoring of vital signs, including BP, heart rate, and urinary output. Therefore, consideration should be given to the most appropriate setting required to monitor, nurse, and medically manage the hypotensive patient.
- Non-haemorrhagic volume losses
- Upper gastrointestinal bleed
- Lower gastrointestinal bleed
- Dialysis-induced hypotension
- Acute coronary syndrome
- Acute heart failure
- Acute pulmonary embolism
- Pregnancy (uncomplicated)
- Vasovagal syncope
- Chronic liver disease
- Parkinson's disease
- Ruptured abdominal aortic aneurysm
- Ectopic pregnancy
- Retroperitoneal bleed
- Carotid sinus syndrome (cardio-inhibitory subtype)
- Severe hypothyroidism
- Tension pneumothorax
- Cardiac tamponade
- Situational syncope
- Severe acute pancreatitis
- Carotid sinus syndrome (vasodepressor subtype)
- Diabetic autonomic neuropathy
- Multi-system atrophy
- Primary autonomic failure
- Adrenal suppression (iatrogenic)
- Addison's disease
- Thiamine deficiency
- Vitamin B12 deficiency
- Carcinoid syndrome
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