What value is considered hypotension?

Defining Low Blood Pressure (Hypotension)

Hypotension is generally defined as a systolic blood pressure less than 90 mmHg or a mean arterial pressure less than 65 mmHg. 1

Standard Definitions of Hypotension

• Absolute systolic blood pressure value of <90 mmHg is the most commonly accepted definition of hypotension 1
• Mean arterial pressure (MAP) <65 mmHg at rest is an alternative definition 1
• In surgical settings, both systolic BP <90 mmHg and MAP <65 mmHg are considered thresholds below which harm may occur 1
• In trauma patients, systolic BP <90 mmHg is considered hypotension, with some guidelines suggesting permissive hypotension of 80-90 mmHg in specific circumstances 1
• In dialysis patients, hypotension is also defined as systolic BP <90 mmHg 1

Context-Specific Definitions

• In heart failure patients with reduced ejection fraction, hypotension is commonly defined as systolic BP <90-100 mmHg 1
• In trauma patients being evaluated for cardiac injury, hemodynamic instability is defined as persistent hypotension (systolic BP <90 mmHg or mean BP <65 mmHg) despite fluid resuscitation 1
• In perioperative settings, harm thresholds appear to be roughly MAP <65 mmHg or SBP <90 mmHg maintained for about 15 minutes 1
• Orthostatic hypotension is defined as a drop in systolic BP ≥20 mmHg or diastolic BP ≥10 mmHg within 1-3 minutes of standing 1, 2

Clinical Significance and Symptoms

• Symptomatic hypotension may include dizziness, syncope, headache, visual disturbances, emesis, or fatigue 1
• Individuals tolerate different levels of low BP differently, so symptoms are important in determining clinical significance 1
• The risk of adverse outcomes increases with longer durations of hypotension 1
• In surgical patients, each 10-minute episode of hypotension on postoperative day 0 is associated with a 3% increase in risk of myocardial infarction and death 1

Special Considerations

• For patients with preoperative hypertension, the threshold at which harm occurs may be higher than a systolic pressure of 90 mmHg 1
• In elderly patients, a diastolic BP <60 mmHg with treated systolic BP <130 mmHg has been associated with increased cardiovascular risk 3
• The optimal diastolic BP range appears to be between 70-80 mmHg for patients with treated systolic BP <130 mmHg 3
• In some clinical trials, the inclusion threshold for clinically relevant low BP is fixed (usually close to 90 mmHg) 1

Pitfalls to Avoid

• Failing to distinguish between asymptomatic low BP and symptomatic hypotension that requires intervention 1, 4
• Not recognizing that the threshold for hypotension may be higher in patients with chronic hypertension 1
• Overlooking orthostatic hypotension, which should be assessed at initial diagnosis of elevated BP or when suggestive symptoms arise 1
• Ignoring the duration of hypotension, which is a critical factor in determining risk 1

Remember that while 90 mmHg systolic is the most widely accepted threshold for defining hypotension, the clinical significance depends on the patient's baseline BP, presence of symptoms, and clinical context.