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Vital Signs

Blood Pressure

February 15th, 2021


Blood pressure is a measure of the arterial pressure during systole and diastole; this may also be used to calculate the mean arterial pressure. Low blood pressure can result in poor organ perfusion, which high blood pressure puts patients at risk of cardiac, cerebrovascular, retinal and renal complications.
    • Normal Blood Pressure

    • < 120 / 80 mmHg

Measuring Blood Pressure

  • Prior to Testing Blood Pressure 

    Ask the patient:
  • Whether they have had dialysis (have an AV fistula)
  • Whether they have had breast cancer surgery (and lymph node dissection)
  • Whether there is any other reason why their blood pressure should not be measured on a particular arm
  • Sizing the Blood Pressure Cuff

  • The blood pressure cuff should measure approximately 80% of the circumference of the arm.
  • How to Measure

  • Place a blood pressure cuff of the correct size around the bulk of the biceps with the artery indicator over the brachial artery.
  • Inflate the cuff until the radial pulse can no longer be palpated, plus a further 30mmHg.
  • Place the diaphragm of the stethoscope over the brachial artery and slowly deflate the cuff (2mmHg/sec)
  • Note when the beating sound is first heard
  • Note when the sound disappears entirely
  • Measuring Blood Pressure
  • Interpretation

  • The systolic blood pressure is the pressure where the first beating sound is heard (the first Korottkoff sound)
  • The diastolic blood pressure is the pressure where the beating sound disappears entirely (the fifth Korottkoff sound)
Ask the patient not to talk or move while the blood pressure is measured as this can cause a false elevation in BP.


Hypertension refers to a persistent elevation in blood pressure. This may be primary and of unknown aetiology, or secondary to a process that raises the blood pressure.
  • Classification

  • Normal <120/80
  • Pre-hypertension 120/80 - 139/89
  • Stage I hypertension 140/90 - 159/99
  • Stage II hypertension >160/100
  • Causes of Hypertension

  • Primary

  • Essential hypertension: unknown aetiologyThe most common cause of hypertension
  • Secondary

  • Chronic kidney disease
  • Renal artery stenosis - fibromuscular dysplasia, atherosclerosis
  • Endocrine - hyperthyroidism, hypothyroidism, Cushing's syndrome, primary aldosteronism, phaeochromocytoma, hyperparathyroidism
  • Drugs - NSAIDs, amphetamines, glucocorticoids, fludrocortisone, erythropoietin, VEGF inhibitors, calcineurin inhibitors
  • Aortic coarctation
  • Obstructive sleep apnoea
  • Factitious

  • White coat hypertension: due to by anxiety in a healthcare setting
  • Recent exercise or caffeine intake


Hypotension refers to systolic BP <100mmHg or a drop in systolic BP to <80% of the patient's baseline.
  • Causes of Hypotension

  • Hypovolaemia

  • Bleeding
  • Dehydration
  • Third Spacing
  • Vasodilation

  • Septic shock
  • Anaphylaxis
  • Neurogenic
  • Blood transfusion reaction
  • Adrenocortical insufficiency
  • Cardiogenic

  • Myocardial infarction
  • Tachycarrhythmia
  • Bradyarrhythmia
  • Obstructive

  • Massive pulmonary embolus
  • Tension pneumothorax
  • Cardiac tamponade
  • Other

  • Drug toxicity (e.g. beta blockers, calcium channel blockers)

Narrow Pulse Pressure

A narrow pulse pressure is a reduced difference between the systolic and diastolic blood pressure.
There is no set reference range for pulse pressure, and this should be taken in the context of the individual patient.
  • Causes of Narrow Pulse Pressure

  • Severe aortic stenosis
  • Severe mitral regurgitation
  • Hypovolaemia

Widened Pulse Pressure

A widened pulse pressure is an increased difference between the systolic and diastolic blood pressure.
There is no set reference range for pulse pressure, and this should be taken in the context of the individual patient.
  • Causes of Widened Pulse Pressure

  • Aortic regurgitation
  • Patent ductus arteriosus

Postural Hypotension

Postural hypotension is present if there is a fall of >20mmHg systolic and >10mmHg diastolic blood pressure following standing.
  • How To Elicit

  • Measure the blood pressure with the patient lying down, and then remeasure it after the patient has been standing for one minute.
  • Causes of Postural Hypotension

  • Reduced intravascular volume - dehydration, haemorrhage
  • Autonomic dysfunction - diabetic neuropathy, vitamin B12 deficiency, hypothyroidism, parkinsonism, amyloidosis, paraneoplastic syndrome
  • Cardiac - congestive cardiac failure, cardiomyopathy, myocarditis, constrictive pericarditis, aortic stenosis
  • Endocrine - Addison's disease, phaeochromocytoma
  • Drugs - nitrates, anticholinergics, antidepressants, antihypertensives, levodopa
  • Prolonged bed rest
  • Alcohol
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