Blood Pressure
November 28th, 2019
Overview
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 / 80mmHg
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) or whether there is some other reason their blood pressure should not be measured on a particular arm.
Ask the patient not to talk or move while the blood pressure is measured as this can cause a false elevation in BP.
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 pulse is first heard (indicative of the systolic pressure) and when it disappears (indicative of the diastolic pressure).
Hypertension
Classification
Persistent high blood pressure- Normal
- 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
Interpretation
- Systolic BP <100mmHg or a drop in systolic BP to <80% of the patient's baseline.
Causes of Hypotension
- Postural (orthostatic) hypotension - related to redistribution of blood following change in position from lying to sitting or standing.
- Cardiac - MI, cardiomyopathy, myocarditis, beta blockers, calcium channel blockers.
- Obstruction - massive PE, tension pneumothorax, cardiac tamponade.
- Vasodilation - sepsis, anaphylaxis, CNS damage (neurogenic), endocrine.
- Hypovolaemia - haemorrhage, dehydration.
Postural Hypotension
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.
Interpretation
- Postural hypotension is present if there is a fall of >20mmHg systolic and >10mmHg diastolic blood pressure following standing.
Causes of Postural Hypotension
- Autonomic dysfunction
- Low intravascular volume - blood / fluid / electrolyte loss
- Vasodilation - nitrates, alcohol, fever
- Cardiac impairment
- Chronic disease - diabetes mellitus, chronic renal failure, chronic liver disease,
- Brain tumour - paraneoplastic syndrome
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