5 tips for interpreting home and pharmacy blood pressure measurements

About one-quarter of Canadian adults have hypertension.(1) Appropriate measurement of blood pressure (BP) is imperative to identify hypertension and monitor the efficacy and safety of antihypertensive therapy. However, inappropriate interpretation of aberrant BP measurements may result in unnecessary utilization of healthcare resources and patient concern. A recent retrospective cohort study from Ontario identified more than 200,000 emergency department visits for hypertension from 2002–2012.(2) Of those, only 8% resulted in hospitalization; overall hospitalizations for hypertension-related complications (at 30 days) and mortality (at 90 days) were both less than 1%. The majority of these emergency department visits occurred after an elevated home or pharmacy BP measurement. The authors noted that additional patient and healthcare professional education may be warranted to identify when to seek emergency care. Pharmacists are ideally situated to help encourage and facilitate BP monitoring. They can help patients with appropriate interpretation of BP results by following these five tips:1. Ensure the BP monitor is accuratePublic BP monitors are an excellent way to allow patients easy access to self-monitoring. However, 'one-size-fits-all' measurement may not provide accurate results in some patients.(3-5) As well, these monitors should undergo regular calibration as per the manufacturer’s instructions. If there are doubts about the cuff size, calibration or accuracy of a public BP monitor, a home BP monitor can be used. When helping patients choose a home BP monitor, recommend a device that has been validated for accuracy by Hypertension Canada (identified by a “Recommended by Hypertension Canada” logo on the box).(6)2. Ensure proper technique and do not rely on a single readingIf a public or home BP monitor detects an elevated BP, ensure the proper technique is being used. Ensure the patient has rested comfortably for at least five minutes, is seated with their back supported, and both feet are touching the floor.(1) The cuff should be placed over the patient’s bare non-dominant arm, which should be supported with the cuff at heart level. Systolic BP may be increased by up to 10 mmHg if the arm is unsupported or positioned below the level of the heart, the cuff is too small, or the patient has their legs crossed.(7,8) Talking or actively listening during the procedure may also elevate BP. Acute exposure to cold, smoking or exercise within 30 minutes before measurement, and the need to urinate may also elevate BP. For a low reading, ensure correct cuff size—a cuff that is too large may result in an erroneously low BP reading.(8) Finally, it is important to consider the BP trend over time, and not rely on a single reading.3. Consider factors that may raise or lower BPPharmacists can provide valuable insight by ruling in or out potential drug-related causes of BP derangements; this may prevent unnecessary referrals to a family physician’s office or the emergency department. Potential drug-related causes for an elevated BP include prescription medications, such as stimulants for attention deficit hyperactivity disorder, nonsteroidal anti-inflammatory drugs, antidepressants, calcineurin inhibitors, corticosteroids and oral contraceptives.(9) Also consider over-the-counter medications (e.g., decongestants), natural health products (e.g., ginkgo biloba, ginseng, St. John’s wort), caffeine-containing products (including energy drinks) and illicit drugs (e.g., cocaine, amphetamines). Finally, consider nonadherence to antihypertensive medications, pain and/or anxiety, or volume overload. Some of these factors may temporarily increase a patient’s BP, and may not need medical intervention.For causes of hypotension, consider recent antihypertensive dose increases or situations where the patient may have inadvertently taken a higher dose than prescribed (e.g., dose change due to drug shortage, inadequate patient education or misunderstanding). Consider other medications that may have BP-lowering effects, including alpha-blockers for benign prostatic hyperplasia, beta-blockers for migraine prophylaxis, diuretics for edema, phosphodiesterase inhibitors for erectile dysfunction and vasodilators for stable angina.4. Know how to identify a hypertensive crisisHypertensive crisis is often defined as a BP > 180/> 120 mmHg.(10) It is further subcategorized as hypertensive urgency (if the patient has no evidence of end-organ damage) or hypertensive emergency (if patient has evidence of end-organ damage). Symptoms such as chest pain, dyspnea or neurologic deficits (e.g., symptoms of a stroke) may represent a hypertensive emergency; this is potentially life threatening and can lead to hypertensive encephalopathy, acute pulmonary edema, stroke and renal failure. Any patient who presents with these signs and symptoms should be immediately referred to emergency medical services. Contrarily, a patient who presents with hypertensive urgency can often be managed safely as an outpatient and should be referred to their family physician.(11) Management often involves re-starting or intensifying antihypertensive therapy and follow-up to ensure the BP is < 160/< 100 mmHg over several hours to days. Rapid BP lowering is not recommended due to the risk of cerebrovascular or myocardial ischemia and/or infarction.5. Know when the BP is too lowAs with hypertensive crises, severe hypotension may result in end-organ damage due to poor perfusion. A systolic BP < 100 mmHg often warrants further investigation, but may be normal in some patients. For example, young persons or those with liver cirrhosis or heart failure may have an acceptably low BP. Despite a numerically low BP, they may be completely asymptomatic and thus do not require any medical intervention. Symptoms of potentially problematic hypotension include dizziness, lightheadedness or syncope. Additional signs that a patient’s BP may be too low include tachycardia, tachypnea, oliguria, altered mental status or cool, clammy and/or cyanotic extremities. Patients with these signs and/or symptoms should be referred for a prompt medical assessment.All patients on antihypertensive therapy should be assessed for orthostatic hypotension, particularly older adults, as it may increase their risk of falls. The definition of orthostatic hypotension is typically a systolic BP drop of ≥ 20 mmHg or a diastolic BP drop of ≥ 10 mmHg on standing.(12) To properly assess for orthostatic hypotension, measure the BP after the patient has been sitting (or lying down) for five to 10 minutes, then repeat the measurements after the patient has been standing for one to three minutes. Orthostatic hypotension can usually be managed in the outpatient setting.Will Shum, at the time of writing, was a pharmacy practice resident with Lower Mainland Pharmacy Services. He is now a clinical pharmacist at the Vancouver General Hospital, Lower Mainland Pharmacy Services in Vancouver, BC.Arden R. Barry (arden.barry@ubc.ca) is a clinical pharmacy and research specialist at the Chilliwack General Hospital, Lower Mainland Pharmacy Services in Chilliwack, B.C. He is also an assistant professor (partner) at the Faculty of Pharmaceutical Sciences, University of British Columbia and an associate member of the Department of Family Practice, Faculty of Medicine, University of British Columbia in Vancouver.References: Nerenberg KA, Zarnke KB, Leung AA, et al. Hypertension Canada's 2018 guidelines for diagnosis, risk assessment, prevention, and treatment of hypertension in adults and children. Can J Cardiol 2018;34:506-25.Masood S, Austin PC, Atzema CL. A population-based analysis of outcomes in patients with a primary diagnosis of hypertension in the emergency department. Ann Emerg Med 2016;68:258-67.Hodgkinson J, Koshiaris C, Martin U, et al. Accuracy of monitors used for blood pressure checks in English retail pharmacies: a cross-sectional observational study. Br J Gen Pract 2016;66:e309-14.Karr S, Gurney MK, Early NK. Accuracy of community-based blood pressure devices versus validated self-use devices. J Am Pharm Assoc 2015;55:419-23.Van Durme DJ, Goldstein M, Pal N, et al. The accuracy of community-based automated blood pressure machines. J Fam Pract 2000;49:449-52.Hypertension Canada. Blood pressure devices. (accessed April 16, 2018).Beevers G, Lip GY, O’Brien E. ABC of hypertension. Blood pressure measurement. Part I-sphygmomanometry: factors common to all techniques. BMJ 2001;322:981-5.Sprafka JM, Strickland D, Gómez-Marín O, et al. The effect of cuff size on blood pressure measurement in adults. Epidemiology 1991;2:214-7.Grossman E, Messerli FH. Drug-induced hypertension: an unappreciated cause of secondary hypertension. Am J Med 2012;125:14-22.Whelton PK, Carey RM, Aronow WS, et al. 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA guideline for the prevention, detection, evaluation, and management of high blood pressure in adults: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Hypertension 2018;71:e13-e115.Yang J, Chiu S, Krouss M. Overtreatment of asymptomatic hypertension-urgency is not an emergency. JJAMA Intern Med 2018;178:704-5.Lanier JB, Mote MB, Clay EC. Evaluation and management of orthostatic hypotension. Am Fam Physician 2011;84:527-36.

5 tips for interpreting home and pharmacy blood pressure measurements

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