BP Measurement Pitfalls & Antihypertensive Adverse Effects

Getting the number right

Confirm before you label. Hypertension is diagnosed from the average of at least two properly taken readings on at least two occasions, and an elevated office value should be confirmed outside the office before drugs are started. Twenty-four-hour ambulatory monitoring is the reference standard and also shows nocturnal dipping; a nighttime BP that fails to fall by about 10% (non-dipping) carries extra cardiovascular risk. Validated home monitoring is the practical alternative.

White-coat and masked hypertension. White-coat hypertension (high in the office, normal outside it) reflects an alerting reaction; it needs lifestyle measures and periodic out-of-office checks rather than drugs, because some patients progress. Masked hypertension (normal in the office, high at home or on ambulatory monitoring) carries the risk of sustained hypertension and is treated as such; suspect it in smokers, people under stress, and patients with diabetes or CKD, and whenever LVH or albuminuria coexists with normal office readings.

Technique. Most errors raise the reading:

• Cuff bladder should encircle ≥80% of the arm; a cuff that is too small (common in obesity) overestimates BP, and one that is too large underestimates it
• Seat the patient for 5 minutes with back supported, feet flat and legs uncrossed
• Support the arm at heart level; a dependent arm reads high
• Empty bladder, no talking, and no caffeine, exercise or smoking in the previous 30 minutes

Clues from the arm and the older patient

Inter-arm difference. Measure both arms at the first visit and use the higher one thereafter. A systolic difference above 15–20 mmHg points to a lesion upstream of the lower-reading arm: atherosclerotic subclavian stenosis (arm claudication; subclavian steal, in which arm exercise reverses vertebral flow and causes dizziness or vertigo), aortic dissection (acute tearing pain), coarctation at or proximal to the left subclavian origin, or Takayasu arteritis in a young woman with diminished pulses.

Pseudohypertension. Heavily calcified, noncompressible brachial arteries in older adults make the cuff read falsely high. Suspect it when apparently resistant hypertension has no target-organ damage and treatment produces dizziness or falls. A radial artery that remains palpable after the cuff is inflated above systolic pressure (the Osler maneuver) is the classic but unreliable sign; intra-arterial measurement confirms.

Orthostatic hypotension. A fall of ≥20 mmHg systolic or ≥10 mmHg diastolic within 3 minutes of standing. Diuretics, α1-blockers (first-dose syncope with prazosin, terazosin and doxazosin) and vasodilators are common culprits, and the consequences are falls and fractures. Measure standing BP in older patients, start low and titrate slowly, and deprescribe when possible.

ACE inhibitors and ARBs

Cough. ACE is also kininase II, so inhibition lets bradykinin and substance P accumulate. The resulting dry, tickling cough is a common class effect, more frequent in women and East Asian patients; it may start weeks to months into therapy and fades 1–4 weeks after stopping. Switching to another ACE inhibitor does not help; switch to an ARB.

Angioedema. Bradykinin-mediated, nonpitting swelling of the lips, tongue, face, airway or bowel — without urticaria or itch — is more common in Black patients and can appear after years of uneventful use. Intestinal angioedema presents as recurrent abdominal pain with bowel-wall edema on CT. Secure the airway first; epinephrine, antihistamines and glucocorticoids often fail because histamine is not the mediator, and bradykinin-directed options such as icatibant or fresh frozen plasma are sometimes tried. Stop ACE inhibitors permanently, never rechallenge, and avoid sacubitril–valsartan; an ARB can be used cautiously.

ACE inhibitors, ARBs and aliskiren are contraindicated in pregnancy: second- and third-trimester exposure causes fetal renal dysgenesis, oligohydramnios, skull hypoplasia, growth restriction and death. Stop them once pregnancy is recognized and use labetalol, nifedipine or methyldopa; discuss contraception with women of reproductive age.

Laboratory monitoring. Recheck creatinine and potassium 1–2 weeks after starting or up-titrating an ACE inhibitor or ARB. Efferent arteriolar dilation lowers glomerular pressure, so a creatinine rise up to about 30% is expected and the drug is continued. A larger rise calls for stopping it and looking for bilateral renal artery stenosis, volume depletion or NSAID use. Hyperkalemia risk climbs with CKD, diabetes, potassium-sparing diuretics, NSAIDs and trimethoprim.

Diuretics and other drug classes

Thiazides. Hyponatremia is most likely in older, low-weight women and can appear within weeks; stop the thiazide and correct gradually, reserving hypertonic saline for severe neurologic symptoms. Thiazides also cause hypokalemia with metabolic alkalosis and hypomagnesemia, plus the hyperGLUC rises — glucose, lipids, uric acid (gout) and calcium. Increased distal calcium reabsorption can unmask primary hyperparathyroidism but benefits patients with osteoporosis or calcium stones. Photosensitivity also occurs.

Why pairing matters. Direct arteriolar vasodilators provoke baroreflex tachycardia and renal salt retention, which blunt their effect and can precipitate angina or heart failure; a beta-blocker and a diuretic counter both.

Beta-blockers hide tremor, palpitations and anxiety during hypoglycemia, but sweating is cholinergically mediated and persists — it may be the only warning an insulin-treated patient gets.

Drug-induced lupus usually spares the kidneys and the anti-dsDNA test and resolves once the offending drug is stopped. In clonidine withdrawal, a pure beta-blocker risks unopposed α-vasoconstriction, and sublingual nifedipine causes unpredictable, dangerous drops.