BP Measurement

Technique & Interpretation Reference · NICE NG136 / RCP 2023 / AAS-AAN · verify vs JRCALC & Greenroom

Reference tool, not a JRCALC extract. Thresholds below are drawn from NICE/RCP/AAS-AAN/ESC consensus. Confirm exact wording against the JRCALC Plus app and NWAS Greenroom before treating as SOP.

Lying → Standing Protocol RCP 2023

≥5 min
Rest SUPINE, then BP #1
Stand
BP #2 within 1st minute
3 min
BP #3 standing
Repeat
If still falling

Use manual sphygmomanometer where possible — automated devices often miss the transient drop. Support the standing arm at heart level; letting it hang at the side can mask a postural drop in up to 2/3 of cases. Document symptoms: dizziness, light-headedness, vagueness, pallor, visual disturbance, palpitations.

Positive for Orthostatic Hypotension

  • ≥20 mmHg fall in systolic (± symptoms)
  • Fall to <90 mmHg systolic on standing, even if drop <20
  • ≥10 mmHg fall in diastolic with symptoms
  • If supine systolic >150: use ≥30 mmHg fall as the criterion
HR clue: rise <15 bpm suggests neurogenic/autonomic cause (e.g. Parkinson's meds). Marked compensatory tachycardia suggests volume depletion (dehydration/haemorrhage).

Prevalence & Causes

~1 in 5
community adults ≥60y
25%
of ED syncope presentations

Leading contributors: antihypertensives, diuretics (esp. loop), nitrates, alpha-blockers; Parkinson's medications (levodopa, dopamine agonists) for neurogenic OH; antidepressants/antipsychotics. Always consider a post-fall medication review.

Inter-Arm Difference NICE NG136

Measure both arms on first assessment. If difference >15 mmHg, repeat — if still >15, use the arm with the higher reading for all future measurements.

DifferenceSignificance
≥10 mmHgPAD association, ↑CV risk
>15 mmHgNICE action threshold — repeat & switch arm
>20 mmHgSuspect aortic dissection / subclavian stenosis
🚩 Large inter-arm difference + tearing chest/back pain → dissection pre-alert. Absence of a difference does not exclude dissection.

Age-Specific Ranges

Adult — NICE NG136 staging

StageClinic BP
Normotensive<140/90
Stage 1≥140/90
Stage 2≥160/100
Severe / Stage 3≥180/120

Paediatric hypotension — APLS/PALS

AgeSystolic <
Neonate 0–28d60
1–12 months70
1–10 years70 + (2×age)
≥10 years90
Children maintain systolic BP until ~30% blood volume lost — hypotension is a late, ominous sign. Watch tachycardia, prolonged cap refill, mottling, narrow pulse pressure first.

Elderly

Isolated systolic hypertension (raised systolic, normal/low diastolic) is the commonest pattern from arterial stiffening. Higher OH prevalence, frailty and polypharmacy — always pair with a postural check and med review in fallers.

Technique Errors & Magnitude

ErrorEffect
Cuff too small+19.5 mmHg avg (XL arm, regular cuff)
Cuff too large−3.6 mmHg
Arm unsupported at side+6.5 (up to +9) mmHg
Arm in lap+3.9 mmHg
Legs crossedup to +15 mmHg
Talking during readingup to +19 mmHg
Cuff below heart level~+8–10 mmHg per 10cm

Cuff sizing: bladder length 75–100% and width 37–50% of arm circumference. Undercuffing is the more common error and overestimates BP.

Manual vs Automated (NIBP)

Oscillometric devices are less reliable in AF, at extremes of BP, and in shock/hypotension with movement or tremor. In AF, triplicate manual auscultatory measurement is preferred where practical. Use manual/palpated systolic if NIBP fails or looks implausible in a shocked or peri-arrest patient.

Action / Escalation

NEWS2 SystolicScore
≤90 or ≥2203
91–1002
101–1101
111–2190

Escalate at aggregate NEWS2 ≥5 or any single parameter = 3. Only systolic scores — diastolic is not part of NEWS2.

🚩 Sepsis red flag: systolic ≤90 mmHg. UK Sepsis Trust prehospital tool triggers at NEWS2 ≥7, or 5–6 with an added concern (single param = 3, mottled/ashen, non-blanching rash, cyanosis, looks very unwell, deteriorating).
Syncope (NICE CG109): convey unless clearly an uncomplicated faint. Red flags — ECG abnormality, HF history, exertional TLoC, FHx sudden cardiac death <40y, new breathlessness, murmur, no prodrome in anyone >65y. Use the 3 P's: Posture, Provoking factors, Prodrome. Record a 12-lead and hand over with the patient.

Always correlate BP with HR response, symptoms, skin signs, cap refill and trend — a single normal reading does not exclude significant pathology, especially in children.

Sources: NICE NG136 (2019, amend. 2023) · NICE CG109 (2010/2014) · RCP Lying/Standing BP Procedure (© RCP 2023) · RCP NEWS2 (2017) · AAS/AAN consensus (1996, updated 2011) · ESC Syncope Guidelines (2018) · INTERPRESS-IPD, Hypertension 2021 · Cuff(SZ) trial, JAMA Intern Med 2023 · UK Sepsis Trust Prehospital Tool (2024) · APLS/PALS paediatric parameters.
NICE falls guideline is CG161 (2013), superseded by NG249 (2025) — NG161 is unrelated (AKI). JRCALC paediatric BP columns not independently verified — check JRCALC Plus / Greenroom.