Reasoning GP · Algorithm · 1-page summary
Low blood pressure in adults
For: adults (16 and over) with low BP, postural symptoms, near-syncope or falls, in hours or OOH. Not for: children (use paediatric pathways). Unexplained blackouts follow the TLoC route (CG109), not a postural label.
Core rule: never diagnose or exclude shock from a BP number — hypotension (or a normal BP) with confusion, poor perfusion, oliguria, chest pain or deterioration is an emergency. In a postural drop, review the medicines first.
0Stop — call 999 now — shock can occur with a normal BP, and with bradycardia
- Shock: confusion, cold clammy or mottled skin, oliguria, falling SpO₂, chest pain, ongoing bleeding, severe or suspected infection (fever may be absent) or deterioration → 999
- Anaphylaxis (sudden hypotension after a possible allergen; skin features can be absent) → adrenaline 0.5 mg IM anterolateral thigh, then 999; lie flat; repeat after 5 min if no better.
- Adrenal crisis — known or suspected adrenal insufficiency with hypotension, collapse, confusion or vomiting → hydrocortisone 100 mg IM/IV now + 999. Do not wait for cortisol.
- While waiting: non-blanching rash → benzylpenicillin or ceftriaxone IV/IM as soon as possible unless it delays transfer. Chest pain/MI → aspirin 300 mg, no fluid loading. Oxygen only if hypoxaemic. Fluids only if local policy allows: 250 ml crystalloid, reassess, up to 1 L. Never delay transfer.
1Triage — what kind of low BP?
| Picture | Action |
|---|---|
| Shock features | Block 0 → 999 |
| BP <90/60 sustained | No clear benign cause, no shock features → Same-day admission |
| Syncope / near-syncope | Lying + standing BP and ECG → Same-day; unexplained → CV assessment (CG109) |
| Postural drop | ≥20/10 mmHg with symptoms → find and treat the cause; medicines and falls review |
| Well, no symptoms | Check pregnancy, bleeding, dehydration, endocrine, medicines, cardiac → then reassure |
2Screen — one row is enough
- Melaena, haematemesis or other bleeding with hypotension → 999
- Low Na⁺ + high K⁺, pigmentation, fatigue, no crisis features → Same-day admission (suspected new adrenal insufficiency)
- Syncope with hypotension after a new medicine in an older person → Same-day admission
- TLoC + abnormal ECG, exertional, heart failure, family history of sudden death, >65 without prodrome, new breathlessness or murmur → Urgent CV assessment
- Critical AS, cardiomyopathy or complete heart block causing hypotension → Urgent cardiology
3Assess — once blocks 0–2 are answered
☐ BP + HR lying after rest, then standing at ≥1 min and up to 3 min; symptoms at each reading (NG136) ☐ HR rise on standing — none suggests autonomic failure ☐ Hydration, perfusion, JVP, pigmentation, petechiae, murmurs, rhythm ☐ ECG, FBC, U&E/eGFR; 9am cortisol if Addison's suspected ☐ All medicines, including OTC sildenafil
4Classify — only if the screen is negative
- Drug-induced (very common) — antihypertensives, diuretics, alpha-blockers, nitrates, TCAs, antipsychotics → medication review.
- Hypovolaemic — losses or poor intake; urea up out of proportion to creatinine → oral fluids/ORS; moderate–severe or unable to drink → Same-day hospital
- Neurogenic — large drop, no HR rise; Parkinson's, MSA, diabetic neuropathy → neurology.
- Post-prandial — dizzy after meals → small frequent meals, sit after eating.
- Constitutional — well young adult, nothing found on assessment → reassure.
- Uncertain — say so, and name who reviews and when.
5Treat today — only these
- Medicines: shared decision, one change at a time (STOPP as a guide). First-dose alpha-blocker at bedtime. Diuretic: check indication, volume, U&E first; heart failure → agree with the treating clinician.
- Measures: rise in stages, fitted compression (check arterial supply), head of bed up 10–15 cm on blocks, fluids tailored to comorbidity, no alcohol; salt only in selected cases, ideally specialist-advised.
- Midodrine or fludrocortisone (off-label here): specialist-guided only; monitor supine BP.
- Adrenal insufficiency: sick day rule 1 — hydrocortisone ≥40 mg/day in 2–4 doses when ill (NG243); in-date IM kit; MedicAlert. Doses: NICE/SPC, BNF, local formulary.
6Refer routinely
- No HR rise + parkinsonism (possible MSA) or complex autonomic neuropathy → neurology.
- Confirmed Addison's or panhypopituitarism → endocrinology to start replacement.
- Falls → NG249 assessment: lying and standing BP, medicines, physiotherapy, vision, OT home hazards.
- After a medicine change → repeat lying and standing BP at 2 weeks.
7Never reassure by
- A normal or only slightly low BP in an unwell patient.
- A low NEWS2 score when you are still worried.
- One standing BP taken straight after standing.
- A symptomatic drop below 20 mmHg — it still counts.
- A "postural" label for syncope without an ECG.
- Waiting for cortisol when adrenal crisis is possible — give hydrocortisone.
8Safety-net — say it, then document it
999 “Call 999 if you collapse and cannot be woken, get new chest pain, or become very unwell with an infection. If you have Addison's and are vomiting and cannot keep tablets down, use your hydrocortisone injection, then call 999.” Same day “Contact us today if you faint or nearly faint, or the dizziness gets worse on a new medicine. At the first warning — greying out, sweating, nausea — sit down at once.”
✓Safe to leave primary care only if — all five, documented
No block 0–2 row applies
Lying and standing BP + HR recorded, with symptoms
ECG done if any syncope or near-syncope
Medicines reviewed; cause or uncertainty stated; review date set
Safety-net given; sick day rules if on steroids
Summary of the full Reasoning GP hypotension algorithm, which holds the detail, examination, drug options and evidence. Sources: NICE NG253, NG240, NG243, NG136, CG109, NG249, ESNM61, ESUOM20; Resuscitation Council UK anaphylaxis (2021); Society for Endocrinology. Clinical reference — follow local emergency-transfer policies and check doses: NICE/SPC, BNF.