Emergency medicine

The A-a gradient is the difference between the calculated alveolar oxygen tension and the measured arterial oxygen tension. A gradient that is normal for age suggests hypoventilation or a low inspired oxygen tension (such as altitude), whereas a widened gradient points to V/Q mismatch, right-to-left shunt, or impaired diffusion. The expected upper limit rises with age, roughly (age / 4) + 4 mmHg on room air at sea level.

A 7-point score (0 to 7) estimating the 2-day risk of stroke after a transient ischaemic attack, from age, blood pressure, clinical features, symptom duration, and diabetes. Higher scores predict higher early stroke risk, but current guidance increasingly favours urgent specialist assessment and imaging over the score alone.

A simple 5-point score (0 to 5) for early risk stratification in acute pancreatitis, predicting in-hospital mortality within the first 24 hours. Each criterion scores 1 point. A score of 3 or more identifies substantially higher mortality and organ-failure risk.

Four clinical criteria (tonsillar exudate, tender anterior cervical nodes, fever by history, absence of cough), each worth 1 point, plus the McIsaac age adjustment, estimate the likelihood of group A streptococcal pharyngitis and frame the decision to test or treat.

A weighted score (0 to 9) that refines stroke risk in non-valvular atrial fibrillation beyond the older CHADS2 schema, adding vascular disease, age 65 to 74, and female sex. It identifies the low-risk patients who can safely avoid anticoagulation and stratifies everyone else.

Five equally-weighted criteria score community-acquired pneumonia severity from 0 to 5, stratifying 30-day mortality risk and informing whether a patient can be managed as an outpatient or needs admission.

The Glasgow Coma Scale grades consciousness across best eye opening (1 to 4), verbal response (1 to 5), and motor response (1 to 6) for a total of 3 to 15. It is the standard way to describe and track impaired consciousness; a total of 8 or less is severe and should prompt consideration of airway protection.

A pre-endoscopy score (0 to 23) using blood urea, haemoglobin, systolic blood pressure, pulse, and clinical features to predict the need for intervention (transfusion, endoscopic therapy, or surgery) in acute upper gastrointestinal bleeding. A score of 0 (some use up to 1) identifies very-low-risk patients who may be considered for outpatient management.

A five-domain score (0 to 10) for adults presenting to the emergency department with chest pain, estimating the 6-week risk of major adverse cardiac events (MACE: death, MI, or coronary revascularisation). Low scorers can often be discharged early; high scorers warrant an early invasive strategy.

Mean arterial pressure estimates the average pressure driving blood to the organs across the cardiac cycle. Because diastole lasts longer than systole, it is weighted toward the diastolic pressure. A MAP of around 65 mmHg is a commonly cited floor for adequate organ perfusion in resuscitation.

NEWS2 aggregates seven routine observations into a single score that standardises how acute deterioration is detected and escalated in adults. Each parameter scores 0 to 3; the total, together with any single parameter scoring 3, determines a low, medium, or high clinical response.

A standardised 15-item neurological examination that grades acute stroke severity from 0 to 42. It is the common language for stroke trials and care: it helps gauge severity, informs reperfusion and triage decisions, and lets a deficit be tracked reproducibly over time.

Eight clinical criteria for patients in whom PE is being considered but gestalt pretest probability is already low. If none of the eight are present, PE can be excluded without D-dimer or imaging. Any single positive criterion means PERC cannot exclude PE and further work-up is required.

Three rapidly-assessed criteria identify patients with suspected infection who are at higher risk of in-hospital death or prolonged ICU stay. A score of 2 or more should prompt escalation, lactate measurement, and a full sepsis assessment. qSOFA is a prompt, not a diagnosis of sepsis and not a screening replacement.

The QT interval shortens as heart rate rises, so it is corrected to a standard rate (QTc) before judging whether repolarisation is prolonged. This tool reports both the Bazett correction (the long-standing clinical default) and the Fridericia correction (more stable at extreme heart rates). Per the AHA/ACCF/HRS statement, a QTc at or above 450 ms in men or 460 ms in women is prolonged, and a QTc at or above 500 ms marks a substantially increased risk of torsades de pointes.

Calculated serum osmolality is estimated from sodium, glucose, and urea (BUN). When a measured osmolality is available, the osmolar gap (measured minus calculated) screens for unmeasured osmoles. A large gap with metabolic acidosis raises concern for toxic alcohols (methanol, ethylene glycol).

A seven-item bedside score (0 to 7) for unstable angina or NSTEMI that estimates the 14-day risk of a composite of all-cause death, new or recurrent myocardial infarction, and severe recurrent ischaemia requiring urgent revascularisation. Higher scores identify patients who derive more benefit from an early invasive strategy and potent antithrombotic therapy.

A clinical prediction rule that places a patient with suspected deep vein thrombosis into a pretest-probability category. The modern two-level version (DVT likely vs unlikely) is paired with D-dimer: an unlikely score plus a negative D-dimer can safely defer or avoid ultrasound. It is a triage tool, not a stand-alone rule-out.

Seven weighted clinical criteria estimate the pretest probability of pulmonary embolism. The result can be read three-tier (low, moderate, high) or two-tier (PE unlikely at 4 or less, PE likely above 4), which guides whether D-dimer or direct imaging is the next step.

Winters formula predicts the PaCO2 the lungs should reach to compensate for a primary metabolic acidosis. Comparing the measured PaCO2 against the expected range tells you whether compensation is appropriate or a second respiratory disorder is present.