Clinical calculators

Quick Calculations, With the Reference

Common calculations for dentists and doctors. Each shows the formula's source. Results support, and never replace, clinical judgement and the product's labelling.

Maximum Local Anaesthetic Dose

Maximum recommended dose by weight, and the number of cartridges that represents.

Reduce doses for children, older adults and medically compromised patients, and use the lowest effective dose. Figures differ between references and countries: some teaching guides use lower values (for example lidocaine 4.4 mg/kg). Always check the product's labelling and your local guidance.

Drug

Patient weight (kg)

Cartridge volume

Adrenaline in cartridge

Adrenaline limit

-maximum dose

-cartridges (by anaesthetic)

-cartridges (by adrenaline limit)

Doses per Malamed SF, Handbook of Local Anesthesia, 7th ed. (2020): lidocaine 7.0 mg/kg (max 500 mg); articaine 7.0 mg/kg (max 500 mg); mepivacaine 6.6 mg/kg (max 400 mg); prilocaine 8.0 mg/kg (max 600 mg); bupivacaine 1.3 mg/kg (max 90 mg). Adrenaline limits per the same source. The lower of the two cartridge counts applies.

eGFR (CKD-EPI 2021, Race-Free)

Estimated glomerular filtration rate from serum creatinine, age and sex.

Serum creatinine

Unit

Age (years)

Sex

Inker LA et al. New creatinine- and cystatin C-based equations to estimate GFR without race. N Engl J Med 2021;385:1737-49. For adults 18 and over; not valid in acute kidney injury or at extremes of muscle mass. G stages per KDIGO.

Creatinine Clearance (Cockcroft-Gault)

Often used for drug dose adjustment. Check which weight your drug reference or local protocol uses.

Serum creatinine

Unit

Age (years)

Weight (kg)

Sex

-mL/min

Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron 1976;16:31-41. CrCl = ((140 − age) × weight) / (72 × creatinine in mg/dL), × 0.85 if female.

Body Mass Index

Weight divided by height squared, with WHO categories.

Weight (kg)

Height (cm)

Cut-offs

WHO. Obesity: preventing and managing the global epidemic (TRS 894, 2000). WHO Expert Consultation. Appropriate body-mass index for Asian populations. Lancet 2004;363:157-63 (public health action points 23 and 27.5 kg/m²). For adults; not for children or pregnancy.

Corrected QT Interval

QT corrected for heart rate by Bazett and Fridericia.

QT interval (ms)

Heart rate (bpm)

-Bazett (ms)

-Fridericia (ms)

Bazett HC. Heart 1920;7:353-70. Fridericia LS. Acta Med Scand 1920;53:469-86. Bazett overcorrects at high heart rates; Fridericia is often preferred above about 90 bpm.

CHA₂DS₂-VA Score

Stroke risk in atrial fibrillation, as recommended by the 2024 ESC guideline (without the sex category).

Congestive heart failure signs, symptoms or reduced ejection fraction Hypertension Age 75 or over Diabetes mellitus Prior stroke, TIA or thromboembolism Vascular disease MI, peripheral artery disease, aortic plaque Age 65 to 74 Female sex tick only for the older CHA₂DS₂-VASc score

Van Gelder IC et al. 2024 ESC Guidelines for the management of atrial fibrillation. Eur Heart J 2024;45:3314-414. Oral anticoagulation is recommended at a score of 2 or more and should be considered at 1. Local guidelines may still use CHA₂DS₂-VASc.

HAS-BLED Score

Bleeding risk on anticoagulation. A high score means addressing modifiable risks, not withholding anticoagulation by itself.

Hypertension, uncontrolled systolic above 160 mmHg Abnormal renal function Abnormal liver function Stroke history Bleeding history or predisposition Labile INR if on a vitamin K antagonist Elderly over 65 Drugs antiplatelets or NSAIDs Alcohol 8 or more drinks a week

Pisters R et al. A novel user-friendly score (HAS-BLED) to assess 1-year risk of major bleeding in patients with atrial fibrillation. Chest 2010;138:1093-100. A score of 3 or more indicates high risk.

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