01 · Body metrics & dosing
The math behind weight-based dosing, ventilator settings, and nutritional needs.
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Body Mass Index (BMI)
Weight category from height + weight
BMI = weight (kg) / [height (m)]². WHO categories: <18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, ≥30 obesity.
HeightWeightSource: WHO Expert Consultation, Lancet 2004
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Body Surface Area (BSA)
For chemo + cardiac dosing
Most common formulas: Du Bois (1916), Mosteller (1987). Mosteller: BSA (m²) = √[(height-cm × weight-kg) / 3600]. Used for chemotherapy and some cardiac drug dosing.
HeightWeightSource: Mosteller, NEJM 1987; Du Bois & Du Bois, Arch Intern Med 1916
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Ideal Body Weight (Devine)
For drug dosing in obese patients
Male: 50 kg + 2.3 kg × (height in inches − 60). Female: 45.5 kg + 2.3 kg × (height in inches − 60). Used for aminoglycoside dosing and other drugs where actual body weight overdoses lean tissue.
SexHeightSource: Devine, Drug Intell Clin Pharm 1974
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Predicted Body Weight (PBW / ARDSnet)
For low-tidal-volume vent settings
Male: 50 + 0.91 × (height-cm − 152.4). Female: 45.5 + 0.91 × (height-cm − 152.4). Tidal volume 4–8 mL/kg PBW per ARDSNet lung-protective strategy.
SexHeightSource: ARDSNet, NEJM 2000
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Adjusted Body Weight
Aminoglycoside dosing in obesity
AdjBW = IBW + 0.4 × (Actual − IBW). Used for aminoglycoside dosing when actual is >120% of ideal.
Actual weightIBWSource: Bauer et al, Am J Hosp Pharm 1980
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Mifflin-St Jeor (BMR / caloric needs)
Resting energy expenditure
Male: 10×kg + 6.25×cm − 5×age + 5. Female: 10×kg + 6.25×cm − 5×age − 161. Multiply by activity factor for total daily calories. Used in nutritional planning.
SexHeightWeightAgeSource: Mifflin & St Jeor, Am J Clin Nutr 1990
02 · Fluid & electrolyte
Maintenance fluid math, corrections, and gaps.
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Maintenance Fluid (Holliday-Segar 4-2-1)
mL/hr for any weight
4 mL/kg/hr for first 10 kg + 2 mL/kg/hr for next 10 kg + 1 mL/kg/hr for each kg above 20. Used for routine maintenance fluid orders in adults and peds.
WeightSource: Holliday & Segar, Pediatrics 1957
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Corrected Sodium (for hyperglycemia)
Adjust Na+ for blood glucose
Corrected Na = Measured Na + [(Glucose − 100) / 100] × 1.6. Important in DKA/HHS — true sodium may be much higher than the lab reports.
Measured NaGlucoseSource: Hillier et al, Am J Med 1999
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Corrected Calcium (for albumin)
Adjust Ca²⁺ for hypoalbuminemia
Corrected Ca (mg/dL) = Measured Ca + 0.8 × (4.0 − Albumin). Hypoalbuminemia falsely lowers total calcium; ionized calcium is the gold standard but corrected formula is bedside-quick.
Measured CaAlbuminSource: Payne et al, BMJ 1973
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Anion Gap
AG = Na − (Cl + HCO₃)
Normal 8–12 mEq/L. Elevated AG metabolic acidosis differential: MUDPILES (Methanol, Uremia, DKA, Propylene glycol, Iron/INH, Lactic acidosis, Ethylene glycol, Salicylates).
NaClHCO₃Source: Kraut & Madias, Clin J Am Soc Nephrol 2007
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Osmolar Gap
Detects unmeasured osmoles
Measured osm − Calculated osm. Calc osm = (2 × Na) + (Glucose/18) + (BUN/2.8). Gap >10 suggests methanol, ethylene glycol, propylene glycol, or other unmeasured osmotic substance.
NaGlucoseBUNMeasured osmSource: Kraut & Mullins, NEJM 2018
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Free Water Deficit
Hypernatremia correction
FWD (L) = TBW × [(Current Na / Target Na) − 1]. TBW = 0.6 × kg (male) or 0.5 × kg (female). Correct slowly to avoid cerebral edema.
WeightSexCurrent NaTarget NaSource: Adrogué & Madias, NEJM 2000
03 · Renal
Creatinine clearance and GFR estimation.
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Creatinine Clearance (Cockcroft-Gault)
Estimate kidney function for drug dosing
CrCl (mL/min) = [(140 − age) × weight (kg)] / (72 × SCr). Multiply × 0.85 for female. Still the formula many drug references key against for renal dose adjustments.
AgeSexWeightSerum CrSource: Cockcroft & Gault, Nephron 1976
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eGFR (CKD-EPI 2021)
Estimated glomerular filtration rate
The race-free CKD-EPI 2021 equation. Used for CKD staging. Note: drug references that key against Cockcroft-Gault may still want CrCl, not eGFR.
AgeSexSerum CrSource: Inker et al, NEJM 2021
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Urinary Output (mL/kg/hr)
Adequate UOP for AKI screening
Adult adequate UOP is generally ≥0.5 mL/kg/hr. Sustained <0.5 mL/kg/hr × 6 hours is KDIGO Stage 1 AKI; <0.3 × 24 h or anuria × 12 h is Stage 3.
UOP (mL)Time (hr)WeightSource: KDIGO Clinical Practice Guideline for AKI, 2012
04 · Cardiac & rhythm
MAP, QTc, AFib stroke risk, bleeding risk.
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Mean Arterial Pressure (MAP)
Perfusion-pressure indicator
MAP = DBP + ⅓(SBP − DBP). Goal MAP ≥65 mmHg for sepsis per Surviving Sepsis. Higher goals (75–85) in some neuro/spinal cord injury patients.
SBPDBPSource: Surviving Sepsis Campaign Guidelines, 2021
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Pulse Pressure
SBP − DBP
Normal 30–40 mmHg. Widened (>40) in aortic regurgitation, hyperthyroidism. Narrowed (<25) in cardiogenic shock, tamponade, severe aortic stenosis.
SBPDBPSource: Braunwald's Heart Disease, current edition
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QTc (Bazett & Fridericia)
Rate-corrected QT interval
Bazett: QTc = QT / √(RR). Fridericia: QTc = QT / ³√(RR). Fridericia is more accurate at extreme heart rates. >500 ms is the typical threshold to notify pharmacy/MD.
QTHeart rateSource: Bazett, Heart 1920; Fridericia, Acta Med Scand 1920
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CHA₂DS₂-VASc Score
AFib stroke risk
C(HF)1, H(TN)1, A(ge≥75)2, D(M)1, S(troke/TIA)2, V(asc dz)1, A(ge 65–74)1, Sc(female)1. Score ≥2 (men) or ≥3 (women) → anticoagulate per AHA.
7 risk factor checkboxesSource: Lip et al, Chest 2010; AHA/ACC/HRS AFib guideline 2023
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HAS-BLED Score
Bleeding risk on anticoagulation
H(TN)1, A(bnormal renal/liver)1ea, S(troke)1, B(leeding history)1, L(abile INR)1, E(lderly ≥65)1, D(rugs/alcohol)1ea. ≥3 = high bleed risk, doesn't preclude anticoagulation, signals closer monitoring.
7 risk factor checkboxesSource: Pisters et al, Chest 2010
05 · Critical-care scoring
Severity scores and consciousness/sedation scales.
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Glasgow Coma Scale (GCS)
Level of consciousness 3–15
Eye (1–4) + Verbal (1–5) + Motor (1–6). ≤8 typically means intubate. Document component scores (E3V4M5), not just the total.
EyeVerbalMotorSource: Teasdale & Jennett, Lancet 1974
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FOUR Score
GCS alternative for ICU
Eye + Motor + Brainstem reflexes + Respiration, each 0–4. Validated for intubated patients where verbal isn't scorable, and adds brainstem detail GCS misses.
EyeMotorBrainstemRespirationSource: Wijdicks et al, Ann Neurol 2005
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RASS (Richmond Agitation-Sedation Scale)
Sedation target for ventilated patients
−5 (unarousable) to +4 (combative). 0 is alert + calm. Most ICUs target −1 to 0 unless deeper sedation is clinically indicated.
Observed behaviorSource: Sessler et al, Am J Respir Crit Care Med 2002
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APACHE II
ICU mortality prediction
Acute physiology + age + chronic-health score, 0–71. Calculated within 24 h of ICU admission. Driver of historical ICU benchmarking.
12 physiologic varsAgeChronic healthSource: Knaus et al, Crit Care Med 1985
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SOFA Score
Organ-failure progression
Respiratory + coag + liver + cardiovascular + CNS + renal, 0–4 each. Tracks daily; rise of ≥2 points in 24 h on ward = sepsis per Sepsis-3.
6 organ-system pointsSource: Vincent et al, Intensive Care Med 1996; Sepsis-3 (Singer et al), JAMA 2016
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qSOFA
Quick sepsis screen at bedside
≥2 of: RR ≥22, altered mentation, SBP ≤100. Triggers escalation outside the ICU per Sepsis-3.
RRMentationSBPSource: Singer et al (Sepsis-3), JAMA 2016
06 · Stroke
Acute neuro scoring + functional outcome.
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NIHSS
Acute stroke severity 0–42
15-item scale: LOC, gaze, visual, facial palsy, motor arm/leg, ataxia, sensory, language, dysarthria, extinction. Required before thrombolytics + thrombectomy decisions.
15 itemsSource: NIH National Institute of Neurological Disorders and Stroke, scale published 1989
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Modified Rankin Scale (mRS)
Functional outcome after stroke 0–6
0 = no symptoms; 1 = no disability; 2 = slight; 3 = moderate; 4 = moderately severe; 5 = severe; 6 = dead. Standard endpoint in stroke trials.
Functional assessmentSource: Rankin, Scott Med J 1957; van Swieten et al, Stroke 1988
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ABCD² Score (TIA risk)
Risk of stroke after TIA
Age ≥60 (1), BP ≥140/90 (1), Clinical features (speech 1, weakness 2), Duration (<10 min 0, 10–59 min 1, ≥60 min 2), Diabetes (1). Higher = higher 2-day stroke risk.
AgeBPFeaturesDurationDMSource: Johnston et al, Lancet 2007
07 · Pulmonary
Oxygenation, ARDS, weaning.
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PaO₂/FiO₂ Ratio (P/F)
Oxygenation index
Normal >400. ARDS thresholds (Berlin 2012): Mild 200–300, Moderate 100–200, Severe <100, all with PEEP ≥5.
PaO₂FiO₂Source: Berlin Definition, JAMA 2012
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A-a Gradient
Cause of hypoxemia
A-a = [FiO₂×(Patm − 47) − PaCO₂/0.8] − PaO₂. Normal ≈ age/4 + 4. Elevated → V/Q mismatch, shunt, diffusion defect. Normal → hypoventilation, low FiO₂.
FiO₂PaCO₂PaO₂Atm pressureSource: West's Respiratory Physiology, current edition
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Rapid Shallow Breathing Index (RSBI)
Weaning readiness
RSBI = RR / Tidal Volume (L). <105 predicts successful extubation in most patients.
RRTidal volumeSource: Yang & Tobin, NEJM 1991
08 · Bleeding & clotting
DVT, PE, and risk-stratification.
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Wells Score for DVT
Pretest probability of DVT
10 clinical criteria. Score ≤0 unlikely, 1–2 moderate, ≥3 high probability. Drives D-dimer vs. ultrasound workup.
10 criteriaSource: Wells et al, NEJM 2003
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Wells Score for PE
Pretest probability of PE
7 clinical criteria. ≤4 PE unlikely (D-dimer rules out), >4 PE likely (CT-PA). Different threshold from the DVT version.
7 criteriaSource: Wells et al, Ann Intern Med 2001
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PERC Rule
PE rule-out (low-risk patients)
If Wells <2 AND all 8 PERC criteria absent, PE can be ruled out without D-dimer. Age <50, HR <100, SaO₂ ≥95% on RA, no hemoptysis, no estrogen, no prior DVT/PE, no surgery/trauma in 4 weeks, no unilateral leg swelling.
8 criteriaSource: Kline et al, J Thromb Haemost 2004
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Glasgow-Blatchford Score
Upper GI bleed risk
Pre-endoscopy risk stratification. Score 0 → may be safely managed outpatient. Higher = inpatient admission and urgent endoscopy.
BUNHgbSBPSexHRMelenaSyncopeLiver dzCardiac dzSource: Blatchford et al, Lancet 2000
09 · Pressure, fall & risk scales
Routine nursing risk assessment scoring.
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Braden Scale
Pressure ulcer risk
Sensory + Moisture + Activity + Mobility + Nutrition + Friction. Max 23. ≤18 = at risk; ≤12 = high risk. Mandates a pressure-injury prevention bundle.
6 sub-scalesSource: Braden & Bergstrom, Decubitus 1987
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Norton Scale
Pressure ulcer risk (older)
Physical + Mental + Activity + Mobility + Incontinence, max 20. ≤14 = increased risk. Still used in long-term care.
5 sub-scalesSource: Norton, Lancet 1962
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Morse Fall Scale
Inpatient fall risk
History of falls + 2° dx + ambulatory aid + IV/heparin lock + gait + mental status. ≥45 = high risk → fall-prevention bundle.
6 itemsSource: Morse et al, Soc Sci Med 1989
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Hendrich II Fall Risk
Inpatient fall risk (alternative)
Confusion + symptomatic depression + altered elimination + dizziness + male + antiepileptics + benzodiazepines + Get-Up-and-Go score. ≥5 = high risk.
8 itemsSource: Hendrich et al, Appl Nurs Res 2003
10 · Pain & sedation scales
Assessment for verbal and non-verbal patients.
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Numeric Rating Scale (NRS)
Self-report pain 0–10
0 = no pain, 10 = worst imaginable. Use for verbal patients ≥7 years old. Document with intervention context, not as a number alone.
Patient self-reportSource: Hjermstad et al, J Pain Symptom Manage 2011
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Wong-Baker FACES
Pain in children + non-verbal adults
Six cartoon faces from no hurt to hurts worst. Validated 3+ years; widely used through adulthood for patients who can't use numerics.
Faces selectionSource: Wong & Baker, Pediatr Nurs 1988
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FLACC Scale
Behavioral pain (peds 2 mo – 7 yr)
Face + Legs + Activity + Cry + Consolability, each 0–2. 0–3 mild, 4–6 moderate, 7–10 severe.
5 behavioral itemsSource: Merkel et al, Pediatr Nurs 1997
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CPOT
Critical-care pain in vented patients
Facial expression + body movement + muscle tension + ventilator compliance, 0–8 total. ≥3 = clinically important pain.
4 behavioral itemsSource: Gélinas et al, Am J Crit Care 2006
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PAINAD
Pain in advanced dementia
Breathing + vocalization + facial expression + body language + consolability, each 0–2. ≥4 = moderate-to-severe pain that warrants intervention.
5 behavioral itemsSource: Warden et al, J Am Med Dir Assoc 2003
11 · OB & pediatrics
Newborn scoring, labor readiness, EDD.
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APGAR Score
Newborn assessment at 1 and 5 min
Appearance + Pulse + Grimace + Activity + Respiration, each 0–2. 7–10 normal, 4–6 moderate distress, <4 severe distress requiring resuscitation.
5 componentsSource: Apgar, Curr Res Anesth Analg 1953
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Bishop Score
Cervical favorability for induction
Dilation + effacement + station + consistency + position. ≥8 favorable for induction; ≤6 unfavorable, consider ripening agent.
Cervical examSource: Bishop, Obstet Gynecol 1964
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Naegele's Rule (EDD)
Estimated delivery date
LMP date + 1 year − 3 months + 7 days. Assumes a regular 28-day cycle.
LMP dateSource: Naegele, 1812 (historical)
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Pediatric GCS
GCS adapted for <2 years
Same Eye/Verbal/Motor structure but age-appropriate verbal criteria (e.g., "coos and babbles" vs. "oriented").
EyeVerbal (age-adjusted)MotorSource: Holmes et al, Ann Emerg Med 2005
12 · Burn
Surface area + fluid resuscitation.
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Rule of 9s (adult)
Quick TBSA estimate
Head 9, each arm 9, anterior trunk 18, posterior trunk 18, each leg 18, perineum 1. Hand area ≈ 1% for irregular patches.
Anatomic regionsSource: Wallace, Lancet 1951
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Lund-Browder
TBSA for peds (age-adjusted)
Age-adjusted body-region percentages — head is proportionally larger in young children, legs smaller. More accurate than Rule of 9s in peds.
AgeAnatomic regionsSource: Lund & Browder, Surg Gynecol Obstet 1944
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Parkland Formula
Burn fluid resuscitation
4 mL × weight (kg) × %TBSA = total LR over first 24 h. Half in the first 8 h from burn time, half over the next 16 h. Titrate to UOP 0.5 mL/kg/hr (adult) or 1 mL/kg/hr (peds).
Weight%TBSASource: Baxter & Shires, Ann NY Acad Sci 1968
13 · PACU & post-anesthesia
Discharge readiness scoring.
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Aldrete Score
PACU discharge readiness
Activity + Respiration + Circulation + Consciousness + SaO₂, each 0–2. ≥9 generally meets PACU discharge criteria.
5 componentsSource: Aldrete, J Clin Anesth 1995
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Modified Aldrete
Adds SaO₂ + dressing/bleeding/pain items
Same structure with two added items for outpatient post-procedure discharge. ≥9 generally permits home discharge.
7 componentsSource: Aldrete, J Perianesth Nurs 1998
14 · Withdrawal & substance use
CIWA, COWS, AUDIT — high-stakes scoring.
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CIWA-Ar
Alcohol withdrawal severity
10 items × 0–7 (vomit cap 7, headache cap 7, orientation cap 4). 8–15 mild, 16–20 moderate, >20 severe. Drives benzo dosing in many protocols.
10 itemsSource: Sullivan et al, Br J Addict 1989
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COWS
Opioid withdrawal severity
11 items, total 0–48. 5–12 mild, 13–24 moderate, 25–36 mod-severe, >36 severe. Used for buprenorphine induction timing — typically need COWS ≥8 before first dose.
11 itemsSource: Wesson & Ling, J Psychoactive Drugs 2003
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AUDIT-C
3-question alcohol-use screen
Three frequency/quantity/binge questions, each 0–4. Positive screen ≥4 (men) or ≥3 (women), ≥1 (pregnant). Triggers SBIRT brief intervention.
3 itemsSource: Bush et al, Arch Intern Med 1998