Calculators & Scales

Predicted body weight by the Devine/ARDSnet formulas with the full 4–8 mL/kg lung-protective tidal volume table.

V̇E = RR × VT with optional alveolar ventilation — normal ranges and what high or low values mean at the bedside.

Set the ventilation to reach a target PaCO₂ — Desired V̇E = (Current V̇E × Current PaCO₂) ÷ Desired PaCO₂, with the rate to set (VT held constant), the formula shown, and an auto-PEEP caution.

Cstat, Cdyn, and airway resistance from ventilator pressures — separates stiff-lung problems from airway-resistance problems.

Airway resistance from ventilator pressures — Raw = (PIP − Pplat) ÷ flow (L/s), the L/min→L/s conversion and formula shown, with the intubated-adult reference range and the resistance-vs-compliance teaching contrast.

The pressure swing the lung sees each breath — ΔP = Plateau − PEEP (and VT ÷ Cstat) with the ≤ 14–15 cmH₂O protective target, the formula shown, and the mortality association in ARDS.

Mean airway pressure from ventilator settings — P̄aw = K × (PIP − PEEP) × (Ti/Ttot) + PEEP with the waveform constant (1.0 pressure-control, 0.5 constant-flow), the I:E derivation and formula shown, and the oxygenation-vs-barotrauma trade-off.

Rapid Shallow Breathing Index (f/VT) with the Yang-Tobin 105 threshold — weaning-readiness interpretation with the evidence cited.

Stepwise arterial blood gas interpretation — primary disorder, compensation with Winter's formula and expected-compensation math shown, plus an oxygenation check.

PaO₂ ÷ FiO₂ with Berlin-definition severity bands — mild, moderate, and severe ARDS ranges with the formula shown.

The noninvasive P/F surrogate — S/F = SpO₂ ÷ FiO₂ with the 2023 global-definition ARDS bands (315 / 235 / 148), the formula shown, and the critical SpO₂ ≤ 97% reliability caveat.

Alveolar–arterial oxygen gradient via the alveolar gas equation, with age-expected normals and every step of the math shown.

Arterial oxygen content from hemoglobin, SaO₂, and PaO₂ — CaO₂ = (1.34 × Hb × SaO₂) + (0.003 × PaO₂), the formula shown, with the bound-vs-dissolved split and why content tracks hemoglobin, not PaO₂.

Intrapulmonary shunt fraction — the classic three-content Berggren equation Qs/Qt = (CcO₂ − CaO₂) ÷ (CcO₂ − CvO₂), or the estimated form with an assumed C(a-v)O₂, with the alveolar PO₂ derived and every oxygen content shown.

Predict high-flow nasal cannula success — ROX = (SpO₂ ÷ FiO₂) ÷ RR with the validated 4.88 and 3.85 thresholds, the formula shown, and the trend-over-time caveat.

Severity of hypoxemic respiratory failure including ventilator support — OI = (FiO₂ × mean airway pressure × 100) ÷ PaO₂ with the PALICC pediatric ARDS bands and the ECMO-consideration threshold, the formula shown.

Bohr-Enghoff dead space — VD/VT = (PaCO₂ − P̄ECO₂) ÷ PaCO₂ with normal ranges, the formula shown, and what a markedly elevated value means (PE, ARDS, low cardiac output).

Cylinder duration from gauge pressure, tank factor (D, E, G, H/K, M), flow, and a safe residual — built for transport planning.

Air-entrainment ('Venturi') mask math — air:O₂ ratio = (100 − FiO₂%) ÷ (FiO₂% − 21) and total flow = (air parts + 1) × O₂ flow, the formula shown, with the standard taught ratios and a check against inspiratory demand.

FEV₁ (or FVC) change after a bronchodilator against the classic ATS/ERS 12% and 200 mL reversibility threshold — the formula shown and the criteria cited.

Calculate the serum anion gap from a basic metabolic panel — Na − (Cl + HCO₃) with the optional albumin correction, the formula shown, and the high vs normal gap interpretation cited.