# Formulae

SHARE VIA:

Body surface index (BSA) = ( [Height(cm) x Weight(kg) ] / 3600 )½

Mean arterial blood pressure (MAP) = (SBP + 2 x DBP) / 3

Transpulmonary gradient (TPG) = mPAP – PCWP or in Glenn/Fontan: SVC (CVP) – LAP

Cardiac output (CO) = SV x HR. normal: 2.1-3.5 l/min/m2

Cardiac index (CI) = CO / BSA. normal 3.0-5.5 l/min/m2

Systemic vascular resistance index (SVRI) –> 80 x (MAP – CVP) / CI. normal 800-1600 dyne*sec/cm5/m2. SVRI / 80 = normal 15 – 30 Wood unit / m2

Pulmonary vascular resistance index (PVRI) —>80 x (MPAP – LAP) / CI. normal 80-240 dyne*sec/cm5/m2. PVRI / 80 = normal 1 – 3 Wood unit / m2

Stroke volume (SV) = CO / HR. normal 1-1.5 ml/kg

Ejection fraction (EF) = (EDV – ESV) / EDV. normal 55-75 %

Fractional shortening (FS) = (LVEDD – LVESD) / LVEDD. normal 28-45 %

Modified Bernoulli equation: p1-p2=4 x v2 relates the pressure drop (or gradient) across an obstruction

Flow resistance. Poiseuille’s Law: R = 8 x η x L / π x r4 ( η = viscosity, L = length, r = radius). laminar flow only

Right ventricular pressure (RVP) = 4 x TR Vmax2 + RAP

Pulmonary to systemic blood (Qp : Qs) –> (SaO2 – SmvO2) / (SpvO2 – SpaO2). Normal 1.0. In parallel circulation Qp : Qs ~ 25 : (95 – SaO2)

Oxygen Delivery (DO2) = CI x Hb (g/l) x SaO2

Oxygen consumption (VO2) –> CI x Hb (g/l) x 1.36 x ((SaO2 – SmvO2) / 100). Normal: infant 160-180, child 100-130, adult 120-150 ml/min/m2

QT interval. Bazett’s formula: QTc = QT (sec) / SqrRt of previous RR interval (sec). normal approximately <0.44 sec

All Marc’s PICU cardiology FOAM can be found on PICU Doctor and can be downloaded as a handy app for free on iPhone or AndroidA list of contributors can be seen here.

## Author

• Marc Anders is a paediatric intensivist.