Library

Equations

• Alveolar gas equationIdeal alveolar oxygen tension.
• Cardiac outputOutput is heart rate times stroke volume.
• Cerebral perfusion pressureNet pressure driving cerebral blood flow.
• ComplianceVolume change per pressure change.
• Continuity equation (aortic valve area)Conservation of mass: the stroke volume through the LVOT must equal the stroke volume through the valve. Since SV = CSA × VTI, measuring the LVOT and the two velocities lets you solve for valve area.
• Ejection fractionFraction of end-diastolic volume ejected.
• Henderson-HasselbalchAcid-base relationship.
• IVC distensibility index (dIVC)Respiratory variation in IVC diameter in a fully ventilated patient; higher values predict fluid responsiveness.
• Mean arterial pressureMean pressure approximated from systolic and diastolic.
• Oxygen deliveryDelivery is output times arterial oxygen content.
• Peak velocity variation (ΔVpeak)Respiratory swing in aortic peak velocity over one breath; ≥12% predicts fluid responsiveness in a ventilated patient in sinus rhythm.
• SVC collapsibility index (ΔSVC)Respiratory collapse of the superior vena cava on TOE; a marker of fluid responsiveness.
• Shunt fractionProportion of shunted blood.
• Simplified BernoulliGradient from peak velocity.
• Stroke volume (LVOT method)Stroke volume = LVOT cross-sectional area (πr²) × the LVOT velocity–time integral.
• VTI variation (ΔVTI)Respiratory variation in the LVOT velocity–time integral; a direct stroke-volume surrogate for fluid responsiveness.