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Minute (or Total) Ventilation
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Alveolar Ventilation (VA): inversely proportional to PaCO2, doubling of VA will halve PaCO2
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Compliance = Change in Volume/Change in Pressure
Static Compliance = VT/(Pplat - PEEP)
Pplat – Plateau pressure
PEEP – Positive end-expiratory pressure
Nl: 60 to 200 mL/cmH2O in adults
>1 mL/cm H2O/kg in pediatrics
Reflects pressure to overcome elastic forces of respiratory system
Dynamic Compliance = VT/(PIP - PEEP)
PIP – Peak inspiratory pressure
Nl: 50 to 175 mL/cm H20 (∼10%–20% less than static)
Reflects lung compliance + pressure to overcome airway resistance
*The difference is an indirect index of flow-resistive properties of the respiratory system
Effective VT/Kg = VT – [(PIP – PEEP) × tubing compliance factor]/weight in kg
Resistance – (Poiseuille's law) R = 8 nl/πr4
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Mean Airway Pressure:
MAP = [It/(It + Et)] × (PIP – PEEP)] + PEEP
Correlated to oxygenation, an increase in MAP will improve alveolar volume and improve oxygenation
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OXYGEN PARAMETERS AND LUNG INJURY CLASSIFICATIONS
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Alveolar-arterial gradient: measure of lung function