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Mask CPAP: Physiologic effects

Gas Exchange

Gas Exchange:improves oxygenationby re-expanding collapsed alveoli (reduced shunt) andredistributing lung waterfrom alveolar to interstitial space, both improve V/Q matching. If too high could hyperinflate impairing blood flow increasing deadspace lowering PaO2 raising PaCO2.

Respiratory Mechanics

Compliance = tidal volume/(Plateau press – PEEP).CPAP/PEEP can increase, decrease, or not change compliance. Increase indicates alveolar recruitment. Decrease indicates overdistention. No change indicates ventilation occurring on the linear portion of volume/pressure curve.


Hemodynamics: generallyincreased intrathoracic pressure decreases venous return.It can alsoincrease right heart afterload, ventricular compliance and contractility.