Overview
PEEP is available with intubation or NIPPV and ranges from 0–24 cmH₂O. It is converted to mmHg before entering the cardiovascular equations. Intrinsic PEEP and mean inspiratory elastic loading from the active ventilator also contribute.
The engine separates hemodynamic loading from displayed pressure transmission. First it changes venous return, ventricular filling and pulmonary resistance; after support and shunts are solved, it adds the transmitted end-expiratory pressure once to the reported pressures.
Transmission assumption
The model assumes 50% of airway PEEP is transmitted as pleural pressure. Thus 10 cmH₂O corresponds to about 7.36 mmHg airway pressure and 3.68 mmHg transmitted pressure. This fixed fraction is not a clinical correction formula for PAWP or RAP. Actual transmission depends on respiratory mechanics.
Volume and lung-congestion estimates use filling after removing the modeled external pressure offset. Adding PEEP therefore does not automatically create ventricular enlargement or additional lung water because the monitor pressure rises.
Competing loading effects
Positive pressure reduces venous return, with greater penalties in depletion, tamponade, tension pneumothorax, HOCM and limited RV reserve. Recruitment can reduce PVR; overdistension increases it. RV backloading and reduced LV delivery can lower forward flow.
Congested LV pump failure or fixed regurgitant disease may gain from reduced transmural afterload. Coexisting mitral/aortic stenosis limits that recruitment; volume depletion, pericardial constraint and RV risk can remove the apparent benefit. Dynamic prolapse is reassessed from the new transmural loads.
What changes on screen
Forward output and resistance determine the resulting arterial/PA pressures. Wiggers and PV use the same treated pressures; chamber-volume loading excludes the external offset. CXR opacity can improve through recruitment without implying instantaneous clearance of pulmonary edema fluid. IVC behavior changes to a positive-pressure pattern.
Respiratory swings use the shared elastic breath, not simply PIP. The hemodynamic effect is a later algebraic teaching equilibrium; it does not predict the timing of venous redistribution, cardiac arrest, barotrauma or fluid removal.
References & further reading
