Q: What is the rule of thumb to calculate effect of PEEP on wedge pressure (Pulmonary Artery Occlusion Pressure - PAOP)?


Answer:  

If swan (pulmonary artery catheter)  is appropriately positioned in zone 3 of lung, ideally PEEP should not be a concern as  airway pressure does not get transmitted to the vasculature. But in real world, there is always some effect of higher PEEP on PAOP. In patients with high PEEP around 10, PAOP can be predicted by subtracting one-quarter of the PEEP - as most patients on higher PEEP usually have compromised compliance. If compliance appears to be normal on ventilator (unlikely in ICU), one-half of the PEEP should be subtracted.



Reference:

Teboul, JL, Besbes, M, Andrivet, P, et al. A bedside index assessing the reliability of pulmonary artery occlusion pressure measurements during mechanical ventilation with positive end-expiratory pressure. J Crit Care 1992; 7:22.