Final answer:
Decreased venous return is a possible cause of hypotension after initiating PEEP, which occurs due to increased chest pressure reducing blood flow back to the heart, similar to the mechanics of orthostatic hypotension.
Step-by-step explanation:
A possible cause of hypotension after the institution of Positive End-Expiratory Pressure (PEEP) is decreased venous return. PEEP can increase the pressure in the chest cavity (intra-thoracic pressure), which can potentially impede the flow of blood back to the heart. With the reduced venous return, the cardiac output might decline because the heart has less blood to pump with each beat, which can result in a drop in arterial blood pressure. This situation is similar to orthostatic hypotension, where an insufficient sympathetic response or low blood volume hampers the body's ability to maintain blood pressure upon changes in body position. Measures such as increasing fluid intake or addressing underlying sympathetic system dysfunction can help counteract these pressures on the cardiovascular system.