What could be a possible cause if arterial pressure changes from -200 to -250 after the initiation of treatment?

The most fitting explanation for arterial pressure shifting from -200 to -250 following the commencement of treatment is tied to hypotension and vasoconstriction.

Hypotension indicates a drop in blood pressure, which aligns with the decrease in arterial pressure observed. This can happen due to various factors, including inadequate blood volume, reduced vascular resistance, or the effects of specific medications that lower blood pressure. In this context, vasoconstriction typically counters hypotension by narrowing blood vessels, helping to elevate blood pressure. However, if the vasoconstrictive response is inadequate in the face of hypotension or the treatment leads to an increased vascular response without sufficient volume, it may result in a further decrease in pressure.

So, the important aspect to recognize here is how hypotension correlates with a reduction in arterial pressure, and while vasoconstriction could be part of the physiological response to combat hypotension, if it fails to sufficiently counter the underlying cause of reduced arterial pressure, the transition from -200 to -250 reflects a worsening state.