Step voltage down via voltage divider, then grab original voltage output
Assuming 'P' is the pressure, you can reason to yourself what the maximum pressure is that you expect it to bear. That lets you calculate the maximum Vout, call it Vout(max). 

You can then scale the voltage down using a 2-resistor potential divider. As you know what Vout(max) is so you're scaling that down to 1.8 V.

This all assumes that your 1.8 V input is an analogue input and not digital. If the latter, you can only determine if the sensor is above or below a threshold. You'd then best use a comparator so that your trip point is clean and you can add hysteresis to ensure noise-free switching.