In most of the decent units those things are protocol driven. The docs prescribe a protocol. It would be up to the nursing staff to implement it based on the specific requirements of patient under care. So lets say for blood sugar control the docs would give you Insulin drip order with the request to optimize the BSLs within 4-10 range. They would not be generally interested in how you achieve that as long as Insulin requirements were not dramatic (>15 units/h).
In Calgary we had protocols for management of traumatic brain injuries where nurses could initiate fluid boluses, start Noradrenalin, bolus hypertonic saline when they see fit in order to achieve certain clinical goals (CVP, CPP, ICP, etc).
Ventilation wise, we would be talking about an order to wean off ventilator. This is Brisbane now. It would be up to nursing staff to decide to ease up sedation to a level of tube tolerance, go down on FiO2/ PS/PEEP based on the gas exchange, transition from lets say SIMV to PS ventilation - generally bringing the patient to the point of extubation. And then, upon a medical review, receive an order for extubation and implement it.
In contrast, Toowoomba hospital ICU would not let nurses make any changes to the ventilators at all.
So again, everything seems to be very unit specific. Unfortunately, someone who used to a certain level of independence in practice would have a major culture shock borderlining depression when they come to a place where their expertise, experience, knowledge and skill set is not generally needed, and they are unable to practice to the full scope of their abilities, capabilities and desire.