adjusting the ventilator
The ventilator, in of itself, cannot do anything to cure a patient. While this seems simple, it’s an often-overlooked concept. The main purpose of mechanical ventilation is to provide support until the patient recovers from whatever illness or injury led to the need for respiratory support.
There are three therapeutic things that the ventilator can do:
Provide a reliably high concentration of oxygen, up to 100%
Take over the work of breathing for someone who is too fatigued or unable to breathe on his own
Use positive pressure to reduce intrapulmonary shunt
It’s also important to remember that the ventilator, or more accurately, the physician, is certainly capable of harming a patient. This is most often done by using too high of a tidal volume, letting the patient unnecessarily fatigue, and keeping him on the ventilator too long. In the last decade, the push has been toward lung protection and away from attaining a perfect ABG. When you’re faced with the choice of normalizing gas exchange at the expense of lung injury, don’t do it. That means using more physiologic tidal volumes (4-6 mL/kg predicted body weight, in most cases); using enough PEEP to open up the lungs; not letting your patient tire out; and by doing a daily assessment for extubation readiness.
As far as adjusting the ventilator to the ABG, remember that oxygenation is affected by FiO2 and PEEP, while ventilation is affected by the minute ventilation (rate × tidal volume). The link to the right will provide some helpful guidance when you aren’t sure what to do.