control of variables

Last reviewed 08/2021

The use of a ventilator allows manipulation of:

• minute volume = tidal volume x respiratory rate
• inspired oxygen concentration

These then can be varied for different patients - size - and different conditions:

• e.g. in ARDS where the patient has stiff lungs and difficulty oxygenating blood, then a large tidal volume - 1 litre - is required with a slow respiratory rate - 10-12/minute - and 100% inspired oxygen.
• e.g. in status asthmaticus with hyperinflated lungs and difficulty breathing, they require small tidal volume - 0.5 litres - and a slow respiratory rate - 12/minute. Also, the expiration time must be at least 50% of the respiratory cycle.

The process of weaning off the ventilator must be gradual.