How A Breath is Delivered Flashcards
What factors does the ventilator control?
Flow, volume, pressure
What are the phases of the breath accomplished?
Trigger variable, limit variable, cycle variable and baseline variable
What are the two forces that act on the respiratory system during mechanical ventilation?
Muscle pressure or ventilator pressure
The amount of volume delivered depends on what?
Compliance and resistance to gas flow
What is the Rhorer equation of motion?
Pmus + Ptr = V/C + (Raw x flow)
What is the ventilator’s single most important function?
Delivery of inspiration
A _______ is the primary variable that the ventilator manipulates to cause inspiration
Control variable
What are the three choices of the control variable?
Volume, flow and pressure (time is implicit and can be a control variable)
How many variables can be controlled at a time?
One
What is volume control?
Volume is controlled, and the volume and flow waveforms are constant. Pressure varies with changes in compliance and resistance. Machine MUST measure volume when using a true volume controller
What are other names of volume control?
Volume ventilation, volume targeted, volume limited
When the ventilator keeps the _______ waveform in a specific pattern, the breath is said to be volume controlled
Volume
What waveform changes during volume control?
Pressure (changes with compliance and resistance)
What does it mean when one uses pressure control?
Pressure delivered is constant but volume and flow vary with changes in compliance and resistance
What are other names for pressure control?
Pressure targeted, pressure ventilation and pressure limited
What is the reality when it comes to pressure controlled ventilation?
The patient feels better but it may be more difficult
What is happening when using flow control?
Flow and volume are constant while pressure varies with changes in compliance and resistance
Any ventilator that has a set _____ waveform and a set _____ also has a set _____ waveform and vice versa
Flow; time; volume
What is time control?
When both pressure and volume waveforms are affected by the changes in lung characteristics
Who is time control used on?
Kids
Time control is also referred to as
High frequency or oscillation, and is not used very frequently
Inspiration is commonly referred to as
Volume or pressure controlled
Flow, volume or pressure waveforms usually take one of four shapes
Rectangular (square or constant), exponential (increasing/decreasing), sinusoidal (sine) or ramp (ascending/descending)
What is the trigger variable?
The start of the breath (initiation). Can be patient or machine
What is the limit variable?
What is controlled during each breath (inspiration itself)
What is the cycle variable?
What terminates the breath (end of the breath)
What is the baseline variable?
Expiratory phase
What is machine time trigger?
The ventilator begins itself by a timing mechanism (each breath is initiated by time) and is insensitive to the patient’s effort
What should you set the rate at if using a machine time trigger?
10 breaths/min (one breath every 6 seconds)
What is the patient trigger?
The machine senses or knows the patient wants a breath
What is response time?
How fast the machine responds (usually at 0.08 seconds) and cannot be adjusted. The longer the response time the more work of breathing (time delay)
What is sensitivity?
Determines the amount of effort
What happens if you decrease sensitivity?
Increase in work of breathing (make it harder for the patient to breathe)
What happens if you increase sensitivity?
Decrease in work of breathing (make it easier for the patient to breathe)
What is pressure trigger assist?
The machine begins inspiration when the patient starts to inspire and removes a small amount of volume from the circuit, which creates negative pressure
What is flow trigger (bias flow)?
A continuous supply of low level flow that is delivered (reduces work of breathing during response time)
What must the base flow be?
Twice the trigger flow
What does it mean if there is no bias flow?
It is a dead circuit and there is no airflow
What does it mean if there is bias flow?
There is enough flow given until the breath is recognized by the machine
What is volume trigger?
The machine cycles when a preset volume has been removed from the circuit
What is manual volume trigger?
A manual button on the machine, that when pushed, will initiate a positive pressure breath
What is limits of ventilation?
One of the four physical parameters that can be reached but not exceeded during a breath. Reaching a limit does NOT end a breath
What is volume limited?
The volume reached will be held in the airway until a preset time is reached, and that time will end the breath
What is time limited?
Limiting inspiration or expiration to a certain time. Cannot trigger or cycle next breath until the time has passed
What is pressured limited?
Pressure is increased to a preset level at the beginning of inspiration and is held at the airway until the breath ends by either time for flow
Why do you have the highest flow at the beginning of inspiration?
That is when the pressure gradient is the largest
When is the breath cycled or ended?
When the machine pressure equals the pressure in the lungs (flow is 0)
What are you guaranteeing with a pressure limit?
Guaranteeing a certain pressure will be applied over the breath while volume and flow vary
What does the patient control while the machine maintains pressure?
Speed and tidal volume
What is rise time (pramp)?
When you set how long you want to take to reach the set pressure level
People who breathe super fast have what?
Low tidal volumes and super turbulent flow (i.e. status asthmaticus)
What is flow limited?
When the flow reaches a constant value before the end of inspiration
Pressure limiting vs pressure cycling
Pressure cycled: in order to prevent excessive pressure from going to the patient, the inspiration is ended
Pressure limited: limiting the amount of pressure that can be delivered to a patient but does not end the breath, just limits the pressure that can be applied from the ventilator
