What is the equation of motion?
Describes the relationships among pressure, volume and flow during spontaneous or mechanical breaths
Ptr = PE+PR
Ptr (transprespiratory pressure), PE (Elastic recoil pressure), PR (Flow resistance pressure)
rearranges into:
Pmus + Pvent = Palv + Pta
Pmus
What are control variables?
The primary variable that the ventilator adjusts to achieve inspiration
can be pressure, volume, flow, time
Describe pressure-controlled breathing
when the ventilator maintains the pressure waveform in a specific pattern
pressure waveform is unaffected by changes in lung characteristic
volume and flow waveforms wll vary with changes in compliance or resistance
Describe volume-controlled breathing
When a ventilator maintains the volume waveform in a specific pattern
volume and flow waveforms remain unchanged
pressure waveforms varies
What are 2 other forms of control?
Flow-controlled (ventilator controls flow - flow and volume remain unchanged, pressure varies)
*
Note flow = volume change/time or volume = flow x time
*
Time-controlled (both pressure and volume waveforms are affected by changes in lung characteristics)
List the 4 phases of a breath
1. Change from expiration to inspiration
2. Inspiration
3. Change from inspiration to expiration
4. Expiration
What is a trigger variable?
The mechanism that the ventilator uses to end exhalation and begin inspiration
Preset time (time triggering)
Patient triggering (pressure, flow, volume)
Freebee look at answer
Ptotal = P-elastic + P-resistive
P-elastic = Volume/Compliance
P-resistive = resistance x flow
How does a patient trigger a breath?
Pressure triggering - the machine senses changes in pressure and triggers the breath
If too sensitive, can autotrigger
Flow triggering - when ventilator detects a drop in flow through the patient circuit during exhalation
If set properly --> less work of
What is a limit variable?
The maximum value a variable (pressure, volume, flow or time) can attain
Limits the variable during inspiration but does not end the inspiratory phase
Explain the difference between pressure-, volume- and flow-limited
Pressure limiting allows pressure to rise to a certain value but does not exceed it
Volume limiting - volume is limited to a specific volume
Flow-limiting - gas flow from the ventilator to the patient reaches but does not exceed a maximum value before the
How is pressure limiting different than pressure cycling?
Pressure cycling is where the ventilator reaches a maximum pressure limit control (used to protect from excessive pressure) and causes the inspiratory phase to end
usually set 10 cm H2O above average PIP
Termination of breaths - describe all 4 types of cycling
Volume-cycled - inspiratory phase of a volume-cycled breath is terminated when the preset volume has been delivered
Time-cycled - inspiratory phase ends when a predetermined time has elapsed (? in airway resistance or compliance do not affect flow pattern
What is an inspiratory pause and what does in measure?
A pause at the end of inspiration
It measures the plateau pressure and this can be used to calculate static compliance
The expiratory phase...
encompasses the period between inspirations
baseline pressure --> atmospheric (zero) or positive (PEEP)
Time-limited expiration--> mode of ventilation that limits the expiratory time
What is NEEP?
Negative end expiratory pressure
What is an expiratory hold (end-expiratory pause)? and what can it tell you?
Pause at the end of exhalation
Measure pressure associated with air trapped in the lungs at the end of expiration
Auto-PEEP is present if flow does not return to zero when a new mandatory ventilator breath begins
What is CPAP?
Continuous positive airway pressure
What is a baseline variable?
The parameter controlled during exhalation
How are mandatory and spontaneous breaths different?
Mandatory breaths are time triggered or tidal volume cycled
Spontaneous breaths are breaths that are started by the patient and tidal volume delivery is determined by the patient (patient cycled)