10 Maxims Fro Modes of Mechanical Ventilation Flashcards
A breath is a cycle of what
A breath is one cycleof positive flow (inspiration) and negative flow (expiration) defined in terms of the flow-time curve
Inspiratory Time Definition
Inspiratory time is defined as the period from the start of positive flow to the start of negative flow
Expiratory Time Definition
Expiratory time is defined as the period from the start of expiratory flow to the start of inspiratory flow
When is a breath considered to be assisted
An assisted breath is one for which the ventilator does some or all of the work of breathing
For constant flow inflation, work is defined as inspiratory pressure multiplied by tidal volume
A ventilator will assist breathing using either
Pressure Control
Volume Control
This will be based on the equation of motion for the respirtory system
Equation of Motion for the Respiratory System
Pvent+ Pmus= Elastance x Volume + Resistance x Flow
Supposing that expiration occurs passively, as it does in the majority of cases, Pmusc and Pvent are absent and the equation of motion therefore becomes:
-Resistance x Flow = Elastance x Volume
The minus sign at the left of the equation indicates the negative direction of the expiratory flow and suggests that during passive expiration the flow is generated by the energy stored in the elastic component during inspiration.
Pressure Control in Regards to Equation of Motion
-Resistance x Flow = Elastance x Volume
Pressure control (PC) means that inspiratory pressure is present as either a constant value or it is proportional to the patient’s inspiratory effort
Volume and flow change will change with elastance and resistance
Volume Control in Regards to Equation of Motion
-Resistance x Flow = Elastance x Volume
Volume control (VC) means that both volume and flow are preset prior to inspiration. In other words, pressure changes with changes in elastance and resistance.
Breaths are classified according to
The trigger which is what starts inspiration
The cycle which is what ends inspiration
The Trigger and Cycle Varible Can Be Either
Patient Initiated or Machine Initiated
Machine Triggered Breath
Inspiration is started due to a signal from the Ventilator which is independant of the patient
Patient Triggered Breath
Inspiration is started due to a signal from the patient which is independant of the ventilator
Patient Cycled Breath
Patient cycling means ending inspiratory time based on signals representing the patient determined components of the equation of motion, (i.e, elastance or resistance and including effects due to inspiratory effort).
Flow Cycline
Form of pt cycling
When the rate of flow decreases to a pre set threshold which is determined through pt lug mechanics
Machine Cycling
Inspiration is ended due to factors determined by the ventilator
Based on the triggering and cycling event breaths are classified as
Sponatneous or Manadatory
Spontaneous Breaths
A spontaneous breath is a breath for which the patient both triggers and cycles the breath
A spontaneous breath may occur during a mandatory breath (e.g. Airway Pressure Release Ventilation)
A spontaneous breath may be assisted or unassisted.
Mandatory Breaths
A mandatory breath is a breath for which the machine triggers and/or cycles the breath
A mandatory breath can occur during a spontaneous breath (e.g., High Frequency Jet Ventilation)
A mandatory breath is, by definition, assisted.
Basic Breath Sequences
Continuous mandatory Ventilation (CMV)
Intermittent Mandatory Ventilation (IMV
Continuous Spontaneously Ventilation (CSV)
Continuous Mandatory Ventilation
Spontaneous breaths are not allowed between mandatory breaths
Intermittent Mandatory Ventilation
Spontaneous breaths may occur between mandatory breaths
Continuous Spontaneous Ventilation
All breaths are spontaneous
5 Basic Ventilatory Patterns
VC-CMV,
VC-IMV,
PC-CMV,
PC IMV,
PC-CSV
VC-CSV
The combination VC-CSV is not possible because volume control implies machine cycling and machine cycling makes every breath mandatory, not spontaneous.
TC-IMV
possible but rare
Within each Ventilatory Pattern there are several types that can be distinguished by their target schemes.
Set-Point
Dual
Bio-Variable
Servo
Adaptive
Optimal, Intelligent
Targeting Scheme
A targeting scheme is a description of how the ventilator achieves preset targets.
A target is a predetermined goal of ventilator output.
Within Breath Targets
include inspiratory flow or pressure and rise time
tidal volume
constant of proportionality between inspiratory pressure
patient effort
Set Point Targeting
Targeting scheme where the operator sets all the parameters or either volume or pressure
Dual Control Targeting Scheme
A targeting scheme that allows the ventilator to switch between volume control and pressure control during a single inspiration (mid breath)
Ex. VAPS
Bio-Variable Targeting Scheme
A targeting scheme that allows the ventilator to automatically set the inspiratory pressure or tidal volume randomly to mimic the variability observed during normal breathing
Will try to mimic variability in human breathing by varying Vt breath to breath
Servo Targeting Scheme
A targeting scheme for which inspiratory pressure is proportional to inspiratory effort
More effort leads to more support
Ex. Tube Compensation
Adaptive Targeting Scheme
A targeting scheme that allows the ventilator to automatically set one target (e.g. pressure within a breath) to achieve another target (e.g. average tidal volume over several breaths)
Ex. Volume support, PAV, NAVA
Optimal Targeting Scheme
A targeting scheme that automatically adjusts the targets of the ventilatory pattern to either minimize or maximize some overall performance characteristic (e.g. minimize the work rate done by the ventilatory pattern)
Tries to achieve optimal breathing based WOB curves
Ex. ASV
Intelligent Targeting Scheme
A targeting scheme that uses artificial intelligence programs such as fuzzy logic, rule based expert systems, and artificial neural networks.
Auto adjust settings based on monitored parameters such as etCO2 and SpO2
Smart Care, Intellivent
A Mode Of Ventilation is Classified Based on What
- Control Varible (pressure or volume) for the primary breath
- Breath Sequence (CMV, IMV, CSV)
- Primary Breath Targeting Scheme (for CMV or CSV)
- Secondary Breath Targeting Scheme (IMV)
The Primary Breath
The “primary breath” is either the only breath there is (mandatory for CMV and spontaneous for CSV) or it is the mandatory breath in IMV.
