Basics Flashcards
Exhalation on a ventilator is?
Passive. Affected by lung and tubing resistance
CMV is?
Controlled mandatory ventilation - fixed volume at a fixed rate
The IE ratio is normally?
1:2
A higher IE ratio is useful in?
COPD, asthma
A lower IE ratio is useful in?
Collapse
The two variables of inspiratory time are?
Inspiratory flow and inspiratory pause
CMV advantages?
Precise control of CO2. Simple
CMV disadvantages?
Very uncomfortable, increasing resistance = increasing pressure until limit reached and cycles to expiration
High tidal volumes cause?
Volu-trauma, or stretch related injury
Limiting volumes to what mL/kg improves outcomes
7mL/kg or less
CO2 in head injury should be?
Kept at the upper limit of normal
Higher FiO2 can cause?
Nitrogen washout causing alveolar collapse, vasospasm, apoptosis, worsened patient outcomes
PEEP minimises… ?
Derecruitment, Work of breathing
PEEP side effects?
Reduced venous drainage from brain, pulmonary hyperventilation and increased shunting
PCV is?
Pressure controlled ventilation
Volume of breath in PCV is determined by?
Pressure, time pressure is applied over, and the circuit
The inflow pattern in PCV can be adjusted by changing the?
Ramp time
Advantages of PCV are?
Limits pressure applied to lungs, better distribution of flow to slow filling lung units
Disadvantages of PCV are?
Less strict control of CO2, can lead to underventilation
2 methods ventilators use to detect patient effort?
flow or pressure trigger
Pressure trigger works by?
Detecting a drop in circuit pressure as the patient attempts to inhale, and opening the demand valve
Flow trigger works because modern ventilators have?
Bias flow
Flow trigger is detected by a reduction in flow to the?
Expiratory flow sensor
Benefits of flow over pressure triggering?
Less effort to reach threshold, also a delay exists between effort and breath in pressure trigger
Sensitivity of triggering needs to be goldilocks because?
Either does not recognise attempts to breathe or other stimuli can cause a breath ‘autocycling’
What can cause autocyclings?
Condensate in the ventilator tubing, cardiac oscillations, patient movements
ACV is?
Assist control ventilation - patient effort will result in a breath identical to the mandatory breath
Limitations of ACV?
Increased respiratory rate from patient effort, tidal volume cannot be regulated by the patient, high proportion of time spent in inspiration - breath stacking and raised intrathoracic pressures
In ACV, respiratory muscles are active…?
Through most/all of the duration of the breath, not just the start
SIMV is?
Synchronised intermittent mandatory ventilation
The point of SIMV is?
To set a mandatory backup breathing strategy, allowing the patient to otherwise regulate breathing
In SIMV the mandatory breaths are?
Timed to coincide with patient effort
SIMV works by?
A set assist window/synchronised period which waits to see if the patient will attempt a breath, then delivers a set breath
Patient triggered breaths can be identified by?
A dip immediately prior to a delivered breath on a flow curve
Additional breaths in SIMV are?
Pressure supported breaths, not mandatory breaths
Advantages of SIMV?
Background strategy for safety
Synchronised
Additional breaths are supported
Patient can partly control volumes
As a weaning tool, SIMV is?
Inferior to other methods
Pressure support breaths are different from PCV because?
The length and tidal volume is influenced by patient effort
Higher volumes occur with higher patient effort in pressure support because?
Negative intrapleural pressures
Exhalation in pressure support is triggered by?
A fall in flow (
Pressure setting in pressure support can be adjusted to?
Allow comfortable amount of effort to achieve a certain tidal volume
If patient effort is too low in pressure support it will manifest as?
Tachypnoea and distress
When is pressure support set to zero
Never, because of resistance of circuit
Automated tube compensation is?
The exact pressure to match the resistance of a circuit
Apnoea mode is?
In pressure support ventilation, as a safety feature
Causes of a high pressure alarm are?
Biting, kinking, sputum, migration of tube, bronchoconstriction, ptx/htx, patient effort, intra-abdominal compartment syndrome
High pressure caused by the patient can be detected by?
Bag valve masking the patient
Causes of falling compliance?
Pneumonia, ptx, ARDS, APO, effusions, burns
Low pressure alarms are used to?
Detect air leaks
Low volume alarms are useful in?
Smaller volume leaks, such as around an underinflated cuff or an access port in the system
High volume alarms usually occur when?
Compliance rises, RR increases or pressure support is too high. Can be from hypoxia, acidosis, anxiety, pain, fever or PE
