Ventilators Flashcards
Minute Ventilation
Respiratory rate x Tidal volume
Normal range: 5-6 L/min
I:E
- Inspiratory: Expiratory Ratio
- How much of each ventilation cycle is devoted to inspiration & expiration
- Normal range: 1:2 or 1:3 in COPD patients
PIP or PAP
Peak Inspiratory Pressure or Peak Airway Pressure
- Measured by the ventilator in the major airways
- Strongly reflects the airway resistance
Ventilator Functions
- Ventilate patient
- Oxygenate patient
Plateau Pressure
Positive pressure supplied the small airways and alveoli
What pressure should we aim to keep plateau pressure under and why?
Goal is to keep plateau pressure under 30cmH20, because excessive alveoli stretch is thought to be the cause of ventilator induced lung injury
Peak Flow
- Determines the rate if tidal volumes delivery to the patient during mandatory volume control breaths.
- It affects the I:E and peak pressure
What are the ventilator modes?
- Volume Control Ventilation (VCV)
- Pressure Control Ventilation (PCV)
- Pressure Support Ventilation (PSV)
- Synchronized Intermittent Mandatory Ventilation (SIMV)
Volume Control Ventilation (VCV)
Tidal volume is preset and resultant airway pressure is a function of lung compliance and other factors
Independent variable(s) of Volume Control Ventilation (things you can set)
Tidal Volume, Respiratory rate , I:E ratio, FiO2, and PEEP (optional)
Dependent Variable(s) of Volume Control Ventilation
Peak inspiratory pressure, Plateau pressure
Pressure Control Ventilation (PCV)
Peak airway pressure is preset and the delivered tidal volume is a product of lung compliance and other factors
Advantage(s) of volume control ventilation
- Guaranteed minute ventilation
- May help lung compliance in certain surgeries (abdominal or chest surgeries)
Disadvantage(s) of volume control ventilation
- Patient does not trigger breath but can see patient effort in capnogram
- May need to reduce tidal volumes if you get high PIP/PAP
Independent variable(s) of pressure control ventilation
Inspiratory Pressure, Respiratory Rate, I:E Ratio, FiO2, PEEP (optional)
Dependent Variable(s) of Pressure Control Ventilation
Tidal volume
Advantage(s) of pressure control ventilation
- reduced ventilator induced lung injury
- improved gas distribution because it uses decelerating flow
- more rapid improvement in lung compliance and oxygenation compared to VCV
Disadvantage(s) of pressure control ventilation
-Does not guarantee minute ventilation
PIP vs Plateau Pressure in VCV
- PIP is determined from tidal volume set
- Plateau pressure is determined by applying an inspiratory hold (0.5 -1 sec). Hold represents no flow, which gives the pressure the alveoli are seeing
PIP vs Plateau pressure in PCV
- PIP is usually the same as plateau pressure because of how breath is delivered
- There is an inherent inspiratory pause
Pressure Support Ventilation (PSV)
Spontaneous ventilation mode that provides constant pressure once patient inspiratory effort is detected
Independent variable(s) of Pressure Support Ventilation
-Support pressure, Inspiratory time, flow trigger, FiO2, PEEP (optional)
Dependent Variable(s) of Pressure Support Ventilation
Tidal volume, respiratory rate
Advantage(s) of Pressure support ventilation
- Able to have patient breathe spontaneously and not fight the ventilator
- Able to augment tidal volume
- Able to adjust ETCO2 with support pressure
Disadvantage(s) of Pressure support ventilation
-requires patient to breathing spontaneously
Synchronized Intermittent Mandatory Ventilation (SIMV)
- Breaths are given at preset time intervals
- Patient can breathe spontaneously between the ventilator breaths
- ventilator will not give a breath if the patient inspires at that same instant
Independent Variable(s) of SIMV
Tidal volume, respiratory rate, I:E ratio, FiO2, Pressure support Level, PEEP (optional)
Dependent Variable(s) of SIMV
Peak inspiratory pressure, plateau pressure
Advantage(s) of SIMV
- Can be used as a way to start building up CO2
- Back-up mode for PSV
Disadvantage(s) of SIMV
-May confuse the patient’s brain because it is not physiological
If I:E ratio is 1:2 (normal) and RR is 10 breaths/min, how long are the inspiratory and expiratory times?
60 seconds/RR = 6seconds/breath
Inspiratory time = I/I+E (6) or 1/3(6)
I = 2 seconds E = 6 - I = 4 seconds
Inspiratory Pause (Tip)
- holds breath at end of inspiration (before exhalation starts)
- Allows breathe to diffuse better
- Only available with VCV
- Usually 25% of inspiratory time
- Takes time from inspiration & adds it as a hold (expiration remains the same)
if the I:E ratio is 1:2 and the RR is 10 breaths/min and the inspiratory pause is set at 25%, how much time is spent in inspiration, inspiratory pause, and expiration?
I = 1.5 sec Tip = 0.5 sec E = 4 secs
PEEP
- constant positive pressure applied at the end of exhalation
- causes airway pressure to not return to 0cmH20
Auto PEEP
- air trapping in the lungs because of insufficient exhalation time
- not a setting
What are the signs of Auto PEEP?
- Non-zero end expiration pressure
- Increasing PIP/PAP
Ventilator settings for tidal volume
500 -700 ml (adults)
6-10 ml/kg (infants, children, and COPD patients)
Ventilator settings for Respiratory Rate
10 breaths/min (initial setting)
Ventilator settings for Minute Ventilation (Ve)
- VT x RR
- 4 x BSA (Men)
- 3.5 x BSA (Women)
