Ventilator functions
Ventilate patient
Volume Control Ventilation (VCV)
Pressure Control Ventilation (PCV)
Pressure Support Ventilation (PSV)
Synchronized Intermittent Mandatory Ventilation (SIMV)
Oxygenate patient
FIO2
Positive End-Expiratory Pressure (PEEP)
Define: Minute Ventilation
Respiratory Rate x Tidal Volume
Normal range 5-6 L/min
Inspiratory:Expiratory (I:E) Ratio
Normal range 1:2 or 1:3 in COPD patient
Peak Inspiratory Pressure (PIP)/ Peak Airway Pressure (PAP)
The pressure measured by the ventilator in the major airways
Strongly reflects airway resistance
Plateau Pressure
Positive pressure applied to small airways & alveoli
Goal is to keep under 30 cmH2O because excessive alveoli stretch is thought to be a cause of ventilator-induced lung injury
Peak Flow
Determines rate of tidal volume delivery to the patient during mandatory volume control breaths
Affects I:E ratio & peak pressure
Inspiratory Pause (TIP)
- Holds breath at end of inspiration (before exhalation starts)
- Allows breath to diffuse better
- Only available with VCV
- Usually 25% of inspiratory time
- Takes time from inspiration & adds it as a hold (expiration remains same)
Auto-PEEP
- Air trapping in the lungs because of insufficient exhalation time
- Signs
- Non-zero end expiratory pressure
- Increasing PIP/PAP
Positive End Expiratory Pressure (PEEP)
- Constant positive pressure applied at end of exhalation
- Causes airway pressure to not return to 0 cmH2O
Volume Control Ventilation (VCV)
- Set TV, RR, & I:E
- Good initial settings are TV 10 mL/kg, RR = 10, I:E = 1:2 (adjust to get ETCO2 30-35)
- Peak airway pressure (PAP) is variable with each breath
- Waveform - Sloped, Ventilator will provide flow gradually until TV is achieved
- Advantages - guaranteed minute ventilation
- Disadvantages - pt doesn’t trigger breath, may need to reduce tidal volume if get high PIP/PAP
Pressure Control Ventilation (PCV)
- Set peak airway pressure (which equals plateau pressure,) RR, & I:E
- Good initial settings are P = 15 cmH20, RR = 10, I:E = 1:2 (adjust to get ETCO2 30-35)
- TV is variable with each breath (increase P will increase TV)
- Advantages:
- Limiting the peak inflating pressure delivered by the ventilator will limit the transalveolar pressure produced, thereby reducing ventilator-induced lung injury.
- The decelerating flow used to produce PCV is thought to improve the distribution of gas flow.
- When compared with volume control ventilation, there is a more rapid improvement in lung compliance and oxygenation
- Disadvantages:
- pressure control does not guarantee minute ventilation, and therefore requires more monitoring by the operator
PIP vs Plateau Pressure
- Volume Controlled Ventilation
- 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 pressure the alveoli are seeing
- Pressure Controlled Ventilation
- PIP usually same as Plateau Pressure because of how breath is delivered
- There is an inherent inspiratory pause
Pressure Support Ventilation (PSV)
- method of assisting spontaneous breathing in a ventilated patient. It can be used as a partial or full support mode
- Independent Variables: support pressure, inspiratory time, flow trigger, FIO2, Peep
- Dependent Variables: Tidal Volume, Respiratory rate
- Advantages: pt breathing spontaneously, can augment TV
- Disadvantages: requires pt to breath spontaneously
Synchonized Intermettent Mandatory Ventilation (SIMV)
- Breaths are given at preset time intervals
- Patient can breathe spontanously between the ventilator breaths
- Ventilator will not give a breath if the patient inspires at that same instant
- This is VCV sychronized patient breathing
- Independent Variables - TV, RR, I:E, FIO2, Pressure support level, PEEP (optional)
- Dependent variables (vary per breath) - PIP, Plateau pressure
- Can be used as a way to start building up CO2
- Disadvantages - may confuse pt becuase not physiological to breathe spontaneously and receive postitive ventilation breaths
Which ventilation mode utilizes a decelerating flow pattern?
PCV
You’re in PSV, patient is taking supported Vt of 1000 mL/breath with pressure support level of 15 cmH20, and you want a Vt of 500. What do you adjust on the ventilator?
A. Decrease RR
B. Decrease pressure support level
C. Decrease tidal volume
D. Increase the peak flow
E. Increase APL valve to 10 cmH2O of resistance
B. Decrease pressure support level
- control Vt by the pressure support. Turn off to see what pt is doing on their own
Which of the following is the best mode of ventilation in order to control the pressure being exerted on the alveoli, but at the same time maximize the amount of tidal volume being delivered in a patient with poorly compliant lungs?
A. PCV
B. PSV
C. VCV
D. SIMV
A. PCV
What is meant by a stacked breath?
A. Rapid positive pressure breaths from venitlator with no patient effort
B. Positive pressure breaths that progressively increase in volume
C. Synchronized breath delivered after a patient inspiratory effort
D. Timing of ventilator breath to coincide with patient inspiratory effort
E. Unsynchonized ventilator breath delivered immediately after full patient inspiration
E. Unsynchonized ventilator breath delivered immediately after full patient inspiration
- this is an advantage of SIMV because it prevents stacked breaths
Changing only the I:E ratio from 1:1 to 1:4 will affect ventilation by:
A. increaseing the inspiratory pause
B. Increasing the plateau pressure
C. Increaseing the tidal volume
D. Increasing the inspiratory flow rate
E. Increasing the respiratory rate
D. Increasing the inspiratory flow rate
- to maintain same Vt
