Ventilators Flashcards
Respiratory rate
8-12 bpm
Vt
5-7mL/kg of IDEAL body weight
MV
- Vt x RR
Flow rate
5 x MV
I:E ratio
Normally 1:2
-increase expiratory time for patients with increased compliance (COPD)
Inspiratory Time
(Vt / Inspiratory flow) x 60
Expiratory Time
60 seconds / RR = time for one breath cycle.
Time for breath cycle - inspiratory time = expiratory time
What is pressure variable
- pressure is impedance to flow.
- this occurs in the breathing circuit or patients airway (trachea, bronchi, bronchioles, alveoli, ETT)
- back pressure from the impedance is from resistance and compliance from chest wall and lungs
- expresses in cmH2O or mmHg or kPa
What do we want the ETCO2 at?
30-33 mmHg
If your ETCO2 is too high, how do you adjust ventilator?
- increase MV by increasing Vt or RR
* * increase Vt first to recruit alveoli
Volume control ventilation
- delivers a set Vt to the patient
- anesthesia provider sets MV or Vt and RR
- time initiated
- volume limited
- loses 4-5cm H2O to circuit compliance
- patient paralyzed
- high PIP can limit inspiratory time and Vt delivery
What is the flow rate like in volume control
- the flow rate is constant
- too low of flows will result in partial Vt delivery
- too high of flows will results in inspiratory pause
What are two disadvantages of volume control?
- high PIP
- ventilator dyssynchrony
Pressure control ventilation
- delivers set pressure to patient
- anesthesia providers sets a max inspiratory pressure above PEEP
- ventilator increases the pressure to set level at start of inspiration time and maintains this pressure until exhalation begins
- patient paralyzed*
What is the flow rate like in pressure control?
-flow rate is highest at the beginning of inspiration and then decreases
What is tidal volume like in this mode?
- varies with resistance and compliance and vent dyssynchrony.
- If resistance increases Vt decreases
- if compliance decreases Vt decreases
- *important that a respirometer be used
Respirometer
- senses tidal volume in the expiratory limb of ventilator
- converts gas flow into electrical pulses
- exhaled Vt expected to measure: Vt set on vent + FGF - Vt lost in vent
- alarm will ring if apnea is present
What does increasing PEEP do in PCV
-increasing PEEP decreases Vt
When do we use PCV
- whenever we want to avoid high airway pressures
- often with LMA
- this reduces ventilator-induced lung injury
- obese patients, lung injury, single lung ventilation, ETT cuff leak
IMV (intermittent mandatory volume)
- ventilator delivers preset Vt at preset rate, permitting spontaneous unassisted breaths
- delivers through separate parallel circuit
- used for weaning
- not synchronized with patient
SIMV (synchronized intermittent mechanical ventilation)
- mix of mandatory breaths and assisted breaths;
- synchronizes mandatory breaths with beginning of spontaneous breath
- contains trigger window on monitor
- if patient does not trigger, a mechanical breath is delivered
- if patient triggers, patient determines Vt delivered
- mandatory Vt and RR is needed
- I:E ratio not required
- not every spontaneous breath is assisted
AC (Assist Control)
-mix of mandatory and assisted breaths
-once triggered every breath is treated the same: given a preset Vt or pressure delivery
Trigger = time, pressure, volume
Control = volume or pressure
Cycling = time
-guarantees MV and requires little respiratory effort
-can have breath stacking and does not protect against hyperventilation
PSV (pressure support ventilation)
- applies positive pressure to airway
- patient’s inspiratory effort generates negative pressure or flow in the inspiratory limb of the ventilator
- delivers small pressure support
- results in larger Vt than the patient would take on his/her own
- for maintenance or emergence of patients who are SV
- patient can become apneic
High Frequency (Jet) Ventilation
- very low Vt with very high rates
- usually seen when shocking kidney stones (ESWL)
- I:E usually 1:3
- 100-200 breaths per minute
- driving pressure 15-30psi