Mechanical Ventilation Flashcards
minute ventilation
RR x Vt = VE (RR x tidal volume - min vent)
Normal range: 4-8 L/min
Average ~ 5 L/min
pets 1-12 yo: 4-8 L/minn
infants 0-1 yo: 0.2-0.3 L/min/kg
Cardiac output range also 4-8 L/min
tidal volume (Vt)
6-8 mL/kg (start with 6)
normal volume of air inspired during each normal respiratory cycle
Should be enough to overcome dead space and supply alveoli with oxygen
Calculated based on ideal body weight
Tidal volumes for artificial ventilation
Normal: 6-8 mL/kg
Lung protective: 4-6 mL/kg
Recommendation: start with 6mL/kg
Respiratory rate for ventilation
Injury approach:
Use minute ventilation calculation to determine RR (100mL/kg/min).
ie: 100mL x 70kg = 7000mL = 7L
(minute ventilation requirement = 7L)
Vt - 70kg x 6mL/kg = 420mL
RR - 7000mL / 420mL = 16.6
(start lung injury pts at 16 RR)
Obstructive approach (asthma/copd)
Start with RR of 10-12 breaths/minn
Respiratory Frequency
The sum of RR set by ventilator PLUS any patient triggered breaths.
Assist control will give a full breath
SIMV allows pt to trigger breath of whatever size they’re able to do
NOT respiratory rate
anatomical deadspace
amount of gas delivered to pt that does NOT reach alveoli for gas exchange.
1mL x 1 pound ideal body weight
ie: 70kg = 150 lb = 150mL anatomical deadspace (Per breath)
tidal volume (420mL) minus deadspace (150) = 270mL
150mL per breath x16 breaths/min = 2.4L per min lost to dead space.
Alveolar minute ventilation
Minute ventilation minus deadspace
Mechanical deadspace
Loss of volume within the vent circuit
ie expansion of tubing due to pressure.
Adults: 2mL x PIP
ie 2mL x PIP 20 = 40mL
peds: 1mL x PIP
ie 1mL x PIP 20 = 20mL (significant percentage of total)
Pressure breaths: account for deadspace because ventilator delivers breath based on pressure, not volume.
Additional hardware like EtCO2 causes more volume loss (EtCO2 ~50ml/min)
Exhaled tidal volume (Vte)
Vte is an accurate measurement of the volume of air received by the patient if no leak is present.
Provides confirmation of volume delivered, while accounting for deadspace.
Will vary by breath based on lung compliance.
Inspiratory / expiratory phases (I:E ratio)
Expiration is longer and takes more energy.
I:E ratio - ratio between inspiratory and expiratory phases.
Adult starting point - 1:2
Ped starting point: 1:3
Asthma respiratory failure: 1:4
Example:
10 breaths /min = 6 second breath cycle.
I:E of 1:2 = 2 sec for insp, 4 sec for expir.
Peak Inspiratory Pressure (PIP)
Measurement of pressure at upper airway, ETT, vent circuit, bronchial tree.
Maintain PIP at 35 cmH2O or less, generally
Asthma/COPD pts may need higher PIP
Causes of increased PIP:
Patient cough, secretion, needing suction, sedation status, small ETT, kinked ETT, kinked vent circuit.
Plateau Pressure
Measurement of pressure when inspiratory flow is zero.
Indicator of alveolar pressure.
Only applicable in a volume breath.
1/2 second inspiratory hold
Maintain plateau pressure less than 30
Sudden spike in Pplat signifies decreased lung compliance and potentially serious lung injury, often caused by pulmonary edema, pneumo, airway obstruction.
High plateau pressure
if greater than 30 cmHg, now what?
Lower Vt (ie from 6 mL/kg to 5 mL/kg)
Continue to reduce if necessary to a minimum of 4mL/kg
Causes of increased plateau pressure
Increased Vt
Decreased pulmonary compliance
Pulmonary edema
Pleural effusion
Peritoneal gas insufflation
tension pneumo
trendelenburg
ascites
Endotracheal intubation
abdominal packing.
Driving pressure
Distending pressure above the applied PEEP required to generate tidal volume.
Keep at 15 or less for ARDS pts
What to monitor in volume controlled ventilation?
PIP, Pplat, and static compliance.
Sudden increase in PIP w/normal Pplat
Pt coughing against ventilator circuit
When using a pressure-control mode, what can you expect?
Ventilator triggers until a pre-set pressure limit is reached.
FIO2
fraction of inspired oxygen
Can be delivered from 21% (atmospheric) up to 100%
Goal is to maintain SpO2 > 93%
USe lowest FIO2 possible for SpO2 >93%
PEEP
Positive End-Expiratory Pressure: used to maintain alveolar recruitment
Improves oxygenation by reducing V/Q mismatch
Fastest way to improve oxygenation
Starting point: 5 cmH2O (physiologic)
PEEP increases intrathoracic pressure
When switching ventilators, clamp ETT at peak of inspiration to maintain PEEP during switch.
Volume vs pressure
Volume breath: similar to BVM
Defined inspiratory volume
Calculations based on ideal body weight
Starting volume 6-8 mL/kg
Lung protection: 4-6 mL/kg
Monitor effectiveness of volume breath with PIP (<35 cmH20 and Pplat <30cmH20).
Guaranteed minute ventilation is the same
Pressure breath:
Considered lung-protective
Compliance-based
Set inspiratory pressure
Adults: 20 cmH2)
Peds: 10 cmH2)
Monitor effectiveness with exhaled tidal volume Vte
In pressure ventilation, monitor volumes
In volume ventilation, monitor pressures
Assist control
AKA continuous mandatory ventilation (CMV)
Vent delivers a breath whether pt triggers it or not.
If pt triggers ventilator, volume is the same every time (preset by clinician)
As soon as ventilator detects negative pressure from pt triggering breath, ventilator delivers a pre-set volume.
Allows clinician not maintain control
Delivers present tidal volume and respiratory rate.
Guarantees minute ventilation Vte
Does not allow for patient respiratory drive
Pts are not allowed to take their own breath
Every time pt initiates a breath, the ventilator will deliver a full tidal volume.
Probably best for hospital setting.
SIMV
Synchronized intermittent mandatory ventilation
Ventilator delivers pre-set breaths in coordination with the respiratory effort of the patient. Spontaneous breathing is allowed between breaths.
Vent delivers a breath when triggered by pt or by time.
When pt triggers a breath, vent delivers a pressure-supported breath.
Initially designed to help wean pts from mechanical ventilation therapy
delivers a preset tidal volume and respiratory rate.
Pt is allowed to trigger spontaneous breath between mandatory breaths.
Decreased chance of hyperventilation.
Possibly best for transport environment.
Spontaneous breaths should not be allowed to exceed 75% of the set Vt.
Pressure support
A mode of mechanical ventilation in which the pt triggers every breath.
Only applies:
…while using SIMV
…During spontaneous pt breaths
Reduces deadspace
Increases pts ability to take spontaneous breath
Reduces pt breathing effort.
Only applied when pt takes own breath
Mechanical ventilation variables
Volume
Pressure
Rate
Flow
O2
Patient in charge
Ventilator in charge
Pressure Trigger
Default adult setting of -2 or -3 cmH2O
peds: -1 cmH2O
Pt must exert negative pressure (inhale) I excess of trigger setting for vent to deliver prescribed volume.
Bias flow is the basis for flow triggering.
Flow sensor detects absence of flow to trigger a full breath.
Minimum pressure (trigger activation) is based on PEEP.
PRVC (pressure regulated volume control)
AKA volume adaptive
…Pressure breath driven by compliance.
Learning/adaptive mode
Test breath - measures exhaled tidal volume.
Then adjusts inspiratory pressure.
Takes time for ventilator to learn ideal settings (can be a problem in a transport environment).
Ppeak (PIP)
Airway resistance
Alveolar compliance
Should be < 35
Pts with more airway resistance will have higher PIPs
Elevated PIP is necessary in pts with high resistance in order to maintain ventilation.
Airway resistance
PIP-Pplat / flow (L Per sec)
Common flow rates:
40 L/min = 0.67 LPS
50 L/min = 0.83 LPS
60 L/min = 1.0 LPS
ie 45-20/0.83 LPS = 30 cmH2O
Dynamic Compliance
Compliance assessed with changing lung volumes during airflow.
airway resistance and alveolar compliance
Vt / (PIP-PEEP)
ie 400mL / (15-5) = dynamic compliance 40
Normal dynamic compliance ~ 40-100
Static compliance
Compliance evaluated without airflow or volume changes
50-100 ml/cmH2O
lower than 40 = poor compliance
Alveolar compliance = Plateau pressure
Vt / (Pplat - PEEP)
ie 400 / (25-5) = static compliance 20
PIP (Ppeak)
The highest pressure reached during inspiration, reflecting the effort required to inflate the lungs.
<35 generally
<30 for lung injury patients
Inspiratory Resistance (Rinsp)
<8 generally
Higher in pts with obstruction (asthma/copd)
Expiratory time constant (RCexp)
Indication of length of time it takes lung units to fill or empty
Goal is 95% of volume exhaled.
4 time constant levels:
1 x RCexp = 63%
2 x RCexp = 86.5%
3 x RCexp = 95%
4 x RCexp = 98%
Mean Airway Pressure (Pmean)
<25
Driving Pressure
Pplat - PEEP
The distending pressure above the applied PEEP required to generate tidal volume.
VLeak
<10
Bipap or CPAP
The lower the better.
Indicative of leak after the flow sensor.
Mask fit problem.
Inspiratory Tidal Volume (VTI)
Volume delivered to pt as measured by flow sensor.
If there is a leak on the pt side of the vent circuit, the displayed VTI may appear larger than the displayed VTE.
Airway Occlusion Pressure
Indication of respiratory drive / sedation status.
beaking
Too much volume
reduce volume
Rinsp
Resistance to inspiratory flow caused by the ETT and the pts airways during inspiration.
High Flow Nasal Cannula (HFNC)
High O2 delivery
High flow delivery
Humidified air at 37 degrees C
Reduces deadspace
Reduction in rebreathing CO2
Improved alveolar oxygenation and ventilation
Reduction in work of breathing
Improved lung compliance
Improved mucous clearance
Decreased airway resistance
Decreased airway inflammation
When to consider HFNC tx
Delivered flow exceeds pts inspiratory demand.
Guaranteed 100% delivery FiO2
Meets pts flow and oxygen demands
O2 Therapy delivery options
Low O2 therapy (NC, NRB, simple mask)
High Flow O2 therapy
CPAP
NiPPV - BiPAP
Mechanical Ventilation
HFNC vs other forms of O2 therapy
Improves lung compliance and resistance by mechanism of an oxygen flow rate that meeds or exceeds the patients inspiratory flow rate.
This high flow also reduces dilution of gas (by room air) delivered through nasal cannula.
HFNC energy reduction
humidifying and raising temp of inspired gases = reduced energy expenditure.
37C / 100% relative humidity (perfect)
Sizing HFNC
Available in sizes 1-4
Should not occlude more than 50% of nare opening.
HFNC settings
Flow: 20-35 L/min, increase by 5-10L/min
FiO2:
based on duration of transport
Start at 50-60% for bronchiolitis (RSV)/respiratory distress.
Target >93% SpO2
37C, 100% humidity.
<1 month <4kg. 5-8L/min
1-12 mo. 4-10kg. 8-20L/min
1-6 yrs. 1-20kg. 12-25L/min
6-12 yrs. 10-20kg 20-30L/min
12-18 yrs. >40kg. 25-50L/min
ROX index
Used to evaluate O2 therapy effectiveness
(SpO2/FiO2) / respiratory rate
At 2, 6,12 hrs, if ROX > 4.88, tx is successful.
At 2 hrs, if ROX < 2.85 consider intubation
At 6 hrs, if ROX <3.47 consider intubation
At 12 hrs, if ROX <3.85 consider intubation
Faster RR causes ROX score to drop
HFNC sizing
1-4 (4 is largest)
Size 1 has greatest flow of 30 L/min
Sizes 2-4 max flow 50 L/min
Sizing = <50% of the nare
Non invasive ventilation (NIV/NIV-ST)
BiPAP vs CPAP
BiPAP adds iPAP
NIV-ST = non invasive spontaneous time
iPAP
…based on pressure support
…ability to deliver minute ventilation
EPAP
…PEEP
…oxygenation
…pt must be able to exhale over pressure
Calculation of Oxygen Duration
[Current PSI - 200 (buffer) x FACTOR] / flow
Each size tank has its own factor.
M tank is 1.6.
ie: [(1800psi - 200) x 1.56] / L/min flow
This will give an estimate of how long you can run your oxygen at a given flow rate
Indications for NIV
COPD
Asthma
CHF - Pulmonary edema
PNA
Covid-19
Undifferentiated hypoxia
Additive ventilators
The sum of IPAP and EPAP should equate to Peak Inspiratory Pressure (PIP).
Additive ventilator example:
if IPIP is 12 and EPAP is 5, on the additive ventilator, Pressure support should be set to 7 and PEEP to 5.
PEEPs
Positive end-expiratory pressure
A constant pressure applied at the end of exhalation, helping to keep alveoli open and improve oxygenation
IPAP
The pressure delivered during inhalation on a ventilator, typically higher than EPAP
EPAP
Expiratory positive airway pressure.
The pressure delivered during exhalation on a ventilator, often considered equivalent to PEEP.
NIV example
If IPAP 12 and EPAP 6
…IPAP = 18, EPAP = 6, so total IPAP is 18 (12 + 6).
Total IPAP >20 cmH2O can cause the gastric sphincter to open and release volume into the stomach; resulting in nausea and potential vomiting.
P-ramp
Controls the time it takes for ventilator to reach desired pressure.
0-200 ms
limited to 1/3 of TI time.
Adds comfort when set correctly.
If someone is air hungry, they’ll likely want a shorter p-ramp.
Expiratory time sensitivity
AKA Flow Termination
Determines at what percentage of peak inspiratory flow a spontaneous breath is terminated.
Range 5-80%. Vent default is 25%
Higher % = shorter inspiratory phase and longer expiratory phase.
NIV additional settings
Trigger (flow) 3-20 L/min
5 L/min is a great place to start
FiO2 - titrate to SO2 >94%
NIV-ST advantages
Sets a minimum respiratory rate (10-12)
Allows pt drive, but insures minimum rate
Differences:
NOT pressure support.
…Pinsp drives mandatory + spont breaths.
Rate and TI define breath timing.
P-ramp 0-200 ms (limited to 1/3 TI time)
Airway Pressure Release Ventilation (APRV)
Time-cycled, pressure-controlled ventilation
Offers 2 levels of positive pressure.
4 settings:
Time high: t-high
Time low: t-low
Pressure high: p-high
Pressure low: p-low
Allows for spontaneous breaths, which contributes to CO2 removal
Paralyzation is contraindicated.
Pts should be sedated, allowing for breathing effort.
Pressure low
Drops: short periods of time that are used as an indicator for CO2 removal.
More drops = less CO2
Can also be viewed as respiratory rate - # drops will be congruent with RR
Time low
Time for CO2 elimination.
intentional addition of auto-peep.
0.5 seconds
Based on maintenance of 50-75% peak expiratory flow.
T-high and P-high
increasing mean airway pressure.
…Improves recruitment
…improves atelectatic lung units
…increased functional residual capacity
APRV settings
T-high: start at 5.5 sec
T-low: start at 0.5 sec
…So Rcycle = 6 seconds = RR 10
Pressure High
can be set based on defined pplat (<30)
Carry-over pplat from previous mechanical ventilation strategy.
Based on PIP
Consider starting with P high of 20.
Time high
Inspiration phase
4-6 seconds
APRV key points
- T-high: optimizing mean airway pressure
…increased functional residual capacity.
…Recruitment of atelectatic airways - Drops: Bulk CO2 removal
- Intentional auto-peep.
- Spontaneous patient breaths.
…good sedation but no paralysis.
APRV supporting evidence
Ppeak lower - reduces driving pressure
Pmean higher - increases mean airway pressure.
P/F ratio improvement - w/early APRV
Hemodynamics: Increased MAP, decreased cardiac output
Barotrauma - no evidence suggesting barotrauma as a result of APRV
ICU length of stay - decreased (if APRV early)
Hospital LOS - no change.
28 day mortality - one trial showed 30% decrease.
Pinsp
Inspiratory pressure, which controls the amount of pressure applied to a patient’s lungs during inhalation.
Increasing Pinsp will lower EtCO2
Decreasing Pinsp will increase EtCO2
