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
