Mechanical Ventilation Flashcards
VE = Minute Ventilation
Vt x RR = VE expressed in L/min
VE range is 4-8L/min (Infant and Adult)
Vt = Tidal Volume
Normal vol of air inspired during each normal quiet respiratory cycle.
Should be enough to overcome dead sapce.
*Starting Vt range is 6-8mL/kg
**Lung protectant 4-6mL/kg
Ideal Body Weight calculation
(2.3 x patient height in inches) + 50kg(male);45.5kg(female)
Obstructive vs Injury?
Obstruction- COPD and Asthma(Ventilation problem-lower RR/>I:E ratio)
Injury- everything else: Pneumonia, ARDS, CHF, trauma..
Alveolar minute ventilation
calculation: Vt x RR - 1mL x IBW in lbs(alveolar VE)
Alveolar VE range = 4-8L/min
Average adult Alveolar VE = 5L/min
Anatomincal deadspace
calculation: 1mL x ideal body weight in lbs OR 33% of Vt.
*average anatomincal dead space in adults is 150mL/breath
FIO2
Maintain the lowest FIO2 possible in order to maintain proper tissue oxygenation and prevent ROS or free radicals that cause cell damage.
*high FIO2 is important with trauma patients and pregnancy.
Absorptive atelectasis
FIO2 concentration that is too high can cause nitrogen washout and lead to alveolar collapse.
Vte(exhaled tidal volume
Most accurate measurement of the volume received by the patient.
Confirms actual volume received by the patient.
Can identify air trapping or a leak.
should be within =/- 50mL of the Vt
DOPE
Disconnection; dislodgement(circuit, ETT)
Obstructions; suction, kinks
Pneumothorax(tension); Pplat >30?
Equipment; troubleshoot vent settings
Mechanical Deadspace
The loss of volume during a VOLUME breath in the vent circuit based on expansion.
Adult circuit: 2mL x PIP
Ped circuit: 1mL x PIP
Trigger(sensitivity)
Flow trigger based ib bias flow(very sensitive)
Trigger setting is shown in L/min(10L/min)
*Pressure Triggers are less sensitive and more commonly used
I:E Ratio
Time spent in inspiration. Inspiration is always active so it requires less time than expiration.
*Respiratory cycle time is 3.75sec.
Add I and E then divide 3.75 by the sum. This gives you your I time.
Adults I:E= 1:2 Peds I:E = 1:3 with I-time of 0.3-0.7
*Obstructive lung 1:4 or greater. Asthma may benefit from 1:1
Expiratory Time Constant
Time it takes for the lungs to fill or empty(suggested time 0.3sec)
Calculation - Raw/flow x time constant = expiratory time needed
Resistance or Raw = PIP-Pplat
Flow is L/min simplified to L/sec
PIP
Peak Inspiratory Pressure
*Attempt to keep <35cmH2O in the majority of patients(COPD or Asthma patients may need higher PIP)
Plateau Pressure(Pplat)
Measures pressure when inspiratory flow is zero
Applied in VOLUME breath only
Inspiratory hold 0.5 sec
**Goal is <30cmH2O will always be <PIP(or the vent is broken)
Determines alveolar health
Can determine if a simple pneumo is progressing to tension pneumo.
Causes of a high PIP and high Pplat
PIP: Upper airway obstruction, suctioning, kinked ETT, kinked vent curcuit, pt trigger(cough), poor sedation, or disease process(asthma, COPD)
Pplat: Pt position(Trendelenburg/pushing things against the diaphragm), Tension Pneumo, abdominal compartment syndrome, Pregnancy, PE, ARDS, or Pulmonary effusions.
*If you have a trauma patient with a suspected/confirmed pneumo and the PIP/Pplat increase, DECOMPRESS THE CHEST!!
How to decrease PIP/Pplat in a medical patient
Adjust the Vt to a protective setting/calculation. Potentially need to swap from a VOLUME to a PRESSURE controlled ventilation(IPAP + EPAP)
Driving pressure
The difference between Pplat and PEEP(Pplat-PEEP=Driving pressure).
Attempt to keep driving pressure<15cmH2O
Decrease Vt<4-6mL/kg
Increase PEEP
Only in ARDS pt
PEEP
Peak End Expiratory Pressure
Pressure applied to the airway at the end of expiration to maintain alveolar recruitment
Quickest way to increase oxygenation
Improves oxygenation by reducing V/Q mismatch
Volume ventilation mode
Volume breath is a set volume that is considered mandatory
Set based on IBW
Standard:6-8mL/kg
Lung protection:4-6mL/kg
Monitored with PIP and Pplat
Pressure ventilation mode
Pressure breath is a pressure set based on inspiratory pressure(PIP)
Adult start: 20cmH2O(IPAP + EPAP)
Ped start: 10-15cmH2O
Monitored with exhaled tidal volume(Vte)
Compliance based
Reduction in potential barotrauma
Assist Control(AC)
Delviers a preset tidal volume & RR
It will deliver preset Vt via volume
Will deliver a pressure where a Vt is targeted
>Indications: normal respiratory drive accompanied by conditions causing increased work of breathing OR Apneic patients
Synchronized Intermittent Mandatory Ventilation(SIMV)
Patient receives a set # of breaths at a preset tidal volume, allowing for spontaneous breathing between mandatory breaths
Pt able to trigger own breath based on sensitivity setting
>Indications: Often used with pressure support(PS), Weaning, Increased comfort, and reduced change of hyperventilation.
Could have risk for increase muscle fatigue
Pressure Support
SIMV application only
Reduction of deadspace
Applied during spontaneous breath only
Decreased effortand workload on patient
Assists in the weaning process
Starting pressure 10cmH2O(PS + PEEP=10)
*Small changes(1cmH2O = 75-150mL of added potential Vt)
*Spontaneous exhaled tidal volume(spVte) should not exceed 75% of set Vt. Provide more sedation if spVte is >75% of Vt.
Rise Time(variable)
Only applies in pressure supported breath(SIMV) or pressure control.
Pressure = the ability to apply Rise Time
Faster Rise Times: (0.1-0.237sec)
Short Inspiratory time(Ti) or Hypoxic/air starved
Slower Rise Times: (0.316-1.0sec)
Small ETT, Bronchospasm, or Pressure Overshoot.
**Your Rise time has to be longer than your Ti or the vent will terminate the breath.
Flow Termination
*Only applied in a pressure supported breath
Limits the amount of flow in a breath displayed as a percentage.
EX: 100L/min of flow- if you set flow term to 25%, the patient only receives 75% of the 100L/min setting.
Higher Flow Term % = less Vt and lower Flow Term % = more Vt.
Injury Approach
Vt = protection
6-8mL/kh based on IBW
4-6mL/kg for Pplat >30cmH2O(adult only) >4mL/kg go to P not Vol.
–Should not be altered to fix ventilation
–Only gets changed for lung protection to present barotrauma. Look at Pplat pressure.
Settings: RR- 100mL/kg/min = 16bpm, PEEP-minimum 5cmH2O, FiO2- lowest to maintain SpO2 >93%, Pplat- <30cmH2O
Obstructive Approach(COPD Asthma only)
RR=protection
RR–10-12bpm. 6-8mL/kg based on IBW.
*COPD I:E ratio >1:4.1 *Asthma - consider I:E ratio of 1:1.1
Rate is not changed to increase VE;Vt only
Expiratory time constant- 0.3sec
Settings: Vt- 6-8mL/kg, Vol mode if available, RR- 10-12, PEEP- minimum 3-5cmH2O, and FiO2- lowest to maintain SpO2 >93%
Quiz question
A Pplat of how many mmHg is considered abnormal?
> 30
Quiz question
Your patient is demonstrating a sudden increase in PIP, with a normal P plat. The most likely cause of this phenomenon would be what ?
Answer: patient coughing against the vent
Explanation : when looking at vent pressures, always look first at PIP. This looks at volume, compliance, airway, resistance, and flow. If PIP is high and you check your Pplat, which reflects low, you know this elevation and pressure is due to something above the Carina. If both your PIP and Pplat are high, you know that the increase in pressure is caused by a change in upper airway as well as an Alveolar issue.
Quiz question
When using a pressure control mode of delivery, what can you expect?
Answer: the vent triggers until a preset pressure limit is reached
Explanation: pressure delivery ventilation is the most gentle way to ventilate your patience. Always remember your patience are sick and have baby lungs. Pressure modes of ventilation are based on compliance and will only apply a pressure based on that compliance.
What is Pinsp?
(Pinsp)Total inspiratory pressure= PEEP + pressure support
Quiz question
When applying pressure support in a patient on SIMV, what is the stopping point for allowing the patient to take a spontaneous breath?
Answer: Do not allow the patient to exceed 75% of the set Vt
