What is the Goal of a ventilator
To maintain alveolar Gas exchange appropriate for the patients metabolic needs and to correct hypoxia and/or hypercapnia.
What is Tidal Volume (Vt) and how is it calculated?
- – Volume of each delivered breath
- – How is it calculated?
- • 7-10 ml/kg of “ideal body weight”
- • Overweight people do not have bigger lungs
What is FiO2?
- – Fraction of inspired concentration of
- • Ranges from 21% to 100%
- • Initially set the FiO2 at 100% and titrate down based on blood gas values
- • Once blood gases have been obtained it is possible to titrate the FiO2
What determines the Respiratory Rate on a ventilated patient?
- – Number of breaths per minute
- – Depends on what is wrong with the patient
- – Initially set at 12-14 (adult) breaths per minute but can be higher or lower
- – Rate must be matched with the Vt to ensure adequate minute volume
What is Minute Volume-Vm?
- – Function of tidal volume and respiratory rate and is normally 6-10 liters in an adult
- – Represented by the following formula:
- • Vm (L/min) = Vt (ml) X respiratory rate (BPM).
What are the four modes for Volume Control on a ventilator?
- – Assist Control-AC
- – Synchronized intermittent mandatory ventilation-SIMV
- – Continuous Positive Airway Pressure- CPAP
- – Bilevel Positive Airway Pressure- BiPAP
How does Assist Control-AC work?
- – Provides full Vt at a minimum preset rate
- – Patient can initiate breaths in this mode, providing additional full Vt
- – Provides near complete resting of the ventilatory muscles
- – Patient can be awake, sedated or paralyzed
- – Pressure support can not be initiated in this mode
- • Since patients can initiate ventilation, they can hyperventilate and become alkalotic. They can also “stack” breaths which can result in air-trapping and the possibility of barotrauma. May want to consider sedation/paralysis to facilitate more effective ventilations
How does SIMV work?
- – Delivers a fixed Vt at a preset rate but allows patient to take their own breaths.
- – When ventilator breath is delivered, ventilator will deliver set Vt.
- – Patient initiated breaths are totally dependant on
- – Advantages-patients are more comfortable since they have more control over ventilations
- – Can result in respiratory fatigue if the rate is set too low causing a rise in pCO2 and air trapping i.e.: stacking breaths or auto PEEP.
How does CPAP work?
- • In this mode you can only have the components of:
- – FiO2
- – PEEP
- – Pressure Support
- • No set rate or Vt.
- • Cannot give neuromuscular blockers to patients in CPAP
- • Use sedation conservatively and with extreme caution
- – Generally used for weaning and mode used prior to
What is PEEP and how does it work?
- • Ventilators can be set to provide a fixed airway pressure at the end of expiration
- • Opens closed alveolar units increasing lung area for gas exchange.
- • PEEP can improve secretion drainage from closed alveoli
- • Typical PEEP settings are from 5-10 but can go over 20
- – PEEP can reduce venous return and lower left ventricular afterload; PEEP especially at high pressures can cause barotrauma
How does Pressure Support work?
- • “Turbo Boost” added to each Patient Initiated breath to help overcome the resistance of the Vent circuit and airway device
- • Patient triggers the ventilator at a predetermined pressure during inspiration (sensitivity), ventilation is terminated when the patient ceases to inspire
- • Patient has full control over his ventilatory pattern and minute volume
- • Cannot be used in heavily sedated, paralyzed or comatose patients
What is the Sensitivity setting on a Ventilator?
- • Amount of inspiratory effort required to initiate an assisted breath – Ranges from 1-8 L/min.
- – 1 L/min. is the most sensitive meaning it is the most sensitive to the patient initiation of a breath which decreases their work of breathing
- – If the sensitivity is turned off that means the ventilator is in full control mode-The patient cannot initiate a breath on their own
- • This is very uncomfortable and frightening for the patient unless they are sedated and paralyzed
What is Flow Rate?
- – Can be adjusted so that the inspiratory volume can be delivered in time to allow for adequate exhalation.
- – Dependant on Vt, and Rate.
- – Most commonly used rates are 40-80 lpm
- • How quickly the breath is delivered
- – If rate is set at 20 lpm the breath will be delivered slowly
- – If the rate is set at 100 the breath will be delivered quickly
What is the I/E Ratio?
- Inspiration/Expiration Ratio
- – Normal starting I/E ratio is 1:2
- • It generally takes the average person to inspire in 1 second and expire in 2 seconds
- – If the patient has an obstructive airway disease (COPD) then consider reducing to 1:3 or 1:4 to prevent air trapping
- – Use Peak Flow to obtain adequate I:E.
What is the DOPE method?
- • Displacement
- • Obstruction
- • Pneumothorax
- • Equipment Failure
- – If equipment failure is suspected the patient should be removed from the ventilator and manually bagged
What affects ETCO2 levels?
- • Two things can change CO2
- – Respiratory rate
- – Vt
- • Change only 1 setting at a time
- • If you have calculated the Vt correctly, adjust the rate
- • If rate changes seem inappropriate, change Vt first
What can change the FiO2?
- • Two things can change oxygenation levels
How do we correct High ETCO2 levels?
- • Consider increasing their respiratory rate
- • Consider increasing Vt.
- • Can result in respiratory acidosis
- •We want to Increase Minute Volume
How do we correct Low ETCO2 levels?
- • Consider decreasing their respiratory rate
- • Consider decreasing Vt
- • Can result in respiratory alkalosis
- • Decrease Minute Volume
How will adjusting the rate effect the patient?
- • Adult 12-14 BPM
- • Increase will increase Vm, and Decrease ETCO2
- • Decrease will Decrease Vm, and Increase ETCO2
How will adjusting the Tidal Volume effect the patient?
- 7-10 ml/Kg
- Increase will increase Vm, and Decrease ETCO2
- Decrease will decrease Vm, and Increase ETCO2
- (Vm=Minute Volume)
What are the differences between CPAP and BiPAP?
- • CPAP-Continuous Positive Airway Pressure
- – CPAP = PEEP
- • BiPAP-Bilevel Positive Airway Pressure
- – BiPAP = Two levels of (PS) PEEP + PS
- • IPAP = Inspiratory PAP (PS)
- • EPAP = Expiratory PAP (PEEP)
What is Normal ETCO2
- • “Normal” ETCO2 is 35 – 45
- • “If V/Q are on equal terms, ETCO2 and PACO2 should be close to equal”
What do you look for in ETCO2 Waveform?
- • There are 4 Questions to use every time you monitor Waveforms.
- – Is there rise and fall of the waveform?
- –What is the number Value and is it “Normal”?
- –What is the shape of the Waveform?
- – Does it return to baseline?
Analysis of ETCO2 waveform
- – Frequency
- A waveform should be present for every exhalation
- Presence of a waveform = presence of carbon dioxide
- – Height
- Hypermetabolic states will increase the height of the capnogram as will prolonged hypoventilation
- Decreases in cardiac output will decrease the height of the capnogram as will hyperventilation
- – Baseline
- Gradual elevations in Phase 0 or Phase I indicate re-breathing
- A sudden rise in EtCO2 AND the baseline is likely indicative of sample contamination
- – Shape
- Deviations from the normal curve of the waveform have specific meanings
- All humans with healthy lungs have the same shaped waveform
- • Any variation warrants an evaluation of the cause
- – Things to assess
- • Expiratory upstroke
- – Steep, sloping, prolonged
- • Alveolar plateau
- – Flat, prolonged, deflection, slope
- • Inspiratory downstroke
- – Steep, sloping or prolonged
- –Whenever possible, compare the EtCO2 with the measured PaCO2on the ABG.
Five Reasons for a “Flat Line” ETCO2 Wave
- – ET Tube becomes Displaced
- – ET Tube is Plugged or Kinked
- – Cardiac Arrest
- – Apnea or Mechanical Ventilator Failure
- – Equipment Malfunction