– 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:
– 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?
– 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?
• 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
• 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?
Increase will increase Vm, and Decrease ETCO2
Decrease will decrease Vm, and Increase ETCO2
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
A waveform should be present for every exhalation
Presence of a waveform = presence of carbon dioxide
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
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
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.