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What is the difference between piston and pneumatic ventilators?
- Pneumatic requires a drive gas to drive bellows
- Piston system does not use a drive gas, so may be used on backup tank
At what pressures are positive and negative safety valves opened on piston ventilator?
- >75 +/-5cmH2O positive pressure relief valve opens
- < - 8cmH2O negative pressure relief valve opens
What does the negative pressure relief valve do on the piston ventilator?
- 1) prevents NEEP
- 2) allows room air to be drawn in
How is gas delivered in volume controlled mode?
- Driving gas flow stops at set tidal volume delivered to breathing circuit
- Or Pmax is reached
How is gas delivered in pressure controlled mode?
- Target pressure is set and maintained for certain time period
- The delivered tidal volume varies depending on compliance
What is the difference between ascending and descending bellows?
- Describes what the bellows do during EXPIRATION
- Descending have potential for NEEP
- Ascending always have some amount of PEEP due to weight of bellows
Why are ascending bellows safer than descending?
They do not fill if there is a disconnect
What is the function of the spill valve in the bellows?
- Opens if set pressure is exceeded to vent gas into WAG system
- It will open at any point if peak pressure is exceeded
At what pressure does spill valve open?
What is the most common course of action with ventilator alarms?
- Switch to manual ventilation
- Increase gas flow
- Check patient and system
Pressure below threshold for how long will signal apnea/disconnect alarm?
What can the reverse flow alarm indicate?
Incompetent expiratory valve
What is a good ventilator mode for difficulty ventilating?
What does PSV require?
Spontaneously breathing patient
What does PSVPro do in the event of apnea?
Switch to backup mode (SIMV on our machine)
In PSVPro backup mode, what happens when spontaneously breathing resumes?
Switches back to PSV mode
What are typical adult settings for VCV?
- TV 10ml/kg
- Rate 6-12
- PEEP 0 to start
What does the PIP alarm in VCV alert you to?
- Pt bucking
- Obstructed circuit
- Obstructed airway
What is the course of action for asynchronous breathing in VCV?
- 1) turn vent off
- 2) hand ventilate
- 3) remedy the situation
- Patients are almost always light
- If 1,2,3 doesn't work, disconnect circuit and ambu pt, call for help, switch to TIVA
- Still difficult, look at what is going on in the airway
What is the typical peak airway pressure alarm setting for relatively healthy adults in VCV?
What types of patients is PCV indicated for?
LMAs, emphysema, neonates and infants
What types of patients have poor airway compliance and require higher volumes?
- Laparoscopic surgeries
- Morbid obesity
What are typical adult settings for PCV?
- 1) pressure limit 20cmH2O
- 2) rate 6-12
- 3) PEEP 0 to start
- This is also good to start for pediatrics
How is pressure limit affected by PEEP in PCV?
PC at 20, 5 of PEEP, inspiratory pressure is 25
What is less likely to occur in SIMV?
What is unique about SIMV?
- Detects spontaneous breaths (if any)
- Delivers controlled breaths in synch with the patient's inspiratory effort
- Helps maintain minute ventilation avoiding breath-stacking or bucking
What is the trigger window in SIMV?
Percentage of expiratory pause the vent monitors for patient effort
What is sensitivity in SIMV?
How much negative inspiratory force the pt must generate to trigger a breath (l/min)
How does PCV-VG work?
- Ventilator operates in PCV with a target tidal volume
- Dynamically adjusts inspiratory pressure until target tidal volume reached
- Does not exceed maxium set Pmax
What type of surgeries is PCV-VG good for?
What advantages does PCV-VG offer?
- Control of PIP - basic PCV mode
- Control of arterial oxygenation - guaranteed tidal volume
- Good default for most machines
What anesthesia considerations are there for ARPV?
Pt will remain on ICU vent and will do TIVA
What is the concept behind APRV?
- Vent cycles between 2 levels of CPAP
- High pressure and low pressure correlate to high volume and low volume
Where does gas exchange occur during APRV?
- When pressure is intermittently released to lower pressure
- 1) waste gases eliminated
- 2) oxygenation occurs
What is the normal I:E ratio?
How does I:E ratoi change in SIMV?
It changes as you change the rate
In what patients would an increased expiratory phase be beneficial?
- Obstructive lung disease
- 1) COPD
- 2) Emphysema
When is institution of PEEP recommended?
- 1) PaO2 cannot be kept >60mmHg
- 2) FiO2 at 50%
What are 3 hazards of PEEP?
- 1) decreased cardiac output
- 2) pulmonary barotrauma
- 3) increased extravascular lung water due to obstructed pulmonary lymph flow
Why is 4l/min FGF common?
From days when safety margin was needed for less accurate flowmeters and vaporizers
What FGF functions essentially the same as a nonrebreather mask?
- 5-8 lpm
- 1-1.5 times minute ventilation
When should high FGF (5-8lpm) be used?
When should low FGF (0.5-2lpm) be used?
During maintenance of anesthesia
What agent requires that you not use FGF <1 lpm for > 2 MAC hours?
What is a key disadvantage of low FGF?
- Accumulation of undesired gases in closed circuit
- Acetone, CO, methane, hydrogen, ethanol, anesthetic agent metabolites, argon, nitrogen
What is the most significant factor in promoting adequate denitrogenation?
Good mask seal
What is the most common site of disconnection?
What is the most common preventable equipment-related cause of mishaps?
What must be used to guard against disconnects?
Either ETCO2 or precordial stethascope
Can you silence apnea alarms?
What is the biggest problem with ventilators?
Failure to initiate ventilation or resume after pause
What is the most important monitor for disconnection?
Precoridal because it's alarms cannot be inactivated like ETCO2