Exam 3- Anesthesia Machine II (7/13/23) Flashcards
A ventilator is an automatic device that will provide what two things to the patient?
- Patient ventilation
- Patient oxygenation
On the anesthesia workstation, ventilators essentially replace what component?
- The green reservoir bag
What ventilation mode was available from old ventilator models?
- Only offered volume-controlled ventilation
- No PEEP
- Couldn’t provide high enough PIP
Barotrauma is an injury that results from ______
- Injury resulting from high airway pressures
Compliance
- Ratio of a change in volume to a change in pressure
Valve that opens to allow driving gas to exit the bellows housing
- Exhaust Valve
What is Fresh Gas Compensation?
- This is a way to prevent FGF from affecting tidal volume by measuring tidal volume and adjusting the volume of gas delivered by the ventilar.
The time during which lungs are held inflated at a fixed volume and pressure. (Inspiratory plateau)
- Inspiratory pause time
I:E ratio
- Ratio of the inspiratory phase time to the expiratory phase time
Normal I:E Ratio
- 1:2
- We spend more time expiring
Inverse ratio ventilation
- Inspiratory phase time is longer than the expiratory phase time
The sum of all tidal volumes in one minute
- Minute volume
Peak Pressure
- The maximum pressure during the inspiratory phase time
Spill Valve
- The valve in the ventilator that allows excess gases to be sent to scavenging system during exhalation
The energy that the patient/ventilator expends to move gas in and out of the lungs.
- Work of breathing
Factors that affect delivered tidal volume.
- Fresh gas flow
- Compliance
- Leak
On older vents, as FGF increases, what happens to tidal volume?
- Tidal volume increase
Newer vents have excess FGF divereted during inspiration
How do newer vents compensate for system compliance?
- New vents will alter the volume delivered to compensate for system compliance (pressure control)
How does a leak affect delivered tidal volume?
- Leaks will cause a decrease tidal volume that can’t be compensated by the ventilator
Components to the ventilator.
- Driving gas supply
- Controls
- Alarms
- Pressure-limiting mechanism
- Bellows (accordion-like device)
- Housing
- Exhaust Valve
What does the driving gas do to the bellows?
- The driving gas is the gas external to the bellows that cause them to collapse.
What are the two standard alarms on the ventilator?
- Low-pressure alarm
- High-pressure alarm
What is the most common cause of low-pressure ventilator alarms?
- Disconnection of a circuit
What are examples of high-pressure ventilator alarms?
- Kinking of the ETT
- Occlusion of mask
What is a good set point for the pressure limit of the inspiratory pressure?
- 10 cmH2O above average inspiratory pressure
What is the housing of the anesthesia machine?
- Clear plastic cylinder
- Allows movement of bellows to be observed
- Has scale on side for rough estimation of tidal volume
What is the function of the exhaust valve?
- Communicates with the housing and allows driving gas to be vented to the atmosphere on exhalation
What are the two kinds of bellows?
Which one is safer?
- Ascending Bellows (standing) safer
- Descending Bellows (hanging)
Why are ascending bellows considered safer?
- If there is a disconnection in the circuit, the bellows will fail to rise on exhalation, which will trigger the CRNA to know something is wrong.
- For descending bellows, they will continue to descend even if there is a disconnection.
What is the most commonly used mode of ventilation?
- Volume control
What is volume control mode of ventilation?
- Preset tidal volume is delivered (fixed parameter)
- The machine will give a set tidal volume regardless of the patient’s condition
Volume control mode can cause excessive ________ pressure.
- inspiratory
Volume control mode will have set:
- Set Tidal Volume
- Set Respiratory Rate
- Set I:E Ratio
What conditions would a volume control mode not be beneficial for the patient?
- Conditions with decreased compliance and FRC
- Obese/Pregnant patients
- Trendelenburg/Lithotomy procedures
- Patients with lung pathology
- Patients that need to be weaned from the vent
How much tidal volume should be delivered to a patient on a ventilator?
- 4-6 mL/kg
Describe pressure control ventilation.
- Preset pressure is quickly achieved during inspiration.
- Set PIP, RR, and I:E Ratio
Describe tidal volume with pressure control ventilation.
- Tidal volume varies with resistance and compliance
What will insufflation of the abdomen do to inspiratory pressure?
- Increase inspiratory pressure, which will cause a low tidal volume.
What is the good thing about pressure control ventilation?
- This vent setting protects lungs from barotrauma of excess pressure
What is the bad thing about pressure control ventilation?
- The pressure delivered in this mode might not develop enough tidal volume for the patient.
- Increase risk for atelectasis
What are ways to deliver more tidal volume in pressure control ventilation mode to patients with low lung compliance?
- Increase PIP
- Use Inverse I:E ratio, longer inspiration than expiratory time. The body will have time to adapt to increased pressure.
Describe Volume Guarantee Pressure-Control.
- Maintain Tidal Volume by adjusting PIP over several breaths.
- Prevent sudden Tidal Volume changes d/t compliance (lost insufflation)
What is Assist Control Ventilation?
- Predetermined negative pressure will trigger breath
- Breath is set tidal volume
What is Intermittent Mandatory Ventilation (IMV)?
- Mandatory ventilator breath is set
- Additional native breaths at variable tidal volume
- Allows breath stacking
What is SIMV?
- Synchronizes ventilatory-driven breaths with spontaneous breaths
- Provides backup to weaning ventilator
- Best for weaning
What is Pressure Support?
- PIP and inspiratory time set
- Vt equates to the native effort
- Need apnea alarm
What are ways to use a ventilator during an MRI?
- MRI compatible machines
- Anesthesia machine kept outside in hallway
- Machine bolted to wall
- Aluminum tanks or pipeline gas supply
General Hazards: What can cause ventilation failure?
- Disconnection from power supply
- Extremely high FGF
- Fluid in electronic circuitry
- Leaking bellows housing
General Hazards: How can there be a loss of breathing system gas?
- Failure to occlude spill valve
- Leak in the system
- Losing pipeline pressure
- Losing cylinders
Need to do daily anesthesia machine check
General Hazards: What can cause incorrect ventilator settings?
- Inadvertent bumping
- Not adjusted for new case
- Not adjusted for position/pressure changes
- Ventilator turned off for xrays (cholangiogram)
Advantages of a ventilator
- Allows anesthesia provider to devote energy to other tasks (free hands)
- Decreases fatigue
- Produces more regular rate, rhythm, and Vt
Disadvantages of a ventilator
- Loss of “feel” (reservoir bag)
- Older versions may not have all the desired modes
- Components are hard to clean or fix
- Lack user-friendliness
- Noisy or too quiet
- May require high-flow driving gases…expensive
What is the trace gas concentration?
- Concentration of a gas far below that needed for anesthesia or detected by smell
Trace concentration units
- PPM (parts per million)
100% of gas is how many PPM?
1,000,000, PPM
1% of gas is how many PPM?
10,000 ppm
Higher levels of trace gas concentration are seen in…
- Pediatric anesthesia
- Dental surgery
- Poorly vented PACU’s
For years what did old studies conclude about trace gas exposure?
- Spontaneous abortions
- Spontaneous abortion in spouses
- Infertility
- Birth defects
- Impaired performance
- Cancer/mortality
- Liver disease
- Cardiac disease
These negative side effects of gas exposure has been mitigated with the scavenger system
Scavenging system function.
- Removes the collection of gases from equipment used to administer anesthesia or exhaled by the patient.
Describe the passive scavenging system.
- Entire volume is exhausted to the atmosphere.
- Disposal tubing from the anesthesia machine is attached to the exhaust grill and removed with room air.
Describe the active scavenging system.
- Attached to central vacuum system
- Must be able to provide high volume (30L/min)
- Need plenty of suction outlets and close to anesthesia machine
How can the ventilator cause hypercapnia?
- Hypoventilation
- Absorbent failure
- Excessive dead space
- Defect coaxial system
How does an anesthetic agent overdose over with the anesthesia machine?
- Tipped vaporizer
- Vaporizer accidentally on
- Incorrect agent in vaporizer
- Interlock system failure
- Overfilled vaporizer
How does Hypoventilation occur on the ventilator?
- Insufficient gas
- Obstruction
- Leaks
- Main machine power off
- Breathing system leaks (disconnections)
What are ways to prevent inadvertent exposure to volatiles?
- Change breathing system hoses and bag
- Change fresh gas supply hose
- Change absorbent
- Use very high oxygen flows to flush the machine
- Remove vaporizers
- Use an axillary flowmeter for supplemental oxygen
