Modern Anesthesia Workstations: Sophistications and Safety Features
Introduction and Evolution
''What is the core concept behind this collaborative learning module?''
It is a reality that we don't have access to all modern machines in a single institution.
Therefore, we intend to have collaborative learning for exploring the technology,
getting institutions across the globe together on this platform.
''How has the anesthesia workstation evolved in terms of its goals?''
The evolution of the anesthesia workstation has provided increased and sophisticated solutions.
These aim to increase patient safety, improve the economy of anesthetic agents,
enhance environmental sustainability, and provide an integrated platform for anesthesia services.
''What is the fundamental anatomy of a basic anesthesia machine?''
We are all familiar with the basic Boyle's machine and its components,
which include the high, intermediate, and low pressure system components.
These are essentially pneumatic components.
''What is the functional anatomy of a modern anesthesia workstation?''
The functional anatomy of a modern anesthesia workstation includes electrical components
in addition to the traditional pneumatic ones.
The gas supply system still includes a high pressure system,
an intermediate system, and a low pressure system.
''Do all modern workstations function the same way?''
Although the basic outline remains the same across manufacturers,
the actual functionality and specific features differ from manufacturer to manufacturer
and from machine to machine.
The universal dictum is to know your machine well before using it for patient services.
''Do more components mean the machine is more complicated to use?''
No, in fact, all the advancements are made to make the workstation more user-friendly
and to improve patient safety measures.
Environmental sustainability is another important feature,
as we have to reduce the carbon footprints from our anesthetic agents.
It is our responsibility to actively pursue reduce, reuse, recycle, and recover.
Key Features of Specific Modern Workstations
''What are the key features of the GE Gas Station 754/750?''
The GE Gas Station 750 has a compact design, is easy to use,
and has tremendous safety features.
It has a simple power on and off button, a premium arm that can be rotated,
efficient power and cable management, and a pin index and cylinder yoke system.
It includes an auxiliary flow meter, an alternate oxygen supply,
an auxiliary common gas outlet, and an integrated auto-playable gas module and breathing systems.
It has an auto-playable canister for soda lime and precise electrical flow.
The integrated monitor offers various parameters with graphical representation alongside numerical values.
''What kind of queries and data can be accessed on the GE 750?''
The display has about five customizable pages.
It shows electronically regulated gas flows and various parameters
like airway pressure, dynamic levels, peak pressure, and plateau pressures.
It also provides compliance data and enables the user to preset the FiO2 and gas flows.
There is an option for trends to see graphical and numerical representation of patient parameters over time.
Recruitment maneuvers are also available.
''What ventilation modes are available on the GE 750?''
It offers a variety of modes, including volume control, pressure control,
pressure control volume guarantee, synchronized volume control,
synchronized pressure control with volume guarantee mode,
PSV Pro (pressure support ventilation pro),
and CPAP with pressure support ventilation.
''What additional features are highlighted on the GE Carestation 620?''
You can navigate to see pressure-volume loops and flow-volume loops,
which can give clues to intraoperative respiratory events.
This screen can be used to teach residents the dynamics during each respiratory phase.
You can also find out how much volatile anesthetic, oxygen, or air is consumed
through the fresh gas usage menu, eliminating manual charting and calculation.
''What are the main parts and features of the Drager Perseus A500?''
It has a fresh gas setting on the screen, an inspiratory and expiratory limb of the circle system,
a connection to the bag, and a soda lime canister to absorb CO2.
It features a unique turbine technology for ventilation.
The gas pipelines and cylinder provision are located at the back,
and the machine goes through a rigorous self-test before use.
It has a virtual flow meter assembly.
''How does the Drager Perseus A500 use patient demographics?''
The machine allows you to set the demographics of any patient, such as weight and height.
The machine then calculates the MAC appropriate for the age,
tells you the ideal body weight, and gives an automatic adjustment for ventilator settings.
''What are the ventilation modes available on the Drager Perseus A500?''
The modes displayed are manual mode, pressure support ventilation,
pressure control ventilation, and volume control ventilation.
A unique mode is volume control with AutoFlow, a dual mode combining characteristics of both volume and pressure control,
useful for robotic and laparoscopic surgery.
''What is the low flow wizard on the Drager Perseus A500?''
The low flow wizard is a tool to keep fresh gas flow settings to a minimum.
It provides an indicator that tells you if the gas flow is less, adequate, or more than required.
The ideal setting is for the indicator to remain in the green range.
For researchers, it provides data like oxygen uptake and trends.
''What are some key safety features and components shown on the Drager Fabius and GE workstations?''
Key components include the gas module with Aladin cassette vaporizers,
a suction with adjustable levels, a master switch, and an alternate oxygen control.
The breathing system module includes inspiratory and expiratory valves, the APL valve,
and a bag/ventilator selector switch.
The self-test process can be a full test or individual tests for ventilation and gas modules.
''How does the GE workstation's alternate oxygen control work as a safety feature?''
If the electronic system of the machine gets damaged and stops showing data,
you can switch over to the alternate oxygen source by pressing a button.
You then manually set the oxygen and dial settings of the inhalation agent.
The machine will deliver this without feedback from the screen until the main system is working again.
''What is the '25% oxygen' anti-hypoxia safety feature?''
In a GE machine using nitrous oxide, as you reduce the oxygen percentage,
the nitrous oxide also decreases to maintain a ratio,
ensuring the oxygen concentration does not fall below a safe level.
''What is the importance of the anti-hypoxia alarm?''
The anti-hypoxia alarm is vital to patient safety, and its immediate recognition is of paramount importance.
As the FiO2 and etO2 come down, the hypoxia alarm will go off to alert the provider.
''What is the significance of the auxiliary common gas outlet (ACOG)?''
The ACOG connection is very important in day-to-day practice.
In most modern machines, the main screen shows an alert window indicating "ACOG in use"
to alert the user regarding the selector switch for the ACOG.
''What are the key features of the Drager Fabius and its piston ventilator?''
In the Drager Fabius workstation, we have piston-driven ventilators.
A key feature is the fresh gas decoupling valve.
During inspiration, the piston moves up, pushing gases into the inspiratory limb.
The positive pressure created closes the decoupling valve,
preventing fresh gas from directly entering the inspiratory limb during this phase.
''What is the advantage and disadvantage of the fresh gas decoupling valve?''
The advantage is that during inspiration, fresh gas is disconnected from the patient.
Even if the oxygen flush is activated, it will not enter the patient,
preventing lung hyperinflation and barotrauma.
It also ensures a precise tidal volume is delivered.
The disadvantage is that changes made to the fresh gas flow are not reflected immediately,
as mixing with expired gases occurs.
''How do turbine ventilators work, and what are their advantages?''
Turbine ventilators use mechanical energy to spin a small turbine or fan at very high speeds
to create pressure and flow.
Potential advantages include better responsiveness to patient triggering,
more effective pressure support ventilation, more accurate tidal volume delivery,
and a high ventilatory workload.
Ventilator Technology and Modes
''How are modern anesthesia ventilators best classified?''
Modern anesthesia ventilators can be best classified as either bellows or non-bellows (piston) types.
Bellows ventilators can be subclassified as ascending or descending.
Mechanically driven, electronically controlled piston-type ventilators use a computer-controlled stepper motor instead of compressed drive gas.
''What is the difference between ascending and descending bellows?''
An ascending bellow rises during expiration and is considered a safety feature,
as it will only fill if the patient exhales, indicating a circuit disconnect if it fails to rise.
A descending bellow descends during expiration and can fill even with a disconnect,
potentially masking a circuit leak.
''What is the significance of the ventilator's location within the breathing circuit?''
You can note the location of the ventilator within the breathing circuit,
between the fresh gas inflow and the inspiratory valve.
The breathing bag participates in the circuit during mechanical ventilation,
acting as the reservoir for re-breathing.
''What is fresh gas decoupling?''
Fresh gas decoupling is a feature where the fresh gas flow is separated from the patient during inspiration.
This is achieved through a decoupling valve.
During inspiration, the valve closes, and fresh gas is diverted to the reservoir bag.
During expiration, the valve opens, allowing the fresh gas to enter the ventilator chamber and mix with the expired gases.
''What is the visual indicator of fresh gas decoupling in a piston-driven ventilator?''
In a piston-driven ventilator with a fresh gas decoupling valve,
the reservoir bag will be seen moving.
As the piston moves up during inspiration, the bag inflates.
As the piston moves down during expiration, the bag deflates.
This is because the bag is included within the circuit.
''How does the bag behave in a bellows-type ventilator without a decoupling valve?''
In a bellows-type ventilator without a decoupling valve,
the bag is totally disconnected from the closed circuit during mechanical ventilation.
This is why the bag will not be moving at all during inspiration or expiration.
''What are recruitment maneuvers, and what is their benefit?''
Present anesthesia ventilators provide lung recruitment maneuvers in single-step or multi-step modes
as per user-defined pressures, without needing to disconnect the circuit.
This facility can contribute to reducing ventilator-induced lung injury,
a major cause of post-operative pulmonary complications.
Recruitment maneuvers and compliance trends help decide the appropriate PEEP to apply.
Vaporizer Technology
''What are Aladin cassette vaporizers?''
Aladin II cassettes contain the anesthetic liquid and serve as the detachable vaporizing chamber.
The electronic vapor control unit is internalized within the anesthesia workstation.
The cassettes have copper contacts for an electronic bus that powers capacitor plates to sense the liquid agent level.
They are color-coded and magnetically coded.
''How do injection vaporizers work?''
Injection vaporizers were introduced with high-end anesthesia workstations.
Electronic control allows instantaneous changes in vapor concentrations
to achieve the set end-tidal anesthetic concentration values, even with very low fresh gas flows.
Advanced Concepts: Target Controlled Anesthesia and Ecoflow
''What is ET Control, and how does it work?''
In ET control mode, the anesthetist sets targets for end-tidal oxygen concentration,
minimum flow rate, and end-tidal anesthetic concentration.
The system uses an algorithm to adjust both fresh gas flow and the vaporizer
to achieve the set values via a negative feedback control system.
Fresh gas flow automatically reduces down to the minimum set value.
''What is the difference in gas consumption between high and low fresh gas flows?''
During the induction phase with high fresh gas flow (e.g., 10 L/min),
all patient gas consumption is made of fresh gas, and about half goes to the waste scavenging system.
At lower fresh gas flows, the patient's delivered minute ventilation is made up of both fresh gas flow and recycled gas.
For example, 40% from fresh gas flow and 60% from recycled gas.
''What is the risk of using very low fresh gas flows?''
As fresh gas flow is reduced, more recycled gas makes up the patient's delivered minute ventilation.
The faO2 decreases because oxygen is not being replenished from the fresh gas flow at this rate.
Eventually, most of the oxygen will be consumed within the recycled gas,
creating a risk of delivering a hypoxic mixture to the patient.
''How does the Ecoflow software help manage low-flow anesthesia?''
Ecoflow provides data on the total oxygen required within the fresh gas flow to help ensure the minimum faO2 target.
It represents the oxygen total flow and a target faO2 flag.
By increasing the O2 flow to meet the flag while maintaining total flow,
low flow can be maintained while ensuring the target faO2 is achieved.
''What are the steps to start ET control?''
You press "start" and then select parameters: set the end-tidal oxygen,
the end-tidal volatile agent required, and set the minimum flow.
The machine will then monitor the end-tidal concentrations and adjust fresh gas flow accordingly.
''What are the advantages of ET control?''
ET control simplifies the management of fresh gas flow and volatile agents.
It reduces the burden and workload for the anesthesiologist,
allowing more time for other patient needs.
It ushers in the era of target-controlled anesthesia,
enabling the most cost-effective anesthesia by keeping gas consumption to an absolute minimum.
Environmental Safety: The Anesthetic Gas Scavenging System (AGSS)
''What are the two main types of AGSS?''
There are two types: active and passive.
In a passive system, waste gases are passively disposed of down a corrugated tubing and vented outside the operating room.
In an active system, a suction or vacuum is applied to actively pull the anesthetic gases and dispose of them to the outside environment.
''What are the basic components of an AGSS?''
An AGSS has basic components like a collecting system, a transfer system, a receiving system, and a disposal system.
In some modern machines, the collecting and receiving systems are integrated into one assembly.
The transfer system is the corrugated tubing that collects gases from the collecting system to the disposal system.
The Modern Operating Room Environment
''What are the features of an MRI-compatible anesthesia workstation and monitors?''
The Fabius MRI workstation is compact, has a piston ventilator, an integrated compact breathing system,
and a broad range of ventilation modes.
MRI-compatible monitors are also available,
and all equipment must be non-ferromagnetic to avoid being attracted to the strong magnetic field.
''What does a modern operating room suite include beyond the workstation?''
Modern practice embraces new-age technology in informatics, pre-operative medicine,
state-of-the-art point-of-care monitors, and precision drug delivery systems.
This includes integrated information management systems,
fluid warmers, twitch monitors, viscoelastic hemostasis assay machines (like Quantra),
and secure medication storage systems (like Pyxis).
''What are the key components of a Pyxis medication storage system?''
The Pyxis system is a secure storage system for most basic medications.
It requires a fingerprint or ID for access.
Commonly used medications for induction and neuromuscular blockers are kept in the top drawers.
Pre-packed syringes of emergency medications like epinephrine are also available.
Additional supplies and medications are stored nearby.
''What patient warming and monitoring devices are standard in a modern OR?''
Standard monitors include EKG, NIBP, pulse oximetry, and temperature probe.
Forced-air warming devices (like Bair Huggers) are used on almost all patients to maintain normothermia.
A twitch monitor is used on all adult patients to ensure full reversal before extubation.
In cardiac ORs, extra monitors like cerebral oximeters are available.
Panel Discussion: Q&A on Practical Use and Safety
''Should we use depth of anesthesia monitors for all patients under GA?''
We first started using this in elderly patients (65+) to prevent overdose and delayed wake-up,
as post-operative cognitive dysfunction was a concern.
By using the monitor, we could lower anesthetic concentration without increasing awareness.
It has become routine in adults and has shown benefit even in children older than three years.
Just as we monitor oxygen, it's a good idea to monitor the sedative effects of anesthetics when the technology is available.
''How do you manage a patient with a family history of malignant hyperthermia?''
We prepare the machine by removing all disposables, putting fresh ones on, changing the soda lime absorber,
and following manufacturer's instructions. If the vaporizer is removable, we remove it; if not, we empty it.
We then flush the machine for 20-30 minutes and use activated charcoal filters on both inspiratory and expiratory limbs.
This process takes about 30-40 minutes.
Alternatively, you can use an ICU ventilator and perform a TIVA, provided the ICU ventilator is also clean.
''Should we still need to heat inspired gases when using low flows and recirculating exhaled gases?''
Although low flows preserve heat and humidity as the patient's exhaled gas is warm and humidified,
research shows it does not match the optimal level of normal breathing.
The addition of an HME filter brings it closer to normal, while a heating filament may not be as beneficial.
''Should oxygen analyzers be calibrated every day?''
It depends on the manufacturer's recommendations.
When using an anesthesia machine for the first time, or after exposure to extreme conditions, calibration is necessary.
However, most recommendations suggest calibrating the analyzer every day in the morning,
though for paramagnetic analyzers, some technicians say once a week is sufficient.
''Should breathing circuits be changed for every patient or at the end of the day?''
The practice in many modern hospitals is to change circuits for every case.
The circuit is cleaned, disinfected, sterilized, and returned in a sterile pack.
HME filters are discarded at the end of each case.
While some hospital policies may be to change at the end of the day,
changing for each patient is better for infection control, especially with the routine use of bacterial filters.
''How much oxygen is spent driving a bellows ventilator, and how should we conserve it?''
The oxygen used to drive bellows can vary from 1 liter to up to 10 liters.
When there is a failure of oxygen from the pipeline, it is better to switch to manual mode to conserve whatever oxygen is left in the cylinder.
Some modern machines can switch the driving gas from oxygen to air to conserve oxygen.
''What are the advantages of piston-driven ventilators over bellows ventilators?''
Piston-driven ventilators are more accurate as they do not use a driving gas and are not affected by external factors.
This precision is especially important when using low flows, ensuring the set tidal volume is delivered.
''How do we know a disconnection has occurred in a piston-driven ventilator?''
The alarm system and safety features in most modern machines will indicate a disconnection at any level.
The machine will also display expired and inspired tidal volumes,
and the included reservoir bag will collapse, serving as a visual indicator.
''How is barotrauma from an accidental oxygen flush prevented in a bellows ventilator without a decoupling valve?''
The oxygen flush button is well-protected, not protruding, and sometimes covered with a guard to prevent accidental pressing.
Modern workstations also have high-pressure relief valves that release pressure, preventing barotrauma.
''When should we use the advanced ventilation modes (like PRVC, PSV Pro) available on modern workstations?''
Knowing the basics of volume and pressure control is sufficient for the majority of patients.
Advanced modes are useful for more complex surgical procedures, thoracic surgeries, airway procedures,
or patients with significant changes in respiratory physiology.
For beginners, it's best to avoid fancy modes until the underlying physiology is well understood.
''Should we use recruitment maneuvers for all patients to prevent postoperative pulmonary complications?''
Recruitment maneuvers should be used more regularly, especially in patients undergoing laparoscopic or robotic surgery,
obese patients, those with rigid chest walls, or patients in odd positions like steep Trendelenburg.
Multi-step recruitment maneuvers are safer than a single sustained vital capacity breath,
which can cause significant hypotension.
''What are the "pause gas" and "cardiac bypass" modes for?''
The "pause gas" mode stops all gases from going to the circuit,
which is useful during intubation to prevent anesthetic agent from being vented into the OT atmosphere.
In "cardiac bypass" mode, the machine stops delivering gases but is not turned off, and alarms can be managed,
preventing lung movement during bypass.
''How do we manage a power failure when using modern, electronically controlled workstations?''
Modern machines have a power backup that lasts about 45 to 90 minutes.
The rotameters have a soft light for visibility in the dark.
If the battery runs out, an additional source of 100% oxygen is available.
However, without anesthetic agents, you may need to switch to intravenous agents.
This is possible if the vaporizer is not electronic.
''How does monitoring end-tidal oxygen (etO2) help in clinical practice?''
End-tidal oxygen reflects oxygen concentration in the alveolar space and is a determinant of arterial partial pressure of oxygen.
It determines if pre-oxygenation is adequate.
When giving 100% oxygen, etO2 should be more than 90%; if less, it indicates impaired gas exchange.
Critically ill patients may have a high etO2 but still have a short safe apnea time due to decreased functional residual capacity.
''What are the key considerations for monitoring in the MRI environment?''
No ferromagnetic equipment can go inside the MRI room.
Monitors must be MRI-compatible, and a slave monitor is often used inside with the main monitor outside.
ECG electrodes should be made of graphite to prevent heating and must be placed close together.
Pulse oximetry uses fiber optic cables.
All equipment, from trolleys to fire extinguishers, must be MRI-compatible.