Machine Flashcards
Why don’t we deliver anesthetic gas in air (21% O2)?
It would lead to hypoxemia due to hypoventilation and V/Q mismatch induced by anesthetics themselves
What is the minimum acceptable O2 amount for people and small animals?
30-35% (FiO2 = 0.30-0.35)
What is the metabolic requirement for O2? What does that mean for anesthesia?
5-10 mL/kg/min This is the minimum O2 flow required
What are the color standards for US air cylinders?
Oxygen = green Nitrous oxide = blue Medical air = yellow
What are 2 ways to avoid fire when dealing with E cylinders?
Clean oils from hands and tank, open cylinder valves slowly. Open and close valve briefly before attaching to machine to remove dust from connecting port
What is cylinder pressure measured in? Breathing system pressure?
Cylinder = psi (pounds per square inch) Breathing system = cmH20 (centimeters water)
What is included in the high pressure system? What is the psi?
The high pressure system is 100-2200+ psi, and includes the gas cylinder, yokes, pressure gauges, and regulators
What is included in the intermediate pressure system? What is the psi?
The intermediate pressure system (50 psi) includes the central O2 supply, post-regulator, flush valve, input to flowmeter, and driving gas for ventilator
What is the low pressure system?
- <15 psi
- Between flowmeter output and common gas outlet
- Breathing system (= pressure in patients’ lungs)
Which cylinder is most common in small animal general practice? What is its capacity and psi?
E cylinder–capacity = 660 L, filled to a pressure of 2200 psi
How do you calculate the remaining O2 in an E cylinder?
(2200psi / 660L) = (psi left on E tank) / X liters
What is the problem with calculating remaining gas in an N2O tank?
The gauge only reads gas pressure; N20 exists in both a gaseous and liquid form in the tank. As a result, it is not possible to calculate the amount of gas remaining based on the pressure if liquid N2O remains–only way to really know is to weigh the tank
What are the 5 safety systems in place for gas tanks?
- Color-coded
- Labeling
- Diameter index safety system
- Pin index safety system
- Quick connectors
What is the diameter index safety system?
Non-interchangeable gas-specific threaded connection system. It is used universally by all equipment and cylinder manufacturers
What is the pin index system?
Gas-specific pin patterns that only allow connections between the appropriate cylinder yokes and E tanks; commonly found on yokes mounted to anesthesia machines, also some cylinder-specific regulators/flowmeters
What are quick connectors?
Manufacturer-specific connectors that facilitate rapid connecting and disconnecting of gas hoses (don’t have to screw in); useful for multipurpose work areas
What is a regulator? What does it do and what does it prevent?
AKA pressure-reducing valve The regulator decreases tank pressure to a safe working pressure (approx. 50 psi) which is supplied to the flowmeter. It prevents pressure fluctuations as the tank empties
What is a flowmeter? What are the pressures of entering/exiting gas?
The flowmeter controls rate of gas flow through the vaporizer (in L/min). Gas enters the bottom at 50 psi and exits the top at 15 psi
What are the types of tapered flowmeters? What are they calibrated for?
- Tapered glass tube with moveable float = narrow at the bottom, wider at the top
- Single- or double-taper = double taper for more accuracy at lower gas flows
- Calibrated for 760 mmHg and 20 C (sea level)
What are the different floats for flowmeters and where do you read each one?
- Floats can be either a ball or bobbin
- Balls are read in the MIDDLE
- Bobbins are read at the TOP
T/F: Flowmeters reduce gas pressure from 50 psi (intermediate) to 15 psi (low) and are gas-specific
TRUE
If there are multiple flowmeters, where should the O2 be located and why?
O2 should be on the far right (downstream of all other gases) to prevent delivery of a hypoxic gas mixture
What does the quick flush do?
Delivers O2 from the intermediate pressure area of the machine (50 psi); bypasses the vaporizer (contains NO anesthetic agent). The quick flush delivers gas at a rate between 35-75 L/min directly to the patient circuit
What is appropriate use of the quick flush?
Quickly decrease anesthetic gas % in the circuit–for emergency or recovery (it is PURE O2)
What should be done to the patient before the O2 flush valve is utilized?
The patient should be DISCONNECTED from the circuit temporarily before utilizing valve
What is a possible complication of the quick flush?
Pneumothorax–small circuit, high pressure, small patient
What is the function of anesthetic vaporizers?
Change liquid anesthetic into vapor; deliver selected % of anesthetic vapor to the fresh (common) gas outlet (‘volumes percent’)
What is the difference between vapor and gas inhalants? What are some examples of each?
Vapor = gaseous state of a substance that is liquid at ambient temp and pressure (ex: halothane, isoflurane, sevoflurane, desflurane) Gas = exists in gaseous state at ambient T and P (ex: N20, xenon)
Vapor pressure
Pressure exerted by vapor molecules when liquid and vapor phases are in equilibrium
T/F: Vapor pressure does not depend on temperature and is proportional to boiling point.
FALSE: Vapor pressure DEPENDS on temperature (increases with increasing temp) and is INVERSELY related to boiling point.
Saturated vapor pressure
Maximum administration percentage of vapors; = vapor pressure / barometric pressure
7 facts about modern vaporizers: GO
- Agent-specific
- Concentration-calibrated
- Variable-bypass
- Flow-over
- Out-of-circuit
- High resistance
- Compensated for temperature, flow, and back-pressure
What does the variable-bypass system in vaporizers create?
Specific concentration, where fresh gas flows over a reservoir of liquid anesthetic and mixes with carrier gas
T/F: All modern vaporizers are out-of-circuit (VOC); carrier gas is from flowmeter and anesthetic % is known (= precision vaporizer)
TRUE
What was the purpose of the wicking material in VICs (non-precision)?
To increase the surface area for vaporization–ensured saturation with anesthetic gas. It also served as a variable bypass
What is the carrier gas in VICs? What does this cause?
The patient’s expired gas–causes an inability to produce a known anesthetic %; it is not temperature compensated and is not currently recommended
What do modern vaporizers compensate for?
- Temperature between 15-35 C
- Flow rate between 0.5-10 L/min
- Back pressure associated with positive pressure ventilation and use of flush valve
How is temperature compensation in vaporizers achieved? How does it act as a mechanical thermocompensation system?
By using materials that are efficient heat conductors . Alters the amount of carrier gas directed through the bypass and vaporizing chambers; has thermal element made of a heat-sensitive metal that reliably expands and contracts based on temperature
How do vaporizers achieve flow rate compensation?
By ensuring saturation of gas moving through vaporizing chamber; use of wicks, baffles, and spiral tracks that facilitate vaporization
Back-pressure: whatchu know ‘bout it
- Can occur during positive pressure ventilation or use of the flush valve
- May increase vaporizer output if compensation mechanisms are not present
- Modern vaporizers use various mechanisms to prevent this from happening
What is a desflurane vaporizer?
Mostly used in human medicine; boiling point is close to room temp. Requires an electric heated vaporizer (desflurane maintained in gaseous form, blends with fresh O2 to achieve vaporizer setting)
How are vaporizers filled?
Using a screw-cap port or agent-specific keyed filler port (prevents filling with the wrong agent)
What are 4 general facts about vaporizers?
Require no external power (except desflurane)
Routine maintenance is required and must be performed by a qualified technician
Mounted on a ‘back bar’ on the machine
Cannot be tipped–must be emptied before transporting
What would happen if a vaporizer was filled with the wrong agent?
- Depends on vapor pressure and potency of each agent
- Iso in sevo vaporizer could produce a lethal concentration (higher vapor pressure AND higher potencty); would need to drain and run 1 L/min O2 until completely dry
What would happen if a vaporizer was tipped?
Anesthetic may enter the bypass channel and deliver a high concentration; would need to run 1 L/min O2 through machine with vaporizer off
What is the common gas outlet?
Where gas exits the vaporizer; connected by a hose to the fresh gas inlet. The hose must be connected so that fresh gas flows to the breathing circuit. It connects to either rebreathing or non-rebreathing system
