Machine

Question 1

Why don’t we deliver anesthetic gas in air (21% O2)?

Answer 1

It would lead to hypoxemia due to hypoventilation and V/Q mismatch induced by anesthetics themselves

Question 2

What is the minimum acceptable O2 amount for people and small animals?

Answer 2

30-35% (FiO2 = 0.30-0.35)

Question 3

What is the metabolic requirement for O2? What does that mean for anesthesia?

Answer 3

5-10 mL/kg/min This is the minimum O2 flow required

Question 4

What are the color standards for US air cylinders?

Answer 4

Oxygen = green Nitrous oxide = blue Medical air = yellow

Question 5

What are 2 ways to avoid fire when dealing with E cylinders?

Answer 5

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

Question 6

What is cylinder pressure measured in? Breathing system pressure?

Answer 6

Cylinder = psi (pounds per square inch) Breathing system = cmH20 (centimeters water)

Question 7

What is included in the high pressure system? What is the psi?

Answer 7

The high pressure system is 100-2200+ psi, and includes the gas cylinder, yokes, pressure gauges, and regulators

Question 8

What is included in the intermediate pressure system? What is the psi?

Answer 8

The intermediate pressure system (50 psi) includes the central O2 supply, post-regulator, flush valve, input to flowmeter, and driving gas for ventilator

Question 9

What is the low pressure system?

Answer 9

• <15 psi
• Between flowmeter output and common gas outlet
• Breathing system (= pressure in patients’ lungs)

Question 10

Which cylinder is most common in small animal general practice? What is its capacity and psi?

Answer 10

E cylinder–capacity = 660 L, filled to a pressure of 2200 psi

Question 11

How do you calculate the remaining O2 in an E cylinder?

Answer 11

(2200psi / 660L) = (psi left on E tank) / X liters

Question 12

What is the problem with calculating remaining gas in an N2O tank?

Answer 12

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

Question 13

What are the 5 safety systems in place for gas tanks?

Answer 13

• Color-coded
• Labeling
• Diameter index safety system
• Pin index safety system
• Quick connectors

Question 14

What is the diameter index safety system?

Answer 14

Non-interchangeable gas-specific threaded connection system. It is used universally by all equipment and cylinder manufacturers

Question 15

What is the pin index system?

Answer 15

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

Question 16

What are quick connectors?

Answer 16

Manufacturer-specific connectors that facilitate rapid connecting and disconnecting of gas hoses (don’t have to screw in); useful for multipurpose work areas

Question 17

What is a regulator? What does it do and what does it prevent?

Answer 17

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

Question 18

What is a flowmeter? What are the pressures of entering/exiting gas?

Answer 18

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

Question 19

What are the types of tapered flowmeters? What are they calibrated for?

Answer 19

• 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)

Question 20

What are the different floats for flowmeters and where do you read each one?

Answer 20

• Floats can be either a ball or bobbin
• Balls are read in the MIDDLE
• Bobbins are read at the TOP

Question 21

T/F: Flowmeters reduce gas pressure from 50 psi (intermediate) to 15 psi (low) and are gas-specific

Answer 21

TRUE

Question 22

If there are multiple flowmeters, where should the O2 be located and why?

Answer 22

O2 should be on the far right (downstream of all other gases) to prevent delivery of a hypoxic gas mixture

Question 23

What does the quick flush do?

Answer 23

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

Question 24

What is appropriate use of the quick flush?

Answer 24

Quickly decrease anesthetic gas % in the circuit–for emergency or recovery (it is PURE O2)

Question 25

What should be done to the patient before the O2 flush valve is utilized?

Answer 25

The patient should be DISCONNECTED from the circuit temporarily before utilizing valve

Question 26

What is a possible complication of the quick flush?

Answer 26

Pneumothorax--small circuit, high pressure, small patient

Question 27

What is the function of anesthetic vaporizers?

Answer 27

Change liquid anesthetic into vapor; deliver selected % of anesthetic vapor to the fresh (common) gas outlet ('volumes percent')

Question 28

What is the difference between vapor and gas inhalants? What are some examples of each?

Answer 28

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)

Question 29

Vapor pressure

Answer 29

Pressure exerted by vapor molecules when liquid and vapor phases are in equilibrium

Question 30

T/F: Vapor pressure does not depend on temperature and is proportional to boiling point.

Answer 30

FALSE: Vapor pressure DEPENDS on temperature (increases with increasing temp) and is INVERSELY related to boiling point.

Question 31

Saturated vapor pressure

Answer 31

Maximum administration percentage of vapors; = vapor pressure / barometric pressure

Question 32

7 facts about modern vaporizers: GO

Answer 32

* Agent-specific * Concentration-calibrated * Variable-bypass * Flow-over * Out-of-circuit * High resistance * Compensated for temperature, flow, and back-pressure

Question 33

What does the variable-bypass system in vaporizers create?

Answer 33

Specific concentration, where fresh gas flows over a reservoir of liquid anesthetic and mixes with carrier gas

Question 34

T/F: All modern vaporizers are out-of-circuit (VOC); carrier gas is from flowmeter and anesthetic % is known (= precision vaporizer)

Answer 34

TRUE

Question 35

What was the purpose of the wicking material in VICs (non-precision)?

Answer 35

To increase the surface area for vaporization--ensured saturation with anesthetic gas. It also served as a variable bypass

Question 36

What is the carrier gas in VICs? What does this cause?

Answer 36

The patient's expired gas--causes an inability to produce a known anesthetic %; it is not temperature compensated and is not currently recommended

Question 37

What do modern vaporizers compensate for?

Answer 37

* 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

Question 38

How is temperature compensation in vaporizers achieved? How does it act as a mechanical thermocompensation system?

Answer 38

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

Question 39

How do vaporizers achieve flow rate compensation?

Answer 39

By ensuring saturation of gas moving through vaporizing chamber; use of wicks, baffles, and spiral tracks that facilitate vaporization

Question 40

Back-pressure: whatchu know 'bout it

Answer 40

* 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

Question 41

What is a desflurane vaporizer?

Answer 41

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)

Question 42

How are vaporizers filled?

Answer 42

Using a screw-cap port or agent-specific keyed filler port (prevents filling with the wrong agent)

Question 43

What are 4 general facts about vaporizers?

Answer 43

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

Question 44

What would happen if a vaporizer was filled with the wrong agent?

Answer 44

* 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

Question 45

What would happen if a vaporizer was tipped?

Answer 45

Anesthetic may enter the bypass channel and deliver a high concentration; would need to run 1 L/min O2 through machine with vaporizer off

Question 46

What is the common gas outlet?

Answer 46

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