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Anesthesiology > Machine > Flashcards

Machine Flashcards

1
Q

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

A

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

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2
Q

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

A

30-35% (FiO2 = 0.30-0.35)

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3
Q

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

A

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

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4
Q

What are the color standards for US air cylinders?

A

Oxygen = green Nitrous oxide = blue Medical air = yellow

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5
Q

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

A

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

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6
Q

What is cylinder pressure measured in? Breathing system pressure?

A

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

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7
Q

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

A

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

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8
Q

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

A

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

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9
Q

What is the low pressure system?

A
  • <15 psi
  • Between flowmeter output and common gas outlet
  • Breathing system (= pressure in patients’ lungs)
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10
Q

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

A

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

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11
Q

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

A

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

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12
Q

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

A

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

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13
Q

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

A
  • Color-coded
  • Labeling
  • Diameter index safety system
  • Pin index safety system
  • Quick connectors
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14
Q

What is the diameter index safety system?

A

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

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15
Q

What is the pin index system?

A

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

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16
Q

What are quick connectors?

A

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

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17
Q

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

A

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

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18
Q

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

A

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

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19
Q

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

A
  • 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)
20
Q

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

A
  • Floats can be either a ball or bobbin
  • Balls are read in the MIDDLE
  • Bobbins are read at the TOP
21
Q

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

A

TRUE

22
Q

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

A

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

23
Q

What does the quick flush do?

A

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

24
Q

What is appropriate use of the quick flush?

A

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

25
Q

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

A

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

26
Q

What is a possible complication of the quick flush?

A

Pneumothorax–small circuit, high pressure, small patient

27
Q

What is the function of anesthetic vaporizers?

A

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

28
Q

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

A

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)

29
Q

Vapor pressure

A

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

30
Q

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

A

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

31
Q

Saturated vapor pressure

A

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

32
Q

7 facts about modern vaporizers: GO

A
  • Agent-specific
  • Concentration-calibrated
  • Variable-bypass
  • Flow-over
  • Out-of-circuit
  • High resistance
  • Compensated for temperature, flow, and back-pressure
33
Q

What does the variable-bypass system in vaporizers create?

A

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

34
Q

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

A

TRUE

35
Q

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

A

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

36
Q

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

A

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

37
Q

What do modern vaporizers compensate for?

A
  • 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
38
Q

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

A

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

39
Q

How do vaporizers achieve flow rate compensation?

A

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

40
Q

Back-pressure: whatchu know ‘bout it

A
  • 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
41
Q

What is a desflurane vaporizer?

A

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)

42
Q

How are vaporizers filled?

A

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

43
Q

What are 4 general facts about vaporizers?

A

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

44
Q

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

A
  • 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
45
Q

What would happen if a vaporizer was tipped?

A

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

46
Q

What is the common gas outlet?

A

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

Anesthesiology (16 decks)

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