Anaesthetic equipment

Question 1

Sources of anaesthetic gases in an anaesthetic machine?

Answer 1

They can be obtained from cylinders or pipelines

Question 2

Types of pressure systems & their component?

Answer 2

1. Cylinders - high pressure system
2. Hospital pipeline - Intermediate pressure system
3. Anaesthesia machine - Low pressure system

Question 3

Components of the high pressure system?

Answer 3

1. Oxygen & nitrous cylinders
2. Non-return valves
3. Pressure guages
4. Primary pressure regulator

Question 4

Pressure regulators?

Answer 4

The transform high pressure systems to intermediate pressure systems.

There are two stages of oxygen pressure regulation

Question 5

Components of the low pressure system?

Answer 5

1. Flow meters
2. Vaporizer
3. Common gas outlet
4. APL valve at 35 kPa
5. Breathing system (Newer machines)

Question 6

Components of the intermediate pressure system?

Answer 6

1. Nitrous & Oxygen pipeline supply
2. Pipeline pressure guage (300 - 400 kPa)
3. Fail safe valve
4. Oxygen supply failure alarm
5. Second stage oxygen pressure regulator
6. Oxygen flush valve
7. Flow control valves

Question 7

Cylinder pressures and reduced pressures?

Answer 7

The pressure is reduced by the presssure regulator from 1,444 - 4000 kPa to 310 - 420 kPa ( To protect patient, apparatus and maintain constant pressure.

Question 8

Cylinders - This is a safety feature in the anaesthetic machine?

Answer 8

Colour coded and specific pin index system

Question 9

ISO system ?

Answer 9

Shoulder-body

1. Carbondioxide - Grey
2. Heliox - White/Brown
3. Air - White/Black
4. Nitrogen - Black
5. Nitrous Oxide - French Blue
6. Oxygen - White / Black
7. Entonox - white/Blue
8. Helium - Brown/Brown

Question 10

Cylinders?

Answer 10

1. Made of chrome-molybdenum steel or carbon steel
2. Size is determined by water capacity in litres
3. N2O & CO2 are liquified gases under pressure. Pressure is constant until cylinder is empty

Question 11

Calculation of cylinder gas content?

Answer 11

Gas content = Water capacity (L) x Pressure (bar)

The pressure must be in bar - Learn conversion of pressures

bar psi kPa MPa
0.1 1.5 10 0.01

The cylinder for N2O and CO2 must be weighed to get the gas content

Question 12

Safety devices to secure oxygen delivery?

Answer 12

1. Fail-safe valve

Limit is 21% oxygen delivery

Detect pressure based on pressure and not flow - Doesn’t protect against hypoxic gas delivery.

2. Anti-hypoxia devices (Flow regulator)- This reduces oxygen pressure to 14 psig and 26 psig for N2O
3. Oxygen flush - @ 35 L/min from pipeline or cylinder. May cause dilution & barotrauma

Question 13

Ritchie whistle?

Answer 13

1. This makes a whistling sound.
2. Its at 60 db
3. At 1 meter form the anaesthetic machine
4. Lasts for 7 secs

Question 14

Properties of mechanical (Rotameter)?

Answer 14

• Constant pressure & variable orifice
• Caliberated for a particular gas
• The flow are within 10% of the indicated flow
• Reading taken from the top of bobbin (triangle shape) or in the middle in the round ones
• Oxygen must be the last rotameter before the gas outlet

Question 15

Hybrid flowmeters?

Answer 15

• Works with needle valve
• Flow generated without electric power
• Measurment and display are electronic.

Question 16

Electronic flow meters?

Answer 16

1. Fully electronic
2. No manual valve
3. Backed up by basic O2 delivery system in case power or machine failure.

Question 17

Where is the location of the vaporizer in the breathing system?

Answer 17

1. Located between the flowmeter and common gas outlet

Question 18

Boiling point and altitude?

Answer 18

• The temperature at which vapor pressure is equal to atmospheric pressure
• Boiling point decreases with increase in altitude.

Question 19

Mechanics of the Variable bypass vaporizers?

Answer 19

1. Split into two by the spliting valve

2. On part free from volatile and the other is saturated with volatile

Question 20

Types of variable bypass vaporizers?

Answer 20

1. Draw over

2. Plenum

Question 21

Properties of the draw over vaporizer?

Answer 21

1. Gases are at atmospheric pressure
2. Drawn through the vaporizer by the inspiratory efforts of the patient
3. Low resistance vaporizer
4. Poor accuracy - Dependent on patient’s effort

Question 22

Plenum vaporizers?

Answer 22

1. Inspired gases are at higher than atm pressure
2. High resistance vaporizer
3. It is accurate is wide rage of flows and temperatures
4. It has a temperature compensator in the bypass circuit
5. It can be used at altitude due to partial pressure remaining constant

Question 23

Patial pressure of Volatile agents at altitude?

Answer 23

1. Partial pressure of volatile agent remains constant at altitute

Question 24

TEC 6 vaporizer for desflurane?

Answer 24

1. It has a boiling point of 23.5
2. Desflurane heated to 39 degrees under a pressure of 194 kPa or 1500mmHg
3. Continuous flow of desflurane is added to the FGF
4. Shut off valve is activated by tilting the vaporizer

Question 25

Sevoflurane vaporizer?

Answer 25

1. No shut off valve 2. It has a transport setting 3. There is a pin safety system for all volatiles

Question 26

Breathing systems?

Answer 26

See mapleson system in pictures

Question 27

Where is the APL valve located in Circle system?

Answer 27

1. APL valve is located in the expiratory limb

Question 28

Soda lime ?

Answer 28

1. Absorbs 23L of co2 per 100 g. 2. Its main component is calcium hydroxide 3. End product : Heat, water and calcium carbonate 4. Barium hydroxide not used as it easily catches fire

Question 29

Anaesthetic gas analysis?

Answer 29

1. Mass spectrometry and Raman spectroscopy are not used anymore 2. Most gases measured by infrared analysis 3. O2 and N2 do not absorb infrared light (Only one atom)

Question 30

CO2 analysis?

Answer 30

1. Infrared analysis | 2. Principle Beer-lambert law

Question 31

Beer-lambert law?

Answer 31

The absorption of infrared light passing through a solvent (gas) is proportional to the amount of the unknown gas

Question 32

Oxygen analysis ?

Answer 32

1. Galvanic cell (Fuel cell) : Lead anode and gold cathode in potassium chloride. At gold terminal hydroxyl ions are formed that react with lead. Used on anaesthetic machines in the inspiratory limb. 2. Paramagmetic analyser: Expands in magnetic field and contracts when magnetic field turned off, its paramagnetic. It requires a water trap. 3. Polarographic electrode: Gold or platinum cathode and silver anode. Separated by semipermeable membrane . Works with small voltage applied to the electrodes. Amount of current flowing through the anode and cathode is proportional to the amount of O2 present

Question 33

Invasive arterial monitoring?

Answer 33

1. It has electromanometer diaphragm with built-in strain guage (Wheatstone bridge principle) 2. Wave form built up by fourier analysis 3. Doesn't matter where the transducer is zero'ed

Question 34

Damping ?

Answer 34

1. Over-damping - Flat arterial curve 2. Under-damping - High peaks 3. Blood clot will cause overdamping 4. Air bubbles will cause under-damping

Question 35

Electrical safety?

Answer 35

1. If the body is in contact with two conductive surfaces at different potential, it may complete a circuit and result in electrical shock 2. Defibrillation threshold is 100microA (fatal to heart) 3. Maximum leakage allowed 10 microAmpre in OR

Question 36

Surgical diathermy ?

Answer 36

1. Uses ultrahigh frequencies - 0.1-3MHz compared with line power 50-60Hz

Question 37

Incidence of Fires and thermal injuries?

Answer 37

1. Incidence of surgical fires 1 in 87,000 cases | 2. ETT to be used if >30% FiO2 and surgical site above the xiphoid