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  1. Cylinders are made up of molybdenum steel
    1. O2 Cylinders
      1. Pressure – 2000 psi (or 137 kg/cm2)
      2. Colour – Black body with white shoulders
      3. Available in sizes from AA to H
      4. Most commonly used cylinder on anaesthesia machine is type E
      5. Liquid O2
      6. Special supply reservoirs are used
      7. Advantages
        1. Can be used away from hospital e.g. in wars, portable low wt. low gas pressure
        2. Liquid O2 must be stored below its critical temperature of – 119oC
        3. 1 ml of liquid oxygen releases 840ml of gas
    2. N2O cylinders
      1. Pressure – 760 psi
      2. Colour – blue
      3. Filled as liquid
  2. ​​Central supply of O2 & N2O
    1. O2 & N2O are supplied at 60 psi through central supply.

2. Colour of Cylinders


Filled as

a. O2–Black body with white shoulders

2000 psi


b. N2O–Blue

760  psi


c. CO2–Grey

750 psi


d. Cyclopropane–orange

75    psi


e. Helium–Brown

1400 psi


f. Air–Grey body with black & white shoulders

2000 psi


g. Entonox -Blue body with blue & white shoulders

2000 psi


    (50% O2 + 50% N2O)

  1. Note: Gas which are there in liquid form in cylinders :N2O, CO2, Cyclopropane (N.C.C.)
    For agents in liquid form contents does not correspond with pressure.
  2. Pin index system
    1. Oxygen 2,5
    2. N2O 3,5
    3. Air 1,5
    4. Nitrogen 1,4
    5. Cyclopropane 3,6
    6. Entonox 7
    7. Carbon dioxide 2,6
  1. It consist of 2 pins 4 mm & 6 mm long on Yoke of machine to be fitted in the corresponding holes of cylinder valve
  2. This pin index system is to prevent wrong fitting of cylinders
  1. Anaesthesia Machine

High pressure

Intermediate pressure

Low pressure system

1. Cylinder

1. From Yoke to flow
control valve

1. Downstream to flow
control valve

2. Pressure regulator

2. O2 failure alarms


3. Yoke assembly

3. Pressure reducing valve


Low pressure system

  1. Flow control valves colour coded
    1. O2 – white
    2. N2O – Blue
    3. CO2 – Grey

Extra Edge

  1. Rotameter is used to measure flow of gases
  2. Flow meters (also k/a as Thorpe tube) are of variable orifice with smallest diameter at base. It contains an indicator K/a BOBIN which is made of aluminum and the upper level of bobbin indicates the flow.
  1. Vaporizers:
    To deliver to inhalational agents. Made of copper colour codes are red – halothane, purple isoflurane, yellow-sevoflurane, orange-enflurane.
  2. Breathing System
    a. Open           b. Semiclosed                 c. Closed
    1. Open Circuit:
      By putting mask or gauge piece directly over nose & mouth previously used for ether, chloroform. A special mask Schimmelbusch mask is used for ether.
    2. Semiclosed Circuit
      1. Described by mapleson

  1. Mapleson A system à also K/a Magill circuit
  2. Best for spontaneous respiration
  3. Fresh gas flow should be Equal to minute volume to prevent rebreathing when patient is on spontaneous respiration.
  4. It is > 3 times the minute volume (and in spite rebreathing may not be prevented) when patient is on controlled ventilation.

Lack circuit – modification of Type A system

Type B – Obsolete circuit, no more used

Type C – Obsolete circuit, no more used (functionally B. C. – equally effective for spontaneous and CV)

Type D

  • Most commonly used circuit is Bain’s (modification of mapleson D system)
  • Length of tubing is 1.5 meters
  • Bain’s circuit is best for controlled ventilation
  • Fresh gas flow should be 1.6 times of minute volume or 70-100 ml/kg if RR is high to prevent rebreathing in Bain’s circuit on controlled ventilation. It is 2.5 times of minutes volume when patient is on spontaneous ventilation.

Mapleson E – AYRES T - Piece

Mapleson F

  • It is Jackson Rees modification of T piece (mapleson E) system
  • Used for children usually < 6 yrs. of age or <20 kg

Extra Edge
FGF = 2 x MV for CV, 2.5 x MV for spontaneous
Best circuit for children both for spontaneous and controlled ventilation
Newer Circuits : Humpry ADE, Penlon, Mera-F, Lacks (all these are co-axial circuits)

  1. Closed Circuit:-
    It is the circle system in which CO2 is absorbed by soda lime from exhaled gases & exhaled gases can be reused.
  2. Anaesthesia Gas Delivery System
  1. Soda lime composition
    1. Soda lime
      1. NaOH (5%)
      2. KOH (1%)
      3. Ca (OH)2(94%)
      4. Water (14-19%)
      5. Silica and Kieselguhr
      6. Indicator
      7. Size (4-8 mesh)
    2. Baralyme
      1. Ca(OH)2(80%)
      2. Ba(OH)2 .8H2O(20%)
      3. KOH(1%)       
      4. Water(11-14%)
      5. Indicator
      6. Size (4-8 mesh
  2. Indicator:
    Silica is added to make it hard so that minimum powdered dust is formed.
    1. Chemistry
      1. CO2 + H2O               = H2CO3
      2. H2CO3 + NaOH         = Na2CO3 + H2O + Heat
      3. H2CO3 + KOH           = K2CO3 + H2O + Head
      4. Na2CO3 + Ca (OH)2  = CaCO3 + NaOH (Regenerated)
      5. K2CO3 + Ca (OH)2    = CaCO3 + KOH (Regenerated)
    2. Indicator of colour changes



i.  Phenolphthalein



ii. Ethyl violet



iii. Mimosa Z



iv. Durasorb



  1. Signs of exhaustion of soda lime (MCQ):
    1. Rise in blood pressure (followed by fall)
    2. Deepening of spontaneous respiration
    3. Rise in pulse rate
    4. Increased bleeding from wounds
    5. Sweating
    6. Change in colour of soda lime granules
  2. Properties of Soda Lime
    1. Size of soda lime granules – 4-8 mesh size
    2. Air space in canister – 53%
    3. Hardness >75
    4. Humidity should be >505
    5. Max amount of CO2 that can be absorbed by 100 gms of soda lime is 26L
    6. 13,700 calories are produced for 1 mole of CO2 absorber.

5. Comparison between semiclosed & Closed system

Semiclosed ( Mapleson System)

Closed (circle system)



a. Light weight easy to carry

a. Heavy weight difficult to carry

b. Due to light weight chances of accidental extubation is not high.

b. Chances are high

c. Work of breathing is less

c. More

d. Danger of hypercapnia is less

f. More

e. No such accumulations

Accumulations of toxic metabolites

f. Can be used safely

f. Use with trielene C/I- reaction wit
Use with trielene C/I- reaction with
soda lime produces Dicholoro
acetylene which is neurotoxic
(encephalitis) & phosgene
which causes ARDS sevoflurane
produces compound DESFLURANE
(is and enf. Also) produces with
dessicated sodalime




a. High flows are required economical

a. Low fresh gas flow required so

b. Scavenging is difficult; high theatre pollution

b. Low pollution

c. Not useful in malignant hyperthermia

c. Can be managed

d. Not well preserved

d. Humidity is preserved 40-100% can

Important :
To & fro system (modification of type C) – Type of closed circuit useful for paediatric anaesthesia

  1. Instruments
    1. AMBU BAG –
      1. Artificial manual breathing unit (capacity 1200 ml)
      2. Max. O2 that can be given by AMBU Bag – 100%
    2. Instruments to preserve Humidity
      1. Water content of inhaled air at 37oC – 44 mg/L
      2. Water content of inhaled air at 21oC – 9 mg/L
      3. Water content of 100% O2 – O
      4. Complete caseation of mucociliary activity occurs <22 mg/L
Various method of preserve humidity are
  1. Heat and moisture exchanger (also called as artificial nose)
  2. Humidifiers
  3. Nebulizers (optimal size 0.5-5 microns)
  1. Scavenging system is used to eliminate the excessive anaesthetic gases
    Max. allowable conc. Of waste gases
    1. N2O <25 ppm
    2. Halogenated agents < 2 ppm
    3. N2O + halogenated agents <25 ppm & <0.5 ppm

Extra Edge
Measuring trace gas levels is most important for N2O

  1. Face Masks
    1. Available in sizes 00 à 4
    2. Dead space and chances of aspiration is significantly increased by mask ventilation
    3. Reservoir Bag
    4. For neonates – 250 ml
    5. For infant & small children – 500 ml  
    6. For adolsents – 100 ml
    7. For adults – 2000 ml

Note: Laryngeal mask airway does not protect against aspiration and thus, increased risk of gastric gurgitation and subsequent aspiration, a cuffed endotracheal tube is preferred over laryngeal mask airway.

  1. Airways
    1. Most commonly used airway – Guedel
    2. Length of airway = Distance between tip of nose & tragus + 1 inch
    3. Laryngeal mask airway
      1. The laryngeal mask airway (LMA) is a supraglottic airway management device. Designed between 1981 and 1988 by Dr. Archie I. J. Brain.
      2. Routine and emergency anesthetic procedures
      3. Known or unexpected difficult airways
      4. Establishing an airway during resuscitation in the profoundly unconscious patient with absent glossopharyngeal and laryngeal reflexes when tracheal intubation is not possible .
      5. As a routine airway, LMA airways are contraindicated in elective patients who:
        1. Are not fasted or where fasting cannot be confirmed
        2. May have retained gastric contents
        3. Have fixed decreased pulmonary compliance
      6. LMA cannot be used for preventing aspiration or removing secretion.
    4. Recommended Size guidelines:
      1. Size 1:                under 5 kg
      2. Size 1.5:             5 to 10 kg
      3. Size 2:                10 to 20 kg
      4. Size 2.5:             20 to 30 kg
      5. Size 3:                30 kg to small adult
      6. Size 4:                adult
      7. Size 5:                Large adult/poor seal with size 4
    5. Advantage
      1. Easy to inset
      2. Can be used in cervical instability
      3. No laryngoscopy required
      4. No muscle relaxants required
      5. Can be used in awake pat
      6. Even paramedical staff can inset
    6. New types of LMA (Laryngeal Mask Airways)
      1. Proseal LMA
      2. Fastrach LMA
  2. Laryngoscope
    Commonly used laryngoscope is Macintosh (curved blade) neonates – straight blade (magill).
    Head & neck position for laryngoscope is extension at Atlanto-occipital joint & flexion at cervical spine Teeth most vulnerable to damage is upper incisors.

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