By Dr. Ahmed Mostafa Assist. Prof. of anesthesia and I.C.U. Medical gas supply By Dr. Ahmed Mostafa Assist. Prof. of anesthesia and I.C.U.

The anesthesia machine consists of the following components: 1- The High-pressure circuit: consists of those parts which receive gas at cylinder pressure: Hanger yoke (including filter and unidirectional valve). Yoke block. Cylinder pressure gauge. Cylinder pressure regulators.

2- The Intermediate pressure circuit: receives gases at low, relatively constant pressures (37-55 psi, which is pipeline pressure, or the pressure downstream of a cylinder regulator): Pipeline inlets and pressure gauges. Ventilator power inlet. Oxygen pressure-failure device (fail-safe) and alarm. Flowmeter valves. Oxygen and nitrous oxide second-stage regulators. Oxygen flush valve.

3- The Low-pressure circuit: includes components distal to the flowmeter needle: Valves. Flowmeter tubes. Vaporizers. Check valves (if present). Common gas outlet.

Gas sources Oxygen is produced by fractional distillation of liquid air. It is non-flammable but supports combustion. Nitrous oxide is manufactured by thermal decomposition of (NH4)2NO3. It is non-flammable but supports combustion (same as oxygen). Air is manufactured either by: Blending oxygen and nitrogen (Medical air). Compression pumps.

Gas sources Nitrogen: is produced by fractional distillation of liquid air. Entonox: is produced by bubbling gaseous oxygen in liquid N2O. CO2:is produced by heating of calcium carbonate and magnesium.

Liquefaction of medical gases Any gas can be liquefied by pressure below its critical temperature. Gas Critical temperature Critical pressure Oxygen -1190C 50 bar N2O 36.50C 72 bar CO2 310C 73 bar Air -1400C  

Delivery of medical gases Medical gas cylinders:   Gas Color Service Pressure Capacity/ L Pin Position Shoulder Body Bar psi E-Cylinder Oxygen white Black 137 2000 660 2-5 N2O blue 50 745 1600 3-5 Entonox White 7 Air black / white Gray 1-5 N2 1- 4 CO2 1- 6

Delivery of medical gases Medical gas cylinders:

Delivery of medical gases Medical gas cylinders: Cylinder component parts: Cylinder valve: Is the most fragile part, so protect during transport. Consists of: Body Port (where the gas exits)

Delivery of medical gases Medical gas cylinders: Stem (shaft). Handle or hand wheel (to open the valve) Safety relief device: Is composed of at least one of: Frangible disc (bursts under extreme pressure), Fusible plug (Wood's metal, which has a low melting point), or Safety relief valve (opens at extreme pressure).

Delivery of medical gases Medical gas cylinders: Conical depression (opposite the port, it accepts the tip of the screw which secures the cylinder in the yoke) PISS pins (Pin Index Safety System): This system prevents the wrong cylinder from being connected to an anesthetic machine.

Delivery of medical gases Medical gas cylinders: Beneath the outlet are six possible positions for indexing holes. Pins on the anesthetic machine inlet fit into these holes.

Delivery of medical gases Medical gas cylinders: 2. The hanger yoke: Orients cylinders. Provides unidirectional flow. Ensures gas-tight seal. 3. The check valve in the cylinder yoke functions to: Minimize trans-filling, allow change of cylinders during use and minimize leaks to atmosphere if a yoke is empty.

Delivery of medical gases Medical gas cylinders: Storage, handling: Use only aluminum cylinders in MRI. Do not oil valve.

Delivery of medical gases Medical gas cylinders: Storage, handling: Protect the valve when transporting. Never stand upright without support.

Delivery of medical gases Medical gas cylinders: Storage, handling: Leave cylinders on machine closed. Don't leave empty cylinders on the machine.

Delivery of medical gases Pipeline system:

Delivery of medical gases Pipeline system: Pipeline inlets are connected with DISS (diameter index safety system) non- interchangeable connections. The check valve, located downstream from the pipeline inlet, prevents reverse flow of gases (from machine to pipeline, or to atmosphere).

Delivery of medical gases Pipeline system: The medical gas pipeline source is the primary source for the anesthesia gas machine. Safety systems and regulators send oxygen to the pipeline at approximately 50 psi; "normal working pressure" of the anesthesia machine.

Delivery of medical gases Oxygen concentrators: It is a device which concentrates and extracts oxygen from atmospheric air.

Delivery of medical gases Oxygen concentrators: Principles: Air is filtered then compressed then cooled then directed though the concentrator filled with inorganic silicate (zeolite) which act as molecular sieve separating O2 from N2 and H2O vapor leaving oxygen and other trace inert gases especially argon.

Delivery of medical gases Oxygen concentrators: Advantages: O2 concentration is about 96%. Compatibility with Most Gas Monitors. Reliability: Perform well for long periods of time. Not affected significantly by altitude changes. Simplicity.

Delivery of medical gases Oxygen concentrators: Disadvantages: Maintenance: Regular servicing is required, particularly for the compressor. It is important that the air intake filters be cleaned or replaced at the intervals recommended by the manufacturer. Should be protected from fire hazards.

Delivery of medical gases Oxygen tank (Vacuum-insulated evaporator):

Delivery of medical gases Oxygen tank (Vacuum-insulated evaporator): A liquid oxygen storage system is more economical for large hospitals. It is stored as a liquid at -150 to -175 degrees C (lower than the critical temperature of oxygen, which is −119◦C, but higher than the boiling point at 1 atm, −183◦C) in a large flask (because the liquid occupies 1/860 of the space the gas would occupy).

Delivery of medical gases Oxygen tank (Vacuum-insulated evaporator):

Delivery of medical gases Oxygen tank (Vacuum-insulated evaporator): A large hospital may have a smaller liquid oxygen supply or a bank of compressed gas cylinders that can provide one day's oxygen requirements as a reserve.

Delivery of medical gases Oxygen tank (Vacuum-insulated evaporator): To guard against a hospital gas-system failure, the anesthesiologist must always have an emergency (E- cylinder) supply of oxygen available in the operating room.

Delivery of medical gases Medical compressed air: In a hospital two types of supply are required, a low pressure supply (420 kPa) for anesthetic machines and ventilators, and a higher pressure supply (700 kPa) to provide power for surgical equipment. The pipeline network may be supplied either by a bank of air cylinders or by a local compressor system. If a local compressor is used care must be taken to ensure the purity of the compressed air produced.

Delivery of medical gases Medical vacuum: Is required for suction and for scavenging of anesthetic gases, but it is not recommended that the same vacuum supply is used for both purposes because: 1. Suction requires low flow rates but high levels of vacuum, which is harmful to patient’s airway.

Delivery of medical gases Medical vacuum: 2. Scavenging requires low vacuum levels with high flow rates. The high flow rates used to remove waste anesthetic gases could reduce suction levels during surgery. 3. Waste anesthetic gases contain volatile vapors which may be absorbed by lubricants and ultimately cause system failure.

Numbers to remember 1)The hospital pipeline is the primary gas source at 50 psi, which is the normal working pressure of most machines. 2)Cylinders - Oxygen is supplied at around 2000 psi (regulated to approximately 45 psi after it enters the machine). 3)Oxygen flush is a "straight shot" from supply to delivery point, 35-75 L/min.

Numbers to remember 4)Occupational exposure should be limited to (an eight hour time-weighted average of) not more than 2 ppm halogenated agents (0.5 ppm if nitrous oxide in use), and not more than 25 ppm nitrous oxide. 5)Tubing sizes- scavenger 19 or 30 mm, ETT or common gas outlet (CGO) 15 mm, breathing circuit 22 mm.

?

Thank you Dr. Ahmed Mostafa