Anaesthesia gases

1. ANESTHETIC GASES
PRESENTER: Dr Djaffar
SUPERVISOR: DR. ASHA

2. OUTLINE
• Introduction
• Oxygen
• Nitrous Oxide
• Entonox (O2/N2O)
• HELIOX (Helium/O2)
• Carbon Dioxide

3. Introduction
• A gas is one of the status of substance or
matter in which:
– it will expand freely to fill their containers
– Having no fixed shape and no fixed volume, So it is
easy to compress
– They occupy far more space than liquid
they remains only in gaseous state under pressure
and any amount of pressure rise cannot liquefy it so
long it is above its critical temperature.

4. Oxygen
• 2 covalent atoms bound and make an Oxygen
molecule (O2).
• Oxygen has a boiling point of -183°C and a critical
temperature of -119°C,
• which means that at room temperature it is above
its critical temperature and always exists as a gas.
• Why is it important in Anesthesia?

5. Nitrous Oxide
• Safest inhalational anesthetic.
• Weak anesthetic but a good analgesic
• No toxic on body organs as heart, Liver and Kidney
• Nitrous oxide is a weak general anesthetic and is
generally not used alone.
• Required caution to be used: Diffusion Hypoxemia

6. Nitrous Oxide
General Characteristics
• N2O is a colourless gas,
• without odour or taste
• The boiling point is -88.6°C and the critical
temperature is +36°C.
• marketed in steel cylinders as a liquid under
pressure in equilibrium with the gas phase at
normal room temperature

8. Chemical Preparation
 prepared commercially by heating ammonium
nitrate between 170-270 °C
NH4NO3 -------- Heat  N2O + 2H2O
 Manufacturing impurities toxic:
 contamination with the higher oxides of nitrogen,
nitrogen dioxide or nitric oxide, may lead to,
– a. laryngospasm
– b. cyanosis due to methaemoglobinaemia
– c. chemical pneumonitis and respiratory failure

9. storage, and supply
• It is stored in a cylinder, compressed as a
liquid/vapour below its critical temperature
(36.5°C)
• Hospitals often supply piped nitrous oxide
at a pressure of 4 bar to theatre
environments

11. Pharmacokinetics
• Nitrous oxide is a weak general anesthetic and is
generally not used alone.
• potent analgesic agent but a weak anaesthetic
agent, producing surgical anaesthesia predictably
only under hyperbaric conditions
• the rate of approach of alveolar to inspired
concentration is rapid due to the low solubility in
blood.
– Speed of onset, second gas, and concentration effects
– Diffusion Hypoxia

12. Indications
• General anesthesia, in combination with other
anesthetics
• Dentistry:
– decrease the pain and anxiety associated with
procedures
Contraindications
• significant respiratory compromise
• pneumothorax, pulmonary
• blebs, air embolism, bowel obstruction, and those
undergoing surgery of the middle ear.

13. Systemic Effects
Central Nervous System
– depresses the CNS and produces analgesia
– increases cerebral blood flow and raises ICP
• good anaesthesia and a moderate fall in ICP
Cardiovascular System
– Used alone
• small, direct myocardial depressant effect
• CO, contractility & HR reduced
– N2O + volatile
• increases the arrhythmogenic potential of all agents
effects on respiration are generally small

14. Entonox
• is the trade-name from BOC Medical for:
50% oxygen + 50% nitrous oxide
• is supplied in cylinders at 13 700 kPa (137bar) at 15°C
or delivered via pipelines in the hospital at 4bar.
• The pseudocritical temperature is approximately -6°C,
allowing for slight variation due to small differences in
cylinder pressure

15. • If there is a possibility of separation occurring, the
manufacturers recommend that prior to use
cylinders should be stored horizontally for 24hrs at
a temperature above 10°C or alternatively, warmed
to 10°C for two hours (or body temperature for 5
minutes) and then completely inverted 3 times.

16. Clinical Uses
• Used as a method of obstetric analgesia with
maintenance of consciousness
• Used in the setting of minor procedures in the
trauma department where transient analgesia
is required

17. Heliox
• Heliox is a mixture of oxygen and helium
• O2 in the mixture can vary : 21% - 50%.
Advantage:
• Theoretically patients with airway obstruction have
a greater amount of turbulent compared to laminar
air flow within their airways. Helium has a lower
density than oxygen (and nitrogen) and this may
increased airway gas flow when flow is turbulent.

18. Clinical Uses
• reduce the work of breathing in patients with an
upper airway obstruction such as a tumor or in
kinked endotracheal tube
• to investigate small airway resistance to flow
• used in the measurement of lung volumes
because of its very low solubility

19. CARBONDIOXIDE
carbon dioxide today plays a very important role in
modern anaesthesia.
-Is a by-product of manufacturing processes and
fossil fuel burning
-Gaseous CO2 is collected, filtered, dried,
compressed and liquefied.
-It is then stored as a liquid in cylinders
-Most commonly used as the insufflation gas during
laparoscopy as it is colorless, non-toxic, non-
flammable and has the greatest margin of safety in
the event of a venous embolus (highly soluble)

20. Physiological effects
• Anaesthetic agents are known depressants of
central nervuous system function.
• The respiratory centre is also depressed, and this
is important for two reasons.
– these agents will decrease ventilation with a resultant
rise in PaCO2 and Respiratory acidosis.
– the sensitivity of the respiratory center will be
lowered, so that the elevated PaCO2 loses its
effectiveness as a stimulus to increase the ventilation.

21. • CVS effects: direct or indirect (↑
catecholamine)-> tachycardia, ↑cardiac
contractility and ↓ in diastolic filling can result
in decreased myocardial oxygen supply to
demand ratio and greater risk of myocardial
ischaemia.

22. Storage and Handling of Medical Gases
• Medical Gases are stored in one of two ways:
– Portable high-pressure cylinders
– Large bulk reservoirs

23. Storage and Handling of Medical Gases
• Cylinder Color Coding
• Gas Cylinders
– High pressure cylinders used to store and ship
compressed or liquid medical gases
Oxygen

24. Storage and Handling of Medical Gases
• Cylinder Color Coding
Air

25. Storage and Handling of Medical Gases
• Cylinder Color Coding
Helium

26. Storage and Handling of Medical Gases
• Cylinder Color Coding
Nitrous Oxide

27. Medical gas cylinder data