4. ANESTHETIC GASES 1.pptx

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

7. 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

8. 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

9. 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

10. 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 .

11. 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

12. 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

13. 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.

14. 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

15. 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.

16. 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

17. 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)

18. 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 .

19. 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 .

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

21. 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

22. Storage and Handling of Medical Gases Cylinder Color Coding Air

23. Storage and Handling of Medical Gases Cylinder Color Coding Helium

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

25. Medical gas cylinder data