Inhalational agents are chemicals that produce general anesthesia when inhaled. They include nitrous oxide, halothane, isoflurane, desflurane, and sevoflurane. These agents work in the central nervous system by augmenting GABA and potassium channels while depressing other neurotransmitter pathways. They provide amnesia, immobility, and some provide analgesia as well. Each agent has different effects on organ systems like the cardiovascular, respiratory, renal, and hepatic systems. The potency of agents is determined by their minimum alveolar concentration needed to prevent movement in response to stimuli. Characteristics of an ideal agent and properties of individual agents are discussed.

1. INHALATIONAL
ANAESTHETIC AGENTS

2. Introduction.
Are chemical cpnds that posses general anaesthetic properties that can be delivered via
inhalation.
They are administered via face mask, laryngeal mask airway or trachea tube connected to
anaesthetic vaporizer and an anaesthetic delivered system.
types;
• Gases ;eg nitrous oxide(N2O), xenon
• Volatile liquids; eg halothane, isoflurane,sevoflrane,desflurane

3. Mechanism of action
• The exact mechanism for inhaled anaesthesia remain mostly unknown. Fundamentally,
inhalational anaesthesia work wthin the CNS by augumenting signals to chloride channels
(GABA receptors) and potassium channels while depresssing neurotransmission pathways
including ACH receptors both muscarinic and nicotinic receptors, glutamate receptors and
serotonin receptors and NMDA receptors.
• Inhalational agents are delivered by vaporizers and mixed with carrier gas (oxygen + N2O or
oxygen alone then reach the patient’s alveoli where it is taken up by blood and reaches different
tissues including brain. The concentaration in the brain is the one which determine the effect of
inhalation agent.
• All inhalational anaesthesia provide amnesia, and immobility, except for nitrous oxide which also
provide analgesia.

4. Characteristics of an ideal anaesthetic agent
• Adequate potency
• Low solubility in blood and tissue
• Resistant to physical and metabolic degradation
• Protect and does not injure vital tissues
• Low cost
• Non explosive and does not support combustion
• Odourless or has a pleasant smell
• Not epileptogenic
• Minimal respiratory depression, does not cause coughing or bronchospasm
• Minimal cardiovascular depression

5. • Has a boiling point well above room temperature
• Does not react with other compound eg soda lime
• Is excreted completely by respiratory system
• No effect on uterine smooth muscles

6. • The potency of an inhalational anaesthetic agent is determined by the minimum alveolar
concentration (MAC) which is the concentration of the inhaled anaesthetic drug in the alveoli
that is needed to prevent movement in 50% of patients in response to standardized surgical
stimulus e.g surgical incision
• It is used tocompare the strength of anaesthetic drugs.
• MAC values for inhalational anesthetic agents
Nitrous oxide; 105%
Halothane;0.75%
Isoflurane 1.2%
Desflurane 6%
Sevoflurane 2%

7. Increase in MAC
• Young age
• Hyperthermia
• Chronic alcohol intoxication
• Hypernatremia
• Amphetamine acute use
• Hyperthyroidism
• Cathecolamines and sympathomimetics
• Chronic opioid use
Decrease in MAC
• Hypothermia
• Increasing age
• Pregnancy
• Hypotension
• Hypothyroidism
• Acute opioid use
• Acute alcohol intake
• Chronic amphetamine intake

8. • No effect on MAC
Sex, weight, and duration of anaethesia.

9. PROPERTIES OF INDIVIDUAL INHALATIONAL
ANAESTHETICS
• NITROUS OXIDE
• Physical properties;
• It is a laughing gas
• It is only inorganic anesthetic gas in clinical use
• Colourless and odorless
• Non explosive and non flammable
• Gas at room temp and can be kept as a liquid under pressure
• It is relatively inexpensive

10. • Effects of N2O on organ system
1.CVS
• stimulates sympathetic nervous system
• Directly depresses myocardial contractility
• Arterial BP, HR, and cardiac output are slightly increased
2. RESPIRATORY SYSTEM
• Increase respiratory rate with decrease tidal volume
• Minimal change in minute ventilation
3. CEREBRAL
• Increase CBF thus increasing intracranial pressure

11. 4. RENAL SYSTEM.
• It decrease renal BF leading to drop in GFR and urine output
5.GI SYSTEM
• It cause PONV
CONTRAINDICATIOS OF N2O
• Air embolism
• Pneumothorax
• Acute IO
• Tympanic membrane grafting
• pneumocephalus

12. • HALOTHANE
• Halogenated alkene
• Non flammable and non explosive
• Least expensive
• Non pungent odor
• Non irritant to airway
Effects on organ system
CVS
• Dose dependent reduction on arterial BP by direct myocardial depression
• It is a coronary artery vasodilator
• Causes bradycardia by slowing SA node conduction

13. RESPIRATORY SYSTEM
• Causes rapid shallow breathing
• Decrease in alveolar ventilation and elevates PaCO2
• Potent bronchodilator
CEREBRAL.
• It increses cerebral blood flow
• Dilate cerebral vessels and lowers cerebral vascular resistance
NEUROMASCULAR
• Relax skeletal musles
• It is a triggering agent of malignant hyperthermia

14. RENAL
• Reduces renal blood flow, GFR and urine output
HEPATIC
• Decrease hepatic blood flow
• Can cause halothane hepatitis
CONTRAINDICATIONS;
• Unexplained liver dysfunction
• Intracranial mass lesions
• Hypovolemic pts with severe cardiac diseases

15. ISOFLURANE
• It is non flammable volatile with pungent smell.
• It suppress seizure activity
Effects on organ system
CVS.
• Causes minimal cardiac depression
• Rapid increase in MAC lead to increase in heart rate and BP
• Dilates coronary arteries
RESPIRATORY SYSTEM
• Respiratory depression
• Good bronchodilator
CEREBRAL
• At conc>1MAC causes increase in CBF and intracranial pressure

16. NEUROMASCULAR
• Relaxes skeletal muscles
RENAL
• Reduces renal blood flow, GFR and urine output
HEPATIC
Reduces hepatic blood flow
Indication for cardiac and neuro surgery

17. DESFLURANE
• Structure similar to that of isoflurane
• Recovery time is approximately 50% less than that of isoflurane
• Boiloing point is 22.8C so would boil at room temp, this necessitated the development of special desflurane vaporizer
Effects on organ systems
CVS
• Increases HR and BP when increased MAC rapidly
• Dilates coronary arteries
RESPIRATORY SYSTEM
• Causes increase in respiratory rate and decrese in tidal volume
• Pungency and airway irritation so causes coughing and sometimes bronchospasm
CEREBRAL
• Increses CBF and intracranial pressure

18. NEUROMASCULAR
Relaxes skeletal muscles
RENAL AND HEPATIC SYSTEM
No evidence have been documented
INDICATION; for heptic and renal surgeries
CONTRAINDICATIONS;
• Severe hypovolemia
• Intracranial hyperntension
• Malignant hyperthermia

19. SEVOFLURANE
• Non pungency and has rapid increase in alveolar anaesthetic concentaration making it an
excellent choice for smooth and rapid inhalation induction in pediatric and adult pts
• Low solubility in blood result in rapid fall in alveolar anesthetic concentration upon
discontinuation
• Single breath induction-4% to 8% sevoflurane in a 50% mixture of N20 and O2 can be
achieved within one minute
Effects on organ systems
CVS
• Mildly depresses myocardial contractictiliy
• Prolonges QT intervals

20. RESPIRATORY SYSTEM
• Depresses respiration and reverses bronchospasm
CEREBRAL
• Causes slight increase in CBF and intracranial pressure
RENAL
• Slightly decreases renal blood flow. Higher concentration causes nephrotoxicity
NEUROMASCULAR
• Produce adequate muscle relaxation for intubation of children following an inhalation
induction

21. CONTRAINDICATIONS;
• Severe hypovolemia
• Intracranial HTN
• Malignant hyperthermia