Dr. Rupak Bhattarai

INTRODUCTIONNitrous oxide, Chloroform and Ether were the

first universally accepted general anesthetics.Ethyl chloride, Ethylene and Cyclopropane were

also used , but the toxicity and flammability led to their withdrawal from the market.

Mainly 5 inhalation anesthetics agents are used in clinical practice these days:

1. Nitrous oxide2.Halothane3.Isoflurane4.Desflurane5. Sevoflurane

MINIMUM ALVEOLAR CONCENTRATION (MAC)DEF: The minimum alveolar concentration of

an inhaled anesthetics is the alveolar concentration that prevents movement in 50% of patient in response to a standardized stimulus (e.g. Surgical Incision)

MAC VALUE OF INHALATION ANESTHETICS AGENTSNitrous oxide: 105%Halothane: 0.75%Isoflurane : 1.2%Desflurane: 6%Sevoflurane: 2%

NITROUS OXIDEPhysical properties:It is a laughing gas.It is only inorganic anesthetic gas in clinical

use.Colorless and odorlessNon Explosive and Non InfammableGas at room temperature and can be kept as

a liquid under pressure.It is relatively inexpensive.

Effects of Nitrous Oxide on Organ System1. CARDIOVASCULAR SYSTEM Stimulate sympathetic nervous system. Directly depresses myocardial contractility. Arterial blood pressure ,heart rate and

cardiac output are slightly increased.2. RESPIRATORY SYSTEM: Increases respiratory rate with decreases

tidal volume. Minimal change in minute ventilation.

3. CEREBRAL:Increases CBF thus increasing intracranial

pressure.

4. RENAL SYSTEM:It decreases renal blood flow thus leads to drop

in glomerular filtration rate and urinary output.

5. HEPATIC SYSTEM:Decreases the Hepatic blood flow but to a

lesser extent than other inhalation agents.

6. GASTROINTESTINAL:It causes post operative Nausea and Vomiting.

CONTRAINDICATION OF N2OAir embolismPneumothoraxAcute Intestinal ObstructionTension PneumocephalusTympanic membrane grafting

HALOTHANEPhysical Properties:It is halogenated alkene.Non Inflammable and Non explosive.Least expensive .

EFFECTS ON ORGAN SYSTEM1. CARDIOVASCULAR: Dose dependent reduction of arterial blood

pressure by direct myocardial depression. It is a coronary artery vasodilator. It causes slowing of SA node conduction

resulting in bradycardia.2. RESPIRATORY SYSTEM: Causes rapid ,shallow breathing. Decrease in alveolar ventilation and Paco2

elevated. Potent dronchodilator.

3. CEREBRAL:It increases cerebral blood flow.4. NEUROMUSCULAR:Relaxes skelatal muscle and potentiates Non

depolarizing neuro-muscular blocking agents.5.RENAL:Reduces renal blood flow, glomerular

filtration rate and urinary output.6. HEPATIC:Decreases hepatic blood flow.

CONTRAINDICATIONUnexplained liver dysfunction.Intra-cranial mass lesions.Hypo-volemic patient with severe cardiac

diseases.

ISOFLURANEIt is non flammable volatile with a pungent

smell.EFFECTS ON ORGAN SYSTEM:1.CARDIOVASCULAR:Causes minimal cardiac depression.Rapid increase in MAC lead to increase in HR

and BP.( Coronary Steal)Dilates coronary arteries.2. RESPIRATORY SYSTEM:Respiratory depression .Acts as a good bronchodilator.

3. CEREBRAL:If con> 1 MAC causes increase in CBF and

Intracranial pressure.4. NEUROMUSCULAR:Relaxes skeletal muscles.5. RENAL:Decreases renal blood flow , glomerular

filtration rate and urinary output.6. HEAPTIC:Reduces hepatic blood flow.INDICATIONS- For Cardiac and Neuro-

Surgery

CONTRAINDICATIONNo such contraindication.Patient with severe hypovolemia may not

tolorate its vasodilating effects.

DESFLURANEStructure much similar to that of isoflurane.Recovery time are approximately 50 % less

than those of Isoflurane. Pungent SmellTEC 6EFFECTS ON ORGAN SYSTEM:1.CARDIOVASCULAR SYSTEM:Similar to Isoflurane( Increases HR and BP

when increased MAC rapidly)Dilates coronary arteries.

2. RESPIRATORY SYSTEM:Causes decrease in tidal volume and increase in

resp rate.Pungency and airway irritation so causes

coughing and sometime bronchospasm.

3. CEREBRAL:Increases CBF and Intracranial pressure.

4. NEUROMUSCULAR:Relaxes skeletal muscle.

5. RENAL AND HEPATIC SYSTEM:No any evidence has been documented.

INDICATION- For Hepatic and Renal Surgery

CONTRAINDICATIONSevere hypo-volemia.Intracranial hypertension.Malignant hyperthermia.

SEVOFLURANEIt is Non pungency.EFFECTS ON ORGANS:1.CARDIOVASCULAR SYSTEM:Mildly depresses myocardial contractility.May prolong QT interval, but no significance.2. RESPIRATORY SYSTEM:Depresses respiratory rate.It reverses broncho-spasm

3. CEREBRAL:Increases CBF and intra-cranial pressure.4. RENAL SYSTEM:Slightly decreases renal blood flow. Higher

Conc Causes Nephro-toxicity5. HEPATIC:Decreases portal vein blood flow but

increases hepatic artery blood flow thus maintaining total hepatic blood flow.

6.NEUROMUSCULAR:Adequate muscle relaxation.

CONTRAINDICATIONSevere hypo-volemia.Intracranial hypertension.Malignant hyperthermia.

ETHERW.T.G Morton on 16th Oct 1846 used for

removal of jaw tumor.PHYSICAL PROPERTIES:Pungent smelling liquid, decomposes in

presence of light, air, heat.Highly inflammable and explosive.Highly irritant vapour.Very Cheap.Also called as Complete Anesthetic agents.Can be used by less experience hands.

Induction very slow, pungent smells and may causes laryngeal spasm

Very good analgesic.Very good muscle relaxants.

Cardiovascular: Does-not depresses myocardium, but stimulates sympathetic system.

Respiratory system: Does-not depresses respiration.

It is a potent bronchodilator.Tracheo-bronchial secretions is markedly

increased.GIT: Nausea and vomiting.Hepatic and renal: Well preserved.Cerebral: Increases intracranial pressure.May causes Hyperglycemia.

STAGES OF ETHER ANESTHESIASTAGE I: (Stage of analgesia) (From

analgesia to loss of consciousness)• Respiration is regular with small tidal

volume.• Pupil is normal in size.STAGE II : (Stage of Excitement): ( From loss

of consciousness to rhythmic respiration)• Respiration is irregular.• Pupil is Mid dilated.• Eyelashes reflex absent.

STAGE III : ( Stage of Anesthesia):• Plane I: ( From rhythmic resp to cessation of eye

movement)Respiration is regular with large volume. Pupil is normal in size. Eyelashes reflex absent, Pharyngeal and vomiting reflex lost.

• Plane II: (From cessation of eye movement to resp paresis)Respiration is regular with large volume , Pupil is mid dilated with corneal reflexes lost.

• Plane III: ( Resp paresis to Paralysis)From Respiration is regular with small volume, Pupil is moderate dilated with laryngeal reflexes absent.

• Plane IV: (Diaphragmatic Paralysis)Respiration is irregular with small volume, Pupil dilated and centrally placed.

Stage IV: (Stage of overdose) (Medullary Paralysis)

• Apnea• Pupil dilated and non reacting to light.

NOTE: Withdrawal of anesthetic agents and administration of 100% oxygen lightens anesthesia with recovery.