Dr. Tarun Yadav

Department of Anesthesiology – JNMC, Sawangi(M) Wardha

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1. Introduction2. Pathway O2-Brain 3.MAC (Definition and Values and factors effecting MAC)

4. Factors determining how quickly the inhalational agent reaches the alveoli reaches and the brain from the alveoli

5. Nitrous Oxide (N2O)5.1. physical properties, Pharmacology and side

effects)5.2. What is diffusion hypoxia? 5.3. Second gas effect

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6. Halothane6.1. properties6.2. Metabolism6.3. Dosage, Administration an Supply6.4. Indications and contraindications6.5. Effect on Organ Systems6.6. Advantages and Disadvantages

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7. Isoflurane and Sevoflurane7.1. properties7.2.Effect on Organ Systems7.3. Advantages and Disadvantages 7.4. Indications and contraindications

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IV anesthesia : induce anesthesia Inhalation anesthesia : maintain anesthesia

IV anesthesia : mg/KG or microgram/Kg Inhalation anesthesia : Percentage of the volume

%EXAMPLE: 2 L/min. O2 + 4 L/min N2O

Conc. Of N2O = 4/(2+4) = 66%

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INHALATIONAL ANAESTHETIC AGENTIntroduction

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MAC Definition Minimal alveolar concentration (MAC): Is defined as the conc. At 1 atmosphere of

anesthetic in the alveoli that s required to produce immobility in 50% of adults patient subjected to a surgical incision

MAC is important to compare the potencies of various inhalational anesthetic agents

1.2 -1.3 MAC prevent movement in 95% of patients

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MAC Value N2O = 105% Halothane = 0.75% Isoflurane = 1.16% Euflurane = 1.68% Sevoflurane = 2% Deslurane = 6%

N2O alone is unable to produce adequate anesthesia ( require high conc. )

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No Effect on MAC Gender Duration of anesthesia Carbon dioxide tension (21-95 mmHg) Metabolic Acid base status Hypertension Hyperkalemia

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Factors determining how quickly the inhalational agent reaches the alveoli?

1-Increasing the delivered concentrations of anesthetic

2- The gas flow rate through the anesthetic machine

3-Increasing minute ventilation MV = Respiratory Rate × Tidal volume

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Factors determining how quickly the inhalational agent reaches the brain from the alveoli in order to establish anesthesia?

1- The rate of blood flow to the brain2- The solubility of the inhalational agent in

the brain3- The difference in the arterial and venous

concentration of the inhalational agent

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NHALATIONAL ANAESTHETIC AGENT

Nitrous Oxide (N2O)

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Physical property:- laughing- Not flammable- Odorless- Colorless- Tasteless

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PHARMACOLOGY:- Good Analgesic- Weak anesthetic- Excreted via lungs- MAC = 105%- Lower water solubility- Not Metabolized in the body

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SIDE EFFECTS:- Diffusion Hypoxia.- Effects on closed gas spaces.(nitrous oxide can

diffuse 20 times faster into closed spaces than it can be removed, resulting in expansion of pneumothorax, bowel gas, or air embolism or in an increase in pressure within noncompliant cavities such as the cranium or middle ear.

- CVS depression- Toxicity- Teratogenic

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What is diffusion hypoxia? Diffusion hypoxia is a decrease in PO2 usually

observed as the patient is emerging from an inhalational anesthetic where nitrous oxide (N2O) was a component. The rapid outpouring of insoluble N2O can displace alveolar oxygen, resulting in hypoxia. All patients should receive supplemental O2 at the end of an anesthetic and during the immediate recovery period.

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Second gas effect: The ability of the large volume uptake of one gas (first gas) to accelerate the rate of rise of the alveolar partial pressure of a concurrently administered companion gas (second gas) is known as the second gas effect.

Apr 12, 2023

Dr. M

ed. Khaled R

adaideh

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Halothane

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Synthesized in 1951.* Volatile liquid easily vaporized, stable, and nonflammable* Most potent inhalational anesthetic•MAC of 0.75%•Colorless liquid , pleasant smell , decomposed by light. So should be stored in container away from light and heat • It has low blood/gas solubility coeffient of 2.5 and thus induction of anasthesia is relatively rapid.

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20% metabolized in liver by oxidative

pathways.

Major metabolites : bromin, chlorine,

Trifloroacetic acid, Trifloroacetylethanl

amide.

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The induction dose varies from patient to patient. The maintenance dose varies from 0.5 to 1.5%.

Halothane may be administered with either oxygen or a mixture of oxygen and nitrous oxide.

How is Halothane Supplied Halothane is supplied in amber colored 250 mL

glass bottles, stabilized with thymol 0.01% (w/w). Store in cool, dry place and protect from undue

exposure to light.

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Indications Halothane is indicated for the induction and

maintenance of general anesthesia. Contraindications Halothane is not recommended for obstetrical

anesthesia except when uterine relaxation is required.

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Respiratory system: Halothane anesthesia progressively depresses

respiration. Its cause inhibition of salivary & bronchial secretion. Its may cause tachypnea & reduce in tidal volume and

alveolar ventilation . Its cause decrease in mucocillary function which lead

to sputum retention. It causes bronchodilation. Hypoxia, acidosis, or apnea

may develop during deep anesthesia.

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Cardiovascular system: Halothane anesthesia reduces the blood pressure, and cause

bradycardia.(atropin may reverse bradycardia.). It cause myocardial relaxation & Hypotention. Its also causes dilation of the vessels of the skin and skeletal

muscles Halothane maybe advantages In pts with CAD , bcz of

decrease of oxygen demand. Arrhythemias are very commone .(especially with

epinephrine).◦ To minimize effects :

Avoid hypoxemia and hypercapnia Avoid conc. Of adrenaline higher than 1 in 10000

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Gastro intestinal tract:Inhibition of gastrointestinal motility.

Cause sever post. Operative nausea & vomiting Uterus: Halothane relaxes uterine muscle, may cause postpartum

hemorrhage . Concentration of less than 0.5 % associated with increase

blood loss during therapeutic abortion.Skeletal muscle: Its cause skeletal muscle relaxation . Postoperatively , shivering is common , this increase oxygen

requirement>>> which cause hypoxemia

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Hepatic dysfunction: Two type of dysfunction: 1- Type I hepatotoxicity ,mild, associated with derangement

in liver function test , this result from metabolic of Halothane in liver. results from reductive (anaerobic) biotransformation of halothane rather than the normal oxidative pathway.

2- Type II hepatotoxicity: fulminate (uncommon); sever jaundice ,fever,progressing to fulminating hepatic necrosis,

Its increased by repeated exposure of the drugs.high mortality 30-70%

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1- A careful anasthetic history .2- repeated exposure of halothane within

3 months should be avoided.3- History of unexplained jaundice or

pyrexia after previous exposure of halothane.

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Rapid smooth induction . Minimal stimulation of salivary & bronchial

secretion. Brochiodilatation. Muscle relaxant . Relatively rapid recovery.

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Poor analgesia.

Arrhythmias.

Post operatively shivering.

Possibility of liver toxicity.

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Enflurane

MAC =1.68%

Potent cardiovascular depressant

Apr 12, 2023Dr. Med. Khaled Radaideh 31

IsofluraneProperties

- isomer of enflurane.- Carcinogenic (not approved)- colorless, volatile, liquid, pungent odor.- stable.- No preservative .- Non-flammable.

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IsofluraneProperties

- Least soluble of the modern inhalational agent

equilibrate more rapidly

- Induction rapid theoretically (pungency??)

- pungency cough, breath holding.

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Isofluraneeffects on systems:-

Respiratory:dose dependent depression of vetilation.CVS:- myocardial depressant (vitro Vs Clinical), coronary vasodilatation (coronary steal syndrome).uterus: relaxation of uterine muscles (same).

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Isofluraneeffects on systems:-

CNS:

low concentration Vs High concentration.

Low : no change on the flow.

High : increase blood flow by

vasodilatation of the cerebral arteries.

-Muscles: relaxation (dose-dependent).

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IsofluraneAdvantages and Disadvantages

Advantages-Rapid induction and recovery.-Little risk of hepatic or renal toxicity.-Cardiovascular stability. -Muscle relaxation.Disadvantages-Pungent odor.-Coronary vasodilatation.

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SevofluraneProperties

-New drug.-Non flammable.-Pleasant smell.-MAC 2%.-Stable.-Low blood/gas partition coefficient faster equilibrium.- non irritant so the fastest for induction.

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SevofluraneAdvantages and Disadvantages

Advantages 1 .Well tolerated (non-irritant, sweet odor), even at high

concentrations, making this the agent of choice for inhalational induction .

2 .Rapid induction and recovery (low blood:gas coefficient)

3 .Does not sensitize the myocardium to catecholamines as much as halothane.

4 .Does not result in carbon monoxide production with dry soda lime .

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SevofluraneAdvantages and Disadvantages

Disadvantages 1 .Less potent than similar halogenated agents.

2 .Interacts with CO2 absorbers. In the presence of soda lime (and more with barium lime) compound A (a vinyl ether) is produced which is toxic to the brain, liver, and kidneys .

3 .About 5% is metabolized and elevation of serum fluoride levels has led to concerns about the risk of renal toxicity .

4 .Postoperative agitation may be more common in children then seen with halothane .

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Sevofluraneeffects on systems

- - Respiratory:-non-irritant, depression.-CVS: same as isoflurane (slightly lower effect)-CNS: same as halothane and isoflurane.-Muscle relaxation: same as isoflurane.

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Desflurane

MAC =6 %

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