2. Introduction
These are volatile liquids used as inhalation anaesthesia
Examples are –
• Halothane
• Enflurane
• Isoflurane
• Sevoflurane
• Desflurane
3. Halothane
— It is the prototype drug
— Physical characteristics –
- volatile
- mild sweetish odour
- non irritant
- non inflammable
— It is a potent anaesthetic
— Poor analgesic and muscle relaxant
4. Advantages
— Pleasant to breathe and not hepatotoxic to children.
— It is a potent anaesthetic also.
— It not only abolishes pharyngeal and laryngeal reflexes
but also is a bronchodilator also; hence preferred for
asthmastics.
— Recovery from halothane is smooth and expect for
shivering ,usual nausea or vomiting are rare.
— It inhibits intestinal and uterine contraction; hence can
be used for assisting external or internal version of
foetus during late pregnancy.
5. Disadvantages and Adverse
Effects
— It has highest blood:gas partition coefficient and
hence induction as well as recovery is
comaparatively slow.
— Poor analgesic and muscle relaxant.
— It has vagomimetic action and causes bradycardia
and transient fall in BP.
— Sensitizes the myocardium to arrhythmic effects of
catecholamines.
6. — Halothane is oxidatively metabolised to tissue toxic
trifluoroethanol and bromide ion.
— Repeated administration of halothane can cause
severe hepatic necrosis(1:50,000).
— Its use during labour can prolong delivery and
cause postpartum haemorrhage.
— Halothane can trigger malignant hyperthermia in
genetically predisposed cases.
— Succinylcholine, if used as a muscle relaxant
alongwith halothane worsens the condition further.
— Halothane causes respiratory depression;
breathing is shallow and rapid.
7. Uses
— Halothane is particularly suitable for use in
children both for induction and maintenance of
anaesthesia.
— In adults it is mainly used as maintenance
anaesthesia after i.v induction.
— Halothane deficiencies in term of poor analgesia
and muscle relaxation are compensated by
concomitant use of nitrous oxide or opioids and
neuromuscular blockers.
8. Enflurane
q Physical Characteristics and Uses:
Ø Non irritating
Ø Non inflammable liquid with mild odour
q Advantages:
Ø Like halothane it decreases heart rate, cardiac output and
B.P
Ø Uterine relaxation is also similar to halothane
Ø Unlike halothane it does not sensitize heart to
catecholamines.
Ø It causes bronchodilation
Ø It is a better skeletal muscle relaxant than halothane.
Ø It has rapid induction and recovery than halothane.
9. q Disadvantages and adverse effect:
Ø Greater respiratory depression.
Ø May cause polyuric renal failure.
Ø Can cause jaundice and hepatotoxicity.
q Contraindications:
Ø In epileptic patients.
Ø In renal failure.
10. Isoflurane
— It has totally replaced its earlier introduced isomer
Enflurane.
— Physical Characteristics and uses:
Ø Structural analogue of enflurane
Ø Non inflammable liquid
Ø Pungent odour
Ø Exhibits rapid induction and recovery than halothane
Ø One and half time more potent than enflurane
11. — Advantages:
Ø Pupil do not dilate and light reflex is not lost.
Ø Undergoes minimal metabolism as result less
fluoride is produced, hence chance of organ toxicity
is rare.
Ø Unlike halothane it does not sensitize myocardium to
action of catecholamines.
Ø Depresses cortical EEG activity and is preferred for
neurosurgery.
Ø Also a muscle relaxant and potent coronary
vasodilator.
Ø Potent Bronchodilator .
12. — Disadvantage and adverse effect:
Ø Pungent odour and causes bronchial irritation.
Ø Exhibit phenomena of coronary steal which may
precipitate regional myocardial ischemia.
Ø Causes hypotension and reflex tachycardia.
13. Desflurane
— Structurally similar to isoflurane.
— Has anaesthetic actions similar to isoflurane .
— Physical Characteristics and Uses:
Ø Non inflammable
Ø Non explosive
Ø Irritant
Ø Volatile Liquid
Ø Rapid induction and recovery.
14. — Advantages:
Ø Used for outpatient surgery as patient can be
discharged few hours after surgery.
Ø Less risk of organ toxicity.
Ø Sensitizes myocardium to catecholamines to a lesser
extent than halothane or enflurane.
Ø Good muscle relaxant.
Ø Seizure provoking potential is negligible.
15. — Disadvantage and adverse effect:
Ø Irritant to airways, may provoke breathholding,
apnea, coughing, increased salivation and
laryngospasm.
Ø Not suitable for induction in children.
Ø Causes respiratory depression.
16. Sevoflurane
— Physical properties and uses:
Ø Anaesthetic properties between isoflurane and
desflurane
Ø Non pungent
Ø Non inflammable
Ø Volatile liquid
Ø Induction is rapid and smooth
Ø Recovery is faster than halothane
17. — Advantages:
Ø Does not cause respiratory irritation.
Ø Acceptability better by children.
Ø Induction and emergence from anaesthesia are as
fast as desflurane.
Ø Good muscle relaxant property.
Ø Cardiovascular effect similar to those of isoflurane
but does not produce “coronary steal”
Ø Sensitizes myocardium to catecholamines to a lesser
extent than halothane or enflurane.
18. — Disadvantage and adverse effect:
Ø Not a bronchodilator.
Ø May trigger malignant hyperthermia in susceptible
patient.
Ø Shivering, nausea and vomiting are reported in post
operative period.
