Halothane

INTRODUCTION
  • General anaesthetic
  • Volatile liquid inhalation anaesthetic
  • 1% Thymol is used as preservative
  • IUPAC Name – 2-bromo-2-chloro-1,1,1-trifluoroethane
  • Brand Name – Fluothane
  • Induction and maintenance anaesthetic agent
  • Halothane sensitizes the myocardium to catecholamines
  • Least expensive & least pungent.
  • Potent anesthetic, no analgesia.
  • Dissolve rubber and corrodes metals.
  • Drager Narko test is done for halothane.
  • Contains 0.01% thymol for stability.
PHYSICAL AND CHEMICAL PROPERTIES:
  • Volatile Heavy liquid (Specific gravity – 1.87)
  • Boiling point – 50.20C
  • Vapour pressure – 243 mmHg at 200C
  • Molecular Weight – 197.4 u
  • Decomposes when exposed to light (Amber colouredbottles and addition of thymol)
  • Non-explosive and non-inflammable
  • Halothane Potentiates competitive neuromuscular blockers
MINUMUM ALVEOLAR CONCENTRATION/MAC:
  • Dogs – 1.87
  • Cats – 1.19
  • Cattle – 0.76
  • Horses – 0.88
  • Humans – 0.76
DOSE:
  • Induction (Halothane alone)
  1. All species : 2.0 – 4.0% (of inspired air)
  • Maintenance (Halothane alone)
  1. Small animals : 0.5 – 1.5%
  2. Large animals : 1.0 – 2.0%
PHARMACOKINETICS:
  • Rapidly absorbed and rapidly excreted through lungs
  1. 20% : Biotransformation in liver and excreted through lungs
  2. 60% : Excreted unchanged through lungs
  3. 20% : Excreted via other routes, either unchanged or metabolised and stored in body for many hours to days
  • Portal flow is maximally reduced by Halothane
  • Presence of trifluroacetic acid (TFA) in urine indicates that volatile anaesthetic agent used was Halothane
ADVESE EFFECTS:
  • Vasodilatation, hypotension, shivering and tremors on recovery
  • Malignant hyperthermia
  • Cardiac arrhythmias
  • postoperative hepatitis( Methoxyflurane avoided in future)
  • Centrilobular necrosis in the liver 
  • Post operative jaundice
  • Cardiopulmonary depression and cardiac arrest
CONTRAINDICATIONS AND PRECAUTIONS:
  • Used with caution in animals with increased CSF, head injury, etc.
  • Not used in animals having problems after previous halothane exposure
  • Halothane is Contraindicated in patients with Cardiac arrythmia
CLINICAL USES AND ADMINISTRATION:
  • Capable of induction and maintenance of anaesthesia without assistance from other CNS depressants
  • Its properties include cardiac depression at high levels, cardiac sensitisation to catecholamines such as norepinephrine, and potent bronchial relaxation
  • Used in a closed rebreathing system with precision thermo-stable or thermo-compensated, calibrated vapourisers
  • Open and semi-open systems are used only in case of very small dogs, cats and laboratory animals
  • Best uterine relaxation is seen with Halothane
AVAILABILITY:
  • Available as a volatile liquid, at 30, 50, 200, 250 ml per container
Exam Question
  • Halothane has the least analgesic effect
  • Halothane sensitizes the myocardium to catecholamines
  • Halothane is a pleasant smelling gas that can cause postoperative hepatitis
  • Portal flow is maximally reduced by Halothane
  • Halothane can cause malignant hyperthermia
  • Methoxyflurane should NOT be used in a patient with previous history of halothane induces hepatitis 
  • Centrilobular necrosis in the liver is due to Halothane
  • Best uterine relaxation is seen with Halothane
  • Halothane Potentiates competitive neuromuscular blockers
  • Halothane is Contraindicated in patients with Cardiac arrythmia
  • Presence of trifluroacetic acid (TFA) in urine indicates that volatile anaesthetic agent used was Halothane
  • In a 2 months old infant undergoing surgery for biliary atresia halothane should be avoided
  • Halothane corrodes metal in vaporizers and breathing systems
  • Post operative jaundice is because of use of Halothane

Don't Forget to Solve all the previous Year Question asked on Halothane