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Complete drug review of Thiopentone Sodium (Intravenous Anesthetics)

Thiopentone Sodium (Intravenous Anesthetics)

  • Thiopentone sodium is a ultra short acting barbiturates.
  • Thiopentone was clinically introduced  by Water and Lundy in 1934 for the induction of anesthesia.

PHYSICAL PROPERTIES OF THIOPENTONE SODIUM

  • It is available as yellow amorphous powder
  • Its PH is 10.5 which is highly alkaline solution .
  • It is a sulphur derivative of Barbituric acid.
  • It is prepared in nitrogen.
  • The preservative used in it is 6% anhydrous sodium carbonate which increases its solubility.
  • Available as 5% and 2.5% solutions ,compatible with normal saline and water for injection.
  • Available as 0.5gm and 1gm powder form.
  • Usually 2.5% solution is preferred because it is highly lipid soluble and solution concentrations greater than the 2.5% can be painful during injection which may lead to venous thrombosis.
  • It is a poor analgesic and weak muscle relaxants.
  • This drug is commonly used as the induction agent .
  • It is highly soluble in water.
  • The refrigerated solution can be used for two weeks .

PHARMACOKINETICS 

  • Onset of action: 10-15 sec
  • Acts for 5-15 min
  • Volume of distribution is 2.5 ml per kg
  • Elimination half life : 10.3 hours
  • Dose: 3-5 mg/kg body weight
  • Equilibrium between brain and plasma is achieved in 1 min

METABOLISM 

  • Metabolism by liver mainly by microsomal enzyme
  • Slightly in the CNS and Kidney

EXCRETION 

  • High lipid solubility increase re-absorption.

MECHANISM OF ACTION

  • It acts on the GABA receptor

EFFECTS OF THIOPENTONE ON THE SYSTEM

CENTRAL NERVOUS SYSTEM (CNS)

  • Unconsciousness is produced with 15 sec after the injection, that’s why it is called as ultra short acting drug.
  • Consciousness is regained in 5-15 min due to the concept of redistribution of the drug into highly perfused organs first and then to the low perfused organs like fat and muscles.
  • Delirium and headache

 CARDIO VASCULAR SYSTEM (CVS)

  • It causes hypotension due to venous dilation which causes decrease in venous return .
  • It is also a myocardial depressant.
  • At the dose of 5mg per kg body weight , it causes decrease in BP due to sympathetic blockade.
  • Direct myocardial depression occurs at the dose used to decrease intracranial pressure.

RESPIRATORY SYSTEM (RS)

  • It causes respiratory depression at higher doses.
  • Transient Apnea is most common.
  • Inadequate depth laryngeal spasm
  • It causes apnea in presence of narcotics .
  • It causes depression of medullary and pontine ventilatory centers.
  • Brocospasm and laryngospasm are likely to occur in light anesthesia.

GASTRO INTESTINAL SYSTEM (GIT)

  • Nausea, salivation and emesis

DERMATOLOGY

  • Thermbophlebities, Necrosis and gangrene

MUSCLE RELAXANTS 

  • It is not a muscle relaxan

EYES

  • It reduces intraocular pressure at higher doses.
  • It dilates the pupil initially and then contract.

SIDE EFFECTS

  • Pain at the injection site.
  • Necrosis and local tissue reaction .
  • Garlic onion taste .
  • Facial edema , bronchospasm and anaphylaxis

CONTRAINDICATIONS

  • Status asthmatics
  • Porphyria’s (Acute intermittent ,Varieget Porphyria)
  • Known hypersensitivity
  • Cardiovascular Instability
  • Patient with respiratory obstructive problems.
  • Hypotension
  • Stenosis , heart block and Constrictive pericarditis.
  • Inflammatory where airway is difficult to manage .
  • Dystrophia myotonica .

COMPLICATIONS (SYMPATHETIC )

  • Laryngospasm
  • Tachyphylaxix
  • Hiccups
  • Respiratory and cardiovascular depression.
  • Coughing

ACCIDENTAL INTRA-ARTERIAL INJECTION 

  • Accidental intra arterial injection may cause
  • Thrombosis
  • Necrosis
  • Vasoconstriction

TREATMENT OF ACCIDENTAL INTRA ARTERIAL INJECTION 

  • Heparinasation
  • Intra arterial injection of lidocaine
  • Brachail plexus block, Steallate ganglion block .
  • a) Leave the needle at the injection site
  • b) Inject 500 units of heparin through the same needle , this will prevent thrombus by making the solution acidic .
  • c) Inject Papaverine 40-80 mg in 20 mg of saline
  • d) Tolazoline 5mL or Phenoxybenzamine 0.5 mg can also be used .
  • e) If none of the above is available , 5-10 ml of xylocaine 1% can be used .
  • f) Oral anticoagulants for 7 to 14 days .
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