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 .
- 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 by liver mainly by microsomal enzyme
- Slightly in the CNS and Kidney
- 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
- Thermbophlebities, Necrosis and gangrene
- It is not a muscle relaxan
- It reduces intraocular pressure at higher doses.
- It dilates the pupil initially and then contract.
- Pain at the injection site.
- Necrosis and local tissue reaction .
- Garlic onion taste .
- Facial edema , bronchospasm and anaphylaxis
- Status asthmatics
- Porphyria’s (Acute intermittent ,Varieget Porphyria)
- Known hypersensitivity
- Cardiovascular Instability
- Patient with respiratory obstructive problems.
- Stenosis , heart block and Constrictive pericarditis.
- Inflammatory where airway is difficult to manage .
- Dystrophia myotonica .
COMPLICATIONS (SYMPATHETIC )
- Respiratory and cardiovascular depression.
ACCIDENTAL INTRA-ARTERIAL INJECTION
- Accidental intra arterial injection may cause
TREATMENT OF ACCIDENTAL INTRA ARTERIAL INJECTION
- 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 .