Thiopentone

Thiopentone is a barbiturate that is used widely as an IV anaesthetic agent. It also has cerebroprotective and anticonvulsant activities.Awakening from a bolus dose is rapid due to redistribution, but hepatic metabolism is slow and sedative effects may persist for 24 hours. Repeated doses or infusion has a cumulative effect. Available in 500-mg ampoules or 2.5-g vial,which is dissolved in 20 or 100 ml WFI respectively to make a 2.5% solution.

Uses
Induction of anaesthesia
Status epilepticus

Contraindications
Airway obstruction
Previous hypersensitivity
Status asthmaticus
Porphyria

Administration
• IV bolus: 2.5–4 mg/kg.After injecting a test dose of 2 ml, if no pain, give the rest over 20–30 s until loss of eyelash reflex. Give further
50–100 mg if necessary

Reduce dose and inject more slowly in the elderly, patients with severe hepatic and renal impairment, and in hypovolaemic and shocked patients. In obese patients, dosage should be based on lean body mass.

How not to use thiopentone
Do not inject into an artery (pain and ischaemic damage)
Do not inject solution >2.5% (thrombophlebitis)

Adverse effects
Hypersensitivity reactions (1:14 000–35 000)
Coughing, laryngospasm
Bronchospasm (histamine release)
Respiratory depression and apnoea
Hypotension,myocardial depression
Tachycardia, arrhythmias
Tissue necrosis from extravasation

Cautions
Hypovolaemia
Septic shock
Elderly (reduce dose)
Asthma

Organ failure
CNS: sedative effects increased
Cardiac: exaggerated hypotension and ↓ cardiac output
Respiratory: ↑ respiratory depression
Hepatic: enhanced and prolonged sedative effect. Can precipitate coma
Renal: increased cerebral sensitivity