CHILD by intravenous injection, 10 micrograms/kg; subsequent dose of 100 micrograms/kg if no response; if intravenous route not possible, may be given in divided doses by intramuscular or subcutaneous injection
NEONATE by subcutaneous, intramuscular or intravenous injection, 10 micrograms/kg, repeated every 2-3 minutes or by intramuscular injection, 200 micrograms (60 micrograms/kg) as a single dose at birth (onset of action slower).
Agents used in Anaesthesia
Thiopental Sodium (aka Thiopentone Sodium) by Andrew Scott Pearson
Intravenous Anaesthetic: Barbiturate
Induction of general anaesthesia; anaesthesia of short duration; reduction of raised intracranial pressure if ventilation controlled; rapid sequence induction to treat status epilepticus.
Thiopentone is a barbiturate, also known as Thiopental. In this form it is not water soluble and is therefore combined with sodium carbonate to form thiopental/thiopentone sodium. This is a very alkaline and unstable solution in water, which requires it to be dissolved immediately before use. Thiopentone is highly lipid soluble and easily crosses the blood brain barrier into the central nervous system. It is a general anaesthetic and induces unconsciousness and suppresses motor and autonomic responses. It does this by binding a distinctive site on GABAA receptors (gammabutyric acid A receptors), a type of neurotransmitter receptor found in nerve cells.
GABAA receptors are inhibitory. When bound and activated by GABA, they facilitate chloride channel opening in the neurone cell. The influx of Cl- into the cell causes it to hyperpolarise; this inhibits the neurone and stops it firing. Thiopentone is thought to enhance this neurone inhibitory effect.
Thiopentone is very fast acting and leads to rapid unconsciousness within approximately 30 seconds, the arm to brain circulation time. It is metabolised relatively slowly by the liver but because of its high lipid solubility, it is rapidly distributed to other high fat content tissues and leads to a very short duration of action. Patients given a single dose of thiopentone are awake within 10 minutes. This however, means that with repeated doses there is drug build up within the body fat which causes post operative drowsiness or ‘post op hangover’. This means thiopentone is only suitable for inducing anaesthesia and cannot be used for maintenance, unlike propofol.
Nerves and Synapses
We evolved from single celled organisms that lived in the sea; as such our cells are used to being bathed in a slightly salty environment. Our cells have developed methods of keeping the majority of Na+ and Cl- outside the cell whilst retaining potassium within the cell. The difference in ion balance allows cells to become polarised. Nerve cells make use of this property to transfer signals rapidly around the body. Nerves are polarised cells with a resting potential of approximately -70mV, i.e. they are more negatively charged inside when to compared to outside. They achieve this polarisation by the Na+K+ATPase which pumps 3 Na+ ions out of the cell and brings 2 K+ ions in.