INTRAVENOUS ANESTHETICS

Intravenous anesthetics act much more rapidly, producing unconsciousness in about 20 seconds, as soon as the drug reaches the brain from the site of its injection. These agents used for induction of anaesthesia followed by inhalation agent. The main induction agent in current use is: thiopentone, etomidate, propofol, ketamine and short acting benzodiazepine (midazolam).

Thiopentone: Thiopentone is a barbiturate with very high lipid solubility. After intravenous administration the drug enters to tissues with a large blood flow (liver, kidneys, brain, etc) and more slowly to muscle. Uptake into body fat occurs slowly because of the low blood flow to this tissue, which may cause prolonged effect if given repeatedly. It causes cardiovascular depression.

Etomidate: It is more quickly metabolized and the risk of cardiovascular depression is less compared to thiopentone. Etomidate suppresses the adrenal cortex, which has been associated with an increase in mortality in severely ill patients.

Ketamine: acts more slowly than thiopentone and produces a different effect, known as dissociative anaesthesia in which there is a marked sensory loss and analgesia, as well as amnesia and paralysis of movement, without actual loss of consciousness. Ketamine causes dysphoria, hallucinations during recovery.

Benzodiazepines including diazepam, lorazepam, and midazolam are used in general anesthetic procedures. Compared with intravenous barbiturates, benzodiazepines produce a slower onset of central nervous system effects. Benzodiazepines prolong the postanesthetic recovery period but also cause a high incidence of amnesia for events occurring after the drug is administered.The benzodiazepines are useful in anesthesia as premedication and intraoperative sedation.

Opioid analgesic anesthesia: Opioid analgesics can be used for general anesthesia, in patients undergoing cardiac surgery and fentanyl and its derivates are commonly used for these purposes.

Preanesthetic medication: It is the use of drugs prior to the administration of anaesthetic agent with the important objective of making anaesthesia safer and more agreable to the patient. The drugs commonly used are, opioid analgesics, barbiturates, anticholinergics, anti emetics and glucocorticoids.