Barbiturates anesthesia induction

Various barbiturates such as the short acting agent pentobarbital and the ultra-short acting agents thiopental and methohexital are used for anesthesia induction. They produce loss of consciousness without analgesia and with little effects on the cardiovascular system. Unconsciousness is combined with respiratory depression as the barbiturates produce non-selective CNS depression. 

Thiopental Pentothal Penthiobarbital Thiopentone Short-acting barbiturate/ anesthetic Induction of presurgical anesthesia o o >r NH... 

Induction is a part of stage I anesthesia. It begins with the administration of an anestheticdrug and lasts until consciousness is lost. With some induction drugs, such as the short-acting barbiturates, this stage may last only 5 to 10 seconds. 

The answer is c. (Hardman, p 323.) Induction of anesthesia by parenteral administration of thiopental sodium and other barbiturates is... 

Thiopental and methohexital belong to the barbiturates which, depending on dose, produce sedation, sleepiness, or anesthesia. Barbiturates lower the pain threshold and thereby facilitate defensive reflex movements they also depress the respiratory center. Barbiturates are frequently used for induction of anesthesia. 

Recovery is sufficiently rapid with most intravenous drugs to permit their use for short ambulatory (outpatient) surgical procedures. In the case of propofol, recovery times are similar to those seen with sevoflurane and desflurane. Although most intravenous anesthetics lack antinociceptive (analgesic) properties, their potency is adequate for short superficial surgical procedures when combined with nitrous oxide or local anesthetics, or both. Adjunctive use of potent opioids (eg, fentanyl, sufentanil or remifentanil see Chapter 31) contributes to improved cardiovascular stability, enhanced sedation, and perioperative analgesia. However, opioid compounds also enhance the ventilatory depressant effects of the intravenous agents and increase postoperative emesis. Benzodiazepines (eg, midazolam, diazepam) have a slower onset and slower recovery than the barbiturates or propofol and are rarely used for induction of anesthesia. However, preanesthetic administration of benzodiazepines (eg, midazolam) can be used to provide anxiolysis, sedation, and amnesia when used as part of an inhalational, intravenous, or balanced anesthetic technique. 

The general pharmacology of the barbiturates is discussed in Chapter 22. Thiopental is a barbiturate commonly used for induction of anesthesia. Thiamylal is structurally almost identical to thiopental and has the same pharmacokinetic and pharmacodynamic profile. 

When utilized as sedative hypnotics, barbiturates are administered orally. They are rapidly and completely absorbed by this route with nearly 100% bioavailability and an onset of action ranging from 10 to 60 min.3 Sodium salts are more rapidly absorbed than free acids. Intramuscular injections of sodium salts should be made deep into the muscle to prevent pain and tissue damage. Some barbiturates are also administered rectally barbiturates utilized for the induction and maintenance of anesthesia (thiopental) or for treating status epilepticus (phenobarbital) are administered intravenously. 

Classification Barbiturates Preoperative Indication Decrease anxiety facilitate induction of anesthesia Drug Amobarbital Butabarbital Pentobarbital Phenobarbital Secobarbital Method of Administration Oral 200 mg 1 to 2 hours before surgery Oral 50-100 mg 60 to 90 minutes before surgery Oral 100 mg IM 150-200 mg IM 130-200 mg 60 to 90 minutes before surgery Oral 200-300 mg 1 to 2 hours before surgery... 

The rapid-acting barbiturates, such as methohexital (Brevital), are used as intravenous anesthetics/induction agents. Advantages are rapid anesthesia and short duration of action. A disadvantage is respiratory suppression with higher doses. 

Propofol (2,6-diisopropylphenol) is an extremely popular intravenous anesthetic. Its rate of onset of action is similar to that of the intravenous barbiturates recovery is more rapid and patients are able to ambulate sooner after propofol. Furthermore, patients subjectively "feel better" in the immediate postoperative period after propofol as compared with other intravenous anesthetics. Postoperative nausea and vomiting is less common because propofol has antiemetic actions. Propofol is used for both induction and maintenance of anesthesia however, cumulative effects can delay arousal following prolonged infusion. These favorable properties are responsible for the extensive use of propofol as a component of balanced anesthesia and for its great popularity as an anesthetic for use... 

Barbiturates are classified according to their duration of action (Figure 9.7). For example, thiopental [thye oh PEN tal], which acts within seconds and has a duration of action of about 30 minutes, is used in the intravenous induction of anesthesia. By contrast, phenobarbital [fee noe BAR bi tal], which has a duration of action greater than a day, is useful in the treatment of seizures (see p. 148). Pentobarbital [pen toe BAR bi tal], secobarbital [see koe BAR bi tal] and amobarbital [am oh BAR bi tal] are short-acting barbiturates, which are effective as sedative and hypnotic (but not antianxiety) agents. 

Rapid induction of anesthesia (short-acting barbiturate)... 

Trade names Anesthal Hypnostan Intraval Nesdonal Sodipental Thiopental (Baxter) Trapanal Indications Induction of anesthesia Category Barbiturate Half-life 3-12 hours... 

Alfentanil, an opiate analgesic (8 to 50 mcg/kg IV), is indicated as an adjunct to general anesthetic in the maintenance of general anesthesia with barbiturate, nitrous oxide, and oxygen. In addition, it is used as a primary anesthetic for induction of anesthesia when endotracheal intubation and mechanical ventilation are required. 

ABSORPTION, FATE, AND EXCRETION For sedative-hypnotic use, the barbiturates usually are administered orally (Table 16-3) absorption is rapid and nearly complete. The onset of action varies from 10-60 minutes, depending on the agent and the formulation, and is delayed by the presence of food in the stomach. When necessary, intramuscular injections of solutions of the sodium salts should be placed deeply into large muscles to avoid the pain and possible necrosis that can result at more superficial sites. The intravenous route usually is reserved for the management of status epilepticus (phenobarbital sodium) or for the induction and/or maintenance of general anesthesia (e.g., thiopental or methohexital). 

Thiopental is used for induction of anesthesia Pharmacokinetics of barbiturates ... 

Methohexital [18652-93-2] (Bievital), C H gN202, (2) is a barbiturate iv anesthetic iuduction agent that has a slighdy faster onset than thiopentone and less accumulation. The recovery from anesthesia is also slighdy faster and better. However, induction is associated with an iucreased iucidence of excitatory phenomena. Methohexital also causes respiratory and cardiovascular depression and is unstable iu solution, necessitating reconstitution before... 

Propofol Propofol produces anesthesia at a rate similar to that of the intravenous barbiturates, and recovery is more rapid. Propofol has antiemetic actions, and recovery is not delayed after prolonged infusion. The drug is commonly used as a component of balanced anesthesia and as an anesthetic in outpatient surgery. Propofol may cause marked hypotension during induction of anesthesia, primarily through decreased peripheral resistance. Total body clearance of propofol is greater than hepatic blood flow, suggesting that its elimination includes other mechanisms in addition to metabolism by liver enzymes. 

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