Commonly used for induction because of rapid onset of action. They act within seconds and produce unconsciousness.
There is no special delivery system required. I/V (bolus/infusion) given.
Two drugs used are:
2. Thiopentone Sodium
Induction / Onset
When administered, produce anesthesia within seconds, even during first circulation through brain this state is produced.
a. Highly lipid soluble goes to the highly perfused organs; brain liver and kidneys. Afterwards to less perfused like muscles, fatty tissue and skin. Due to lipophilic nature, is redistributed to fatty tissues.
b. T1/2 – 3 min / 12 hrs
As redistributed to fatty tissues, so has 2 half-lives, one 3-5 minutes, action of which remains for 10-15 minutes.
Drowsiness remains for 12-24 hours, due to redistribution.
c. Metabolism / Excretion
Elimination half-life is 12 hours, during which it is excreted out. Metabolized in liver and metabolites are excreted in urine.
1. CVS / Respiration
Depressant effect on CVS and respiratory system.
Decrease in cardiac output and blood pressure
2. CNS – metabolism
Decreased metabolism and cerebral blood flow, so beneficial in patients having increased intracranial pressure or with pressing lesion (tumor) or head injury.
3. Pain / muscle relaxation
It does not have good analgesic property and is not a good muscle relaxant, so along with it analgesic and muscle relaxant is administered.
Dental / Endoscopy / Circumcision/ Orthopedics / Dressings / Psychoanalysis
Used mostly for short surgical procedures like dental extractions, endoscopy, orthopedic, changing painful dressing, psychoanalysis bio psychiatrist leading to diagnosis of psychiatric problems and treatment.
Named ‘truth drug’ because patient specks many things under its influence.
3. Restlessness –during recovery
4. Injection site pain
5. Inadvertent injection –artery or vein causing necrosis, thrombosis or damage to nerves
6. Acute porphyria –known to precipitate in susceptible patients. Also seen with Thiopentone sodium.
Very short duration of action
Repeated doses accumulate
Insignificant analgesic action
Rapid and pleasant induction
Cannot be used alone as an anesthetic
Less incidence of nausea/ vomiting
Coughing, hiccough, laryngospasm, bronchospasm may develop during induction
Muscle relaxation is not adequate
1. Clearance –cleared out rapidly, with shorter half-life of 4 hours
2. Potency –3-5 times potent than Thiopentone sodium.
3. Central excitation –whenever excitatory focus providing seizure like activity (epileptic), used for ablation of foci.
Use – ECT (anti-seizure) generally antiseizure activity, so given during ECG
Available as different formulations:
Emulsion (Conventional) oily preparation
Ampofol has less lipid content
Fospropofol; water soluble/aqueous preparation –prodrug
Disadvantage of oily preparations is that once they are opened up for use, there are chances of bacterial growth.
Disadvantage of aqueous preparation is that they are more painful at injury site.
a. Onset / recovery– induction is within seconds (10-15 sec)
b. . T1/2 – 2-8 / 30-60 min –has distributive half-life as well as elimination half life. Metabolism is ten times faster than Thiopentone sodium, so less hang over effects.
c. Metabolism / excretion –metabolized in liver, excreted as glucuronide and sulphate conjugation
1. CVS / Respiration
Depressive action on CVS and respiration. Much severe effect.
2. CNS (thiopental)
Decreases metabolic rate and cerebral blood flow.
3. Pain / Muscle relaxation
Not good muscle relaxant, with no analgesic property, supplemented analgesia and muscle relaxant are applied.
1. Advantages – post-op N/V
2. Used in ambulatory surgeries because propofol post–op volume is very less, so person feels much better earlier.
3. Also used for sedation, for which lesser dose is required. This sedation is for procedures like endoscopy or for prolonged periods in critically ill patients, e.g. on ventilators.
1. CVS / respiration –highly depressive
2. Injection site (lignocaine) –pain in water soluble preparations, either mixture of lignocaine and propofol is given or lignocaine is administered before at site of administration.
3. Elevated lipid levels in blood (conventional) –lipid preparations if used for prolonged periods
4. Muscle movements –hypotonus and sometimes tremors
5. Children (respiratory infections) – when used for prolonged periods lead to acidosis
– neurological effects when withdrawn or discontinued
Onset / recovery –onset of action within seconds
T1/2 – biphasic distribution with two distributive half-lives – 3 min and 29 min –elimination half-life of 4-6 hrs.
Metabolism occurs in liver
Excretion –renal (78%) / biliary (22%)
1. CVS / Respiration –does not affect very much, either no or minimal, so used in patients having poor cardiovascular reserves
2. CNS / Pain (thiopental) –decrease in blood flow and metabolism. No effect on pain so combined with analgesic.
Main use is in patients having poor cardiovascular reserves e.g. old or with IHD or cardiomyopathies.
1. Injection site –pain, so lignocaine is used
2. Nausea / vomiting / restlessness / tremors
3. Steroidogenesis inhibition – cortisol
Inhibition of adrenocortical hormone formation by inhibitory beta hydroxylation esp. cortisol and when given for short periods, transient effect occurs. If given for prolonged period, this effect can be responsible for severe side effects like hypotension and electrolyte imbalance, oliguria, etc.
Ketamine is hallucinogenic drug, available as racemic mixture of S and R enantiomers.
S enantiomer is more potent with less side effects, still administered as racemic mixture.
Phencyclidine (PCP) congener
Mechanism of action
- It blocks NMDA receptors in CNS, decreasing excitatory effects of glutamate, producing anesthesia.
- It dissociates thalamus from limbic system, producing dissociative anesthesia.
Mostly given I/V; but also I/M; oral; rectal
It is highly lipid soluble, so has wide distribution; rapidly crosses blood brain barrier to enter brain.
Metabolism occurs in liver and excretion occurs in urine.
Different mechanism of action. It binds NMDA receptors and blocks them, so that glutamate (excitatory neurotransmitter) cannot bind.
Psychoactive drug, has been abused as hallucinogenic drug.
2. Cerebral BF / metabolism
Effects cerebral blood flow and intracranial pressure, causes increase in cerebral metabolism and increase in cerebral blood flow, leading to increased intracranial pressure, so should be avoided in patients of head injury or space occupying lesion.
3. CVS – stimulation (2-20 min)
Cardio stimulatory by two mechanisms:
a. Sympathetic stimulation
b. Prevents reuptake of norepinephrine from adrenergic terminals.
Cardio stimulatory effect peaks within 2-4 minutes and normalizes in around 12-20 minutes.
4. Respiratory – reflexes / bronchodilation
No effect on reflexes and does not abolish ventilator reflexes. Person respires spontaneously without outside assistance.
Another advantage is that it causes bronchodilation due to:
a. Sympathetic stimulation
b. Mild degree of direct bronchodilatory effect
1. Dissociative anesthesia – cataleptic state
In which patient experiences analgesia, catatonia, amnesia, hypnosis, eyes open but unresponsive to painful stimuli, respiring spontaneously, patient is disassociated from surroundings, appears awake but cannot perceive what is going on around him, so called dissociative anesthesia.
Good analgesia given for short surgical procedures, where complete loss of consciousness is not required like
a. Old age
old age, where poor cardiovascular reserves are present (cardio stimulatory action).
Also commonly used in children
c. Hemodynamic stability
In patients with hemodynamic instability (septic shock, cardiogenic shock) or patients bleeding profusely.
Also useful for patients of chronic obstructive airway disorder, where bronchodilation has beneficial effect.
e. Topical – arthritic pain
Newer preparations of Ketamine are available for topical application for arthritic pain.
1. CVS – IHD
As cardio stimulatory avoided in patients with ischemic heart disease
2. Emergence delirium – BZD
Seen during recovery. Patient experiences hallucinations, illusions and dream like state. This is due to very high lipid solubility. Ketamine dissolves in nervous tissue, when plasma levels are decreased, effects are still present.
To avoid this patient is administered benzodiazepines like diazepam or midazolam.
|No sensitization of heart to catecholamines||pharyngeal/ laryngeal reflexes are not abolished|
|Rapid recovery||In over dosage depression of VMC, myocardium and respiration|
|No excitement during induction||Regurgitation due to relaxation of gastro esophageal sphincter|
|Injection may cause necrosis, thrombophlebitis, nerve damage, vasospasm on intra – arterial injection (may lead to gangrene)|
|Effective by both i/v & i/m injection||No muscle relaxation|
|Anesthesia is accompanied by profound analgesia||Tends to raise intraocular, intra cranial blood pressures and heart rate|
|Can be used alone for minor surgery||Hallucinations, nightmares and delirium may last up to 24 hrs.|
|Does not produce vomiting, hypotension, bronchospasm||Cannot be used for surgery on larynx, pharynx, bronchi|
|Less respiratory complications due to less impairment of pharyngeal/ laryngeal reflexes||Poor in relieving visceral pain|