7..intravenous anaesthesia 2

7/31/2019 7..Intravenous Anaesthesia 2

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INTRAVENOUS ANAESTHESIA

E OMONGE


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Anaesthetic drugs - qualities Readily controllable

Induction and recovery rapid


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General anaesthesiaAdjunct to surgery renders the patient

unaware or unresponsive to pain stimuli

Systemic

effect on the CNS

Intravenous agents act more rapidlyproducing unconsciousness in

20sec.thiopental, etomidate andpropofol are used in induction ofanaesthesia


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Other induction drugs Benzodiazepines diazepam,

midazolam( less rapid action)

Propofol and Ketamine can be used forshort operations . Most of the otheragents need maintenance with other

drugs Droperidol causes deep sedation and

analgesia


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GENERAL ANAESTHESIA PARENTERAL( INTRAVENOUS )

INHALATIONAL


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PHARMAKOKINETICS Small, hydrophobic, substituted

aromatic or heterocyclic compounds

Hydrophobic

preferential partition inperfused and lipophilic brain and spinalcord anaesthesia

Blood level fall and back diffusion inthe less well perfused muscle ,visceraand at slower rate in hydrophobic

adipose


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KINETICS Termination redistribution out of CNS

Blood level fall , metabolism and lipophilicity

of drug in peripheral compartment Half-life dependent hydrophobicity ,

metabolic clearance , and time

t initial redistribution and subsequentmetabolism take minutes and hoursrespectively with awakening level in between


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VARIABILITY Cardiac output

Septic shock

Cardiomyopathy

Age


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CONTEXT SENSITIVE HALF-TIME Modest for etomidate, propofol and

ketamine

Increase with infusion time fordiazepam, thiopental

Determined by redistribution from

active site


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BARBITURATES Derivatives of barbituric acid Sodium thiopental ,thiomylal

,methohexital

Racemic mixtures withenantioselectivity

Sodium salts

Stability post reconstitution

1 weekand 6 weeks respectively for thiopentaland thiomylal

Precipitates when mixed with more


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KINETICS Duration of action dependent on

redistribution- very high lipid solubility

makes thiopental rapid acting Clearance influence duration following

multiple doses

Methohexital much rapid clearance

Prolonged use of thiopental andthiomylal can cause long duration

coma due to slow elimination and large


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KINETICS Methohexital outpatient, rapid return

to consciousness where propofol is

unavailable Elimination hepatic metabolism and

renal excretion

Inactive metabolites Plasma protein binding is high- Vd

decrease in hepatic disease andcondition that decrease protein


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INDICATIONS Induction of anaesthesia- rapid

unconsciousness in seconds, peak in 1

minute, duration of 5-8 minutes (thiopent-al )

Higher doses for neonates and infants

Smaller doses for elderly and inpregnancy

Reduce doses after diazepam premed

Thyomylal equipotent andmethohexital is 3x more potent


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INDICATIONS Methohexital produces pain on injection

Pain reduction by using large veins orLA

Avoid intra-aterial injection

Dygeusia with thiopental

Excitement e.g tremors, hypertonus,hiccoughs with methohexital

Rectal route x10


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SIDE EFFECTS Cerebral metabolic rate reduction

Reduced intraocular pressure

Dose dependent decrease BP due tovasodilatation

Myocardial contraction reduced

Compensatory HR rise

Care in patients with heart disease and

b- adrenoceptor blockers


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SIDE EFFECTS

Respiratory depression

Care with opiods but can be used in

asthmatics due to little effect onbronchomotor response


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PROPOFOL

I V

Kinetics similar to thiopental

Rapid recovery due to high clearance

Metabolites from liver less active andloss via kidney

PPB high

Used in induction and maintanance of

GA in short procedures


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ETOMIDATE

Large margin of dose that causeanaesthetic effect and that which

causes respiratory depression More rapidly metabolised than

thiopental

Less likely to cause prolonged hangover

More involuntary movement duringinduction


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Etomidate

Adrenocortical suppression seen

Useful in day case surgery


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KETAMINE

Resembles phencyclidine

Produce anaesthesia like state and

profound analgesia

Less euphoria and sensory distortion cf.phencyclidine

Block activation of NMDA-receptor(excitatory receptor)


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Ketamine

IV

Slow effect 2-5 min.

Dissociative anaesthesia

Sensory loss ,analgesia and amnesiaand paralysis of movement withoutactual loss of consciousnessinvoluntarymovement during induction andrecovery


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Ketamine

BP and HR increases

Respiration unaffected with effective

anaesthetic doses

Hallucinations, delirium, and irrationalbehaviour common during recovery

Less adverse effects in children


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Midazolam

Benzodiazepene

Slower onset and offset of action

Respiratory and cardiovasculardepression

Perioperative sedative in endoscopy

7..intravenous anaesthesia 2

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