BIOM 3090 Lecture Notes - Lecture 22: Premedication, Central Nervous System Depression, Inhalant
9 Jun 2018
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Induction agents
Induction agents
- Induction agents are general anesthetics that are administered by the IV
route
o Goal is to render patient unconscious rapidly
o Short duration; effect wears off within a short time (1-3 min)
o Patient is then transferred to an inhalant anesthetic
- Why not just give a long-lasting injectable general anesthetic? → Higher risk
o In an emergency (e.g. patient stops breathing) we can reduce
concentration of inhalant anesthetics within minutes via artificial
ventilation
▪ Manual ventilation: squeezing the anesthetic machines
reservoir bag forces air into the patient’s lungs
o We cannot, however, remove injectable anesthetics → must wait for
metabolism and excretion to occur → may take too long → higher risk
of death as anesthetic continues to depress CNS excessively if
administered as bolus (though relatively safe if administered via a
constant rate infusion)
- Why bother with the induction agent? Why not just give the inhalant? →
Onset of effect is too slow
- A patient passes through various stages or planes of anesthesia during
induction
o I. Stage of analgesia
▪ Analgesia, amnesia, euphoria, then semi-consciousness
o II. Stage of excitement
▪ Struggling, delirium, irregular breathing, +/- vomiting,
urination, defecation, combative behaviour (semi-conscious)
o III. Stage or plane of surgical anesthesia
▪ Unconscious; regular breathing returns, movements cease
o If process goes too far → IV. Stage of medullary depression
▪ Breathing stops, heart stops → death
- Want to get through excitement phase so rapidly that it may not even be
experienced
- Inhalant anesthetics work too slowly
o Patient struggles, etc. during induction
- Rapidly acting injectables are used
- As we have seen, general anesthetics cause unconsciousness but do not stop
the production or propagation of action potentials in peripheral pain
pathways
o Patients may awaken if large numbers of pain signals are delivered to
the reticular activation system
▪ This is true of both IV and inhalant anesthetics
▪ Prior to painful procedures, an analgesic is administered (as
part of the premedication) to inhibit pain signal propagation
• Painful manipulations → possible arousal → prevent
with analgesic
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Document Summary
Induction agents are general anesthetics that are administered by the iv route: goal is to render patient unconscious rapidly, short duration; effect wears off within a short time (1-3 min, patient is then transferred to an inhalant anesthetic. A patient passes through various stages or planes of anesthesia during induction: i. Stage of analgesia: analgesia, amnesia, euphoria, then semi-consciousness, ii. Stage of excitement: struggling, delirium, irregular breathing, +/- vomiting, urination, defecation, combative behaviour (semi-conscious, iii. Stage or plane of surgical anesthesia: unconscious; regular breathing returns, movements cease, if process goes too far iv. Stage of medullary depression: breathing stops, heart stops death. Want to get through excitement phase so rapidly that it may not even be experienced. Inhalant anesthetics work too slowly: patient struggles, etc. during induction. Compatible with other agents and iv fluids within precipitating. Minimal cardiovascular or respiratory effects or visceral toxicity.
