BIOM 3090 Lecture Notes - Lecture 23: Propofol, Sodium Thiopental, Barbiturate
9 Jun 2018
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Physiological effects of Barbiturates
- CNS:
o Dose-dependent depression in 15-30s
▪ Unconscious for ~2-3 min
▪ Do not give full dose all at once (inject ½ to 2/3 of dose & wait
15s to see effect; may or may not need more)
o A partial dose (i.e. less than ~ half of calculated dose) is likely to cause
intense CNS excitation (may resemble seizure)
o Barbiturates are not analgesics; they actually enhance pain sensitivity
- Respiratory tract:
o Dose-dependent depression of respiration
o 20-40s period of apnea following a bolus, then deep breathing
resumes
- CVS:
o Directly depress cardiac contractility & decrease venous tone →
hypotension (for 30-60 min)
▪ Blood pools in visceral veins → decreased flow to brain
▪ Worse if inject too fast: if patient has CV disease & low BP, you
can kill by injecting thiopental (or propofol) too fast →
excessive drop in BP
▪ Classic sign of death from barbiturate overdose is a spleen
enlarged 4-5 fold, engorged with blood
- Main adverse effects:
1) Hypotension from venodilation
2) Extravascular damage
a. Pain, ulceration, necrosis → be sure to inject IV
- Main clinical uses
1) Induction (sedatives decrease the dose needed)
2) Short term anesthesia
Propofol
- Sedative & anesthetic – one of the most popular intravenous anesthetics
o Sedation & anesthesia (poor-to-nil analgesia)
o Smooth onset of unconsciousness within ~ 30s (as for thiopental)
o Duration ~ 2-4 min. (as for thiopental)
o Main use: induction
o Also short surgical procedures
o May be used as an IV infusion in place of an inhalant in adults
contraindicated in children, who may develop propofol infusion
syndrome: acidosis, arrhythmias, lipidemia; may be fatal
o Premedicate patient first → about 50% less propofol needed → less
resp. & BP depression
- Mechanism:
o Facilitates the effect of GABA at GABAA receptors in the brain (directly
activates the GABAA receptors) → inhibits Aps
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Document Summary
Cns: dose-dependent depression in 15-30s, unconscious for ~2-3 min, do not give full dose all at once (inject to 2/3 of dose & wait. Respiratory tract: dose-dependent depression of respiration, 20-40s period of apnea following a bolus, then deep breathing resumes. Main adverse effects: hypotension from venodilation, extravascular damage, pain, ulceration, necrosis be sure to inject iv. Main clinical uses: induction (sedatives decrease the dose needed, short term anesthesia. Mechanism: facilitates the effect of gaba at gabaa receptors in the brain (directly activates the gabaa receptors) inhibits aps, relatively low therapeutic index, but somewhat safer than barbiturates. Inhibitory (chloride) currents activated by gaba are larger in the presence of propofol: propofol also activates gabaa receptors in the absence of. Gaba, but not as effectively as barbiturates: in the absence of gaba, the emax associated with sodium pentobarbital is ~3 x greater than the emax produced by propofol.
