Barbiturates Flashcards
Awakening
due to redistribution
termination of action
due to redistribution, metabolism, renal excretion
thiopental uptake
- depends on blood flow
- heart/brain/liver/kidneys greatest delivery
elimination
depends on liver metabolism
Thiopental
- high solubility/slow ionization=rapid penetration
- pka is 7.6
- acidosis creates greater unionized fraction, enhancing BBB passage
- highly lipid soluble and protein bound (uremia/cirrhosis patients have inc effect)
- dose on lean body mass for initial dose b/c goes to vessel-rich group, not fat
- hypovolemia potentiates effects
Thiopental: peds
-recover more quickly b/c more rapid hepatic clearance
thiopental: obese
-increased elimination half life
thiopental: CV
- peripheral vasodilation, venous pooling
- activates sympathetic NS
intra-arterial injection of thiopental
- leave needle in place
- inject with papaverine (40-80 mg) or 10 cc 1% procaine–inhibits smooth muscle spasm, also lidocaine
- perform sympathetic block of brachial plexus or stellate ganglion
- heparinize to prevent thrombus formation
- alpha adrenergic blockade (phentolamine)
thiopental and geriatrics
- slower passage from central to peripheral compartments
- initial Vd unchanged
- higher plasma concentrations for brain distribution, greater anesthetic effects
action of barbiturates on CNA
-decreased:
-awareness (hypnotic)
-ICP
CBC
CMRO2
seizures
-decreases CMRO2>than CBC–improves supply demand relationship
-increase CSF absorption by arachnoid villi to dec ICP
-prevents brain injury during focal, not global ischemia
CPP
MAP-ICP or CVP, whichever greater
normal CPP=80-100
normal ICP=<10
CPP usu dependent on MAP
CPP benchmarks
<25 irreversible brain damage
methohexital
-activates seizure foci (eg pts with temporal lobe epilepsy)
