ketamine Flashcards
what is the classification of ketamine?
- dissociative
- non-barbiturate IV anesthetic
- disconnects brain from body; hallucinations
who can ketamine not be given to r/t job?
public transport personnel (pilots, bus drivers, etc.) d/t possible reoccurrence of symptoms, may be barred from job
what is the MOA of ketamine?
- binds non-competitively to N-methyl-D-aspartate (NMDA) receptors
- exert some effect on opioid receptors
what is the onset of ketamine?
- rapid, similar to thiopental
- within 1 min (30-60 sec) of IV injection, less than 5 min (2-4 min) IM
what is the duration of ketamine?
- short, similar to thiopental
- larger doses take longer to wear off
how does ketamine cross the BBB?
- rapid transfer across, greater than thiopental (4-5x faster)
- reason it is such a quick dissociative
what patients are more at risk for side effects of ketamine?
- < 15 y/o (kids already have nightmares)
- female (tend to have more vivid dreams)
- doses > 2 mg/kg
- history of frequent dreams/nightmares
- don’t give to PTSD
- don’t give to pts. with mental disorders with hallucinations (schizophrenia)
what drugs help reduce side effects of ketamine?
benzodiazepines reduce emergence delirium and increase seizure threshold
- midazolam
- diazepam
- lorazepam
what is observed with ketamine effects?
- open eyes (glazed over)
- behavior like catatonic state (seem really high)
- nystagmus (eye twitching)
- may move with no regard to surgical stimulation
- amnesia
- pain free
- 1.4 in 100,000 have bradycardia related death (glycopyrrolate and versed lessens)
- oculocardiac reflex is enhanced (certain nerves cause vagal decrease in HR, so pre treatment helps)
describe emergence delirium with ketamine
- 5-30% incidence
- visual, auditory, proprioceptive and confusing illusions/hallucinations
- dreams can occur up to 24 hrs after administration
- central misinterpretation of visual and verbal stimuli
- pt. may be combative
- pad bed, surrounding
- recover in quiet environment; not regular PACU
- abuse potential
what are anticholinergic effects of ketamine at muscarinic receptors?
- delirium
- bronchodilation
- sympathomimetic action
- give glycopyrrolate
what is action of ketamine terminated and how is it eliminated?
- redistributed form the brain to tissues that are highly perfused
- high hepatic clearance that prolongs elimination 1/2 life as much as 2-3 hrs (less than 4% excreted renally)
- chronic administration stimulates CP450
how is ketamine metabolized?
- hepatic microsomal enzymes
- CP450
- active metabolite: Norketamine
- liver disease not a good candidate for ketamine
what pts. may require an increased dose of ketamine?
pts. with induced CP450
- alcoholics
- smokers
- drug abusers
describe Norketamine
- active metabolite of ketamine
- onlyu 1/5 to 1/3 as potent
- provides analgesia
- contributes to prolonged analgesic effect of ketamine
what are clinical uses of ketamine for analgesia?
- unique drug that provides wonderful analgesia at subanesthetic doses
- provides prompt induction of anesthesia at higher doses
- hip fracture or replacement and need to do a spinal: hurts to sit up; 30-40mg ketamine allows to sit up to place spinal
- give antisialogogue like glycopyrrolate since atropine and scopolamine may cause emergence delirium also
describe ketamine use for analgesia
- intense analgesia can be accomplished with subanesthetic doses
- works in the thalamic and limbic systems to inhibit interpretation of painful stimuli
- used in conjunction with opioids as an adjuvant
what is the analgesic dose of ketamine?
0.2-0.5 mg/kg
when should ketamine be used in OB?
- emergent use only! (there is no time for an epidural, spinal, or other inductions and need to get baby out quick!)
- not good use in OB but better than thiopental
- neurobehavioral scores of infants born by vaginal delivery are lower with ketamine than those born with epidural anesthesia (crosses placental barrier)
what are neuraxial effects of ketamine?
- limited efficacy
- extradural dosages may be as weak as 10,000 fold weaker than morphine
- has additive or synergistic effect when given with opioids neuraxially (can give less opioid)
what are induction doses of ketamine?
IV: 1-4.5 mg/kg (avg. 2-3 mg/kg)
IM: 3-5 mg/kg OR 6-8 mg/kg
*0.25-1.0 mg produces minimal to mild effects
what should be considered with dosing and onset of ketamine in elderly?
- require lower induction mg d/t smaller central distribution volume
- allow for circulation time (onset may be slower)
what dose is typically used for maintenance after induction with ketamine?
half the initial dose usually every 10-20 min
when is ketamine especially good to use?
- induction of severely hypovolemic pts.
* CV stimulation (increased BP, HR, CO)
what are CV effects of ketamine?
- stimulating effects
- maintains BP, HR, and CO d/t central stimulation of SNS and inhibition of nor-epi reuptake (*not good if already stimulated: tachycardia, HTN)
- generally considered a myocardial depressant mostly seen with pts. with sympathetic blockade or have exhausted catecholamine stored
- regional anesthesia
- spinal cord transection
- pts. in shock
- drug abuse crisis
- no histamine release
- inhibits platelet aggregation
what are clinical uses of ketamine apart from analgesia?
- induction of children with management issues
- mentally retarded/challenged pts.
- burns and dressing changes (pain)
- no prolonged pain effect, give something after!
- beneficial bronchodilation makes useful in asthmatics (not 1st line)
- hx of asthma ok, don’t use if active wheezing or bronchospasm
- induction of pts. with history or family history of malignant hyperthermia (does not stimulate)
- antidepressant (acts as chemical ECT)
- restless leg syndrome (blunts inflammatory mediators that impair spinal cord blood flow)
what are CNS effects of ketamine?
- emergence delirium
- increased ICP: potent cerebral vasodilator
- less increase in ventilated pts., can be given to ventilated pt. with mildly elevated ICP (sedated so not as stimulating)
- EEGs show that ketamine possesses anticonvulsant properties (but it is a direct CNS stimulant)
what are respiratory effects of ketamine?
- maintains CO2 drive for respirations
- upper airway tone is maintained
- good choice for full neck, big guys
what are renal and hepatic effects of ketamine?
lab tests show it does not significantly alter renal or hepatic function
what are drug interactions with ketamine?
- hemodynamic depression with inhaled anesthetics
- midazolam and diazepam can prevent cardiac stimulating effects and hallucinations
- can enhance non-depolarizer actions (good with long surgeries)
- avoid use with/or near aminophylline drugs, this can cause seizures
