Ketamine

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KETAMINE

Phencyclidine derivative, dissociative anaesthetic, analgesic, preserver of tone in larynx/pharynx

200mg = £5

Used in the US Army in 1962, Vietnam. Civilian use ensued in 1970.

Racemic mixture of isomers (optical isomer/chiral). pKa of 7.5.

One of the isomers, s+ketamine is more potent and has a faster recovery time.

Ketamine has a high lipid solubility (5–10 times that of thiopental) and crosses the blood-brain barrier faster.

Metabolism = demethylation and hydroxylation of the cyclohexanone ring.

Metabolites are conjugated and excreted in the urine as glucuronides.

Norketamine (a metabolite) has 20–30% of the activity of the parent compound.

↑HR, BP, CO due to ↑sympathetic tone
Baroreceptor function preserved
Stimulates respiration, preserved AW reflexes
?↑IOP, ICP, CMRO2 - research ongoing
Amnesia common and sometimes useful
Visceral pain poorly obtunded
LA at higher doses
Emergence delirium and hallucinations- ?need benzo
PONV common
↑Uterine tone and ↑catecholamines
Rashes in 15%
Can work epidurally(!)

Non-competative antagnoism of NMDA receptors at both Ca2+ pore and phencyclidine binding site- modulates mACh and opioid receptors

Loss alpha-rhythm and theta predominance on EEG

+ve ionotrope ?due to cAMP and calcium influx

Sympathetic stimulation of the peripheral circulation is decreased = vasodilatation in tissues innervated predominantly by α-adrenergic receptors, and vasoconstriction in those with β-receptors.

Transient apnoea post induction dose, then preserved

30-60s onset IV (3-4mins IM), Peak at 1 minute. 5 - 20 minute duration depending on dose.

Good For Bronchospastic or Hypotensive Patients

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Good oral absorption but unfortunately only 20% available due to first pass metabolism

Distribution and elimination are slower if halothane, benzos or barbituates are concurrently administered.

1.5-2mg/kg in IV induction

EMERGENCE DELIRIUM

A higher incidence is associated with factors such as increasing age, female gender, patients who normally dream, rapid intravenous administration, and large doses. Benzo use can reduce the effect.

Doses

Dr. David Lyness

@Gas_Craic

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propofology.com

0.15- 0.25mg/kg bolus for analgesia (17.5mg in 70kg)

0.5-3mg/kg/hr for infusion (35mg-210mg/hr in 70kg)

Intranasal dose = 0.5-1mg/kg for mod/severe pain

Sublingual = 2.5 - 5mg (from palliative care G/L)

http://www.wales.nhs.uk/sites3/Documents/814/Ketamine%2DSpecialistGuidelinesOnUse.pdf

http://rsds.org/wp-content/uploads/2015/02/2014-sub-dissociative-dose-intranasal-ketamine.pdf

http://intensivecarenetwork.com/ketamine-how-to-use-it-fearlessly-for-all-its-indications-by-strayer/ (K Graphic)

http://emj.bmj.com/content/suppl/2004/04/28/21.3.386.DC1/213386appendix.pdf

Hypersalivation can occur; glycopyrolate can alleviate this

Ketamine for Analgesia

20mg over 10mins then 20mg/hr titrated to effect.

Ketamine should be considered for analgesia when opiates are not desired or tolerated.

Think about it in acutely sore chronic pain patients on opiates, recovered opiate addicts, or those with marginal BP/breathing issues.

Paeds IM Sedation - 4 mg/kg intramuscular as initial dose.

One booster dose of 2 mg/kg is allowed after 10m

if adequate sedation has not been achieved.

Bioavailability of the intranasal ketamine is between 40-50%

SL dose can be higher in certain indications

Mixes of ketamine are used in some practices:

combined with PROPOFOL (KETOFOL) or MAGNESIUM (KETANESIUM)

Ketamine

David Lyness | March 08, 2020