Ketamine Flashcards
Is ketamine a weak acid or base, and what is its pKa?
Weak base with a pKa of 7.5
Which isomer of ketamine is the more useful one?
S (+) ketamine
R (-) ketamine
S (+) ketamine has a number of beneficial pharmacokinetic properties with clinical implications.
S(+) ketamine has greater affinity than R(-) ketamine at phencyclidine binding sites on the N-methyl-D-aspartate (NMDA) receptor, with a resultant doubling of potency compared to the racemic mixture (equal amounts of R(-) and S(+) isomers) in producing anaesthesia and analgesia.
S(+) ketamine also has a reduced recovery time and, since the incidence of psychological sequelae are equal at equal plasma concentrations, the lower dose required of S(+) ketamine results in fewer psychological side-effects.
What is the typical induction dose of ketamine (racemic mixture)? Give both IV and IM doses
0.5 - 2 mg/kg IV
4-10 mg/kg IM
What is the oral bioavailability of ketamine?
20-25%
What percentage of ketamine is protein bound?
20-50%
What is the volume of distribution of ketamine?
3 L/kg - it is increased in the critically ill
What is the elimination half life of ketamine?
2-3 hours
How is ketamine metabolised?
In the liver, by cytochrome P450, undergoing demethylation and hydroxylation of the cyclohexanone ring to metabolites norketamine (20% relative activity) and dehydronorketamine.
What is the clearance rate of ketamine metabolites?
The metabolites are conjugated and excreted in the urine with a relatively large clearance of 890-1227 ml/min. Elimination half-life is 2-3 hours.
An adult male is admitted to the ICU after an acute asthma attack. He is intubated, sedated and on full intermittent positive-pressure ventilation.
He has widespread expiratory wheezes on auscultation of his chest, saturations of 85%, high peak airway pressures and is sweating profusely. His BP is 180/80.
Which of the following are true statements regarding appropriate treatment options?
A. Administer 100% oxygen
B. Corticosteroid administration is inappropriate due to the slow onset of action
C. Atenolol should be safe to treat hypertension
D. Exclude a pneumothorax by doing a CXR
E. Ketamine is contraindicated due to the significant hypertension
F. Ketamine is a potent bronchodilator in status asthmaticus
A. True. Administer 100% oxygen to treat hypoxia.
B. False. Corticosteroids should be administered to treat the inflammatory component of asthma.
C. False. Β-blockers should be avoided in asthma as they may worsen bronchoconstriction.
D. True. An acute pneumothorax should be excluded.
E. False. Although ketamine stimulates the sympathetic nervous system it is not contraindicated since ketamine causes bronchodilatation.
F. True. Ketamine causes bronchodilatation.
Is the following a true reflection of the effect of ketamine on the respiratory system?
Respiratory drive remains relatively unaffected
True. Ketamine has minimal effects on respiratory drive.
Is the following a true reflection of the effect of ketamine on the respiratory system?
All doses of ketamine lead to respiratory depression
False. Low dose ketamine use does not depress respiration significantly.
Is the following a true reflection of the effect of ketamine on the respiratory system?
Ketamine causes tachypnoea
False. Ketamine has minimal effects on respiratory drive.
Is the following a true reflection of the effect of ketamine on the respiratory system?
Children are predisposed to laryngospasm and upper airways obstruction
True. Children may develop laryngospasm due to increased salivation
Is the following a true reflection of the effect of ketamine on the respiratory system?
Owing to bronchoconstriction, ketamine should not be used in patients with asthma
False. Ketamine causes bronchodilatation which is beneficial in treating acute asthma.
Is the following a true reflection of the effect of ketamine on the respiratory system?
Silent aspiration is a potential problem during anaesthesia
True. Depressed airway reflexes may lead to silent aspiration.
Is the following statement a true reflection of the effect of ketamine on the CNS?
There is an increase in cerebral metabolism
True. Ketamine leads to an increase in cerebral metabolism.
Is the following statement a true reflection of the effect of ketamine on the CNS?
Patients may appear to be in a cataleptic state
True. Ketamine leads to dissociative anaesthesia.
Is the following statement a true reflection of the effect of ketamine on the CNS?
There is a decrease in cerebral oxygen metabolism
False. Ketamine causes an increase in cerebral metabolism.
Is the following statement a true reflection of the effect of ketamine on the CNS?
Alpha rhythms are abolished
True. The EEG predominantly reveals theta activity.
Is the following statement a true reflection of the effect of ketamine on the CNS?
Cerebrovascular responsiveness to CO2 increases
False. Responsiveness to CO2 seems preserved.
Is the following statement a true reflection of the effect of ketamine on the CNS?
Hallucinations and other emergence reactions are heightened in the paediatric population
False. Emergence reactions are more common in adults.
Is the following statement a true reflection of the effect of ketamine on the CNS?
Benzodiazepines are effective in reducing the emergence reactions in the adult population
True. Benzodiazepine co-administration reduce emergence reactions.
Ketamine (true or false):
Is a phencyclidine derivative
True
