Ketamine

Ketamine

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  KETAMINE • Presented by:- • Dr. Vishal kr. Kandhway
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  Introduction : • Ketamineis a phencyclidine derivative that produces dissociative anesthesia characterised by evidence on the EEG of dissociation between the thalamocortical and limbic system. • Ketamine is frequently described as a "unique drug" because it has hypnotic, analgesic and amnesic effects - no other drug used in clinical practice combines these three important features. • It was first used clinically in 1970, and because of these combined effects it was thought that it might be the perfect anesthetic agent. • Ketamine has advantages over propofol & etomidate in not requiring a lipid emulsion vehicle.
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  • Ketamine iswater soluble molecule that structurally resembles phencyclidine. Mechanism of Action :- • The mechanism of action of ketamine induced analgesia & dissociative anesthesia is unknown. • It interacts with multiple CNS receptors. • Ketamine binds non-competetively to the phencyclidine recognision site on N-methyl-D- aspartate(NMDA) receptors. • In addition ketamine exerts effect at other sites including opioid receptor & muscarinic receptors & nicotinic acetylcholine receptors.
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  Pharmacokinetics • Rapid onsetof action, relatively short duration of action & high lipid solubility. • Peak plasma concentrations of ketamine occur within 1 min after IV administration & within 5 mins after IM injection. • Initially ketamine is distributed to highly perfused tissues such as brain & extreme lipid solubility ensures its rapid transfer across the BBB. • Ketamine has high hepatic clearance rate(1 L/min).
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  Actions of Ketamineon the Body: Central Nervous System (CNS): After an i/v injection the effects of ketamine on the CNS begin slowly than other anaesthetic induction agents (1-5 minutes for ketamine compared with 30 -60 seconds for Thiopentone). • The anesthetic state produced is frequently called "dissociative anesthesia" which implies that the patient is detached from the environment and self. • The patient's eyes often remain open and constantly move from side to side.
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  • The durationof action depends on the route of administration. • In contrast to the smooth induction of anaesthesia, the patient may be agitated on recovery from ketamine. • This is often called "emergence delirium", during which the patient may be disorientated, restless, and crying. • Patients may continue to experience unpleasant dreams up to 24 hours after the drug has been given. • Ketamine is potent cerebral vasodilator & capable of increasing cerebral blood flow by 60% in normal indivisual & causes a rise in intracranial pressure and should not be used in patients who have sustained a recent head injury
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  Cardiovascular System (CVS): •Ketamine causes mild stimulation of the CVS. • The systolic blood pressure rises about 20 to 40 mmhg & small increase in diastolic. The heart rate is increased by about 20% - the overall effect is therefore to increase the workload of the heart. • In the majority of patients the blood pressure rises steadily over 3-5 minutes and then returns to normal 10-20 minutes after injection. • There is wide individual variation in cardiovascular responses. • These increases do not seem to be dose-related when more than 1 mg/kg is given and larger doses do not necessarily cause a greater increase in pressure. • There is no evidence to suggest that patients with a high preoperative blood pressure are at greater risk of developing a rise in blood pressure following ketamine administration when compared with normotensive patients.
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   Premedication withmidazolam may reduces this rise in blood pressure.  As the cardiovascular stimulation following ketamine is mediated through the sympathetic nervous system it would seem appropriate to give alpha or beta blockers to patients who develop excessively high blood pressures.  However, the effects of these drugs are unpredictable, and they are probably best avoided in otherwise normal patients as there is no evidence of damage occurring from these short episodes of elevated blood pressure.
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  Respiratory system: • IfKetamine is administered rapidly by intravenous injection it often causes the patient to stop breathing for a short time (up to one minute). • After a slow intravenous induction, breathing is well maintained and may even increase slightly. • The airway is usually well maintained during Ketamine anesthesia and there is some preservation of pharyngeal and laryngeal reflexes in comparison with other intravenous agents. • However this cannot be guaranteed, and normal airway care must be maintained to prevent obstruction or aspiration
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  • Recent researchusing a pulse oximeter has shown that following an intravenous induction with ketamine (2 mg/kg) the oxygen saturation falls • A simple oxygen mask or nasal prongs may be used. • Ketamine produces some bronchodilation making it a useful anaesthetic drug for patients with asthma
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  Skeletal muscle Muscle toneis often increased. Spontaneous movements may occur during anesthesia but reflex response to surgery is uncommon if the patient is adequately anaesthetised. Placenta Ketamine crosses the placenta easily . Secretions Salivation is increased.
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  The Eyes • Theintra-ocular pressure rises for a short time following administration. • Eye movements may continue throughout surgery. • It is not suitable for use in patients with a perforated eye injury or for ophthalmic surgery where a still eye is required. • Pupils are moderately dilated.
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  Routes of Administration: •Ketamine can be given by either the intravenous route 1-2 mg/kg or intramuscular route 4-8 mg/kg to provide anesthesia.
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  Indications for Use: •Analgesia : - Intense analgesia can be achieved with sub- anesthetic doses of 0.2 – 0.5 mg/kg IV. - Analgesia is thought to be greater for somatic than for visceral pain - Analgesia can be produced during labor without associated depression of the neonate. - Ketamine is useful as an analgesic adjuvant in patients with pre-existing chronic pain syndromes who require surgery
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  Induction of Anesthesia: • Induction of anesthesia is produced by administration of ketamine 1-2 mg/kg or intramuscular 4-8 mg/kg to provide anesthesia. • Consciousness is lost in 30-60 seconds after IV administration & 2-4 mins after IM administration. • Return of consciousness usually occurs in 10-20 mins after an injected induction dose of ketamine but return of full orientation may require additional 60-90 mins. • Amnesia persists for about 60-90 mins after recovery of consciousness. • Because of its rapid onset of action ketamine has been used as an IM induction drug in children and been used extensively for burn patients, debridement & skin grafting procedures. • Induction of anesthesia in acute hypovolemic patients is often accomplished with ketamine.
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  Reversal of OpioidTolerance : • Administration of sub-anesthetic doses of ketamine i.e. 0.3 mg/kg/hr improves analgesia and may reduce the likelihood of opioid tolerance. Improvement of Psychiatric Disorders : • Ketamine in small doses improves the post-operative depressive state in patients with mental depression. • Intermittent treatment with low dose ketamine also results in long-term suppression of obsessions & compulsions in patients with obsessive compulsive disorder.
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  Short term sideeffects of Ketamine are: • Increase in heart rate • Slurred speech • Confusion, disorientation • Out-of-body experience • Shifts in perception of reality • Nausea • Sedation • Hypertension • Euphoria • Distortion or loss of sensory perceptions (common) • Open- and closed-eye visuals (common) • Dissociation of mind from body • Numbness • Ataxia (loss of motor coordination) • Significant change in perception of time • Double-vision
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  References • Stoelting’s Phramacology& Physiology.
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