Which of the following is contraindicated in an epileptic patient posted for general anesthesia?(Asked twice in the exam)
Ans. c. Ketamine (Ref: Morgan 4/e p197-199; Ajay Yadav, 3/e p73-75)Ketamine should be avoided in patients with history of seizures as it further increases ICP and also causes delirium and hallucinations.Ketamine:Ketamine should be avoided in patients with history of seizuresIncreases brain oxygen consumption and metabolic rate, intracranial tension is highly raisedQEmergence reactionsQ (vivid dreaming, illusion, etc) is seen.Hallucinations: both auditory and visual (mainly auditoryQ), incidence is 30-40%Hallucination is MC side effects of KetamineQThiopentone:Decreases cerebral oxygen consumption, cerebral metabolic rate and intracranial tension.Agent of choice for cerebral protection.Anticonvulsant action due to its phenyl group.Propofol:Decreases ICPNeuroprotectiveMidazolam:Benzodiazepine, which has anti-seizure potentialUsed in treating seizuresThis patient of placenta previa is in labor and has bled into shock. She should be delivered by cesarean section under general anesthesia. General anesthesia is preferred as it is a more controllable modality and there is a significant risk of hypotension associated with spinal anesthesia. Ketamine is the preferred agent in cases of acute shock.Ketamine stimulates sympathetic system causing tachycardia and hypertension, so it is intravenous anaesthetic of choice for shock. "KetaminePhencyclidine derivativeQ, contains benzthonium chlorideQ as preservativeStrong analgesic, but not a muscle relaxant (rather it increases the muscle tone)QPrimary site of action is thalamoneocortical projectionQ, inhibits cortex (unconsciousness) and thalamus (analgesia) and stimulates limbic system (emergence reaction and hallucination)Produces dissociative anaesthesiaQ, individual is in cataleptic stateActs on NMDA receptorQ, dose is 2 mg/kg I.V.QOnset of action in 30 to 60 seconds, elimination half life is 2-3 hoursEarly regain of consciousness because of redistributionQSystemic Effects of KetamineCNSCVSRespiratory system* Increases brain oxygen consumption and metabolic rate, intracranial tension is highly raised* Emergence reactionsQ (vivid dreaming, illusion, etc) is seen.* Hallucinations: both auditory and visual (mainly auditoryQ), incidence is 30- 40%, hallucination is MC side effects of KetamineQ these hallucinations and emergence reactions can be decreased by giving benzodiazepinesQ along with ketamine.* Ketamine stimulates sympathetic system causing tachycardia and hypertension, so it is intravenous anaesthetic of choice for shockQ.* Benzodiazepines attenuate this hemodynamic responseQ (tachycardia, hypertension and increased oxygen demand of myocardium) of Ketamine,Stimulates respiration, potent bronchodilator & is intravenous anaesthetic of choice for asthmaticsQPharyngeal and laryngeal reflexes are preservedTracheobronchial and salivary secretions are increasedEyeGITMuscular system* Increased intraocular tensionQ* Increased intragastric pressure & salivary secretions* Increases muscle toneQAdvantages & uses of KetamineInduction agent of choice for:Asthmatics, shockQConstrictive Pericarditis, cardiac tamponadeQ (n theses conditions cardiac output is dependent on tachycardia and Ketamine causes tachycardia)Right to left shunt like TOFQ (Ketamine by causing hypertension increases the afterload there by decreasing the right to left shunt fraction)Can be used as sole agent for minor procedures, safely used in remote placesPreferred agent for patients with full stomach (pharyngeal and laryngeal reflexes are preserved)QContraindications of KetamineHead injury, intracranial space occupying lesion, eye injuryQ (increases ICT, IOT)Ischemic heart disease, vascular aneurysm & hypertensionQ (increases myocardial oxygen demand & hypertension)Psychiatric diseases & drug addictsQ (more incidence of hallucination & emergence reaction)
Propofol
Thiopentone
Ketamine
Midazolam
Miscellaneous General Anesthesia