Anaesthesia pharmacology: MRCEM Primary questions with answers

Anaesthesia pharmacology looks at the drugs used to anaesthetise patients, including how they act, what they do to the body and what can go wrong. Pharmacology carries 24 of the 180 questions in MRCEM Primary, and anaesthesia is one of its listed areas. Emergency physicians use these drugs when intubating critically ill patients and when sedating for painful procedures, so safe use matters.

5 free questions below, each with the answer and the full explanation · 68 in the full bank · Last updated after the 27 October 2026 MRCEM Primary sitting.

1. Question 1 · Anesthetic drugs

   You need to perform procedural sedation in a patient who requires propofol. What is the mechanism of action of propofol?

   1. ANMDA receptor antagonist
   2. BNMDA receptor agonist
   3. CNa channel blocker
   4. DGABA receptor activation
   5. EGABA receptor inactivation
   Show answer and explanation

   Answer: D. Propofol positively modulates inhibitory GABA-A receptors, producing sedation and anaesthesia.

   • A: NMDA antagonism is the mechanism of ketamine.
   • B: NMDA agonism is not an anaesthetic mechanism.
   • C: Sodium channel blockade is the mechanism of local anaesthetics.
   • E: Propofol enhances, not inactivates, GABA receptor function.

   Full explanation: Anesthetic drugs

   Benzodiazepines and Muscle relaxants:

   Muscle relaxants (Neuromuscular blocking agents)

   Benzodiazepines

   Muscle relaxants, also known as neuromuscular blocking agents (NMBAs), play a crucial role in anesthesia by inducing muscle relaxation and paralysis such as during surgery and endotracheal intubation. 1: Depolarizing neuromuscular blocking agent: Suxamethonium Suxamethonium is a depolarizing neuromuscular blocker that is used to induce muscle relaxation and short-term paralysis, usually to facilitate endotracheal intubation. Suxamethonium causes a 'persistent' depolarization by mimicking the effects of acetylcholine without being rapidly hydrolyzed by acetylcholinesterase. It therefore inhibits the action of acetylcholine at the neuromuscular junction and the propagation of an action potential is Prevented. Contraindications of Suxamethonium: Spinal injury Muscle trauma Neuromuscular disease Hyperkalemia History of malignant hyperthermia Side effects: Hyperkalemia, malignant hyperthermia and bradycardia 2: Non-Depolarizing neuromuscular blocking agent: Atracurium These agents work by blocking the action of neurotransmitter acetylcholine at the neuromuscular junction prevents muscle contraction and results in muscle paralysis. Atracurium competes with acetylcholine for nicotinic (N2) receptor binding sites at the post-synaptic membrane of the neuromuscular junction. This prevents acetylcholine from stimulating the receptors. Because the blockade is competitive muscle paralysis occurs gradually. Neostigmine used specifically for reversal of non-depolarizing neuromuscular drugs Note: Rocuronium: Also, non-depolarizing neuromuscular blocking agent and its antidote is sugammadex

   Benzodiazepines enhance the effects of GABA resulting inhibitory synaptic transmission throughout CNS Features: Sedative, hypnotic, anxiolytic, anticonvulsant and muscle relaxant properties Examples: Long-acting benzo: Diazepam (Half-life 24-48 hours) Intermediate acting: Lorazepam (12-18 hours) Short acting:(Half-life <6 hours) Midazolam, Alprazolam and oxazepam Note: Benzodiazepines can precipitate coma if used in hepatic impairment. If treatment is required benzodiazepines with shorter half-lives in reduced doses should be used Contraindications of benzodiazepines: Neuromuscular respiratory disease e.g., myasthenia gravis Severe hepatic impairment Respiratory depression Obstructive sleep apnoea Benzodiazepines toxicity: Respiratory depression and coma Nystagmus Ataxia, dysarthria Antidote: Flumazenil High yield: Oral lorazepam 1-2 mg or IM lorazepam 2-4 mg are recommended for the emergency tranquilization of violent or disturbed patients IV lorazepam should be administered as first-line treatment in status epilepticus patient, IV diazepam can be used if IV lorazepam is not available and buccal midazolam can be used if intravenous access cannot be rapidly established

   Local anesthetic drugs:

   Anesthetic induction and maintenance agents:

   Ketamine

   Propofol

   Ketamine is NMDA receptor antagonist, the only anesthetic agent available that has analgesic, hypnotic, and amnesic properties. Note: Ketamine is preferred anesthetic agent in haemodynamically unstable patients. Ketamine causes tachycardia, an increase in blood pressure, central venous pressure and cardiac output, secondary to an increase in sympathetic tone. Ketamine in asthma: Ketamine protects respiratory drive. The bronchodilatory effects of ketamine can provide some benefit in asthmatic patients who require anesthesia or sedation for procedures. By helping to relax the smooth muscles of the airways, ketamine might temporarily improve airflow and prevent bronchoconstriction that could be triggered by other anesthetic agents. Side effects: Hypertension Nystagmus Tachycardia Transient psychosis effect Note: Ketamine is dissociative anesthesia that causes high incidence of hallucinations and transient psychotic effects. These can be reduced by the co-administration of a benzodiazepine, such as diazepam or midazolam.

   Short acting phenol derivative. Used as both induction and maintenance agent. Circulatory effects: Propofol avoided in haemodynamically unstable patients causes decrease in blood pressure and systemic vascular resistance without a compensatory increase in heart rate. Respiratory effects: Decreased tidal volume and respiratory rate producing respiratory depression Decrease ventilatory response to carbon dioxide Reduced upper airway reflexes Side effects: Pain on injection (in up to 30%) Hypotension Transient apnoea Hyperventilation Coughing and hiccough Headache Thrombosis and phlebitis

   Anesthetic induction and maintenance agents: (Continues)

   Thiopental sodium	Etomidate	Entonox
   Thiopental is a very short acting barbiturate that is primarily used for the induction of anesthesia. Thiopental sodium is preferred drug of rapid sequence induction in adults Side effects: Hypotension Arrhythmias Involuntary muscle movements Myocardial depression Cough and Laryngeal spasm Headache Rash Hypersensitivity reactions Contraindications: Acute intermittent porphyria Myasthenia gravis Severe respiratory disease	Etomidate is an induction agent notable for its relative cardiovascular stability. It causes less hypotension than thiopental sodium and propofol during induction. Etomidate is associated with rapid recovery without hangover effect. Side effects: Pain on injection (in up to 50%) Phlebitis and venous thrombosis Arrhythmias and heart block Hyperventilation Respiratory depression and apnoea Can cause both hypo- and hypertension Increased mortality in critically ill patients	50/50 mix of 02 and NO used in maintenance of anesthesia in sub anesthetic concentration for analgesia and CNS depression Side effects: Inhibition of Vit B12 synthesis causes megaloblastic anemia Euphoria Contraindications: Reduced conscious level Diving injury Pneumothorax Middle ear disease Sinus disease Bowel obstruction Psychiatric patients

2. Question 2 · Anaesthesia pharmacology

   Your consultant decides to use ketamine for a patient needing procedural sedation in the Emergency Department. On which receptor does ketamine mainly act:

   1. ANMDA receptor
   2. BMu-opioid receptor
   3. CNicotinic receptor
   4. DGABA receptor
   5. EMuscarinic receptor
   Show answer and explanation

   Answer: A. Ketamine primarily acts as an antagonist at the NMDA receptor.

   • B: Opioid effects are secondary rather than primary.
   • C: Not its target.
   • D: GABA-A is the target of propofol and benzodiazepines.
   • E: Antimuscarinic effects are secondary.

   Full explanation: Ketamine

   Ketamine has hypnotic, analgesic and local anaesthetic properties. Ketamine is an NMDA receptor antagonist, but it may also have other actions. Ketamine produces so-called ‘dissociative’ anaesthesia. Transient psychotic effects including alterations in mood state, floating sensations, vivid dreams and hallucinations are common during emergence from ketamine anaesthesia. These usually resolve on full wakening. Benzodiazepine premedication e.g. with diazepam or midazolam reduces this delirium, which also occurs less often in children and the elderly.

   The onset of action is slower than other induction drugs (unconsciousness in about 1 - 2 min for IV use), and the end point can be difficult to judge with patients staring into the distance for a short period of time. The duration of action of a single dose is approximately 5 - 10 minutes. Recovery is relatively slow.

   Uses

   Ketamine has a unique combination of cardiovascular effects. Unlike other induction drugs it has sympathetic effects with increased heart rate, increased blood pressure and an increased cardiac output; this makes ketamine useful in the shocked, unwell patient. It is used mainly for paediatric anaesthesia, particularly when repeated administration is required (such as for serial burns dressings).

   Ketamine has a minimal effect on respiratory drive and protective airway reflexes remain well preserved, this makes ketamine an ideal anaesthetic drug to be used in the prehospital environment. Ketamine is also a bronchial smooth muscle relaxant and therefore has a special role in the management of severe asthma.

   Contraindications

   Ketamine is contraindicated in acute porphyrias, head trauma, stroke and raised intracranial pressure, hypertension and severe cardiac disease.

   Side Effects

   There is a high incidence of extraneous muscle movements and postoperative nausea and vomiting. Other common side effects include hypertension, tachycardia and transient psychotic effects.

3. Question 3 · Anesthetic drugs

   A patient aged 45 is scheduled to undergo elective knee arthroscopy because of persistent joint pain. The anesthesiologist decides to give Bupivacaine, a local anesthetic, to manage perioperative pain effectively. The primary mechanism of action of Bupivacaine is?

   1. AStimulation of voltage-gated N-type calcium channels
   2. Bblockage of Magnesium channels
   3. CBlockade the GABA-gated chloride channels
   4. DBlockade of voltage-gated sodium channels
   5. EActivation of ligand-gated potassium channels
   Show answer and explanation

   Answer: D. Bupivacaine blocks voltage-gated sodium channels, preventing nerve impulse initiation and conduction.

   • A: Calcium channels are not stimulated.
   • B: Magnesium channels are not involved.
   • C: GABA-gated chloride channels are not its target.
   • E: Potassium channels are not activated.

   Full explanation: Anesthetic drugs

   Benzodiazepines and Muscle relaxants:

   Muscle relaxants (Neuromuscular blocking agents)

   Benzodiazepines

   Muscle relaxants, also known as neuromuscular blocking agents (NMBAs), play a crucial role in anesthesia by inducing muscle relaxation and paralysis such as during surgery and endotracheal intubation. 1: Depolarizing neuromuscular blocking agent: Suxamethonium Suxamethonium is a depolarizing neuromuscular blocker that is used to induce muscle relaxation and short-term paralysis, usually to facilitate endotracheal intubation. Suxamethonium causes a 'persistent' depolarization by mimicking the effects of acetylcholine without being rapidly hydrolyzed by acetylcholinesterase. It therefore inhibits the action of acetylcholine at the neuromuscular junction and the propagation of an action potential is Prevented. Contraindications of Suxamethonium: Spinal injury Muscle trauma Neuromuscular disease Hyperkalemia History of malignant hyperthermia Side effects: Hyperkalemia, malignant hyperthermia and bradycardia 2: Non-Depolarizing neuromuscular blocking agent: Atracurium These agents work by blocking the action of neurotransmitter acetylcholine at the neuromuscular junction prevents muscle contraction and results in muscle paralysis. Atracurium competes with acetylcholine for nicotinic (N2) receptor binding sites at the post-synaptic membrane of the neuromuscular junction. This prevents acetylcholine from stimulating the receptors. Because the blockade is competitive muscle paralysis occurs gradually. Neostigmine used specifically for reversal of non-depolarizing neuromuscular drugs Note: Rocuronium: Also, non-depolarizing neuromuscular blocking agent and its antidote is sugammadex

   Benzodiazepines enhance the effects of GABA resulting inhibitory synaptic transmission throughout CNS Features: Sedative, hypnotic, anxiolytic, anticonvulsant and muscle relaxant properties Examples: Long-acting benzo: Diazepam (Half-life 24-48 hours) Intermediate acting: Lorazepam (12-18 hours) Short acting:(Half-life <6 hours) Midazolam, Alprazolam and oxazepam Note: Benzodiazepines can precipitate coma if used in hepatic impairment. If treatment is required benzodiazepines with shorter half-lives in reduced doses should be used Contraindications of benzodiazepines: Neuromuscular respiratory disease e.g., myasthenia gravis Severe hepatic impairment Respiratory depression Obstructive sleep apnoea Benzodiazepines toxicity: Respiratory depression and coma Nystagmus Ataxia, dysarthria Antidote: Flumazenil High yield: Oral lorazepam 1-2 mg or IM lorazepam 2-4 mg are recommended for the emergency tranquilization of violent or disturbed patients IV lorazepam should be administered as first-line treatment in status epilepticus patient, IV diazepam can be used if IV lorazepam is not available and buccal midazolam can be used if intravenous access cannot be rapidly established

   Local anesthetic drugs:

   Anesthetic induction and maintenance agents:

   Ketamine

   Propofol

   Ketamine is NMDA receptor antagonist, the only anesthetic agent available that has analgesic, hypnotic, and amnesic properties. Note: Ketamine is preferred anesthetic agent in haemodynamically unstable patients. Ketamine causes tachycardia, an increase in blood pressure, central venous pressure and cardiac output, secondary to an increase in sympathetic tone. Ketamine in asthma: Ketamine protects respiratory drive. The bronchodilatory effects of ketamine can provide some benefit in asthmatic patients who require anesthesia or sedation for procedures. By helping to relax the smooth muscles of the airways, ketamine might temporarily improve airflow and prevent bronchoconstriction that could be triggered by other anesthetic agents. Side effects: Hypertension Nystagmus Tachycardia Transient psychosis effect Note: Ketamine is dissociative anesthesia that causes high incidence of hallucinations and transient psychotic effects. These can be reduced by the co-administration of a benzodiazepine, such as diazepam or midazolam.

   Short acting phenol derivative. Used as both induction and maintenance agent. Circulatory effects: Propofol avoided in haemodynamically unstable patients causes decrease in blood pressure and systemic vascular resistance without a compensatory increase in heart rate. Respiratory effects: Decreased tidal volume and respiratory rate producing respiratory depression Decrease ventilatory response to carbon dioxide Reduced upper airway reflexes Side effects: Pain on injection (in up to 30%) Hypotension Transient apnoea Hyperventilation Coughing and hiccough Headache Thrombosis and phlebitis

   Anesthetic induction and maintenance agents: (Continues)

   Thiopental sodium	Etomidate	Entonox
   Thiopental is a very short acting barbiturate that is primarily used for the induction of anesthesia. Thiopental sodium is preferred drug of rapid sequence induction in adults Side effects: Hypotension Arrhythmias Involuntary muscle movements Myocardial depression Cough and Laryngeal spasm Headache Rash Hypersensitivity reactions Contraindications: Acute intermittent porphyria Myasthenia gravis Severe respiratory disease	Etomidate is an induction agent notable for its relative cardiovascular stability. It causes less hypotension than thiopental sodium and propofol during induction. Etomidate is associated with rapid recovery without hangover effect. Side effects: Pain on injection (in up to 50%) Phlebitis and venous thrombosis Arrhythmias and heart block Hyperventilation Respiratory depression and apnoea Can cause both hypo- and hypertension Increased mortality in critically ill patients	50/50 mix of 02 and NO used in maintenance of anesthesia in sub anesthetic concentration for analgesia and CNS depression Side effects: Inhibition of Vit B12 synthesis causes megaloblastic anemia Euphoria Contraindications: Reduced conscious level Diving injury Pneumothorax Middle ear disease Sinus disease Bowel obstruction Psychiatric patients

4. Question 4 · Anaesthesia pharmacology

   You are being observed while performing procedural sedation in the Emergency Department. You have been advised to use midazolam. On which receptor do benzodiazepines mainly act:

   1. ANMDA receptor
   2. BGABA receptor
   3. COpioid receptor
   4. D5-HT receptor
   5. EMuscarinic receptor
   Show answer and explanation

   Answer: B. Benzodiazepines such as midazolam enhance inhibitory GABA receptor function.

   • A: NMDA is the target of ketamine.
   • C: Opioid receptors are the target of opioids.
   • D: 5-HT receptors are not their target.
   • E: Muscarinic receptors are not their target.

   Full explanation: Benzodiazepines

   Mechanism of action

   Benzodiazepines are gamma-aminobutyric acid (GABA) receptor agonists which enhance inhibitory synaptic transmission throughout the central nervous system, with sedative, hypnotic, anxiolytic, anticonvulsant, and muscle relaxant properties.

   Indications

   Benzodiazepines are indicated for the short-term relief (two to four weeks only) of anxiety that is severe, disabling, or causing the patient unacceptable distress, occurring alone or in association with insomnia or short-term psychosomatic, organic, or psychotic illness. The use of benzodiazepines to treat short-term ‘mild’ anxiety is inappropriate. Benzodiazepines should be used to treat insomnia only when it is severe, disabling, or causing the patient extreme distress.

   Prescribing of these drugs is widespread but dependence (both physical and psychological) and tolerance may occur. Therefore hypnotics and anxiolytics should be reserved for short courses to alleviate acute conditions. Withdrawal of a benzodiazepine should be gradual because abrupt withdrawal may produce confusion, toxic psychosis, convulsions, or a condition resembling delirium tremens.

   Benzodiazepines possess useful properties for premedication including relief of anxiety, sedation, and amnesia; short-acting benzodiazepines taken by mouth are the most common premedicants. Benzodiazepines are also used in intensive care units for sedation, particularly in those receiving assisted ventilation.

   Contraindications

   Benzodiazepines are contraindicated in:

   • Respiratory depression
   • Marked neuromuscular respiratory weakness, such as unstable myasthenia gravis
   • Obstructive sleep apnoea syndrome (symptoms may be aggravated)
   • Severe hepatic impairment (the elimination half-life of diazepam may be prolonged; increased risk of coma)
   • Phobic or obsessional states, chronic psychosis or hyperkinesis (paradoxical reactions may occur)

   Cautions

   Benzodiazepines should be used with caution in:

   • Respiratory disease
   • Muscle weakness and myasthenia gravis  (symptoms may be aggravated)
   • Organic brain disease
   • Severe renal impairment (increased cerebral sensitivity to diazepam; a reduced dose may be appropriate)
   • Dependent, obsessive-compulsive, or avoidant-type personality disorders (may increase the risk of dependency)
   • Frailty and the elderly (increased falls risk; a reduced dose may be appropriate)
   • A history of drug and/or alcohol misuse or dependency (increased risk of dependency)
   • Patients taking other central depressants concomitantly e.g. alcohol, barbiturates

   Side Effects

   Adverse effects include:

   • Drowsiness and lightheadedness
   • Confusion and ataxia (especially in the elderly), amnesia, muscle weakness
   • Headache, vertigo, tremor, dysarthria, hypotension, decreased libido, erectile dysfunction, gynaecomastia, urinary retention
   • Paradoxical effects such as talkativeness, excitement, irritability, aggression, anti-social behaviour, and suicidal ideation
   • Withdrawal symptoms, for example anxiety, depression, anorexia, impaired concentration, insomnia, abdominal cramps, palpitations, tremor, tinnitus and perceptual disturbances
   • Tolerance and dependence (people who use benzodiazepines longer term can develop tolerance and eventual dependence)

   Toxicity

   Features of benzodiazepine toxicity include:

   • drowsiness
   • ataxia
   • dysarthria
   • nystagmus
   • occasionally respiratory depression and coma

   Flumazenil is used to antagonise the effects of benzodiazepines. It can be used to reduce the sedative effects of benzodiazepines in anaesthesia, intensive care, diagnostic procedures and in overdose.

   Type Examples

   Midazolam has a short duration of action (< 6 hours), lorazepam and temazepam have an intermediate duration of action (12 - 18 hours) and diazepam and chlordiazepoxide have a long duration of action (24 - 48 hours). Shorter-acting compounds may be preferred in patients with hepatic impairment but they carry a greater risk of withdrawal symptoms.

   Chlordiazepoxide is routinely used for symptoms associated with acute alcohol withdrawal.

   Diazepam is used to produce mild sedation with amnesia. It is a long-acting drug with active metabolites and a second period of drowsiness can occur several hours after its administration.

   Temazepam is given by mouth for premedication and has a shorter duration of action and a more rapid onset than oral diazepam; anxiolytic and sedative effects last about 90 minutes although there may be residual drowsiness.

   Lorazepam produces more prolonged sedation than temazepam and it has marked amnesic effects.

   Midazolam is a water-soluble benzodiazepine that is often used in preference to intravenous diazepam; recovery is faster than from diazepam, but may be significantly longer in the elderly, in patients with a low cardiac output, or after repeated dosing. Midazolam is associated with profound sedation when high doses are given intravenously or when it is used with certain other drugs.

5. Question 5 · Anesthetic drugs

   A male aged 30 presents to the ED feeling unwell after he was injected with prilocaine for a minor surgical procedure. Blood taken for arterial blood gas analysis appears chocolate brown. What is the immediate management for this patient?

   1. AAdminister lipid emulsion
   2. BAdminister N-acetylcysteine
   3. CAdminister activated charcoal
   4. DAdminister flumazenil
   5. EAdminister methylene blue
   Show answer and explanation

   Answer: E. Chocolate-brown blood after prilocaine indicates methaemoglobinaemia, treated with methylene blue.

   • A: Lipid emulsion treats local anaesthetic systemic toxicity, not methaemoglobinaemia.
   • B: N-acetylcysteine treats paracetamol overdose.
   • C: Activated charcoal is for oral poisoning.
   • D: Flumazenil reverses benzodiazepines.

   Full explanation: Anesthetic drugs

   Benzodiazepines and Muscle relaxants:

   Muscle relaxants (Neuromuscular blocking agents)

   Benzodiazepines

   Muscle relaxants, also known as neuromuscular blocking agents (NMBAs), play a crucial role in anesthesia by inducing muscle relaxation and paralysis such as during surgery and endotracheal intubation. 1: Depolarizing neuromuscular blocking agent: Suxamethonium Suxamethonium is a depolarizing neuromuscular blocker that is used to induce muscle relaxation and short-term paralysis, usually to facilitate endotracheal intubation. Suxamethonium causes a 'persistent' depolarization by mimicking the effects of acetylcholine without being rapidly hydrolyzed by acetylcholinesterase. It therefore inhibits the action of acetylcholine at the neuromuscular junction and the propagation of an action potential is Prevented. Contraindications of Suxamethonium: Spinal injury Muscle trauma Neuromuscular disease Hyperkalemia History of malignant hyperthermia Side effects: Hyperkalemia, malignant hyperthermia and bradycardia 2: Non-Depolarizing neuromuscular blocking agent: Atracurium These agents work by blocking the action of neurotransmitter acetylcholine at the neuromuscular junction prevents muscle contraction and results in muscle paralysis. Atracurium competes with acetylcholine for nicotinic (N2) receptor binding sites at the post-synaptic membrane of the neuromuscular junction. This prevents acetylcholine from stimulating the receptors. Because the blockade is competitive muscle paralysis occurs gradually. Neostigmine used specifically for reversal of non-depolarizing neuromuscular drugs Note: Rocuronium: Also, non-depolarizing neuromuscular blocking agent and its antidote is sugammadex

   Benzodiazepines enhance the effects of GABA resulting inhibitory synaptic transmission throughout CNS Features: Sedative, hypnotic, anxiolytic, anticonvulsant and muscle relaxant properties Examples: Long-acting benzo: Diazepam (Half-life 24-48 hours) Intermediate acting: Lorazepam (12-18 hours) Short acting:(Half-life <6 hours) Midazolam, Alprazolam and oxazepam Note: Benzodiazepines can precipitate coma if used in hepatic impairment. If treatment is required benzodiazepines with shorter half-lives in reduced doses should be used Contraindications of benzodiazepines: Neuromuscular respiratory disease e.g., myasthenia gravis Severe hepatic impairment Respiratory depression Obstructive sleep apnoea Benzodiazepines toxicity: Respiratory depression and coma Nystagmus Ataxia, dysarthria Antidote: Flumazenil High yield: Oral lorazepam 1-2 mg or IM lorazepam 2-4 mg are recommended for the emergency tranquilization of violent or disturbed patients IV lorazepam should be administered as first-line treatment in status epilepticus patient, IV diazepam can be used if IV lorazepam is not available and buccal midazolam can be used if intravenous access cannot be rapidly established

   Local anesthetic drugs:

   Anesthetic induction and maintenance agents:

   Ketamine

   Propofol

   Ketamine is NMDA receptor antagonist, the only anesthetic agent available that has analgesic, hypnotic, and amnesic properties. Note: Ketamine is preferred anesthetic agent in haemodynamically unstable patients. Ketamine causes tachycardia, an increase in blood pressure, central venous pressure and cardiac output, secondary to an increase in sympathetic tone. Ketamine in asthma: Ketamine protects respiratory drive. The bronchodilatory effects of ketamine can provide some benefit in asthmatic patients who require anesthesia or sedation for procedures. By helping to relax the smooth muscles of the airways, ketamine might temporarily improve airflow and prevent bronchoconstriction that could be triggered by other anesthetic agents. Side effects: Hypertension Nystagmus Tachycardia Transient psychosis effect Note: Ketamine is dissociative anesthesia that causes high incidence of hallucinations and transient psychotic effects. These can be reduced by the co-administration of a benzodiazepine, such as diazepam or midazolam.

   Short acting phenol derivative. Used as both induction and maintenance agent. Circulatory effects: Propofol avoided in haemodynamically unstable patients causes decrease in blood pressure and systemic vascular resistance without a compensatory increase in heart rate. Respiratory effects: Decreased tidal volume and respiratory rate producing respiratory depression Decrease ventilatory response to carbon dioxide Reduced upper airway reflexes Side effects: Pain on injection (in up to 30%) Hypotension Transient apnoea Hyperventilation Coughing and hiccough Headache Thrombosis and phlebitis

   Anesthetic induction and maintenance agents: (Continues)

   Thiopental sodium	Etomidate	Entonox
   Thiopental is a very short acting barbiturate that is primarily used for the induction of anesthesia. Thiopental sodium is preferred drug of rapid sequence induction in adults Side effects: Hypotension Arrhythmias Involuntary muscle movements Myocardial depression Cough and Laryngeal spasm Headache Rash Hypersensitivity reactions Contraindications: Acute intermittent porphyria Myasthenia gravis Severe respiratory disease	Etomidate is an induction agent notable for its relative cardiovascular stability. It causes less hypotension than thiopental sodium and propofol during induction. Etomidate is associated with rapid recovery without hangover effect. Side effects: Pain on injection (in up to 50%) Phlebitis and venous thrombosis Arrhythmias and heart block Hyperventilation Respiratory depression and apnoea Can cause both hypo- and hypertension Increased mortality in critically ill patients	50/50 mix of 02 and NO used in maintenance of anesthesia in sub anesthetic concentration for analgesia and CNS depression Side effects: Inhibition of Vit B12 synthesis causes megaloblastic anemia Euphoria Contraindications: Reduced conscious level Diving injury Pneumothorax Middle ear disease Sinus disease Bowel obstruction Psychiatric patients