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Pharmaco ++ > General Anesthetics > Flashcards

General Anesthetics Flashcards

1
Q

What is general anesthesia?

A

A medically induced coma and loss of protective reflexes

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2
Q

What are the overall aims of general anesthesia?

A

Unconsciousness
Amnesia
Analgesia
Relaxation of skeletal muscles
Loss of autonomic nervous system reflexes

Ideally, should have rapid and smooth loss of consciousness, fast and easy recovery, and a high margin of safety with no adverse effects

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3
Q

General anesthesia vs monitored anesthesia?

A

General anesthesia is best used for extensive procedures

Monitored anesthesia is best used in minor procedures where the patient can maintain a patent airway and respond to commands

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4
Q

What are the stages of anesthesia?

A

Analgesia (initially without amnesia, then with amnesia)

Excitement (amnestic but delirious, with irregular respiration and can easily retch or vomit if stimulated)

Surgical anesthesia (regular respiration recurs with apnea, loss of eye movements and eye reflexes)

Medullary depression

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5
Q

What stage of anesthesia is avoided?

A

Excitement

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6
Q

What is the most reliable sign of surgical anesthesia?

A

Loss of motor and autonomic response to noxious stimuli

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7
Q

What are the broad categories of inhalational general anesthetics?

A

Gas
Liquids

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8
Q

What are the broad categories of intravenous general anesthetics?

A

Inducing agents
Dissociative anesthesia
Neurolept analgesia

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9
Q

How does PK affect inhaled anesthetics?

A

Absorption and distribution influence onset of anesthesia, where brain concentration depends on transfer of anesthetic from alveolar air to blood then from blood to brain

Absorption and distribution also affect recovery time, where if the drug is more widespread in other tissues you take longer to recover as the drug has to escape back out from the lungs

Metabolism and excretion affect rate of recovery

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10
Q

How does solubility affect inhaled anesthetics?

A

E.g. nitrous oxide: Low solubility in blood = transfer to brain quickly = reaches arterial tension quickly and rapidly equilibrates with brain to induce fast onset

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11
Q

How does anesthetic concentration in the inspired air affect inhaled anesthetics?

A

Increased rate of transfer into blood and therefore brain

Anesthetics with moderate solubility can be given at a higher concentration initially to induce fast onset, then lowered to maintain optimal depth of anesthesia

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12
Q

How do rate and depth of pulmonary ventilation affect inhaled anesthetics?

A

Increase in ventilation can significantly increase anesthetics with moderate to high solubility like halothane

Depression in respiration by opioid analgesics reduces onset of anesthesia

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13
Q

How does pulmonary blood flow affect inhaled anesthetics?

A

Increase in blood flow decreases the rate of rise of anesthetic tension in blood as blood flows too fast, decreasing rate of rise of anesthetic concentration in the brain for anesthetics with moderate to high solubility

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14
Q

How does the arteriovenous concentration gradient affect inhaled anesthetics?

A

Concentration gradient depends on uptake of anesthetic by tissues

A high concentration gradient increases the time taken to achieve equilibrium with the brain, increasing onset

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15
Q

How do metabolism and excretion affect rate of recovery of inhaled anesthetics?

A

Relatively soluble anesthetics are eliminated faster. More insoluble anesthetics accumulate in muscle, skin and fat and are more slowly eliminated

More anesthetic in the body = longer recovery time

Pulmonary blood flow (to a point) and rate of ventilation increase = increase rate of recovery via respiratory excretion

Hepatic metabolism contributes to clearance, e.g. halothane

Bacteria in the GI tract break down nitrous oxide

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16
Q

How do inhaled anesthetics work?

A

Interact with ligand gated ion channels to reduce function (GABA, nicotinic and glycine)

Act at multiple levels of the CNS depending on the sensitivity of specific neurons and pathways (spinothalamic tract and reticular activating system)

17
Q

What are the effects of inhaled anesthetics on the CVS?

A

Reduces cardiac output and systemic resistance to reduce mean arterial pressure

Variable effect on heart rate

Depression of myocardial function

18
Q

What are the effects of inhaled anesthetics on the respiratory system?

A

Decrease in minute ventilation

Reduced response to hypercapnia

Increase apneic threshold (means you need to support ventilation in recovery)

Depression of mucociliary function

Halothane and sevoflurane cause bronchodilation

19
Q

What are the effects of inhaled anesthetics on the brain?

A

Increases cerebral blood flow by decreasing cerebral vascular resistance

Can be bad for patients with increased intracranial pressure

Nitrous oxide is least likely to increase cerebral blood flow, good for neurosurgery

20
Q

What are the effects of inhaled anesthetics on the kidneys?

A

Impairs renal autoregulation by reducing renal blood flow

Methoxyflurane releases fluoride during metabolism, may cause renal dysfunction

21
Q

What are the effects of inhaled anesthetics on the liver?

A

Decreased hepatic blood flow

Repeated exposure to halothane may cause liver damage

Reactive metabolites may directly damage the liver or initiate immune mediated responses

22
Q

What are the effects of inhaled anesthetics on the uterus?

A

Halogenated anesthetics are potent uterine muscle relaxants

23
Q

What is malignant hyperthermia?

A

An autosomal dominant skeletal muscle disorder, where general anesthesia triggers hypertension, tachycardia, severe muscle rigidity, hyperthermia and acidosis, can be fatal

Caused by an increase in muscle cell calcium levels

Treated with dantrolene to reduce calcium release

24
Q

What is halothane?

A

An inhaled general anesthetic, mostly used to maintain anesthesia but sometimes used for induction esp in children

Relaxes skeletal muscles, potentiating skeletal muscle relaxants

Can cause dose-dependent respiratory depression

Decreases blood pressure as it depresses cardiac output with little change in systemic resistance

Can rarely cause hepatitis

25
Q

What is nitrous oxide?

A

An odourless inhaled general anesthetic

Rapid onset and recovery but lacks potency, where it can produce significant analgesia and sedation but cannot produce complete unconsciousness or surgical anesthesia

Used as an adjunct for other inhaled anesthetics, and used as an analgesic agent for labour pain

26
Q

Pros and cons of using intravenous general anesthetics?

A

Fast onset and recovery, commonly used for induction or short outpatient procedures

Do not require specialized vaporiser equipment or disposal equipment

Most lack analgesic properties, have to be combined with inhaled or local anesthetics

27
Q

What are barbiturates?

A

An intravenous general anesthetic

Binds to GABA receptors, increasing duration of chloride channel opening, and also acts on AMPA receptors to depress glutamate mediated excitation

Thiopental used for induction as it rapidly crosses BBB

High doses or continuous infusion decreases arterial blood pressure, stroke volume and cardiac output

Potent respiratory depressants

Decreases cerebral metabolism, oxygen consumption and blood flow, good for decreasing intracranial pressure

28
Q

What are benzodiazepines?

A

An intravenous general anesthetic

Potentiates GABA without directly activating GABA receptors, increasing frequency of chloride channel opening

Diazepam, lorazepam and midazolam are used as pre-anesthetic medication and during procedures performed under LA due to sedative, anxiolytic and amnestic properties

Alone do not act very quickly and do not induce surgical anesthesia

High doses may prolong post anesthetic recovery and cause anterograde amnesia

Can have flumazenil to accelerate recovery

29
Q

What are benzodiazepines?

A

An intravenous general anesthetic

Potentiates GABA without directly activating GABA receptors, increasing frequency of chloride channel opening

Diazepam, lorazepam and midazolam are used as pre-anesthetic medication and during procedures performed under LA due to sedative, anxiolytic and amnestic properties

Alone do not act very quickly and do not induce surgical anesthesia

High doses may prolong post anesthetic recovery and cause anterograde amnesia

Can have flumazenil to accelerate recovery

30
Q

What is propofol?

A

An intravenous general anesthetic

Potentiates GABA receptor activity, slowing channel closing time, blocks sodium channels and has some endocannabinoid system activity

Rapid onset, recovery faster than barbiturates, patients feel subjectively better with less nausea

Used for induction, maintenance, sedation and monitored anesthesia

Rapidly metabolized by the liver and excreted by the kidneys

Decreases blood pressure and respiration

31
Q

What is ketamine?

A

An intravenous general anesthetic

NMDA receptor antagonist producing dissociative anesthesia, associated with catatonia, amnesia and analgesia without a loss of consciousness

Highly lipophilic, rapidly distributes to the brain

Metabolised by the liver and excreted by the kidneys and in bile

Has analgesic and anesthetic properties!

Stimulates CVS, useful in elderly patients or patients with cardiogenic/septic shock

Increases intracranial pressure, decreases respiratory rate

Associated with post-op disorientation, illusions and dreams

32
Q

What is balanced anesthesia?

A

IV for induction
Inhaled for maintenance

Muscle relaxants to facilitate tracheal intubation and to optimize surgical procedures
LA to provide pre- or peri-operative analgesia
CV drugs to control transient autonomic responses to noxious surgical stimuli

33
Q

What is monitored anesthesia?

A

Use regional or local anesthesia supplemented by IV anesthetics

Midazolam for pre-medicative anxiolysis, amnesia and mild sedation

Propofol for moderate to deep sedation

Opioid analgesics or ketamine

Patients might still require respiratory support!

34
Q

What is conscious sedation?

A

Patient retains the ability to maintain a patent airway and respond to commands

Midazolam, diazepam for anxiolysis, amnesia and mild sedation

Propofol for sedation

Opioid analgesics reversible via nalaxone

Pharmaco ++ (7 decks)

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