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**1.Anesthesia and Surgery > 1.General & IV Anesthesia > Flashcards

1.General & IV Anesthesia Flashcards

1
Q

Guedel’s Depths of Anesthesia:

Stage 1

A

Analgesia or Disorientation

  • decreased awareness of pain, sometimes with amnesia.
  • impaired consciousness
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2
Q

Guedel’s Depths of Anesthesia:

Stage 2

A

disinhibition: Excitation or Delirium

  • Amnesia, enhanced reflexes, and irregular respiration
  • retching and incontinence may occur
  • should be traversed as rapidly as possible
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3
Q

Guedel’s Depths of Anesthesia:

Stage 3 (overview)

A

Surgical anesthesia:

  • unconscious, no pain reflexes;
  • very regular respiration; blood pressure maintained
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4
Q

Guedel’s Depths of Anesthesia:

Stage 4

A

Overdose/ medullary depression:

  • severe respiratory and cardiovascular depression;
  • require mechanical and pharmacologic support
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5
Q

Stage 3: Plane 1

A
  • regular spontaneous breathing, constricted pupils, and central gaze.
  • Loss of reflexes: eyelid, conjunctival, and swallow
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6
Q

Stage 3: Plane 2

A
  • intermittent cessations of respiration
  • loss of reflexes: corneal and laryngeal reflexes
  • Halted ocular movements and increased lacrimation may also occur
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7
Q

Stage 3: Plane 3

A

*“true surgical anesthesia”

  • complete relaxation of the intercostal and abdominal muscles
  • loss of reflex: pupillary light
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8
Q

Stage 3: Plane 4

A
  • irregular respiration, paradoxical rib cage movement
  • full diaphragm paralysis resulting in apnea
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9
Q

General Anesthesia: Goals

A
  • unconsciousness
  • analgesia
  • amnesia
  • immobility, skeletal muscle relaxation without impairing breathing
  • inhibition of autonomic reflexes that causes bronchospasm, excess salivation, arrhythmias

Of note, no single anesthetic can achieve all of the above, needs combination

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10
Q

Ideal Anesthetic:

Characteristics

A
  • should induce rapid and smooth induction
  • be rapidly reversible upon discontinuation
  • possess a wide margin of safety
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11
Q

Balanced Anesthesia

A

a combination of agents and techniques (e.g., premedication, regional anesthesia, and general anesthesia with one or more agents) is used to produce the different components of anesthesia

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12
Q

General Anesthetics:

Two Types

A
  • Inhaled Gases: Nitrous Oxide, Sevoflurane, Desflurane, Isoflurane, Enflurane, Halothane
  • Intravenous Drugs: Thiopental & Methohexital (ultrashort-acting barbiturates), *Propofol, Etomidate

Propofol is most commonly used

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13
Q

Molecular Targets of Anesthesia

A

Ligand-Gated Ion Channels

  • may increase inhibitory synaptic activity
    • GABAa receptors
    • Potassium Channels
  • may reduce excitatory synaptic activity
    • Nicotinic acetylcholine receptors
    • Ionotrophic Glutamate Receptors (AMPA, Kainate, NMDA)
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14
Q

Anesthetic Hypnosis

A
  • General anesthetics cause direct activation of sleep-promoting neurons in the ventrolateral preoptic nucleus of the hypothalamus
  • These neurons preferentially fire during natural sleep.
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15
Q

Anesthetic Gases

list

A
  • Nitrous Oxide (laughing gas)
  • Volatile liquids with low or no flammability:
    • Sevoflurane
    • Isoflurane
    • Desflurane
    • Enflurane
    • Halothane
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16
Q

Anesthetic Gas:

Main Advantage

A

can easily change blood concentration by altering gas mixture to achieve anesthesia and reduce toxicity

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17
Q

MAC - Minimum Alveolar Concentration

A

index of potency of an inhaled GA

Alveolar concentration of an anesthetic gas at which 50% of patients become un-responsive to a standard surgical stimulus

Lower the MAC, the more potent the drug

(rate of induction is NOT related to MAC)

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18
Q

Pharmacokinetics

A
  • The lower the blood : gas partition coefficient, the faster the induction rate

more soluble anesthetic gas = slower induction

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19
Q

Speed and Solubility of Inhaled Anesthetics

A

The alveolar anesthetic concentration (FA) approaches the inspired anesthetic concentration (FI) fastest for the least soluble agents

Faster if LESS SOLUBLE

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20
Q

Inhaled Anesthetics:

Least soluble → Most Soluble

A

No DISH

  • Nitrous Oxide (least soluble, fastest)
  • Desflurane
  • Sevoflurane
  • Isoflurane
  • Halothane (slowest, most soluble)
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21
Q

How does ventilation rate affect rate of induction?

A

Increasing the Ventilation Rate Increases the Rate of Induction

Effect of ventilation on FA/FI: Increased ventilation (8 versus 2 L/min) has a greater effect on equilibration of halothane than nitrous oxide

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22
Q

Relationship between blood:gas partition coefficient and rate of elimination of inhaled anesthetic?

A

The lower the blood : gas partition coefficient, the faster the elimination rate

Inhalational anesthetics are eliminated by the lungs

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23
Q

Which inhaled anesthetic is metabolized by the liver?

A

Halothane

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24
Q

Second Gas Effect:

Define

A

By giving 2 inhalational anesthetics TOGETHER, with one at high concentration [NO] →

the second gas will enter the blood faster than if it was given along

25
Q

Major Pharmacologic Effects of Inhaled GA

A
  • ➤ Liver
    • depress hepatic blood flow by 15 to 45%. usually
      reversible. normally of minimal consequence
    • Liver metabolism is low for all agents except
      halothane
  • ➤ Kidney
    • depress glomerular filtration and renal plasma
  • *flow**. normally of minimal consequence.
26
Q

Nitrous Oxide (N2O)

properties

A

(+) strong analgesic, rapid onset and recovery

(-) *low potency, no muscle relaxation, hypoxia (>75% after removal)

  • Indications:
    • sole agent for sedation and analgesia (in comb. w/ other GAs)
    • non-irritating can be used in asthmatics
    • pregnant women
  • Contraindications:
  • Complications:
    • a drug of abuse:causes depersonalization, dizziness,
      euphoria, and some sound distortion
    • Long term abuse: Brain damage, peripheral sensory
      neuropathies
27
Q

Sevoflurane

properties

A

(+) rapid induction and recovery, *MC used

(-) high liver metabolism (3%)

  • Indications:
    • popular for same-day surgery
    • not pungent
    • used for mask induction in children
  • Contraindications:
  • Complications:
    • relatively high liver metabolism (3%) → no hepatotoxicity or nephrotoxicity
    • interacts with soda lime of re-breathing apparatus,
      resulting in a metabolite that may have kidney toxicity.
      (fresh gas rather than recycled gas should be used)
28
Q

Desflurane

properties

A
  • *(+) Rapid induction and recovery. *Recovery is 2x as**
  • *fast as isoflurane, LOW liver metabolism**

(-) pungent

  • Indications:
    • outpatient surgery
  • Contraindications:
    • mask induction
  • Complications:
    • irritating to the airways and may cause laryngospasm during induction
29
Q

Isoflurane:

properties

A

(+) medium induction rate and recovery rate (improved over halothane and enflurane), potent, safe, less reduction in cardiac output, good muscle relaxant

(-) pungent

  • Indications:
    • pts w/ ischemic heart disease
  • Contraindications:
    • not as useful in children
  • Complications:
    • *No major side effect
      • minimal liver metabolism → no metabolic toxicities
30
Q

Enflurane

properties

A

(Limited use)

(+) medium rate of induction and recovery, slightly better than halothane.

(-) slow induction and seizure-like activity

  • Indications: limited due to slow induction and side effects
  • Contraindications:
    • pts w/ abnormal EEG or Hx of seizures
  • Complications:
    • seizure-like EEG activity
31
Q

Halothane

properties

A

(+) highest solubility in blood (of currently used anesthetics), *not pungent

(-)

  • Indications:
    • mask induction for children
    • low cost → used in developing countries
  • Contraindications:
    • side effects have reduced use
  • Complications:
    • >20% undergoes liver metabolism
    • Malignant hyperthermia, Hepatotoxicity, Arrhythmias
32
Q

Halothane:

major side effects

A
  • Malignant Hyperthermia -
    • Muscle contraction, runaway temperature – fatal.
    • Withdraw anesthetic and give Dantrolene
  • Hepatotoxicity - can cause hepatic necrosis due to
    Immune response
  • Arrhythmias - sensitizes the heart to catecholamines
33
Q

Malignant Hyperthermia

pathophysiology

A
  • a genetic disorder of skeletal muscle (Ryanodine Receptor Type 1, located on the sarcoplasmic reticulum)
  • due to an increase in intracellular calcium concentration in the skeletal muscle
34
Q

Which GA agents are MOST likely to trigger Malignant hyperthermia?

A

Volatile Anesthetics

  • halothane
  • Isoflurane + succinylcholine
35
Q

Which GA agents are LEAST likely to trigger Malignant hyperthermia?

A

Desflurane

because it decreases the amount of calcium released from the sarcoplasmic reticulum leading to muscle relaxation

36
Q

Malignant Hyperthermia:

symptoms & tx

A
  • a rare, but important, cause of anesthetic morbidity and mortality
    • occurs in susceptible individuals exposed to volatile anesthetics or succinylcholine
  • Sxs:
    • hyperthermia
    • muscle rigidity
    • rapid onset of tachycardia and hypercapnia
    • hyperkalemia
    • metabolic acidosis
  • Tx: Stop the triggering agent, give dantrolene, treat fever, acidosis and arrhythmia
37
Q

IV General Anesthetics

list

A
  • Thiopental & Methohexital (ultrashort-acting barbiturates), Propofol, Etomidate:
    • enhance action of GABA on GABAA receptors
    • increases Cl- influx
  • Ketamine:
    • NMDA receptor antagonist
38
Q

IV General Anesthetics

advantages and disadvantages

A
  • Advantages
    • Lower cost
    • Rapid onset of action
  • Disadvantage
    • Harder to lower blood level, so shorter-acting
      agents are preferred
39
Q

IV General Anesthetics

pharmacologic and clinical properties

A

highly lipophilic in general

IV into Blood → distributed to the brain and spinal cord, viscera → redistributed to muscle → redistributed to fat

Following prolonged infusion, there is a buildup in fat which varies with the agent used

40
Q

Which IV general anesthetic has relatively shorter half-life?

A

Even after a prolonged infusion, the half-time of propofol is relatively short, which makes propofol the preferred choice for intravenous anesthesia.

Ketamine and etomidate have similar characteristics but their use is limited by other effects

41
Q

IV General Anesthetics:

Ultra-short-acting Barbiturates

Thiopental & Methohexital

A

(+) Potent; can induce Stage III anesthesia;

(-) poor analgesic, increased half-life → prolongs “grogginess”

MOA: redistribution to muscle and then fat. prolonged infusion leads to increased half-life.

Indications: Induce anesthesia prior to the use of another agent for maintenance (propofol has better pharmacokinetic properties)

42
Q

IV General Anesthetics:

Ultra-short-acting Barbiturates

Side Effects

A
  • Decreased cerebral metabolism (oxygen utilization), cerebral blood flow and intracranial pressure (This can be useful in cerebral ischemia)
  • hypotension due to vasodilatation and slight depression of myocardial contractility
  • Respiratory depression
  • Laryngospasm (bronchospasm) during induction
  • When used for maintenance, patient recovers slowly and feels groggy
43
Q

Propofol

properties

A

(+) rapid induction, less distribution to musc/fat, more rapid recovery than thiopental, less groggy, potent (can induce stage III anesthesia)

(-) no analgesia, poorly soluble, pain at injection site

  • Indications:
    • induction and maintenance of anesthesia
    • Popular for same-day surgery, low or no grogginess
    • also used at lower doses as an ICU sedative
  • Contraindications:
  • Complications:
    • decreased cerebral metabolism and respiratory depression
    • greater hypotension than thiopental; less likely to induce bronchospasm
44
Q

Fospropofol

properties

A
  • a water-soluble prodrug of propofol
    • onset & recovery are prolonged, less injection pain
    • paresthesia in perianal region
45
Q

Etomidate

properties

A

(limited use)

  • Pharmacokinetic - similar to propofol
    • stage III anesthesia, no analgesia
    • minimal effect on cardiovascular system
    • mild respiratory depression
  • clinical use: for anesthetic induction, but not maintenance
  • complications:
    • Major
      • An increase in death rate. attributed to suppression of adrenocorticosteroids
      • Nausea and vomiting.
    • Minor
      • injection can be very painful
      • causes myoclonic movements (can be suppressed by opioids and benzodiazepines)
46
Q

Ketamine

properties

A

(+) “ dissociative anesthesia”, good analgesia, produces anesthesia

(-) inc. HR, CO, and BP, causes bronchodilation, little effect on respiration

  • PK: Related to phencyclidine (PCP) (street name: angel dust), similar to those of propofol
  • Indications:
    • pediatric pts
    • asthmatics - pts at risk for hypotension and bronchospasm
    • cardiac patients
  • Contraindications:
  • Complications:
    • inc cerebral BF → inc intracranial pressure
    • hallucinations
    • drug of abuse → long term abuse causes bladder damage
47
Q

Anesthetic Adjuncts

list

A
  • Benzodiazepines
  • Opioids
  • Neuroleptic-Opioid Combinations
  • Dexmedetomidine
48
Q

Benzodiazepines

properties

A

enhance GABAA receptor activity

(-) does not achieve true anesthesia, poor analgesic

  • Indications
    • Cause Sedation, reduce anxiety, induce amnesia
  • Contraindications
    • reduce dose of other drugs (e.g. thiopental) needed to achieve anesthesia
  • Complications
    • High doses will induce hypnosis and unconsciousness
    • can prolong recovery
    • Depress respiration and blood pressure
49
Q

reversal agent for Benzodiazepine overdose

A

Reversed
with Flumazenil

50
Q

Differences b/w:

Diazepam, Lorazepam, and Midazolam

A
  • Diazepam – long-acting;
  • Lorazepam - intermediate acting;
  • Midazolam – short-acting
    • MC used because of its short half-life.
    • Can be injected or given orally or rectally
51
Q

Opioids (for surgery)

properties

A

primary analgesic agents used for major surgery

  • acts as µ-opioid receptor agonists
    • Excellent analgesia
    • Full anesthesia when given high enough doses
    • Lower doses (used w/ sedative → sedation analgesia)
  • Indications
    • relieve pain during/after sx
    • adjunct to reduce amount of anesthetics
    • cardiac sx - high doses can be primary anesthetic
  • (-)/ Contraindications
    • NOT good for amnesia
52
Q

Opioids (for surgery)

differences

A
  • Morphine
    • longest duration of action
  • Fentanyl, sufentanil, and alfentanil
    • intermediate half-lives
    • vary in duration of action after infusion
    • *Fentanyl is most prolonged by infusion
  • Remifentanil
    • shortest half-life
    • used in briefly painful short procedures
53
Q

Opioids (for surgery)

Complications

A
  • Prolonged respiratory depression
    • This is due to rigidity of the muscles of the diaphragm sometimes called “stone chest”
  • Nausea and vomiting
  • Constipation
  • Drugs of abuse
54
Q

American Society of Anesthesiologists (ASA)

Surgical Risk Classification

A

physical status classification system was developed to offer clinicians a simple categorization of a patient’s physiological status that can help predict operative risk

*Modified by E for emergent procedures

(rate of post-operative pulmonary complication)

55
Q

ASA: Class 2

A

patient w/ mild systemic disease

(e.g. essential HTN, NIDDM)

56
Q

ASA: Class 3

A

patient w/ severe systemic disease that limits activity

(e.g. angina, COPD)

57
Q

ASA: Class 4

A

patient with incapacitating systemic disease that is constant threat to life

58
Q

ASA: Class 5

A

moribund patient not expected to survive 24 hours w/ or w/o surgery

(moribund: in terminal decline, at the point of death)

59
Q

ASA: Class 6

A

patient declared legally brain dead and awaiting organ harvesting

**1.Anesthesia and Surgery (7 decks)

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