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
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
3
Q
Guedel’s Depths of Anesthesia:
Stage 3 (overview)
A
Surgical anesthesia:
- unconscious, no pain reflexes;
- very regular respiration; blood pressure maintained
4
Q
Guedel’s Depths of Anesthesia:
Stage 4
A
Overdose/ medullary depression:
- severe respiratory and cardiovascular depression;
- require mechanical and pharmacologic support
5
Q
Stage 3: Plane 1
A
- regular spontaneous breathing, constricted pupils, and central gaze.
- Loss of reflexes: eyelid, conjunctival, and swallow
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
7
Q
Stage 3: Plane 3
A
*“true surgical anesthesia”
- complete relaxation of the intercostal and abdominal muscles
- loss of reflex: pupillary light
8
Q
Stage 3: Plane 4
A
- irregular respiration, paradoxical rib cage movement
- full diaphragm paralysis resulting in apnea
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
10
Q
Ideal Anesthetic:
Characteristics
A
- should induce rapid and smooth induction
- be rapidly reversible upon discontinuation
- possess a wide margin of safety
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
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
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)
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.
15
Q
Anesthetic Gases
list
A
- Nitrous Oxide (laughing gas)
- Volatile liquids with low or no flammability:
- Sevoflurane
- Isoflurane
- Desflurane
- Enflurane
- Halothane
16
Q
Anesthetic Gas:
Main Advantage
A
can easily change blood concentration by altering gas mixture to achieve anesthesia and reduce toxicity
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)
18
Q
Pharmacokinetics
A
- The lower the blood : gas partition coefficient, the faster the induction rate
more soluble anesthetic gas = slower induction
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
20
Q
Inhaled Anesthetics:
Least soluble → Most Soluble
A
No DISH
- Nitrous Oxide (least soluble, fastest)
- Desflurane
- Sevoflurane
- Isoflurane
- Halothane (slowest, most soluble)
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
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
23
Q
Which inhaled anesthetic is metabolized by the liver?
A
Halothane
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
Major Pharmacologic Effects of Inhaled GA
* ➤ **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
Nitrous Oxide (N2O)
properties
**(+) 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
Sevoflurane
properties
**(+) 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
Desflurane
properties
* *(+) 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
Isoflurane:
properties
**(+) 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
Enflurane
properties
(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
Halothane
properties
**(+) 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
Halothane:
major side effects
* **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
Malignant Hyperthermia
pathophysiology
* 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
Which GA agents are **MOST** likely to trigger Malignant hyperthermia?
Volatile Anesthetics
* halothane
* Isoflurane + succinylcholine
35
Which GA agents are **LEAST** likely to trigger Malignant hyperthermia?
**Desflurane**
because it decreases the amount of calcium released from the sarcoplasmic reticulum leading to muscle relaxation
36
Malignant Hyperthermia:
symptoms & tx
* 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
**IV** General Anesthetics
list
* **Thiopental & Methohexital (ultrashort-acting barbiturates), Propofol, Etomidate:**
* enhance action of GABA on GABAA receptors
* increases Cl- influx
* **Ketamine**:
* NMDA receptor antagonist
38
**IV** General Anesthetics
advantages and disadvantages
* Advantages
* **Lower cost**
* **Rapid onset of action**
* Disadvantage
* **Harder to lower blood level,** so shorter-acting
agents are preferred
39
**IV** General Anesthetics
pharmacologic and clinical properties
highly lipophilic in general
## Footnote
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
Which IV general anesthetic has relatively shorter half-life?
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
IV General Anesthetics:
**Ultra-short-acting Barbiturates**
**Thiopental & Methohexital**
(+) 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
IV General Anesthetics:
## Footnote
**Ultra-short-acting Barbiturates**
**Side Effects**
* **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
Propofol
properties
**(+) 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
Fospropofol
properties
* a water-soluble prodrug of propofol
* onset & recovery are prolonged, less injection pain
* paresthesia in perianal region
45
Etomidate
properties
(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
Ketamine
properties
**(+) “ 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
Anesthetic Adjuncts
list
* Benzodiazepines
* Opioids
* Neuroleptic-Opioid Combinations
* Dexmedetomidine
48
Benzodiazepines
properties
**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
reversal agent for Benzodiazepine **overdose**
Reversed
with **Flumazenil**
50
Differences b/w:
Diazepam, Lorazepam, and Midazolam
* **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
Opioids (for surgery)
properties
primary analgesic agents used for major surgery
* acts as **µ-opioid** receptor ****_agon_**ists**
* 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
Opioids (for surgery)
differences
* **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
**Opioids** **(for surgery)**
Complications
* **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
American Society of Anesthesiologists (ASA)
Surgical Risk Classification
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
ASA: Class 2
patient w/ **mild** systemic disease
(e.g. essential HTN, NIDDM)
56
ASA: Class 3
patient w/ **severe** systemic disease that limits activity
(e.g. angina, COPD)
57
ASA: Class 4
patient with **incapacitating** systemic disease that is **constant threat to life**
58
ASA: Class 5
**moribund** patient **not expected to survive 24 hours** w/ or w/o surgery
(moribund: in terminal decline, at the point of death)
59
ASA: Class 6
patient declared **legally brain dead** and **awaiting organ harvesting**
