Anasthetic Agents Flashcards
inhalable anesthetics:
nitrous oxide halothane isoflurane desflurane sevoflurane
advantages and disadvantages to general anesthesia:
- adv: body wide
- disadv: disturbance of all organ systems
advantages and disadvantages to local anesthesia:
- adv: limit anesthesia to small area; minimal system disturbance
- disadv: may not be adequate
IV (fixed) anesthetics:
thiopental
propofol
etomidate
ketamine
two general side effects with anesthetics?
decreased respiration
decreased BP
*What is the triad of anesthesia?
Asleep, pain-free and still
**factors for ideal anesthetic:
1) unconscious - hypnosis
2) amnesia - produce sleep without recall
3) analgesia - abolish pain
4) skeletal muscle relaxation
5) areflexia - eliminate noxious reflexes
6) good minute to minute control
**Adjuvant drugs and conditions given prior to anesthesia to improve outcomes:
1) relieve anxiety - benzodiazepines
2) prevent allergic reactions - antihistaminics
3) prevent nausea and vomiting - antiemetics
4) provide analgesia - opioids
5) prevent bradycardia and secretion -atropine
**Important conditions to know about prior to anesthesia administration?
- *1) CV problems
- *2) respiratory disease
3) altered kidney or liver fx
4) abn tissue blood flow
5) psychiatric history
6) drug/medication/supplement history
7) allergies
8) prior anesthesia history
9) so maaannnnyy!
phases of general anesthesia:
1) induction phase-initial administration until desired level of anesthesia achieved
2) maintenance phase-starts once the desired depth/level of anesthesia is achieved; anesthetic concentration is maintained at or above a minimum necessary to stay at this level
3) emergence phase-waking up period
4) recovery period-from discontinuance of anesthetic agent administration until full restoration of consciousness and normal function
Stages of general anesthesia -effects on the the brain:
- Stage 1: Analgesia- amnesia, euphoria
- Stage 2: Excitement- delirium, combative beh
- Stage 3: Surgical anesthesia- unconsciousness, regular respiration, decreasing eye movement
- Stage 4: Medullary Depression- respiration arrest, cardiac depression and arrest, no eye movement
Commence surgery at what stage of general anesthesia?
Stage 3 - surgical anesthesia-unconsciousness, regular respiration, decreasing eye movement
Anesthetics - MOA?
1) depress spontaneous and evoked neuronal activity
a) induce neuronal hyperpolarization
b) increase firing threshold (lesser activity)
c) inhibit synaptic transmission and response to released neurotransmitters
2) anesthetics may alter ion channel function
* a) increase GABA_A receptor channel activity-enhanced inh neurotransmission and CNS depression
* b)activate voltage-gated K channels - hyperpolarization of neurons and reduced activation
* c) inhibit glutamate NMDA receptors - decreased excitatory neurotransmission
Which anesthetic inhibits glutamate NMDA receptors?
ketamine
Volatile inhalable anesthetic agents:
halothane
isoflurane
gaseous inhalable anesthetic agents:
NO
xenon
Advantages and disadvantages to inhalable anesthetics?
ADV:
-easy to control depth of anesthesia
-readily reversible, minute to minute control
DISADV:
-induction not as fast or smooth as with fixed agents
Inhalable anasthetics - pharmacokinetics:
Factors for uptake and distribution… and rate of onset and recovery…
- anesthetic concentration in inspired air
- pulmonary ventilation rate
- solubility in blood and lipid
- pulmonary blood flow
- arteriovenous concentration gradient
- elimination
Anasthetic concentration in inspired air factor
- relationship partial pressure or tension?
- main partial pressure factor?
- concentration in inspired air is proportional to partial pressure or tension
- partial pressure depends on the ability to vaporize the agents (heat of vaporization) - use of vaporizer
So the higher the inspired anasthetic concentration in the inspired air… then the _____ partial pressure in the lungs which has what result?
- HIGHER the partial pressure in the lung
- results in faster achievement of anesthetic concentration in the blood = gets to the brain faster
Pulmonary ventilation rate factor:
- better ventialation result in more rapid onset of anasthesia
- may be altered by pre-anesthetic medication or in some disease
- **partial pressure anesthetics with higher solubility are affected by ventilation rate
**solubility in blood and lipid factor info:
- Blood:gas partition coefficient (otswald coefficient) - solubility in blood
- brain:blood partition coefficient - solubility in lipid
So the lower the blood gass partition coefficient, then the ____ soluble results in a _____ in partial pressure in blood –> ___ equilibrium with brain and induction.
LESS SOLUBLE
MORE RAPID RISE IS PARTIAL PRESSURE IN BLOOD
FASTER EQUILIBRIUM WITH BRAIN AND INDUCTION
*Pulmonary blood flow/cardiac output factor info:
higher/lower blood flow?
- higher blood flow = slower partial pressure in blood and brain = slower onset (reasoning: more anesthetic distributes to other tissues due to high BF = less drug for brain)
- low blood flow = faster partial pressure rise in blood and brain = faster onset
Arteriovenous concentration gradient factor info:
- dependent on?
- increased difference b/w arterial and venous gas tensions means what?
- dependent on rate and uptake of the anesthetic by the tissues
- increased difference bw arterial and venous gas tensions == SLOWER onset
Elimination factor info:
- reverse of uptake
- dependent mainly on blood:gas partition coefficient (Otswald)
- LESS SOLUBLE = faster elimination
- Minimum alveolar concentration (MAC) definition:
* -Combining drugs and MAC?
the concentration of anesthetic % in the inspired air at equil when there is no response to noxious stimulus in 50% of patients
**-MAC values are additive if multiple drugs combined
**LOWER MAC=
more potent anesthetic
**Higher lipid solubility=
more potent anesthetic (LOWER MAC)
Anesthesia is produced when (relationship to MAC)…
when anesthetic partial concentration in brain is GREATER than or equal to MAC
*Important factor that INCREASES MAC value?
exposure to other CNS depressant agents
Nitrous oxide:
- onset and recovery?
- agent details?
- major limitation?
- onset and recovery = rapid (low blood/gas coefficient)
- Almost ideal agent - good anelgesia and relatively non-toxic/safe
- BUT its an incomplete anesthetic - LOW potency with a MAC = 110% –> insufficient potency for surergy
poor solubility in blood means?
fast onset of anesthesia
Advantages to using N2O:
-**2nd gas effect: reduces the induction time for the primary agent – used as acarrier for volatile anesthetics (primary agents)
- N2O is quickly taken up which concentrates the primary agent in the lungs –> FASTER ONSET
- **Dec induction time for primary agents (additive MAC values)
- **dec required concentration of primary agent
- **dec toxicity of primary agent
MINIMUM TOXICITY
*Side effect of N2O:
*Diffusion hypoxia: with abrupt discontinuation it diffuses quickly out of the body into the alveoli and dilutes O2
=bone marrow depression
=miscarriage with chronic use
=some evidence for depression immune system
N2O uses:
1) widely used for general anesthesia as a complementary agent - CAN NEVER BE USED AS SOLE ANESTHETIC AGENT
2) Analgesic for minor procedures (dentistry) or EMS (field analgesia)
Halogenated agents:
effects of halogenating the volatile agents:
- non-explosive and non-flammable
- increased potency
- increase toxicity and side effects
Halogenated agents - general properties:
- *-POTENT- usually used for maintenance of anesthesia
- adjuncts usually required (poor muscle relaxation/analgesia)
- toxicity increases with each use
- good minute to minute control (via inhalation)
- moderately rapid recovery (via inhalation)
-usually used for maintenance
halothane -
- type of drug?
- onset/recovery?
- potency?
- toxicity?
- halogenated agent duh
- medium rate of onset and recovery (Blood/gas=2.3)
- highly potent (MAC=.76%, very lipophilic) –> makes for slower recovery
- not used much any more bc of high incidence of post-op hepatitis esp with prolonged or repeated use
halothane - effectS:
- Complete anasthetic, poor analgesia, and muscle relaxation
- Systemic: respiratory depression, decreased myocardial contractility and HR –> decreased cardiac output and hypotension
Enflurane:
- specific physical feature?
- systemic effects?
- why is its use not as popular?
-PUNGENT ODOR
-respiratory depression, reduced cardiac contractility and HR
-smiliar to halothane but less hepatotoxic - MORE RENAL TOXIC
-some CNS stimulation effects = EEG convulsive pattern, jerking, twitching
(do not use in patients with seizures)
Isoflurane:
- type of drug?
- typically used for what?
- onset/recovery/potency?
- Is mask use ok?
- how administered?
- toxicity?
- halogenated agent
- typically used for maintenance
- medium to rapid onset and recovery (b/g = 1.4)
- relatively potent (MAC=1.4%)
- no mask bc pungent
- administered with air or pure O2
- LOWER toxicity = can be used in sick patients with impaired liver/kidney function
Desflurane
- primary advantage?
- min to min control?
- issues?
- potency?
- adv is that has very rapid onset and recovery (b/g =.42)
- min-min control is awesome!
- more irritating to respiratory passages than others –> bronchial irritation with cough and laryngeal spasm
- less potent - MAC=6.0%
Shorter or outpatient surgery most likely to use what anesthetic?
Desflurane
Also IV anesthetics are becoming more common in short or outpatient surgeries
Less potent MAC value is
HIGHER
more potent, MAC value is..
LOWER
- Sevoflurane-
- onset/recover/potency?
- min-min control?
- *-issues?
- rapid onset and recovery (b/g=.69)
- very potent, MAC = 2%
- excellent control min to min bc of low solubility and high potency
- **- lower airway irritation and not pungent –> OK for mask induction
- but may cause renal and hepatic toxicity
-MOST COMMONLY USED
inhalable anesthetic - general adverse effects:
1) depression of CV function
a) dec BP and periph vasc resis
b) depress myocardium
c) dec CO
d) arrhythmias and or tachycardia
e) sensitization to catecholamines
2) depression of respiration and response to CO2
3) decreased blood flow to liver and kidneys
4) organ toxicity
5) malignant hyperthermia
Which agent has liver toxicity?
halothane (and sevoflurane)
Which agent has kidney toxicity?
enflurane (and sevoflurane)
Which agent has BM suppression?
N2O
**Important feature of desflurane?
(LUNG) IRRITANT!
Primary use of IV anesthetics?
used for induction
Advantages and disadvantages of IV anesthetic agents:
adv:
* -quick, easy, smooth induction
* -rapid and complete recovery
disadv:
- -cant reverse the effects, except via metabolism
- slow elimination
Thiopental:
- type of drug?
- not used how?
- info?
- IV anesthetic
- NOT used for maintenance and NOT used as sole anesthetic (often used with N2O)
- NO anelgesia (hyperalgesia)
- Short duration - rapid diffusion from brain
- redistributes to other tissues - accumulation in adipose = toxicity
- crosses BBB quickly
- rapid onset and recovery–>quick induction
Propofol
- preparation?
- used for?
- induction/duration?
- how is recovery?
-milky white solution
-used for induction and maintenance for outpatient procedures
-very rapid induction and short duration
recovery is great - awake and clear headed without hangover
propofol vs thiopental-
propofol used as a continuous IV drip vs thiopental which is given in one injection?
ketamine:
- MOA?
- common issues?
- non-competitive glutamate NMDA receptor antagonist
- Dissociative anesthesia - intense analgesia, catalepsy and amnesia–> seems like patient is awake but they are not aware
- Emergence phenomenon-unpleasant dreams, hallucinations, and disorientation during emergence
Emergence phenomenon-what is it? what drug?
With ketamine:
-unpleasant dreams, hallucinations, and disorientation during emergence
Ketamine contraindication
-patients with psichiatric Hx
use of ketamine:
-limited to diagnostic procedures, and mainly to children and infants, bc of increased side-effects in older patients (except in patients with asthma)
adjuvant drugs - why use them?
- inc rate of induction
- decrease anxiety
- decrease pre and post op pain
- decrease side effects of general anesthetics
- reduce amount of general anesthesia required
***—> in combo help produce balanced anesthesia- closer to ideal anesthetic agent
Various combos with adjuvants?
- anxiolytics/hypnotics
- analgesics
- antiemetics
- anticholinergics
- neuromuscular blocking agents - paralytics
- **Midazolam:
- good for what?
- uses?
- onset/recovery?
benzodiazepine
- *-good for sedation, amnesia, and anxiolytic properties - via potentiation at GABA_A receptors
- provides CV stability
- Uses: sedation for painful procedures; induction agent; substitute for thiopental/propofol in high risk patients(with CV and/or pulmonary issues)
