General Anesthesia and Adjuncts Flashcards
Triad of Anesthesia
- Analgesia
- Amnesia
- Skeletal muscle relaxation
Triad plus of anesthesia includes
loss of consciousness, loss of sensory function, autonomic inhibition
Types of Anesthesia
- General
- Spinal (subarachnoid in CSF)
- Epidural
- Regional (Nerve trunk block)
- Local
- Monitored anesthesia care/sedation
General anesthesia modes of deliver
- Inhalational
- Intravenous
- Lipid soluble or able to cross BBB
Properties of inhalational anesthetics
rapid access to vascular system (brain); allows direct effects on pulmonary system
Properties of IV anesthetics
immediate access to vascular system; less than a minute (in the brain in 26 sec); advent of computer controlled pumps
Balanced anesthesia
combination of inhaled intravenous medications
Major anesthesia
IV induction, inhalational maintenance, muscle relaxant
Characteristics of anesthetic
- reduces excitability of the membranes
- no anesthetic specific receptors known
- no anesthesia specific antagonists
Stage 1 of anesthesia
analgesia - initially without amnesia
Stage 2 of anesthesia
disinhibition - delirium and excitement; amnesia, irregular respiration, retching, incontinence
Stage 3 of anesthesia
surgical anesthesia: unconscious, no pain perception, respiration regular again to apneic, BP maintained, 3 planes with eye changes
Stage 4 of anesthesia
Medullary depression: spontaneous respiration ceases, severe respiratory cardiovascular depression, death ensues without support
Characteristics of the ideal anesthetic
- quick in - rapid induction of anesthesia
- quick out - rapid recovery
- non-irritating to airway
- minimal physiologic trespass - nondisruptive and nontoxic
- lack of interactions with other drugs
- nonflammable, muscle relaxant properties
Dalton’s law
anesthetic exerts partial pressure proportional to % anesthetic in mixture
Fick’s law
anesthetic diffused down its concentration gradient
Henry’s law
amount of anesthetic dissolved in a liquid is proportional to partial pressure of the anesthetic in the mixture
Minimum alveolar concentration (M.A.C.)
minimum alveolar concentration at 1 atm that prevents movement in 50% of patients in response to a painful stimulus such as a surgical incision or clamping of the tail with a hemostat/clamp
Defines potency of inhalational anesthetics and serves as a means to compare anesthetics
Minimum alveolar concentration (M.A.C.)
The lower the MAC,
the more potent the agent
Factors decreasing MAC (less anesthetic agent is required)
increasing age, hypothermia, CNS depressants/drugs, acute EtOH intoxication, pregnancy, alpha adrenergic drugs (clonidine)
Factors that increase the MAC requirements (more anesthetic agent is required)
hyperthermia, chronic ethanol abuse, increase CNS neurotransmitters (MAO inhibitors)
Factors that have no change in MAC
duration of anesthetic, gender
Blood-gas partition coefficient
relative solubility in blood vs air; determines uptake alveoli to blood, thus determines rate of induction
Solubility is approximately
blood-gas coefficient
High blood solubility
slow induction
Low blood solubility
rapid induction
Induction of high solubility anesthetic hastened by
hyperventilation
“Laughing gas”
nitrous oxide
Properties of nitrous oxide
insoluble, nonflammable, rapid onset, excellent analgesia and sedation, no skeletal muscle relaxation
Disadvantages of nitrous oxide
not an anesthetic unless >100%, nausea, oxidizes cobalt in B12, expansion in closed spaces, diffusion hypoxia on emergence
Properties of diethyl ether
liquid at room temp, easy to administer, explosively flammable, very slow induction, respirator irritant, complete anesthetic (muscle relaxant, unconsciousness, analgesia)
Advantages of halothane
sweet nonpungent odor, smooth, rapid inhalation induction, fair analgesia, muscle relaxation, excellent hypnosis, fruity smelling
Disadvantages of halothane
CV depression, catecholamine sensitization, hepatotoxicity, poor skeletal muscle relaxant, poor analgesic, strong respiratory depressant, direct CV depressant, sensitizes myocardium to catecholamines
Why is halothane no longer used in the US?
hepatotoxicity: massive hepatic necrosis, death, probably immune related
Advantages of Enflurane
rapid induction and recovery; good analgesia, muscle relaxant, hypnosis; no catecholamine sensitization
Disadvantages of Enflurane
pungent (breath holding, coughing); CNS stimulation at high concentrations (may induce seizures); CV depression, decreased CO, renal >9.6 MAC hrs
Advantages of isoflurane
rapid induction and emergence, good analgesia, sedation
Disadvantages of isoflurane
more pungent/irritating than enflurane, decreases BP by decreasing SVR (used on HTN patients in surgery)
Advantages of sevoflurane
rapid induction of anesthesia, non-irritating to airways (allows smooth inhalational induction); non flammable
Disadvantages of sevoflurane
inability to use for low flow anesthesia
Desflurane
rapid achievement of anesthesia; uterine relaxant; rapid recovery and awakening, decrease in CO, BP>forane; too quick?; used in balanced anesthetic
Cardiovascular effects of anesthesia
- All halogenated agents decrease MAP
- All affect heart rate
- N2O stimulates sympathetics obscuring
Halothane and Enflurane depress
CO
Isoflurane, Desflurane and Sevoflurane decrease
SVR
Respiratory effects of anesthetics
- All decrease tidal volume, increase rate
- Impair mucociliary apparatus (pooling of mucus, atelectasis, pneumonia)
- Bronchodilation (Halothane is best)
CNS effects of anesthetics
- Decrease cerebral metabolic rate
- Most decrease CVR, thus in CBF
- May increase ICP
- Enflurane may induce seizures
- N2O is analgesic/amnestic even at low concentrations
Renal effects of inhaled anesthetics
- All decrease GFR, RPF, increase fitration fraction
- Methoxyflurane high metabolized
- Enflurane, sevoflurane produce fluoride
Malignant HTN
Potentially fatal result of anesthesia, autosomal dominant
Triggers of malignant HTN
- Halogenated inhalational agent
2. Depolarizing muscle relaxant (Succinylcholine)
What happens in malignant HTN?
Ca2+ in sarcoplasmic reticulum is unleased; hypertension, tachycardia, skeletal muscle rigidity, acidosis, hyperthermia, hyperkalemia, excess CO2
Treatment of malignant HTN
IV Dantrolene Sodium
Sedative hypnotics
- Barbiturates
- Ketamine
- Propofol
- Etomidate
- Benzodiazepines
Barbiturates uniquely depress the
reticular activating system and CNS sympathetic outflow
Clinical uses of Barbiturates
- Induction of anesthesia
- Treatment of ICP
- Decreases cerebral blood volume
- Decrease in cerebral metabolism
Most common Barbiturates
- Sodium Pentothal (thiopental)
- Methohexital (Brevital)
- Thiamylal (Surital)
- Secobarbital (intermediate acting)
- Pentobarbital (intermediate acting)
Barbiturates used for the induction of anesthesia
Thiopental (Pentothal) and Methohexital (Brevital)
What does it mean to say that “barbiturates have antianalgesic properties”?
if undergoing a painful procedure, it may make it even more painful afterwards
Sodium pentothal (Thiopental) can trigger
intermittant porphyria
Properties of sodium pentothal (thiopental)
sedation; hypnosis; anesthesia; rapid onset; short duration; isoelectric EEG; no muscle relaxation/antianalgesic; profound respiratory depression; cough, bronchospasm, laryngospasm
Ketamine (Ketalar)
glutamic acid antagonist at NMDA receptor; dissociative anesthetic; rapid onset, short duration of action, profound anterograde amnesia; profound analgesia; copious salvation
Which patients do you not give ketamine to?
do not give in someone with a head injury - increases ICP
MOA of ketamine
sympathomimetic; blocks reuptake of catecholamines, smooth muscle relaxant
Emergence delirium is associated with?
ketamine
What is emergence delirium?
auditory hallucinations, vivid dreams, reduced by benzodiazepines
Propofol (Diprivan)
IV - rapid onset, short duration, hypnosis; sedation, hypnosis, anesthesia, no analgesia, but antiemetic
Etomidate (Amidate)
Nonbarbiturate, more rapid awakening, non analgesic, minimal cardiac depression, pain on injection, myoclonus, adrenal supression
MOA of benzodiazepines
receptors on alpha subunits GABA in CNS; enhance Cl- channel gating function (hyperpolarization); post-synaptic CNS
Common benzodiazepines
- Dizepam (Valium)
- Lorazepam (Ativan)
- Midazolam (Versed)
Clinical uses of Diazepam (Valium)
- Preoperative medication
- Induction of anesthesia
- IV sedation
- Anticonvulsant activity
- Treatment of delirum tremens
- Skeletal muscle relaxation
Difference between Midazolam and Diazepam
Negative effects of diazepam (valium) are gone; more rapid onset of action; 2-3X as potent as valium
Properties of Lorazepam (Ativan)
More potent amnestic than diazepam; slow onset, long duration, slow dissociation, confusion; minimal effects on skeletal muscle, CV/pulmonary systems