General Anesthesia

Question 1

What is anesthesia?

Answer 1

• a combo of amnesia, analgesia and muscle relaxation to allow the performance of surgery or other procedures

Question 2

3 phases of general anesthesia?

Answer 2

• induction
• maintenance
• emergence

Question 3

What are the agents used in induction?

Answer 3

• “putting to sleep”
• most commonly used induction agent is propofol
  which causes:
  drop in BP and CO, antiemetic properties
  other agents:
• etomidate:
  doesn’t cause vasodilation, higher rate of post op nausea, inhibits the biosynthesis of cortisol, use is limited due to increase risk of death by 2.5x
• ketamine:
  used in pts w/ hemodynamic instabilility, cardiac stimulant, significant analgesia, bronchodilation, hallucinations

Question 4

What are the agents used in maintenance?

Answer 4

• use inhaled (volatile) or IV
• anesthetics inhalation anesthetic agents:
• volatile anesthetic agents: sevoflurane and desflurane
• nitrous oxide: can be used in combo w/ volatile gases
• IV anesthetic agents: propofol and remifentanil

Question 5

Emergence phase? What can this result in? What can blunt this autonomic response?

Answer 5

• waking up
  can result in autonomic hyper-responsiveness:
• tachycardia, HTN, bronchospasm, laryngospasm
• short acting narcotics, BBs or lidocaine can blunt this autonomic response

Question 6

What is propofol (Diprivan)?

When is it used? Onset of action? Duration? Effects?

Answer 6

• non-barbiturate hypnotic agent
• rapidly metabolized in liver and excreted in urine, so it can be used for long durations of anesthesia
• used for general surgery, cardiac surgery, neurosurgery, and ped surgery
• rapid onset of action (distribution 2-4 minutes), rapid clearance, and reversibility of effect once the drip is shut off
• onset 40 sec
• duration: 1-3 hrs
• some anti-emetic effect so less nausea and vomiting assoc w/ use
• weaker amnestic effect thanmidazolam (Versed)
• no analgesic effect
• milky looking soln (emulsion)
• clear-headedness during recovery

Question 7

Adverse effects of propofol?

Answer 7

• can support rapid growth of microorganisms
• hypotensive (administer slowly)
• may cause hypertonia and movement
• respiratory depression

Question 8

Use of ketamine (ketalar)? affects what? Duration?

Answer 8

• affects senses, produces a dissociative anesthesia (catatonia, amnesia, analgesia) in which the pt may appear awake and reactive, but can’t respond to sensory stimuli
• frequently used in ped pts b/c anesthesia and analgesia can be achieved w/ an intramuscualr injection
• also used in high-risk geri pts and in shock cases, b/c it also provides cardiac stimulation
• rapid onset: 30sec
• short duration: 5-10 min

Question 9

What are the anesthestic gases used in surgery?

Answer 9

• isolflurane (Forane)
• desfluorane (Suprane)
• sevofluorane (Ultane)
• nitrous oxide

Question 10

What is an impt property of anesthetics?

Answer 10

• reversibility
• once anesthetic gas is turned off, blood stream brings the gas back to lungs where it is eliminated: more soluble the gas is in blood, the longer it takes to eliminate
• nitrous oxide and desflurane are the shortest acting anesthetic gases b/c they are the least soluble in blood

Question 11

How do inhaled anesthetics work?

Answer 11

• inhaled anesthetics act in different ways at level of CNS
• disrupt normal synaptic transmission by:
  interfering w/ release of neurotransmitters from presynaptic nerve terminal (enhance or depress excitatory or inhibitory transmission).
  Alter re-uptake of neurotransmitters, and changes binding of NTs to post-synaptic receptor sites

Question 12

MAC of inhaled agents?

Answer 12

- Minimum alveolar concentration:
inhaled anesthetic concentration (steady state) at which 50% of pts move in response to a std midline abdominal incision (37C, 30-55yo, 1 atm) 
- nitrous oxide: 105%
- isoflurane: 1.15%
- sevoflurane: 1.8%
- desflurane: 6.2%

Question 13

Characteristics of isoflurane? What can it cause?

Answer 13

• higher blood-gas solubility so takes longer for onset and longer for emergence
• causes tachycardia
• causes peripheral vasodilation
• airway irritation, coughing

Question 14

What does Desflurane require? What can it cause?

Answer 14

• reqrs a heated-pressurized vaporizer for delivery
• causes tachycardia
• causes peripheral vasodilation
• least well-tolerated on the airway - can cause coughing, bronchospasm
• not used for mask induction
• fastest onset and off-set of volatiles

Question 15

What does sevoflurane cause? Onset?

Answer 15

• doesn’t cause tachycardia
• causes peripheral vasodilation
• well-tolerated for mask induction
• fast onset and quick awakening

Question 16

Effects of nitrous oxide?

Answer 16

• MAC is 105%: therefore alone, can’t provide anesthesia
• nitrous oxide diffuses into air containing cavities 34x faster than nitrogen can leave that space: so bowel, middle ear, pneumothorax, pneumocranium, pneumo-peritoneum, or cuffs of endotracheal tubes can all increase in size when nitrous oxide is being used
• increases post-op nausea
• has analgesic properties

Question 17

Advantages of Nitrous oxide?

Answer 17

• inexpensive
• readily available
• odorless/slightly sweet
• limited effect
• no special equipment
• sympathomimetic
• will not cause malignant hyperthermia

Question 18

Disadvantages of nitrous oxide?

Answer 18

• high MAC/FIO2
• sympathomimetic
• methionine synthetase inhibitor
• expands air-filled spaces

Question 19

CI to potent inhaled anesthetic agents?

Answer 19

• inability to tolerate the physiologic alterations produced

- malignant hyperthermia

Question 20

What are the NMBD drugs used?

Answer 20

• succinylcholine (Anectine)
• Rocuronium (Zemuron)
• Vecuronium (Norcuron)
• Pancuronium (Pavulon)
• Cisatracurium (Nimbex)

Question 21

NMBDs produce what?

Answer 21

immobility needed for:

• endotracheal intubation
• surgical immobility/relaxation (Abdominal)
• mechanical ventilation

Question 22

Action of ACh?

Answer 22

• released into synaptic cleft and binds to nicotinic cholinergic receptors
• then opens ion channel which causes depolarization along the muscle - and then contraction

Question 23

2 types of NMBDs?

Answer 23

• depolarizing: succinylcholine (Anectine)
• nondepolarizing:
  rocuronium
  vecuronium
  pancuronium
  cisatracurium

Question 24

MOA of depolarizing agents (NMBDs)?

Answer 24

• causes brief twitches or fasciculations, followed by flaccid paralysis
• paralysis is due to depolarization of the nerve terminal and the nerve being in a refractory state b/c the membrane is depolarized

Question 25

MOA of Succinylcholine (Anectine)? When is it used? Onset, duration?

Answer 25

- causes depolarization at motor endplate - in contrast to ACh, succinylcholine slowly dissociates from ACh receptors, resultign in an inactive state - broken down by butyrylcholinesterase to choline and succinylmonocholine - often agent of choice when rapid control of airway is necessary - rapid onset: less than 1 min - short duration: 6-10 min

Question 26

Disadvantages of Succinylcholine?

Answer 26

- cardiac dysrhythmias (tachyarrhythmias) - sinus bradycardia - myalgias - myoglobinuria - hyperkalemia - pt restrictions (kids) - masseter spasm (not good for intubation) - malignant hyperthermia trigger - possible increases in intraocular, gastric, and intracranial pressures - dependent upon normal (rare genotype that doesn't metabolize properly)

Question 27

MOA of nondepolarizing NMBDs?

Answer 27

- reversible competition b/t drug and ACh binding site - no fasciculations - nerve stimulation exhibits a fade in train-of four or tetany - best clinical marker of strength is sustained head-lift

Question 28

Nondepolarizing agents?

Answer 28

- long acting: Pancurounium (onset: 1-1.5 min, duration 60 min, met: renal, SE: vagolytic) - intermediate acting: Vecuronium (1.5-2 min, duration: 40 min, hepatic, no SE) Rocuronium (1-1.5 min, 35 min, hepatic, none) Cisatracurium (2.5-3 min, 25 min, other metabolism, no SE) - short acting: Mivacurium

Question 29

What is the train of 4?

Answer 29

way you can measure concentration of NMBDs - when 4 twitches seen: 0-75% of receptors blocked - 3 twitches: at least 75% blocked - 2 twitches: 80% blocked - 1 twitch: 90% blocked - no twitches: 100% of receptors are blocked

Question 30

Reversal for NMBDs?

Answer 30

Acetylcholine esterase inhibitors: - neostigmine, edrophonium result in accumulation of Ach at neuromuscular jxn - sugammadex: no anticholinergic effects like those above, reverses vecuronium and rocuronium