L 21-22 General Anesthetics I

Question 1

What is dissociative anesthesia and what drug is used?

Answer 1

Ketamine is used for dissociative anesthesia which is an eye open yet completely unresponsive type of anesthesia. The lights are on, but no one is home.

Question 2

How does propofol work?

Answer 2

Facilitate GABAa receptors

Usually given IV

Question 3

How does Ketamine work?

Answer 3

Blocks NMDA receptors

Usually given IV

Question 4

Blood Gas Partition and speed of onset

Answer 4

When a drug is inhaled, its partial pressure in the gas must first equilibrate to the alveoli and then to the blood and then to the brain.
The less soluble the drug is in blood, the quicker the partial pressures will equilibrate and the quicker the speed of onset.
The lower the blood gas partition the faster it gets in.

Question 5

Relationship between pulmonary blood flow and induction using inhaled drugs

Answer 5

Increased pulmonary blood flow means it will take more gas to saturate and will take longer to reach induction.
Each unit of blood will have a lower partial pressure and therefore will be slower at delivering blood to the brain and will have a slower rate of induction.

Question 6

Inhaled drug elimination speed variables

Answer 6

The faster the blood flow to a tissue, the faster the drug will be removed–brain, liver, kidneys fast; fat slow

The less soluble the drug is in the blood, the faster it will be eliminated

Question 7

What is MAC?

Answer 7

Minimum Alveolar Concentration
Analogous to ED50 which is the concentration at which 50% of patients respond as desired
The lower the MAC, the more potent
MAC values are additive and goal in gas mixture is to have 1 MAC total

Question 8

Blood gas coefficients and speed of changing effect

Answer 8

The lower the coefficient, the quicker the response when you try to change the dose.

Question 9

What is diffusion hypoxia?

Answer 9

Inhaled drugs that are insoluble will rush back to the lungs when you stop administration and will displace O2 and cause hypoxia. This is worst with N2O.

Question 10

Dalton’s law, N2O and its use with other gases

Answer 10

Dalton’s law saws that the total pressure of a gas is the sum of the partial pressures of all the gases present.
N2O has a low solubility and therefore has a quick rise in partial pressure when administered which allows it to get to the brain quickly. This apparently is useful in helping to speed up the induction of other drugs that otherwise would be slower. The increase in partial pressure from the N2O speeds up the transfer of the slower drugs.

Question 11

Halothane

Answer 11

Gas general anesthetic
No longer used in USA, sensitized the heart to catecholamines => arrhythmias
Slow induction, well soluble in blood
Causes miscarriages, hepatitis
Most likely to cause malignant hyperthermia–treated with dantrolene

Question 12

Isoflurane

Answer 12

Gas general anesthetic
Can’t be used for induction–pungent odor that is irritating
Decreases BP
Increases HR
Resp depression
Decreases O2 demand in brain, dilates cerebral BVs

Question 13

Sevoflurane

Answer 13

Gas general anesthetic
Can induce–rapid induction and recovery
Often used in kids
Low toxicity
Least effect on BP and heart
Safest in CV disease

Question 14

Desflurane

Answer 14

Gas general anesthetic
Rapid effect
Depth easily controlled
Too pungent for induction
Increases intracranial pressure–avoided with increased resp rate
Low toxicity
No liver kidney toxicity
Patient wakes up quick (Low blood /gas)

Question 15

Malignant Hyperthermia

Answer 15

All the inhaled drugs can trigger except N2O
Treated with Dantrolene
Happens more with succinylcholine co-administration

Question 16

Nitrous Oxide

Answer 16

Analgesia, not anesthesia
The other drugs knock you out, but don’t control pain.
Rapid onset and recovery
Euphoria
Watch out for diffusion hypoxia
Sympathetic stimulation
Reduces hypotension caused by other drugs
Little resp depression
Little to no toxicity
Causes N/V postop!
Can cause N2 trapping in body that can be a problem
Chronic use can cause peripheral neuropathy

Question 17

Midazolam

Answer 17

Short-acting benzodiazepine–anxiolytic and sedating
Pre-anesthetic for induction
Can be used alone in short procedures with an opioid like fentanyl
Can be reversed with flumazenil
Really causes amnesia

Question 18

Etomidate

Answer 18

Facilitates GABA transmission
Fast onset, short duration
Used for induction, good for patients with already low BP
Can cause N/V and hiccups
Adrenal insufficiency possible by causing decreased corticosteroid synthesis

Question 19

Propofol

Answer 19

Widely used
GABAa receptor
Hypnotic, no analgesia
Rapid induction and fast recovery
Causes resp depression esp with opioids (killed Michael Jackson)
Decreases BP and vasodilation
Inhibits baroreflex
Decreased cerebral blood flow, metabolism, and intracranial pressure

Can cause N/V but is rare
Emulsion in egg lecithin
Painful injection–Lidocaine reduces pain at injection site

Question 20

Ketamine

Answer 20

Dissociative anesthesia
Binds to PCP site on NMDA receptor
Potent analgesia with some amnesia
Rapid onset, increased HR & BP
Causes amnesia–date rape
Fast acting
Used in kids and vet med, adults have bad emergence delirium
Little N/V–good for emergency use
Drug of abuse

Question 21

Fentanyl

Answer 21

Opioid
Rapid onset, short duration
With midazolam for short procedures
Lollipops for pre-anesthesia

Question 22

What is the relationship between lipid solubility, MAC, and potency?

Answer 22

The more lipid soluble a drug is the more potent it is and therefore the lower the MAC for that drug