Surgery - Physiological Effects Of Inhalation Anesthetics

Front 1

Reasons why inhalation anesthetics are such potent drugs

Back 1

-low margin of safety
-small therapeutic index (2-4)

Front 2

Therapeutic index
-calculation

Back 2

LD50/ED50

Front 3

Effect of inhalants on Blood Pressure

Back 3

-Dose dependent decrease in BP (except NO)
-HYPOTENSION

Front 4

Inhalant caused decrease in blood pressure
-due to

Back 4

-myocardial depression
-vasodilation
-dec. sympathetic outflow

Front 5

Dose-dependent vasodilation
-inhalants

Back 5

-Isoflurane
-Sevoflurane
-Desflurane

Front 6

Dose-dependent increase in HR
-inhalants

Back 6

-Isoflurane
-Desflurane

Front 7

Dose-dependent increase in HR
-reason

Back 7

-maintain Cardiac output

Front 8

What blocks a dose-dependent increase in heart rate by isoflurane and desflurane?

Back 8

-opioids

Front 9

Potent cardiac depressant
-inhalant

Back 9

-halothane

-isoflurane, sevoflurane, desflurane decrease contractility in animals with heart disease

-all inhalants at MAC >2

Front 10

Cardiac depression by inhalant
-mechanism of action

Back 10

-dec. calcium availability/sensitivity of the contractile apparatus of the myocyte

Front 11

Increase in cardiac contractility
-inhalant
-mechanism of action

Back 11

-NO

-stimulation of the SNS

Front 12

Inhalant caused arrhythmias
-mechanism of action

Back 12

-change in autonomic tone

-inhalant effects on action potential (dec. refractory period, delay repolarization)

Front 13

Catecholamine-induced arrhythmias
-inhalant

Back 13

-halothane with stress/excitement (inc. catecholamine)

Front 14

Inhalation anesthesia effects on ventilation

Back 14

-dec. minute ventilation (inc. rate, dec. volume)
-dec. sensitivity to PaCO2
-depress hypoxic drive
-depress hypoxic pulmonary vasoconstriction

Front 15

Hierarchy of inhalant effects on respiratory depression

Back 15

-isoflurane
-sevoflurane

-halothane

-NO

Front 16

Effects of inhalation anesthetics on the respiratory system

Back 16

-dec. lung volume (functional residual capacity)
-bronchodilation
-airway irritation from pungency

Front 17

Functional residual capacity
-define

Back 17

-amount of air in the lung at the end of passive expiration

Front 18

Dec. lung volume from inhalant anesthetic
-cause

Back 18

-atelectasis due to 100% O2 causing all gas in alveoli to be absorbed and the alveoli collapsing

Front 19

Effects of bronchodilation from inhalation anesthetics

Back 19

-reduced bronchospasm (good for asthma)
-increased dead space ventilation

Front 20

Airway irritation due to pungency
-main inhalation anesthetic
-main effect

Back 20

-desflurane

-prevents mask induction

Front 21

Effects of inhalation anesthetics on the CNS

Back 21

-Cerebral vasodilation
-Depress seizure activity

Front 22

Inhalant anesthetic cerebral vasodilation
-contraindication

Back 22

-brain tumor or head trauma (inc. intracranial pressure)

Front 23

How to dec. cerebral blood flow due to inhalation anesthetics

Back 23

hyperventilation (PaCO2 < 35) reduces blood flow with
-isoflurane
-sevoflurane
-desflurane

Front 24

Normal PaCO2

Back 24

-40 mmHg

Front 25

Renal effects of inhalant anesthetics

Back 25

-dose dependent dec. renal blood flow, glomerular filtration, renal output

-Nephrotoxicity from degradation of Sevoflurane to compound A by dry CO2 absorbant (soda lime)

Front 26

Inhalation anesthetic dec. in renal blood flow
-due to

Back 26

-pre-renal effect from dec. cardiac output and blood pressure

Front 27

How to prevent toxicity from sevoflurane degradation

Back 27

Avoid:
-low oxygen flow rates
-dry CO2 absorbent
-prolonged anesthetic times (5-6 hrs)

Front 28

Inhalation anesthetic
-GI effects

Back 28

-dec. hepatic perfusion via dec. portal blood flow (most O2 via hepatic a.)

Front 29

Inhalation anesthetics that maintain hepatic perfusion of O2 the best

Back 29

-Isoflurane
-Sevoflurane

Front 30

NO contraindicated in what GI cases?
-why

Back 30

-obstructive bowel dz
-GDV
-bowel surgery

-diffusion into air-filled space

Front 31

Isoflurane
-B:G
-MAC
-Metabolism

Back 31

-B:G = 1.4
-MAC = 1.3%
-Metabolism = 0.2%

Front 32

Isoflurane
-facts

Back 32

-pungent odor (slowely increase anesthetic from 0 when masking)
-very stable

Front 33

Sevoflurane
-B:G
-MAC
-Metabolism

Back 33

-B:G = 0.6

-MAC = 2.3%

-Metabolism = 3.3%

Front 34

Sevoflurane
-effect of low B:G ratio

Back 34

low solubility agent
-more rapid induction and return but generally isn't seen due to a higher MAC

Front 35

Sevoflurane
-why is the higher metabolism surprising?

Back 35

-due to the low solubility
-but not as stable as isoflurane

Front 36

Sevoflurane
-facts

Back 36

-high metabolism (despite low solubility)
-unstable in baralyme and sodalime (Compound A = nephrotoxic)
-well tolerated for masking

Front 37

Desflurane
-B:G
-MAC
-Metabolism

Back 37

-B:G = 0.4

-MAC = 7.4%

-Metabolism = 0.02%

Front 38

Desflurane
-facts

Back 38

-high vapor pressure = boil at room temp
-can't use standard vaporizer ($$$)
-Can't use for mask induction (airway irritation, cough, laryngospasm, excitation)

Front 39

Nitrous Oxide
-B:G
-MAC
-Metabolism

Back 39

-B:G = 0.5
-MAC = 188%
-Metabolism = 0%

Front 40

Nitrous oxide
-facts

Back 40

-liquid/gas interface in cylinder
-can't be used as sole anesthetic (high MAC)
-dec. dose of more potent agents used
-speeds induction of higher solubility agents
-diffusion into air-filled cavities
-can cause diffusion hypoxia (rapidly diffuses through alveoli)