Inhalant Anesthetics Flashcards Preview

Anesthesiology > Inhalant Anesthetics > Flashcards

Flashcards in Inhalant Anesthetics Deck (79):
1

Why use inhalant anesthetics?

1. Predictable effects
2. Rapid adjustment of anesthetic depth
3. Minimal metabolism
4. Economical

2

Nitrous oxide

- Low blood gas PC (0.47)
- Mild analgesic
- Accumulation in closed gas spaces

3

Xenon

Expensive, used mostly experimentally

4

Solubility

Anesthetic vapors dissolve in liquids and solids

Equilibrium is reached when the PP of the anesthetic is the same in each phase (pressure, not number of molecules)

5

Partition coefficient

Expression of solubility
Concentration ratio of an anesthetic in the solvent and gas phases, describes the capacity of a given solvent to dissolve an anesthetic

6

Blood-gas partition coefficient

Most clinically useful number

Describes amount of anesthetic in the blood vs. alveolar gas at equal partial pressure

7

What does the pressure of anesthetic in the alveolar gas represent?

Brain concentration- location of effect

8

T/F: Anesthetic in blood is pharmacologically active?

False

9

Most to least soluble anesthetics

Halothane= 2.54
Isoflurane= 1.46
Sevoflurane= 0.68
Desflurane= 0.42

10

Low blood-gas PC

1. Less anesthetic dissolved in the blood at an equal PP
2. Shorter time required to attain PP in brain
3. Shorter induction and recovery

Clinically more useful

11

High blood-gas PC

1. More anesthetic dissolved in the blood at an equal PP
2. Longer time required to attain PP in brain
3. Longer induction and recovery

Not very clinically useful

12

Effect of solubility on recovers

The lower the solubility, the faster the recovery

13

Order of inhalant uptake

Vaporizer > breathing circuit > alveoli > arterial blood > brain

14

Partial pressure in the brain is roughly equal to...

Partial pressure in the alveoli

15

Ways to increase partial pressure in the alveoli

1. Increase anesthetic delivery to alveoli
2. Decrease removal from the alveoli

16

Increased alveolar delivery

1. Increase inspired anesthetic concentration
2. Increase alveolar ventilation

17

How do you increase inspired anesthetic concentration?

1. Increase vaporizer setting
2. Increase fresh gas flow
3. Decrease breathing circuit volume

18

How do you increase alveolar ventilation?

1. Increase minute respiration
2. Decrease dead space ventilation

19

Decrease removal from alveoli

1. Decrease blood solubility of anesthetic
2. Decrease cardiac output
3. Decrease alveolar-venous anesthetic gradient

20

Concentration effect

The higher the inspired pressure the more rapidly alveolar pressure approachs inspired pressure

21

As uptake into blood decreases, inspired pressure can...

be decreased

22

A ____ inspired pressure is required at the beginning of gas anesthesia to quickly increase____

High, alveolar pressure

23

Anesthetic elimination

Requres decrease in alveolar concentraions

24

Anesthetic elimination is most effected by:

1. Anesthetic solubility
2. Alveolar ventilation

(same that effect alveolar concentration)

25

How do you quickly decrease alveolar concentration?

1. Turn off vaporizer
2. Disconnect patient and flush O2
3. Turn up O2 rate- dilutes the circuit
4. Increase ventilation (IPPV)- increase fresh gas to alveoli

26

Definition: Minimum Alveolar Concentration (MAC)

Minimum alveolar concentration of an anesthetic that prevents movement in 50% of patients exposed to noxious stimulus

27

Relationship between MAC and potency of an anesthetic

Inversely proportional

High MAC = low potency

28

T/F: Alveolar concentration is NOT the same as the vaporizer setting

True

29

How is MAC measured?

Percent of agent in expired gas

30

MAC: Halothane

Dog- 0.9%
Cat- 1%
Horse- 1%

31

MAC: Iso

Dog- 1.3%
Cat- 1.3-1.6%
Horse- 1.3-1.6%

32

MAC: Sevo

Dog- 2.3%
Cat- 2.6%
Horse- 2.3-2.8%

33

MAC: Desflurane

Dog- 7.2%
Cat- 9.8-10.3%
Horse- 7-8%

34

MAC: N2O

Dog- 188%
Cat- 255%
Horse- 205%

35

Increase in MAC

Hyperthermia
Hypernatremia
Drugs causing CNS stimulation

36

Decrease in MAC

Hypothermia
Hyponatremia
Drugs causing CNS depression
MAP 95mmHg
Pregnancy
Increasing adult age

37

What is MAC multiples?

Used to describe dose of gas in relaiton to pharmacologic and physiologic effect

38

What multiple of MAC ensure immobility in 95% of patients?

1.2-1.4x

39

Is MAC additive?

Yes

40

Why is the additive effect of MAC important?

1. Changing gasses in the middle of a case
2. Using N2O
3. Using partial intravenous anesthesia (PIVA)

41

Cardiovascular effects of volatile anesthetics

Decrease: CO, BP, vasculara resistance, contractility

No change in HR

42

Respiratory effects of volatile anesthetics

Decrease ventilation- depress chemoreceptors and response to CO2

Bronchodilation

Irritating odor

Respiratory arrest at 1.5-3MAC

43

Neurologic effects of volatile anesthetics

Increase ICP @ >1MAP
Decrease cerebral metabolic rate
Acts on brain and spinal cord to produce immobility
Suppress seizure activity (except enflurane)

44

Renal effects of volatile anesthetics

Decrease GFR- decreased CO

Renal failure- methoxyflurane

45

What anesthetic produces compound A?

Sevoflurane

46

What is compound A?

A compound produced from sevoflurane breakdown in CO2 absorbant

47

What species is compound A nephrotoxic in?

Rats

48

Higher concentrations of compound A are formed in:

1. Prolonged anesthesia
2. Low fresh gas flows
3. Desiccated absorbent

49

Hepatic effects of volatile anesthetics

Reduce liver blood flow and O2 delivery

Halothane- hepatotoxicity

50

Halothane hepatitis

Immune mediated, often fatal

51

Malignant hyperthermia

Myopathy occuring in genetically predisposed pigs, dogs cats, and horses with exposure to halothane especially

52

Cllinical signs of malignant hyperthermia

Rapid increase in EtCO2
Uncontrolled muscle contraction, severe hyperthermia, death

53

Treatment of malignant hyperthermia

1. Discontinue volatile anesthetic, flush line, switch to a new anesthetic
2. Provide 100% O2
3. Administer dantrolene
4. Fluids and active cooling

Usually still fatal

54

Nitrous oxide

Mostly humans

max 75%, low solubility, minimal CV/resp depression, mild analgesia

55

Diffusion hypoxia

When N2O is stopped, it diffuses quickly out of the blood and displaces O2 in the alveoli

Must continue 100% O2 after discontinuing N2O for 5-10min to prevent

56

Reducing gas exposure

1. Scavenging system
2. Minimize leaks
3. Avoid mask or chamber induction
4. Keep patient attached to circuit after anesthetic gas is turned off
5. Minimize exposure to exhaled gas from patient
6. Maximize ventilation
7. Monitor waste gas concentrations

57

Anesthetic related complications

Hypotension
Hypoventilation
Hypothermia

58

Machine related complications

Closed pop-off
Stuck inspiratory-expiratory valves
Exhausted soda lime
Inadequate O2 flow in non-rebreathing system

59

Human error complications

Improper intubation
Anesthetic overdose

60

Hypotension

MAP

61

Evaluating hypotension

Turn down the vaporizer if patient is too deep (often resolves issue)

OR

Consider adding MAC sparing drug and then turn down the vaporizer if patient is appropriately deep

62

MAC sparing drugs

Opiods, benzodiazapines, lidocaine, ketamine, etc.

63

If still hypotensive after turning down vaporizer:

Evaluate underlying cause and treat

1. Hypovolemia- crystalloid/colloid bolus
2. Vasodilation- give vasopressor
3. Decreased contractility- give inotrope

64

Hypoventilation

PaCO2>40mmHg or EtCO2>45mmHg

Turn down the vaporizer and perform IPPV (manual or mechanical)

65

T/F: Inhalant anesthesia abolishes the normal vascular compensatory mechanisms to conserve heat.

True.

Causes peripheral vasodilation which increases heat loss

66

Treatment for hypothermia

Prevention easier

Heating blankets, warm water blankets, warm room, keep patient covered etc.

67

What happens when the pop-off/APV valve is closed?

Resevoir bag fills, breathing system pressure increases, pressure transmitted to patient lungs/throracic cavity

Decreased CO and potential for pneumothorax

68

Clinical signs of a closed pop-off

Apnea, bradycardia, fading doppler signal

69

Treatment for closed pop-off

1. Pull reservoir bag
2. Start CPR is patient has arrested
3. Evaluate for pulmonary injury

70

Stuck inspiratory-expiratory valves

Signs: rebreathing capnograph and hypercarbia

Treatment: dry and clean valves and replace as needed

71

Exhausted Soda lime

Signs: rebreathing capnograph and hypercarbia

Looks the same as stuck valves

72

Rebreathing capnograph

Waveform does not return to baseline between breaths- build up of CO2

73

Causes of rebreathing capnograph/hypercarbia

1. Stuck insp/exp valves
2. Exhausted soda lime
3. Inadequate O2 flow in a non-rebreathing system

74

Tracheal tears

Associated with over filling the cuff

Not uncommon in cats

75

Signs of tracheal tears

Subcutaneous emphysema
Pneumomediastinum and pneumoretroperitoneum

76

Treatment of tracheal tears

Supportive care

May need surgical repair

77

Anesthetic overdoses

Very low therapeutic index- overdosing not uncommon and can happen very quickly

If there is any doubt in patient status, turn the inhalant down or off while evaluating

78

Indications of anesthetic overdose

Very low BP (MAP

79

Do sick patients often need more or less anesthetic?

Often less, usually the sicker the patient the less inhalant you will need

MAC sparing drugs should be used in these patients to offset inhalant needs