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AP1 Final > General Anesthesia Maintenance > Flashcards

General Anesthesia Maintenance Flashcards

1
Q

what are the objectives of Anesthesia

A

AMNESIA,

ANALGESIA

, MUSCLE RELAXATION,

control of SNS during noxious stimulation

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2
Q

what equation is used for maintaining oxygen requirement?

A

Bordy equation

VO2 = 10 x kg0.75 mL O2/min

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3
Q

what are normal values of ETCO2

A

35 mmHg

PaCO2 (40) - PA-aCO2 (5)

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4
Q

convert ETCO2 to a %

A

ETCO2 (mmHg)/(PB - PH2O) = %

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5
Q

how to calculate eucapnic ventilation (example 70 Kg pt)

A

VaCO2 = VCO2/ % in lungs

VaCO2 + anatomic deadspace = eucapnic ventilation

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6
Q

what is formula for ventilation of CO2

A

VCO2 = 8 x kg.075

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7
Q

How do you calculate anatomical dead space?

A

2 ml x kg x 10

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8
Q

what is the alveolar gas equation?

A

PAO2 = [(FiO2)(PB-PH20)] - (PaCO2/R)

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9
Q

what is Alveolar-arterial partial pressure gradient (AaO2) formula?

also expressed as (PA-aO2)

A

AaO2 = PAO2 - PaO2

(normal < 10 mmHg)

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10
Q

what causes Abnormal alveolar arterial O2 gradient?

A
  1. Anatomic shunting: R → L (thebesian, bronchiole, etc), Pulmonary AVM, etc
  2. Diffusion impairment: thickended capillary membrane, Low V/Q areas (intrapulmonary shunt), High V/Q areas (alveolar dead space)
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11
Q

which respiratory limb is peep valve placed on ?

A

expiratory

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12
Q

what are benefits of PEEP? disadvantages?

A

a) Increase FRC (recruitment)
Improved lung compliance
VQ corrections

b) barotrauma

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13
Q

what are drawbacks of inhalation agents?

A

PONV d/t ethers

no analgesia (N2O exception)

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14
Q

what is value of MACBAR

A

BAR = blocks anatomic receptors

1.5

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15
Q

what is MACawake value

A

(10% of MAC)

0.3 - 0.5

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16
Q

What is value of MACamnestic

A

0.25

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17
Q

what are 3 major factors that effect MAC?

A

extremes in age (increases and decreases MAC)

acute intoxication (decreases MAC)

pregnancy (decreases MAC)

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18
Q

which way do anesthetic gases move in regards to pressure

A

down the pressure gradient

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19
Q

what does Rise of FA/Fi depend on ?

A

solubility of agent

20
Q

Agents Rise FA/Fi

From greater to lesser ratio (most insoluble to most soluble)

A

N2O

Des

Sevo

ISO

Halothane

21
Q

what are factors that affect inspiratory concentration (Fi)?

A

Fresh gas flow (increases)
Circuit Volume (decreases)
Any machine/circuit absorption (decreases)

22
Q

formula for time constant of agent Fi

A

Time constant = Vc/FGF

FGF = fresh gas flow

Vc = volume in circuit

23
Q

what is important about time constants inregards to wash in

A

instead of looking how much is left in a system (i.e. 1 t = 37%), you look at how much change has occured (i.e. 1 t = 63 %)

24
Q

in regards to Rate of Rise of FA/Fi, how do you speed up equilibrium?

A

decrease FRC

increase volume in Alveoli

25
Q

what is Most important factor in rate of rise FA/Fi

A

uptake

26
Q

what is relationship of uptake to rise of FA/Fi

A

increase in uptake = decrease in FA/Fi

27
Q

why does increased uptake slows the rate of induction

A

less remains in the lung to increase concentration

28
Q

when will FA = Fi

A

when uptake is 0

29
Q

what how does an agents blood gas partition coefficient effect uptake

A

the higher the partition coefficien

the greater the solubility which means more of the agent is taken up into the pulmonary circulation

this causes the alveolar concentration to rise more slowly, and prolong induction

30
Q

how does alveolar blood flow effect uptake?

A

less blood flow means less agent is taken up, which speeds induction…

but at what cost…the same things that determine pulmonary blood flow, help to determine cerebral blood flow…if we hyperventilate the patient to decrease pulmonary flow and speed induction, we decrease delivery of the agent to the brain…

31
Q

which partition coefficient effects how fast patient goes to sleep?

A

blood:gas

Des 0.42

N20 0.47

Sevo 0.65

Iso 1.4

Halo 2.4

32
Q

which partition coefficient effects how fast patient wakes up

A

muscle:blood

N20 1.2

Des 2.0

Sevo 3.1

Halo 3.5

Iso 4.0

33
Q

How do we overcome the issue of decreasing alveolar concentration by uptake

A

increasing alveolar concentration (hyperventilation)…by doing this we are constantly replacing the anesthetic, and maintaining a more constant alveolar concentration
Concentration of the inhaled agent can also be increased…turn up the dial…to increase the rate of rise of agent concentration

hyperventilation more effective for highly soluble agents

34
Q

How does a large FRC slow the rate of Rise FA/Fi

A

slows the rate

35
Q

what happens to FA (alveolar partial pressure/concentration) with increased Cardiac output

A

slower uptake with an increaes flow (Cardiac Output)

36
Q

what are advantages of using N2O

A

Powerful analgesic properties
Decreases MAC of other inhal. Agents
Safe in MH patients
Rapid induction/recovery

37
Q

What are some disadvantages of N2O

A

Decreases myocardial contractility
Increase risk PONV
Increase ICP by inc CBF
Teratogenicity

38
Q

what are contraindications for N2O

A

Air embolism
Pneumothorax (75% 2-3x 10 min)
Acute intestinal obstruction
Intracranial air (tension pneumocephalus)
Pulmonary air cyst
Intraoccular air bubbles
Tympanic membrane grafting

39
Q

what is a concern regarding Sevo

A

Compound A (low gas flows, high temperatures, disiccated absorbent)

40
Q

advantages of Sevo

A

Non-irritant sweet odor
Rapid induction/recovery
Does not sensitize myocardium to catecholamine
No CO production with Na lime

41
Q

disadvantages of sevo

A

Compound A production (< 2L/min)
Contraindicated with Baralyme
Post op agitation in children

42
Q

advantages of Des

A

Rapid onset/recovery
Stable with CO2 absorbers

43
Q

disadvantages of des

A

Requires special vaporizer
Low potency
Pungency
Rapid increase >1.25 MAC SNS stimulation

44
Q

what are agent effects on MAP

A

Iso, Des, and Sevo (all produce dose dependent) decrease in MAP

Result from sympathectomy causing peripheral vasodilation.

Nitrous oxide No Change or increases MAP

45
Q

what are agent effect on HR

A

iso, des, sevo increase HR

(d/t stimulation of carotid baroreceptors– decrease MAP cause increase HR)

46
Q

what is effect of agent on Cardiac Output

A

Most agents cause some reduction of CO (Isoflurane exception)

CO mildly increased or NC by N2O
Sympathomimetic

AP1 Final (3 decks)

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