General Anesthesia Maintenance

Question 1

what are the objectives of Anesthesia

Answer 1

AMNESIA,

ANALGESIA

, MUSCLE RELAXATION,

control of SNS during noxious stimulation

Question 2

what equation is used for maintaining oxygen requirement?

Answer 2

Bordy equation

VO₂ = 10 x kg^0.75 mL O₂/min

Question 3

what are normal values of ETCO₂

Answer 3

35 mmHg

P_aCO₂ (40) - P_A-aCO₂ (5)

Question 4

convert ETCO₂ to a %

Answer 4

ETCO₂ (mmHg)/(P_B - P_H2O) = %

Question 5

how to calculate eucapnic ventilation (example 70 Kg pt)

Answer 5

VaCO2 = VCO2/ % in lungs

V_aCO₂ + anatomic deadspace = eucapnic ventilation

Question 6

what is formula for ventilation of CO₂

Answer 6

VCO₂ = 8 x kg^.075

Question 7

How do you calculate anatomical dead space?

Answer 7

2 ml x kg x 10

Question 8

what is the alveolar gas equation?

Answer 8

P_AO₂ = [(FiO₂)(PB-P_H20)] - (PaCO₂/R)

Question 9

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

also expressed as (P_A-aO₂)

Answer 9

AaO2 = PAO2 - PaO2

(normal < 10 mmHg)

Question 10

what causes Abnormal alveolar arterial O2 gradient?

Answer 10

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)

Question 11

which respiratory limb is peep valve placed on ?

Answer 11

expiratory

Question 12

what are benefits of PEEP? disadvantages?

Answer 12

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

b) barotrauma

Question 13

what are drawbacks of inhalation agents?

Answer 13

PONV d/t ethers

no analgesia (N2O exception)

Question 14

what is value of MAC_BAR

Answer 14

BAR = blocks anatomic receptors

1.5

Question 15

what is MAC_awake value

Answer 15

(10% of MAC)

0.3 - 0.5

Question 16

What is value of MAC_amnestic

Answer 16

0.25

Question 17

what are 3 major factors that effect MAC?

Answer 17

extremes in age (increases and decreases MAC)

acute intoxication (decreases MAC)

pregnancy (decreases MAC)

Question 18

which way do anesthetic gases move in regards to pressure

Answer 18

down the pressure gradient

Question 19

what does Rise of FA/Fi depend on ?

Answer 19

solubility of agent

Question 20

Agents Rise FA/Fi

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

Answer 20

N2O

Des

Sevo

ISO

Halothane

Question 21

what are factors that affect inspiratory concentration (Fi)?

Answer 21

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

Question 22

formula for time constant of agent Fi

Answer 22

Time constant = Vc/FGF

FGF = fresh gas flow

Vc = volume in circuit

Question 23

what is important about time constants inregards to wash in

Answer 23

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 %)

Question 24

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

Answer 24

decrease FRC

increase volume in Alveoli

Question 25

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

Answer 25

uptake

Question 26

what is relationship of uptake to rise of FA/Fi

Answer 26

increase in uptake = decrease in FA/Fi

Question 27

why does increased uptake slows the rate of induction

Answer 27

less remains in the lung to increase concentration

Question 28

when will FA = Fi

Answer 28

when uptake is 0

Question 29

what how does an agents blood gas partition coefficient effect uptake

Answer 29

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

Question 30

how does alveolar blood flow effect uptake?

Answer 30

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…

Question 31

which partition coefficient effects how fast patient goes to sleep?

Answer 31

**blood:gas** Des 0.42 N20 0.47 Sevo 0.65 Iso 1.4 Halo 2.4

Question 32

which partition coefficient effects how fast patient wakes up

Answer 32

**muscle:blood** N20 1.2 Des 2.0 Sevo 3.1 Halo 3.5 Iso 4.0

Question 33

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

Answer 33

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

Question 34

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

Answer 34

slows the rate

Question 35

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

Answer 35

slower uptake with an increaes flow (Cardiac Output)

Question 36

what are advantages of using N2O

Answer 36

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

Question 37

What are some disadvantages of N2O

Answer 37

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

Question 38

what are contraindications for N2O

Answer 38

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

Question 39

what is a concern regarding Sevo

Answer 39

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

Question 40

advantages of Sevo

Answer 40

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

Question 41

disadvantages of sevo

Answer 41

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

Question 42

advantages of Des

Answer 42

Rapid onset/recovery Stable with CO2 absorbers

Question 43

disadvantages of des

Answer 43

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

Question 44

what are agent effects on MAP

Answer 44

**Iso, Des, and Sevo (**all produce dose dependent) _decrease_ in MAP Result from sympathectomy causing peripheral vasodilation. **Nitrous oxide** No Change or _increases_ MAP

Question 45

what are agent effect on HR

Answer 45

iso, des, sevo increase HR (d/t stimulation of carotid baroreceptors-- decrease MAP cause increase HR)

Question 46

what is effect of agent on Cardiac Output

Answer 46

Most agents cause some reduction of CO (Isoflurane exception) CO mildly increased or NC by N2O Sympathomimetic