General Anesthesia Flashcards
Maintaining O2 requirement is accomplished by the ______ ______.
The formula for VO2 is:
Brody equation
10 * kg3/4 = ml/min
or 2.5 * kg + 67.5
For maintaining oxygenation/ventilation O2 saturation > _____ %
97%
Clinically treat if you see >3% change
Normal ParterioleCO2 = _______mmHg
PA-aCO2 = _______ mmHg
EtCO2 is _____%
40 mmHg
5 mmHg
35
Normal PA-a CO2 = _____ mmHg
5
EtCO2 = _____ mmHg
35 mmHg
VAlveolarCO2 = ________
8 * kg3/4
about = 200 ml/min
VaCO2 = __________ (equation)
VCO2 / % CO2 in lungs (5%)
= 200/0.05 = 4000 ml CO2/min
not enough ventilation because of dead space
Anatomic dead space = (formula?)
2 ml/kg *kg
140 ml/Breath * 10 breaths/min =
1400 ml/min
VACO2 = _____ ml/min
5400 ml/min
or 540 ml/Breath
4000 + 1400 dead space
Alveolar Gas Equation
PAO2 =
PAO2 =
FiO2 (PB - PH2O) - (PaCO2/R)
If O2 saturation begins dropping, what is the first treatment?
increase FiO2
Normal AaO2 equation:
Normal is:
PAO2 = PAO2 - PaO2
Normal is < 10mmHg
Abnormal PA-aO2 gradients caused by:
anatomic shunting like pulmonary AVM, thebesian minute vessels in heart
diffusion impairment: thickened capillary membrane
low V/Q areas intrapulmonary shunt
high V/Q areas: alveolar dead space
Increase FiO2 by: (3)
- increasing TV
- increase PEEP
- change position
Benefits of improved oxygenation by adding PEEP: (3)
- increase FRC (recruitment)
- improve lung compliance
- VQ corrections
Advantages of inhalation agents:
- rapid appearance of drug in arterial blood
- efficient to distribute
- easy to deliver
- predictable recovery
- high safety profile
Drawbacks to inhalation agents (2)
- no analgesia (N2O is exception)
- PONV
Effectiveness of inhalation agent is measured by: (2)
- ET% agent
- established MAC
MAC is an average, NOT a predictor
MAC amnestic is _____.
0.25
MAC awake is ______
0.3-0.5
MACBAR = ______
BAR means:
1.5
blocking adregernic receptor
Factors that affect MAC: (3)
- extremes in age (up or down)
- chronic alcohol abuse (increase MAC)
- pregnancy (decrease MAC)
Desflurane FA/Fi is ______.
0.8
It is the least soluble and works the fastest.
The FA/Fi of sevoflurane is: ______
about 0.7
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Factors affecting inspiratory concentration (Fi): (3)
- increase fresh gas flow
- decrease circuit volume
- decrease any machine/circuit absorption
Time constant is :
volume / flow
Volume of circuit / FGF
How many liters in circuit of anesthesia machine?
This includes bag, piping, CO2 canister.
6L
To increase FA/Fi equilibrium (2)
- decrease FRC
- increase VA (minute ventilation)
Most important factor in the rate of FA/Fi is _______.
uptake
Increase uptake _____ rise of FA/Fi
decreases
If uptake = 0, then FA = Fi, uptake influencing factors include (3)
solubility (partition coefficient)
blood flow (CO)
concentration
What coefficient is “blood solubility” based upon?
blood/gas partition coefficient
Blood/gas partition coefficients:
describes relative affinity of anesthetic gas for blood
increased partition coeff –> increased solubility –> increased agent uptake
The more soluble agent, larger capacity blood, longer to take to saturate. True or false?
true
Blood/gas coefficient of isoflurane
1.4
Desflurane blood/gas coefficient is:
0.42
Sevoflurane blood/gas coefficient is
0.6
Overcome uptake of anesthetic gas by changing ventilation:
- hyperventilate
- large FRC causes dilution and thus slower rate of rise of FA/Fi
How to increase CO?
- increase Q
- flow
- CO = SV * HR
- so increase HR
Factors affecting FA/Fi
- uptake
- blood/gas coefficient
- cardiac output
- hyperventilation
- anesthetic overpressurizing
Factors affecting arterial concentration:
- V/Q mismatch
- venous admixture
- alveolar dead space
- nonuniform alveolar gas distribution
Nitrous oxide advantages:
- powerful analgesic
- decreases MAC of other inh. agents
- safe in MH patients
- rapid induction/recovery
Nitrous disadvantages:
- decreases myocardial contractility
- increase PONV
- increase ICP by increase CBF
- teratogenicity
Contraindications of N2O
- air embolism
- pneumothorax
- acute intestinal obstruction
- pneumocephalus
- pulmonary air cyst
- intraocular air bubbles
- tympanic membrane grafting
Sevoflurane advantages:
non-irritant sweet odor
rapid
does not sensitize mycardium
No CO production with NA lime
Sevo disadvantages:
- Less potent
- compound A production (contraindicated with baralyme)
- post op agitation in children
Which agent is a vapor at RT
desflurane
What agent is capable of increasing HR and documented myocardial ischemia?
desflurane
Disadvantages of desflurane:
- special vaporizers
- low potency
- pungency
- rapid increase > 1.25 MAC SNS stimulation
What agent is good for renal/hepatic dysfunction?
isoflurane
Eucapnic ventilation = ____ ml/min
5400 ml/min
R = respiratory quotient =
1.2
Abnormal PA-aO2 gradient (should be
Anatomic shunting: R-L thebesian, bronchiole, pulmonary AVM
diffusion impairment: thickened capillary membrane
Low V/Q areas due to position (supine, to lateral)
Lung volume recruitment calculation:
Compliance = ►V / ►P
If compliance = 50
PEEP = 5 cmH20, then…
Lung volume : 250 ml
Adverse effects of PEEP: (2)
barotrauma/pneumothorax
decreased VR/CO