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1.
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Describe design elements of the anesthesia delivery system
intended to prevent delivery of a hypoxic gas mixture. Consider the pathway
followed by gases, from source to patient.
·PISS, DISS
·Color-coded gas cylinders and tubing (O2 green, N2O
blue)
·Fail-safe alarm
·N2O - O2 flowmeter coupling
·Flowmeter color-coding
·Flowmeter positioning (oxygen last)
·FiO2 monitor (ventilator)
·Gas-monitoring device (Datex)
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2.
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Describe changes in O2 pressure, from source to
destination (end of endotracheal tube). How are these changes regulated?
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Wall 50psi.
Cylinder pressure depends on content
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1st pressure
regulator, down to ?16
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Flowmeters
variably reduce pressure, depending on setting
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3.
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How does pressure change in E size oxygen and nitrous
oxide cylinders as gas content changes?
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O2:
compressed gas. Full = 625L, 2000 psi. Linear decrease, 3.2 psi/L lost.
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N2O:
liquid and gas at equilibruim. 750 psi until all liquid gone. Full = 1590L.
Pressure starts to fall at about 400L
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4.
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Draw internal circuitry of an anesthesia machine. Explain
function of each part
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5.
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Describe how the modern vaporizer works. Compare with the
Tec 6 vaporizer.
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an
“agent-specific, variable bypass, flow-over, temperature-compensated, out-of
circuit vaporizer”
·
calibrated
for particular volatile agent (vapor pressure)
·
dial controls
portion of fresh gas that bypasses liquid
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remainder of
gas (20% or less of total) flows over liquid agent and agent-saturated wicks
(inc. surface area). Output stable unless <250ml/min total flow (output
lower than setting due to pressure insufficient to move relatively heavy
agent molecules upward) or >15L/min (lower due to incomplete mixing)
·
a bimetallic
strip or expansion element modifies amount of bypass depending on
temperature. vaporizer output nearly linear at 20-35 Centigrade
·
Desflurane
vapor pressure is 664mmHg, near 1atm at 20deg. Tec6 is heated to constant
temp (23-25 deg) and pressure (1500 mmHg) for controlled delivery, with
computer-controlled flow
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6.
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Describe the Mapleson and Bain breathing circuits.
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7.
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Draw a picture of the circle absorption breathing system
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8.
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What are the advantages of the circle system?
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some
conservation of moisture and heat
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can use fresh
gas flow less than minute ventilation ==> decreased pollution
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9.
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What are the disadvantages of the circle system?
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increased
resistance to breathing (valves, CO2 cannister
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bulkiness of
equipment
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more parts
==> inc chance for malfunction
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10.
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Compare closed circle system and semiclosed circle system.
Circle:
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=APL
completely closed, fresh gas flow low (150-500 ml/min)
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(metabolic
need under anesthesia = 150-250 ml/min)
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maximal
preservation of heat and moisture
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less
pollution
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less agent
used (cheaper)
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cannot change
agent concentration or FiO2 quickly
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unpredictable
FiO2 (esp if N2O used, due to variable
uptake)
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unknown
anesthetic concentration (due to changing uptake; high initially, then
decreased)
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11.
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Describe the machine checkout
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emergency
equipment
·
oxygen
cylinder, at least 1000 psi
·
oxygen wall
supply
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negative
pressure leak test (machine switch OFF; check with each vaporizer on)
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flowmeter
function, oxygen-nitrous coupling
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calibrate
machine oxygen monitor
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breathing
system leak check/APL check/scavenging check
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unidirectional
valve check
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ventilator
check
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monitor check
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12.
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Compare soda lime with baralyme
Both
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add moisture
and heat to inhaled gases
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(dry gases
can damage respiratory epithelium within one hour. After several hours,
inspissated secretions ŕ ETT obstruction)
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(cold gases
can lead to significant heat loss, especially in infants and children, who
are rendered poikilothermic by GA)
Soda lime:
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Ca(OH)2,
NaOH, KOH and water. Silica to give granules hardness (minimize formation of
alkaline dust, which could cause irritation or bronchospasm if inhaled)
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CO2
+ H2O ŕ H2CO3
H2CO3 + 2NaOH ŕ Na2CO3 (rapid) + 2H2O
+ heat
H2CO3 + Ca(OH)2 ŕ CaCO3 (slow) + 2H2O
+ heat
Baralyme:
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Ba(OH)2
and Ca(OH)2 (+bound water of crystallization)
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CO2
+ H2O ŕ H2CO3
H2CO3 + Ba(OH)2 ŕ BaCO3 (rapid) + 2H2O
+ heat
H2CO3 + Ca(OH)2 ŕ CaCO3 (slow) + 2H2O
+ heat
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bound water č more reliable performance in dry
environments
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13.
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What factors determine efficiency of carbon dioxide
neutralization?
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size of
granules: optimal = 4-8 mesh; compromise between surface area and resistance
to air flow
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channeling =
preferential passage of gases through low-resistance channels, which bypasses
most of the absorbent granules. Most often caused by loose packing of
granules. Granules may be held in place by screens or baffles to help prevent
channeling
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optimally,
full tidal volume can be accommodated within the void space of the canister
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14.
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What elements of the anesthesia delivery system act to
prevent equipment contamination or cross-infection between patients?
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only small
amount of bacteria released during anesthesia
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bacteria
released with coughing unlikely to be pathogenic
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bacteria
released often susceptible to even low concentrations of oxygen
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bacteria in
circle system exposed to shifts in humidity and temperature (probably the
most important factors responsible for bacterial killing in the ADS)
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bacteria do
not survive in vaporizers, although clinical concentrations do not kill them
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metallic ions
present in machine are highly lethal (copper, zinc, chromium, brass)
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acid-fast
bacilli (TB) are the most resistant - should use disposable circuit or
disinfect non-disposable equipment
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