Flashcards in Principles 4 Deck (87):
How does vapor pressure vary with temp?
VP increases w temp
What are 3 fxns of interlocks?
Prevents the operator from delivering more than one VA simultaneously
*only one vaporizer, seated correctly
*must be on for carrier gas to enter
*no trace output from other vaporizers
Classification of variable bypass vaporizers
*out of circuit
What is splitting ratio?
The gas entering the vaporizing chamber divided by the fresh gas flow. Controlled by concentration control dial and temperature compensation valve
What effect does flow have on vaporizer design?
FGF okay btw 0.2-10 L/min
What effect does temp have on vaporizer design?
Okay btw 20-35 C
What effect does the pumping effect have on vaporizer design?
Oscillating pressures distal to outlet cause exited vaporizer gas to reenter, so delivered vapor is higher than dialed... so check valves at outlets and inlets to vaporizers are used.
Classification of the tec 6 vaporizer
*Heated, dual circuit
*gas/vapor blender (FGF never comes into contact or flows over the liquid agent)
*no output during warm up or if power lost
Checkout routine for the Tec 6
Mute buttons (check lights, alarms)
w 1% on dial, unplug (checks battery power)
Correct procedure to fill vaporizer
*Watch the liquid level indicator as to not overfill
*Must be in horizontal position
Funnel-type and keyed-filler
Hazards of contemporary vaporizers
*Awareness or hypoxemia d/t leaks or empty vaporizers (prevent w negative pressure check)
*reliance on breath by breath gas analysis rather than preventive maintenance
What are the fnxs of the breathing circuit?
*deliver oxygen and anesthesia
*eliminate CO2 (by washout w adequate FGF or chemical absorption)
Open drop or NC
*no reservoir (aka breathing bag)
Non rebreather or FGF > VE (high FGF)
*reservoir (aka breathing bag) present
Circle (FGF < VE)
Circle (APL closed) (little to no FGF)
What is rebreathing and how is it used in anesthesia?
Rebreathing of exhaled gases
*increased as FGF is decreased
*increase is tracheal warmth and humidity
*decrease staff exposure to VA
High FGF and low rebreathing during induction and emergence - Low FGF and high rebreathing during maintenance
How is CO2 rebreathing prevented in conventional circuit and non-rebreathing circuits?
*Washout w adequate FGF
*absorption by granules
What is dead space and where does it end?
Ends where inspiratory and expiratory gas streams diverge (Y-piece in circle systems)
Increase VD = increase chances of rebreathing
Vd/VT ratio in spontaneous, intubated, and FM
Vd/VT = dead space / tidal volume
spontaneous = 0.33
intubated = 0.46
FM = 0.64
Advantages of circle breathing systems
*constant inspired concentrations
*conserve respiratory heat/humidity
*useful for all ages
*useful for closed systems or low flow
*low resistance (< ETT but > NRB)
Disadvantages of circle breathing systems
*Increased VD (dead space)
*Malfunctions of I/E unidirectional valves
Considerations for children
*uncuffed ETT (leak)
Use NRB circuits
*no unidirectional valves or absorbent
*FGF determines amt of rebreathing, >5
Mapleson D and F circuits
gas escapes via tail of bag (bag-tail valve), IPPV, resp mvmts easily seen
inner tube inside outer tube
*increased dead space
*unrecognized disconnection or kinking causing complete rebreathing
What do you do when changing from one circuit to another on AGM?
*Repeat compliance/leak check
*Repeat auto vent check (allows machine to compensate for different compliance and deliver accurate VT)
What specific changes must you make when using the ADU AGM?
*use small spirometry sensor (effect VT)
*choose Peds sensor in monitor setup
Baby < 10 kg
Hand bag and use precordial
Fabius breathing system
*FGF decoupling - bag not still, it moves opposite
of bellows, in sync w chest
*Piston driven vent - very quiet, no gas needed
*FGF enters behind insp unidirectional valve
*No bag/auto switch in breathing circuit
ADU breathing system
*Vertical check valves - less resistance
*Breathing bag at end of hose - no fixed position
*Checked for leaks/compliance - part of electronic
*Optimized for low flow
What is the size of CO2 absorbent?
4 - 8 mesh
What is the main constituent of absorbent?
Calcium hydroxide - CA(OH)2
What is the final product of absorbent?
Calcium carbonate - chalk - CaCO3
What is the amt of water content in soda lime?
15 - 20%
What is the first neutralization rxn in CO2 absorption?
formation of carbonic acid
CO2 + H2O → H2CO3
What is the second rxn?
Carbonic acid and Lye produce sodium carbonate, water and heat
H2CO3 + NaOH → Na2CO3 + H20 + heat
What is the final rxn (second neutralization rxn) in CO2 absorption?
Sodium carbonate and calcium hydroxide produce chalk (calcium carbonate) and lye
Na2CO3 + Ca(OH)2 → CaCO3 + NaOH
What are the recommended practices for safety in handling soda lime?
*Check color at the end of the case
*Change on a regular basis (q 48 hrs)
*Do not assume that lack of color change means
granules are intact
How do you change Aestiva prefilled canisters?
Discard top canister, promote bottom to top, and put fresh one on the bottom
*remove plastic wrap before
*check for leaks after
*don't change mid case, convert to semi-open circuit (FGF to > 5 L/min)
How do you change ADU CO2 absorber?
*Quick release can change during ventilation
*smaller canister (good bc avoids dry granules, des
produces carbon monoxide, sevo produces
compound A, bad bc freq change $)
*Alarms when inspired CO2 > 3
If no replacement, turn up FGF
What is a toxic product of sevo?
*Keep flows > 1 L/min (for not > 2 MAC hr)
What situations would cause inspired CO2 to increase?
1. Malfunctioning unidirectional valve
2. Exhausted absorbent
What is the management plan when inspired CO2 increases?
1. Increase FGF 8-10 L/min ( > VE) = semi-open,
almost no rebreathing
*if CO2 returns to normal, than its exhausted
granules, if CO2 remains high...
2. Inspect unidirectional valves
What are the toxic breakdown products of current VA?
Sevo → Compound A
Des → Carbon monoxide
What causes this toxic breakdown?
Degradation of VA by the activator KOH (a strong
*take out activators (NaOH and KOH)
*do not use Sevo at FGF < 1 L/min for more than
2 MAC hours
Dry absorbents also cause breakdown
What is the indicator used for changing absorbent?
Ethyl violet ~ indicates when absorbent pH has reached 10.3 (alkaline), but there maybe color reversion
Classify mechanical ventilators by power source:
- Electric (Piston ventilator)
*just controls or piston-driven motor
- Pneumatic (Gas-driven bellows)
*if dual circuit bag-in-bottle - gas powered
*if pipeline lost, hand ventilate!
Classify mechanical ventilators by drive mechanism:
*Pneumatic, double circuit - O2 or air drives bellows
*Electric motor drives bellows
Classify mechanical ventilators by cycling:
Time cycled, electronically controlled
*volume mode - flow stops when set VT delivered
OR when max pressure reached
*pressure mode - flow generated to maintain set
pressure, no guaranteed volume
Classify mechanical ventilators by bellows type:
* Ascending - standing (most common - PEEP)
* Descending - hanging (datascope)
(Divan and Fabius)
Why would hanging bellows be less safe than standing bellows?
The bellows will still fill (with RA) in the event of a disconnect
Water can gather in the bellows (decreasing VT
and increasing risk of infection
Note: decoupling - bag remains in circuit
How do you choose safe initial ventilator settings?
Are they breathing spontaneously, is there a reason to have limited pressure, do they need a certain amt of volume (limited).
How do the bag-in-a-bottle ascending bellows and relief valve work?
The bellows is like an anesthetist squeezing the bag, within the bellows is the gas insp and exp by the pt.
With the addition of FGF, there must be a spill valve or barotrauma would result
Gas is released to the scavenger in an equal amt of FGF per minute (exp only)
Note: when switching from bag to vent or auto, removes bag and APL valve from breathing circuit
How is 2 to 3 cm H2O of PEEP implicated in all standing bellows?
During early exp, a weight w/in the VRV (APL)holds pathway to scavenger closed until bellows have filled
What is VCV?
Volume controlled ventilation setting:
*desired VT delivered at constant flow (unless
excessive pressure is reached)
*time cycled (you set resp rate)
Adjust VT to prevent atelectasis, adjust RR for
desired CO2 level
I:E ratio 1:2
What is PCV?
Pressure controlled ventilation:
*cycle controlled by time
*decelerating flow pattern
*VT uncontrolled - increase if compliance increases or PIP decreases
*High flow needed at first, then less to maintain
*Target pressure is adjusted for the desired VT
Set pressure limit to 20 cc H2O, adjust RR for
desired CO2 level
I:E ratio 1:2
Indications for PCV:
If high insp pressure is dangerous - LMA, neonates,
Low compliance - obesity, pregnancy, ARDS
Compensates for leaks - LMA, uncuffed ETT
What is PCV-VG?
Pressure controlled ventilation with volume guarantee:
Basic controls are target pressure and RR, AND a
desired VT is also set.
*decelerating flow pattern at a constant pressure
(just like PCV)
*BUT the insp pressure is adjusted to deliver the
This compensates for changes in the pt's lung
What is SIMV?
Synchronized intermittent mandatory ventilation:
*Full to partial support of ventilation
*Can be PCV or VCV
*Intermittent mandatory breaths delivered in
synchrony and triggered by the pt's
*Settings include: volume or pressure, rate, trigger
window and sensitivity
What is PS?
*Pressure targeted mode
*Rate of ZERO - only for spontaneously breathing
*Thus, no minimum minute ventilation
*Start at 10 cm H2O and adjust as needed
How do modern vents accomplish VT compensation?
Accuracy at lower VT - compensating VT for
compliance and leak testing, and changes in
FGF (use smaller circuits and change D-lite,
don't forget to change settings, and repeat leak
and compliance tests)
Enter pt's wt and it will select VT and parameters
What are signs of carbon monoxide poisoning during anesthesia?
Why is des compensation used on the Fabius GS?
What is the proper procedure for denitrogenation?
*FGF 4-6 L/min
*APL valve open fully
**TIGHT MASK FIT**
What should flows look like during induction?
High MAC, High FGF (5-8 L/min) = overpressure
when end-tidal agent @ MAC, turn down VA to MAC w high flows OR leave VA high and turn down flows
What should flows look like during maintenance?
Low flows = 1 L/min, to conserve heat/humidity
What should flows look like during emergence?
High FGF w NO VA (washout)
Avoid low flows if...
High VO2 needed or toxic gases to washout
*MH, smoke inhalation, sepsis
*necessary equipment broken/missing
-O2 analyzer, agent analyzer, absorbent
*case < 15min
*leaks to expected (older machine, FM, uncuffed
ETT, rigid bronchoscopy
What are the s/sx of MH?
List the differential diagnosis's of MH:
Ventilator problems, unidirectional valve malfunction, exhausted granules, pneumoperitoneum
What are the triggers of MH?
Succs and VA
What is the definitive treatment for MH?
Dantrolene 2.5 mg/kg (up to 10 or more)
What is safe supportive treatment for MH?
Cooling, NaHCO3 for acidosis, treat high K+
gas machine: Stop VA and succs, High FGF,
hyperventilate, charcoal filters, change soda lime
What is the set up for managing known MH pt?
*use TIVA, N2O
*Roc instead of Succs
*change granules and breathing circuits
*Flush (FGF 10 L/min for 20 min)
What are the most common problem areas of the old vents?
*lack PCV (used in children/obese/ARDS)
*lack VT precision (neonates = nonrebreather)
*lacks adaptive ventilation (no compensation)
*lacked integrated PEEP
*no electronic checklist
*limited low flow capability
How do you choose new vent modes for maximum pt safety?
Think of Peds, barotrauma, etc...
VCV: salient characteristics/settings -
*VT 8-10 ml/kg - prevent atelectasis
*RR 6-12 (titrate to ETCO2)
can add in PEEP, FIO2, I:E ratio
VCV: indications -
VCV: controls -
Tidal volume and RR
VCV: caveats -
VILI - ventilator induced lung trauma
no support for spontaneous ventilation
VCV: contraindications -
Obese, neonates, pneumoperitoneum, steep trendelenberg
PCV: characteristics/settings -
*P insp set: 15-20
*RR (titrate to ETCO2)
COPD, LMA, uncuffed ETT, emphysema, neonates, pregnancy, obesity, ARDS
SIMV: characteristics/settings -
senses insp effort and delivers breaths in sync,
no breath stacking, can breath spontaneously in btw vent breaths
Based on VOLUME
Set VT and RR
can add PEEP, change I:E ratio
for SIMV mode on ADU - the fraction of expi cycle sensed - default is 50-70%
more = stacking
less = no sync breaths delivered