APRV Flashcards
What are the advantages of APRV?
- uses lower peak and mean airway pressures
- increases cardiac index
- decreases central venous pressure
What is the open lung approach?
high peep, low lung pressure
What is the best mode to help limit lung damage?
low volume settings adjusted to maintain plateau pressures between 25-30 cmH2O simulating PCV
What are some lung protective strategies?
- ALI and ARDS
- keep plateau pressures <30 cmH2O
- low tidal volume ventilation (4-6 mL/kg)
- peep to restore FRC
What are the current strategies for ventilating between upper and lower inflection points?
- increase MAP while limiting peak alveolar pressure
- preventing alveolar collapse by ventilating above the lower inflection point
- preventing over distention by ventilating below the upper inflection point
What is BiLevel in comparison to APRV?
a form of pressure ventilation designed to embrace dual peep levels and inspiratory/expiratory times that allow traditional PC-like breath delivery to APRV-like breath delivery
What are the four main settings in APRV?
P-high
P-low
T-high
T-low
P-high and P-low are specific independent settings, therefore what happens to P-high when you raise P-low?
does not change
If your P-low is set to 5 and you P-high is set to 15, what is your set PS?
15 cmH2O
If your P-low is set to 5, your P-high is set to 15 and your PS is 15, what are all spontaneous breaths at P-high supported by??
5 cmH2O
How does bilevel look similar to PCV-SIMV?
by setting P-high, T-high and frequency close to typical ventilation settings
What are the clinical advantages to spontaneous breathing at 2 peep levels?
- a potential decrease in sedation (sedation due to patient/ventilator dyssynchrony may be kept at a lower level)
- less sedation could result in: less interaction with other organ function, patients can be mobilized easier, an active cough may improve secretion removal, inability to identify complications that can be masked by sedation
How does spontaneous breathing ventilation differ from paralyzed patients?
it provides ventilation to dependent lung regions which get the best blood flow
How does paralyzed ventilation differ from spontaneous breathing?
during PPV for paralyzed patients, the anterior diaphragm is displaced towards the abdomen with the non-dependent regions of the lung receiving the most ventilation where the perfusion is the least
Is there mechanical breathing in APRV?
no
What is APRV?
utilizes very short expiratory time. this short time at a low pressure allows for exchange of gas
What is the critical setting in APRV?
T-low
How is T-high used in APRV?
it varies with frequency changes and merely determines the interval that the lungs are held at P-high
When should you consider APRV?
- bilateral infiltrates
- p/f ratio <300 and falling
- plateau pressure
What are the goals with APRV? (first five)
- to prove LPV supported by the ARDSnet research
- minimize alveolar over distension
- avoid repeated alveolar collapse and reexpansion
- restore FRC through recruitment and maintain FRC by creating intrinsic peep
What are the goals with APRV? (last five)
- lower FIO2
- protect lungs
- make patient comfortable
- use less sedation
- wean patient off the ventilator
What are the three types of lung units in ARDS pattern?
- normal region (primarily non-dependent area)
- consolidated, edematous, atelectatic region (dependent area)
- region that is collapsed during exhalation and recruitable during inspiration
What are the clinical advantages to spontaneous breathing in ARDS during APRV?
- APRV with spontaneous breathing showed a decrease in V/Q mismatch that increased over time
- spontaneous breaths in APRV as small as 70-150 mL in adults improved oxygenation and CO2 removal
What are the similarities of APRV to high frequency ventilation?
- both hold lungs at near constant lung MAP, limiting pressure swings
- both shown to be effective in decreasing dead space, improving gas exchange, increasing cardiac output
- APRV is accomplished with a conventional ventilator, a conventional circuit and is less technically challenging
What is high frequency ventilation?
breathing in and out at the same time. like filling a glass all the way and still put in water so it over flows
Who are poor candidates for APRV?
- patients with increase RAW
- patients who are unable to empty their lungs in 2 seconds
- asthma and COPD patients
What is a reliable indicator that tells if a patient is a poor candidate for APRV?
examine their expiratory flow pattern to determine increased resistance
What are the APRV clinical guidelines?
- APRV has been suggested for restrictive patients only (obstructive easily develop air trapping)
- start early with CPAP and switch to APRV as CO2 clearance and/or decreased work of breathing is desired
How do you set up APRV?
- P-high: set so plat is not above 30
- P-low: 0
- T-high: start at 5
- T-low: start at 0.5
Initial settings of P-high
typically about 20-25, however in patients with play at or above 30, set at 30 (in desperation can go to 35)
What are the exceptions to setting really high P-high settings?
- morbid obesity
- decreased thoracic or abdominal compliance
What should you set P-low to and why?
zero because it creates the greatest pressure gradient and fast expiratory flows
What is T-high and how should you set it?
the inspiratory time that is set to a minimum of 5 seconds, and is progressively increased. do NOT use rate of over 15. its target is oxygenation
Establishing T-low
do not want to let exhalation go to complete emptying and regional auto-peep is desirable outcome
How would you set T-low?
set time low so that expiratory flow from patient ends at about 75-50% of peak expiratory flow OR one time constant (i.e, if peak expiratory flow is 80 L/min, then “dump” should end when flow is between 60-40 L/min
How would you improve oxygenation with APRV?
- reduce sedation
- re-assess peep (move towards 75%)
- decrease T-low
- increase P-high, T-high, FIO2
What should you NOT do if a patient has a high CO2?
increase T-high
What should you do if your patient has PaO2 that is too low?
decrease T-low
What should be your goal for all oxygenation choices?
increase MAP
How could you improve CO2?
- reduce sedation
- upper pressure is adjusted to maintain dec WOB or O2 delivery goals
- increase T-low and PS of spontaneous breaths
- decrease T-high
What are you doing when you increase P-high?
increasing the pressure gradient which increases flow
What should you do to decrease CO2?
- decrease T-high
- increase P-high to increase change in pressure and volume exchange
- check T-low and increase if possible
What should you do to increase CO2?
- increase T-high
- decrease P-high to decrease change in pressure
- it may be better to accept hypercapnia than to reduce P-high so much that oxygenation decreases
What are the disadvantages of APRV?
- potential for alveolar de-recruitment during the pressure release
- APRV is affected by changes in lung compliance
- if release phase is not synchronous with patient’s effort, discomfort may result
What patients should you be cautious with using APRV?
- patients that have COPD, asthma or any other type of air trapping disease
- barotrauma could be a side effect
What are the overall advantages?
- spontaneous breathing
- maintains peak airway pressures at CPAP levels (over distention minizmed)
- continuous lung recruitment maneuver
What should you accomplish before weaning from APRV?
- FIO2 40-50%
- reduce P-high by 2 until it is below 20
- increase T-high to change vent set rate by 5 releases/time
What is DROP and DRAG?
DROP- drop P-high in increments of 1-3 (usually about 2)
DRAG- increase T-high
^do the above until it looks just like CPAP
For a P/F ratio of greater than or equal to 300, what should your estimated MAP requirements be?
10-15 cmH2O
For a P/F ratio of greater than or equal to 250, what should your estimated MAP requirements be?
15-20 cmH2O
For a P/F ratio of greater than 200, what should your estimated MAP requirements be?
20-25 cmH2O
For a P/F ratio of greater than 150, what should your estimated MAP requirements be?
25-30 cmH2O
For a P/F ratio of greater than 100, what should your estimated MAP requirements be?
30-35 cmH2O
