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Determining the appropriate level of PSV. By Elizabeth Kelley Buzbee AAS, RRT-NPS, RCP. According to Egan’s Fundamentals there are three methods to set appropriate levels of PSV for a patient get an appropriate Vt [10-15 ml/kg] and titrate the PS level to achieve this Vt

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determining the appropriate level of psv

Determining the appropriate level of PSV

By Elizabeth Kelley Buzbee AAS, RRT-NPS, RCP

slide2
According to Egan’s Fundamentals there are three methods to set appropriate levels of PSV for a patient
  • get an appropriate Vt [10-15 ml/kg] and titrate the PS level to achieve this Vt
  • increase the PS level till the respiratory rate is normalized [25 bpm or less]
  • [Egan’s page 1018] increase the PSV until you decrease the work of breathing through the endotracheal tube
    • To select the appropriate level of PSV to overcome the RAW use this formula

PSV= (PIP - PPlat) x spont insp. Flow rate [lps]

Ventilator flow rate [lps]

this tutorial will use case studies to go through each of these three methods
This tutorial will use case studies to go through each of these three methods
  • Case study # 1

Mr. Casey is a 45 year old WM who has been on CMV for several weeks following successful treatment for ARDS triggered by smoke inhalation. He is alert and wants off the ventilator. His current ABG show a normal PaC02 and normal oxygenation on his current settings: A/C 10 Vt 700 ml and PEEP 5 Fi02 40%. He is breathing at a rate of 12 bpm with a return Vt of 705 ml

slide4
You see that his lung compliance has risen from a low of 17 ml/cmH20 to a current level of 45 ml/cmH02
  • because he is ready to wean you need to challenge him to breath by getting him off CMV onto some support mode.
  • You suggest what ventilator change?
answer
ANSWER
  • : change him from A/C of 10 to SIMV of 10
slide6
When his mode is changed from A/C of 10, you see that his return Ve has fallen from 8.4 Liters to 7.5 Liters.
  • Why?
answer1
ANSWER:
  • his mechanical Ve dropped because he is now unable to trigger ventilator breaths. He now has a spontaneous Ve.
slide8
When you subtract Mr. Casey’s mechanical Ve [7.] from his total [Ve 7.5 L] you see that his spontaneous Ve is what?
answer2
ANSWER:
  • 7.5 L – 7.0 L = spont. Ve of .5 L
answer3
ANSWER
  • : spont Ve/ spont RR = spont Vt .5/10 = 50 ml Vt
slide12
You see that his spontaneous respiratory rate is 10. When added to the 10 bpm of the mechanical ventilator, he has a total respiratory rate of what? Is it excessive?
answer4
ANSWER:
  • 20 bpm. It’s a bit fast, but not dangerously fast
slide14
When you get ABG on this setting you see that the PaC02 has risen from 40 to 45. He is looking a little anxious, and his breathing a little labored at a SIMV 10 Vt 700
  • The doctor orders you to decrease him from SIMV 10 to SIMV 5. Do you agree?
answer5
ANSWER:
  • No, his current spontaneous Vt is only 50 ml. His Vd is 150 so you know that he doesn’t have enough Vt to get gas into his alveoli where it will do some good.
slide16
Doctor disagrees and you put the patient on SIMV 5. You stick around because you want to see his reaction to this.
  • The patient increases his spontaneous respiratory rate from 10bpm to 35 bpm.
  • Why?
answer6
ANSWER:
  • he must raise his spontaneous Ve from .5 to 3.75 Liter to keep the total Ve that he had earlier. Because he cannot breath any deeper than 50 mL, he must increase his RR to 75 bpm—this is impossible and his C02 will rise and he will get exhausted.
answer7
ANSWER:
  • give him enough PSV to raise his Vt, that will drop his respiratory rate
slide20
The doctor agrees to add PS to him. He give you a free hand to select the appropriate level. You look at what?
answer8
ANSWER
  • : put him on a PSV of 5 and watch his return Vt. Increase the PSV until his return Vt is 10 mL/kg IBW.
slide22
Mr. Casey’s IBW is 65 kg. When you select PSV 5 you see that his return spont Vt is now 200 ml. You increase his PSV to 10 and see that he now gets 400 ml Vt. What do you do next?
answer9
ANSWER:
  • you see that on PSV his dynamic C is 40 ml/cmH20 so you increase his PVS to 16 [ 16 cmH20 x 40 = predicted 640 ml.
  • At this point, the patient’s respiratory rate goes from 36 bpm to 6 bpm. Now is total respiratory rate is 5 + 6 = 11 bpm. His color gets better and he stops retracting.
case study 2
CASE STUDY # 2
  • Your patient is Mrs. Ortagus who has been on A/C 15 and Vt 500 PEEP 5 and Fi02 45% for the last few days. She intubated and ventilated for viral pneumonia and is now getting better.
  • To wean her you request what mode change?
answer10
ANSWER:
  • switch her to SIMV and get a gas. If it is good reduce the SIMV rate
slide26
The doctor agrees and when she is on SIMV 10 bpm, she starts to breath on her own. You see that her spont Ve is 3.0 and her spont respiratory rate is 12 bpm. What is her spont Vt?
answer11
ANSWER:
  • Ve / rate = Vt so 3.0 L/ 12 = 250 ml
slide28
The doctor orders her down from SIMV 10 to SIMV 5 and her respiratory rate rises to 23 bpm. What do you suggest?
answer12
ANSWER:
  • put her on SIMV + PSV
answer13
ANSWER:
  • start at PSV 5 or 10 watch the respiratory rate for a few minutes. Increase the PS until the respiratory rate drops to less than 25 bpm
slide32
When you select PSV 5 you see her rate decreases to 20 bpm [total is 5 + 20 = 25]
  • Are you happy with this?
answer14
ANSWER:
  • if the gas is good and she is not working too hard to breath.
casestudy 3
CASESTUDY # 3
  • Your patient is Mr. Blake a 50-year-old BM with a history of COPD. He was placed on SIMV 12, Vt 500, Fi02 34% and has been on these settings for two weeks. The doctor orders you to decrease his rate to 8 bpm. When you do this he starts to breath on his own. He seems to be working hard to breath and the doctor asks you to put him on enough PSV to overcome the RAW of the endotracheal tube.
  • What information do you need to do this?
answer15
ANSWER:
  • look at his flow/time curve and find his spontaneous inspiratory flow rate
  • look at the flow/time curve and find his ventilator flow rate
  • look at the pressure/time curve and find his PIP
  • put him on .5 seconds of pause time and find his Pplat
slide36
You get the following information:
  • spontaneous inspiratory flow rate 20 lpm /60 = .33L/sec
  • ventilator flow rate = 50 lpm/60 = .83 lps
  • PIP 45
  • Pplat 23
slide37
Calculate the PSV he needs through this endotracheal tube to over come resistance.

PSV= (PIP - PPlat) x spont insp. Flow rate [lps]

Ventilator flow rate [lps]

answer16
ANSWER:

PSV= (45 - 23) x .33 [lps]

.83 [lps]

PSV= 22 cm H20 x .33 [lps]

.83 [lps]

PSV= 7.26

.83

PSV = 8.7 cm H20

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