Transcript Ventilators and ABG*s

Ventilators and ABG’s
PHILIP L. KALARICKAL, M.D., M.P.H.
Objectives
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Review and understand Intubation criteria
Understand basic ventilator settings and
mechanisms
Understand how to monitor a patient on a
ventilator
A systematic review of ABG analysis
Understand the physiology of ventilation and
oxygenation.
Patient in ER
 55 y.o. Male
 CC: SOB and cough
 Vitals: Ht: 5’10”, Wt: 70kg
 T: 38.7
RR: 35 HR: 105 BP: 140/95
 Pox: 90% on 100% NRBM
 What do you do?
Intubation Criteria
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Intubation Criteria
1. Hypoxemia: PaO2 < 60mmHg on >.6 FiO2
2.Hypercarbia: PaCO2 > 60mmHg
3. RR > 30
4. GCS <8
5. Hemodynamic instability - Pressors
says, “What vent settings do you want
doc?”
What settings need to be programmed into the
ventilator?
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The respiratory tech turns to you and
says, “What vent settings do you want?”
 What settings need to be programmed into the
ventilator?
1. Mode
2. Tidal volume
3. RR
4. FiO2
5. PEEP
Initial Vent Settings
Mode:
TV:
RR:
FiO2:
PEEP:
Initial Vent Settings
Mode:
2 basic modes – pressure control & volume control. TV depends on
lung compliance. Usually pick SIMV or PRVC
TV:
5-7 cc/kg IBW
RR:
start at 20. Can adjust based off of ABG
FiO2:
start at 1.0. Can adjust based off of ABG
PEEP:
start at 5cm H2O
Ok, the patient is on the vent. Now what?
How do we assess patients on vents?
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ABG’s
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ABG’s
1. pH: 7.35 – 7.45
2. PaCO2: 35-45 mmHg
3. PaO2: 80-100 mmHg
4. HCO3-: 22-28 mEq/dL
5.BE: -2 - +2
6. Sat: 97 – 100%
You get your first gas….
 7.30/55/200/24/0/100
 What do you think?
 What do you want to do?
1.
Acid/Base
2. Ventilation
3. Oxygentation
Acid/Base
1.
Look at pH to determine primary process
2. Then look at PaCO2 and HCO3- to determine
relative contribution of Respiratory and Metabolic
components to acid/base disturbance and the
degree of compenation.
Ventilation
 Measured by PaCO2
 ***Oxygentation and Ventilation are independent
processes***
 Ventilation is a function of MV
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MV= TV x RR
Usually by RR rather than TV
 This patient has an elevated PaCO2. He is
hypoventilating (retaining CO2).
 We should increase RR
Ventilation
 You ask the Resp Tech to increase RR to 24 and
check an ABG in an hour
 The repeat gas is:
7.40/40/200/24/0/100
 Now what?
 Have we addressed oxygenation yet?
 What do you think about the PaO2 of 200mmHg?
Oxygenation
 How do we assess oxygenation?
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 What is PaO2? What does PaO2 mean?
 It is the pressure of oxygen that is dissolved in plasma
 It contributes very little to oxygen delivery
 CaO2 = 1.34 x Hb x sat + .003(PaO2)
 Helps assess how well oxygen exchange occurs at the
alveolus
 You need to compare it to PAO2.
P AO 2
 PAO2 = [(Patm – PH2O)FiO2] –
(PaCO2/0.8)
 Because oxygen and carbon
dioxide are small molecules,
there should be almost
perfect gas exchange across
the alvelous to pulm capp.
P AO 2
 Example: on 100% oxygen,
 PAO2 = [(760-47)x 1] – (40/0.8)
= 710 – 50
= 650mmHg
 Rule of Thumb: PaO2 should be about 5x O2%
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Ex: on 100% O2, PaO2 should be approx 500mmHg
 Now what do you think about the PaO2 of 200 mmHg on
our ABG?
 If we have an unexpected result, we should correlate it
clinically.
 Why would this patient have problems with oxygen
exchange across the alveolus?
 In other patients, different causes may be higher on
the differential
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CHF exacerbation and pulm edema
Pneumothorax
Mucous plug
ETT in main stem bronchus
Etc…
Ok, we know we have a problem with
oxygenation, now what?
 How do we improve oxygenation?
 2 ways:
 Increase FiO2
 Increase PEEP
 Are there any drawbacks to PEEP?
 Yes Barotrauma
 Inhibits venous return
Effect of Increased PEEP- example
•“Best” PEEP – the level of PEEP at which you
improve oxygenation the most without
significant effects on venous return
PEEP (cm H2O ) Sat
PaO2
BP
5
100
200
135/90
7
100
250
130/80
9
100
350
115/70
11
100
450
85/55
 In this example, 9cm H2O is the “Best” PEEP
Oxygenation
 Ok, we’ve improved oxygenation via PEEP and hope
to improve it further with anitbiotics for his
pneumonia.
 Now what?
 Are we happy with his FiO2?
 Are there problems with high FiO2?
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Oxygenation
 You should wean FiO2 to minimum to maintain sats
> 95% (PaO2 > 80)
 Why?
Oxygenation
 Problems with high FiO2
 “oxygen toxicity” – due to oxygen free radicals that may cause
alveolar damage
 Risk factor – FiO2 > .6 for greater than 24 hours
 High FiO2 is not safe for patients
 Saturation is a relatively insensitive measure of oxygenation
(sats won’t drop until PaO2 is less than 80-100)
Low FiO2 allows you to know your PaO2 within a
narrow range without drawing an ABG.
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Ex:
Pt. on 100% O2 with sats 100%
 The lowest PaO2 can be is 80 mmHg
 The highest PaO2 can be is 500-600mmHg
 Pt on 30% O2 with sats 100%
 The lowest PaO2 can be is 80 mmHg
 The highest PaO2 can be is 150 mmHg
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2. Low FiO2 will allow you to identify problems
earlier
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A patient on 30% O2 will desat sooner than a patient on
100% O2
In other words, 100% O2 will “mask” a problem
3. If a patient is on a low FiO2 you can increase to
100% to buy time to make a diagnosis and treat.
Now you know almost everything you need to
know about Vents and ABG’s
Intubation Criteria
2. Basic ventilator settings
3. Assessing patients on vents
1.
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2.
Pulse oximeter
ABG’s
4. Analyzing ABG’s
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Acid/Base
2.
Ventilation
3.
Oxygenation