Chapter 13: Imporving 02 & ARDS Flashcards
What are the formulas for calculating 02 consumption (VO2) and 02 delivery (D02)
VO2 = cardiac output X CaO2
DO2 = Cardiac output x CaO2(10)
Calculating oxygen delivery provides information about how much oxygen is available to the tissues. You can also be used as a tool for evaluating the effectiveness of PEEP. Oxygen delivery provides in valuable information about cardiac and pulmonary functions, as well as oxygen carrying capacity of the blood
How to calculate the desired Fio2?
Fi02d = FiO2 known X PaO2 desired / PaO2 known
What is the classic (physiological) shunt equation for calculating the patient’s pulmonary shunt?
Qs/Qt= (Cco2-Cao2) / Cco2-Cvo2
Qs: the shunted portion Qt: total cardiac output Cc02: content of 02 of the alveolar capillaries CaO2: arterial 02 content Cv02: mixed venous O2 content
Normally 0.02 to 0.05 or 2-5%
Some say to use 3.5% for this measurement
What happens with Cs (static compliance) when PEEP is applied
Compliance is considered a good indicator of affected PEEP on the lung. As people progressively restores FRC, complains should increase.
It’s important to recognize, however, that when PEEP reaches a point where it over to Stan’s along, compliance will decrease
Evidence of this reduction in compliance due to over distention of the alveoli can be seen in the P-V graphic. A characteristic duck billed appearance will occur at the top of the P-V Loop
What is the target value of Pa02/Fi02?
A target value greater than >300 is optimum but not always realistic
Example PaO2 100 with Fi02 0.33
Remember: normal 450 critical <200
An improvement in the P(A-a)o2 = alveolar to arterial tension, typically suggest what ?
Decreases in P(A-a)o2 (with increases of PEEP) reflects improvement in V/Q
P(a-etCo2) can also represent what? What are normal values
Indirect assessment of the effectiveness of ventilation or dead space to tidal volume Vt/Vd
This would be lowest when gas exchange units are maximally recruited without being over to standby PEEP
Normal 2.5 - 4.5
An increase in PEEP that leads to increases in this value above 2.5 to 4.5 signifies that there is too much PEEP
What are the normal values of C(a-v)O2?
The arterial to mixed venous oxygen content difference which normally rests at 5% reflects O2 utilization by the tissues
And increase in this value with an increase in PEEP meat indicate hypovolemia, cardiac malfunction, decrease venous return to the heart, decreased cardiac output, or increase VO2
A decrease in this value with an increase in PEEP May also associate with increasing cardiac output resulting from improved or augmented cardiac function. Reduction in O2 extraction by the tissues can also result from reduce metabolic rate or a histotoix hypoxia
What’s is a normal Pv02
Normal 35-45 mmHg or Svo2 =75%)
28mmhg is probably the minimum acceptable level which is a svo2 of 50%
List 5 factors that affect mean airway pressure
PEEP (auto and external) I:E ratio PIP RR Flow pattern
List for methods for increasing mean airway pressure
PEEP
APRV
Increase I:E time
HFOV High frequency oscillating ventilation
What are the goals of PEEP in CPAP
Enhance tissue oxygenation
Maintain a PA02 equal or greater to 60 mmHg and an SPO2 of equal to or greater than 90%
Recruit Alviola and maintain them in an arated state
Restore functional residual capacity
List 6 indications for PEEP therapy
Bilateral infiltrates on chest radiograph
Reduce lung compliance
Recurrent atelectasis with low functional residual capacity
PaO2 less than 60 mmHg on FIO to greater than .5
Pa02/F I O2 ratio less than 300 for ARDS
Refractory hypoxemia
List 5 criteria that may indicate a patient is ready for a reduction of PEEP
Acceptable Pa02 on FiO2
What are the basic points that should be kept in mind when managing ventilated patients with ARDS using an open-lung or Lung protective strategies
Use of small VT 46 mL per kilogram has been shown to be effective. Use of low VT should be accompanied with PEEP to avoid alveolar collapse
PEEP has a protective effect against the lung damage, and helps keep the lungs open. Maintaining a minimum and expiratory volume with PEEP helps avoid widespread alveolar Adema, damage, and sheer stress between Alviola that can occur when the long units are repeatedly open and closed
As PEEP is increased, PA O2 increases, remember using PAO to alone is not always a good indicator of an appropriate PEEP level
PEEP should be applied early
If it becomes difficult to maintain low pressure during volume control ventilation, switch to pressure control
There is a risk that the areas of the long that appear normal may become overinflated. Keep a plateau pressure below 30 mmHg
When ventilation cannot be maintained at a normal level without risk damage to lung tissue, consider allowing PA CO2 to rise
