PaO2 : How Low Can You Go ? In ARDS Az Rifki Siti Rahmah Islamic Hospital Padang, West Sumatra
ARDS <ul><li>First description was in Lancet – 1967  when Ashbaugh, Bigelow and Petty described 12 patients with…,  </li><...
1994 American-European Consensus Conference  Definition   <ul><li>Acute onset </li></ul><ul><li>Bilateral diffuse infiltra...
ABNORMALITIES OF GAS EXCHANGE <ul><li>Hypoxemia: HALLMARK of ARDS </li></ul><ul><ul><li>Increased capillary permeability <...
Mechanical Ventilation induced lung injury <ul><li>1. Volutrauma </li></ul><ul><li>can occur secondary to alveolar overdis...
Ventilator induced lung injury <ul><li>3. Biotrauma </li></ul><ul><ul><li>characterized by the  release of inflammatory me...
Lung Protective Ventilator Strategies <ul><li>Goal </li></ul><ul><ul><li>Avoid extension of lung injury </li></ul></ul><ul...
1. Permissive Hypoxemia   2. Low Tidal Ventilation and  Permissive Hypercapnia   3.   Positive End-Expiratory  Pressure (P...
How much FiO2? <ul><li>There is no clinical evidence to support the use of specific FiO 2  </li></ul><ul><li>FiO2 of 0.6 o...
How much Tidal volume?  ARDS Network
How much Tidal volume?  ARDS Network   <ul><li>Low tidal volume  -31% </li></ul><ul><li>(6 mL/kg predicted body weight) </...
Lower PEEP/Higher FiO 2 FiO 2   .3  .4  .4  .5  .5  .6  .7  .7  .7  .8  .9  .9  .9  1.0 PEEP  5  5  8  8  10  10  10  12  ...
Results <ul><li>Trial stopped @ the 2 nd  interim analysis after 549 pts. Had been enrolled. </li></ul><ul><li>Stopped bas...
Prone position ventilation <ul><li>Improve oxygenation </li></ul><ul><ul><li>Better FRC </li></ul></ul><ul><ul><li>Recruit...
 
P aO2 : How Low can You Go ?
Severe hypoxemia without evidence of tissue hypoxia in adult respiratory distress syndrome. Lund T ,  Koller ME ,  Kofstad...
How harmful is hypoxemia? <ul><li>Unclear </li></ul><ul><li>Rare cause of death in A RDS </li></ul>Your pO2  and SO2  here...
How harmful is hypoxemia? <ul><li>Unclear </li></ul><ul><li>Rare cause of death in  ARDS </li></ul>Your pO2  and SO2  here...
What levels of PaO 2  can be targeted? <ul><li>What specific levels of PaO 2  can be targeted in patients is not known. </...
<ul><li>The key question that has to be asked if one is considering targeting lower levels of PaO 2  is the clinical &quot...
<ul><li>Most intensive care practitioners aim to maintain PaO2 between 8 and 10kPa (or 60 – 80 mm Hg). Although direct evi...
Oxygen Dissociation Curve ARDSnet Study 88-94% PaO2 55-80
Tissue Oxygenation <ul><li>Reflects the balance between DO2 and VO2 </li></ul><ul><li>Determined by : </li></ul><ul><ul><l...
Maintaining Tissue Oxygenation <ul><li>Normalized Oxygen Delivery : </li></ul><ul><ul><li>Cardiac Output </li></ul></ul><u...
OXYGEN EXTRACTION VO 2  = Q x Hb X 13.4 X (SaO 2  - SvO 2 ) Arterial Inflow (Q) capillary O 2 O 2 O 2 O 2 O 2 O 2 O 2 Veno...
OXYGEN DELIVERY DO 2  = Q X CaO 2 DO 2  = Q X (1.34 X Hb X SaO 2 ) X 10 Q = cardiac output CaO 2  = arterial oxygen conten...
HEMODYNAMIC SUPPORT Max O 2 extraction Critical DO 2 Abnormal Flow Dependency DO 2 VO 2 Septic Shock/ARDS Max O 2 extracti...
Protective lung ventilation protocol from the ARDSNet study <ul><li>Initial tidal volume – 6ml/kg </li></ul><ul><li>Plat. ...
Summary  <ul><li>Low PaO2  in critically ill patients is frequent.  </li></ul><ul><li>A PaO 2  value between 50 and 70 mm ...
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  • Pa O2 How Low Can You Go

    1. 1. PaO2 : How Low Can You Go ? In ARDS Az Rifki Siti Rahmah Islamic Hospital Padang, West Sumatra
    2. 2. ARDS <ul><li>First description was in Lancet – 1967 when Ashbaugh, Bigelow and Petty described 12 patients with…, </li></ul><ul><ul><li>acute respiratory distress </li></ul></ul><ul><ul><li>cyanosis refractory to oxygen therapy </li></ul></ul><ul><ul><li>decreased lung compliance </li></ul></ul><ul><ul><li>diffuse infiltrates on chest X-ray </li></ul></ul><ul><li>Difficulties: </li></ul><ul><ul><li>lacks specific criteria </li></ul></ul><ul><ul><li>controversy over incidence and mortality </li></ul></ul>
    3. 3. 1994 American-European Consensus Conference Definition <ul><li>Acute onset </li></ul><ul><li>Bilateral diffuse infiltrates on chest radiograph </li></ul><ul><li>PAWP < 18 mm Hg </li></ul><ul><li>Two categories : independent of PEEP. </li></ul><ul><ul><li>Acute Lung Injury - PaO 2 /FiO 2 ratio < 300 </li></ul></ul><ul><ul><li>ARDS - PaO 2 /FiO 2 ratio < 200 </li></ul></ul>Mortality - 26% to 74%
    4. 4. ABNORMALITIES OF GAS EXCHANGE <ul><li>Hypoxemia: HALLMARK of ARDS </li></ul><ul><ul><li>Increased capillary permeability </li></ul></ul><ul><ul><li>Interstitial and alveolar exudate </li></ul></ul><ul><ul><li>Surfactant damage </li></ul></ul><ul><ul><li>Decreased FRC </li></ul></ul><ul><ul><li>Diffusion defect and right to left shunt </li></ul></ul><ul><li>Mechanical Ventilation : life-saving therapy </li></ul>
    5. 5. Mechanical Ventilation induced lung injury <ul><li>1. Volutrauma </li></ul><ul><li>can occur secondary to alveolar overdistension when large TV and/or excessive PEEP are used, causing increased permeability, worsening compliance, and a vicious cycle of progressive lung injury; </li></ul><ul><li>2. Atelectrauma / Inadequate levels of (PEEP) </li></ul><ul><li>transalveolar pressure falling below the critical closing pressure of alveolar units at the end of expiration, promoting atelectasis, and also causing alveolar injury due to cyclical closing and opening of alveolar units with ventilation. </li></ul>
    6. 6. Ventilator induced lung injury <ul><li>3. Biotrauma </li></ul><ul><ul><li>characterized by the release of inflammatory mediators from the injured lungs into the systemic circulation, can promote further lung injury and contribute to developement of multi-organ failure. </li></ul></ul><ul><ul><li>May explain why the mortality of ARDS remains high ( about 50%), as most patients die of multi-organ failure than respiratory failure </li></ul></ul>
    7. 7. Lung Protective Ventilator Strategies <ul><li>Goal </li></ul><ul><ul><li>Avoid extension of lung injury </li></ul></ul><ul><ul><li>Minimize oxygen toxicity </li></ul></ul><ul><ul><li>Minimize peak airway pressure </li></ul></ul><ul><ul><li>Recruit alveoli </li></ul></ul><ul><ul><li>Prevent atelectasis </li></ul></ul><ul><ul><li>Uses sedation and paralysis judiciously </li></ul></ul>ARDS Network
    8. 8. 1. Permissive Hypoxemia 2. Low Tidal Ventilation and Permissive Hypercapnia 3. Positive End-Expiratory Pressure (PEEP) 4. Prone ventilation 5. Lung recruitment maneuvers (LRM) 6. Pressure controlled Inverse Ratio Ventilation (PC-IRV) Lung Protective Ventilator Strategies
    9. 9. How much FiO2? <ul><li>There is no clinical evidence to support the use of specific FiO 2 </li></ul><ul><li>FiO2 of 0.6 or less is usually considered to be safe to get PaO2 60 mmHg </li></ul><ul><li>However, the diseased lungs, in ARDS, may be more susceptible to oxygen toxicity at a relatively low FiO2 </li></ul>Am Rev Respir Dis 1981;123:98-103
    10. 10. How much Tidal volume? ARDS Network
    11. 11. How much Tidal volume? ARDS Network <ul><li>Low tidal volume -31% </li></ul><ul><li>(6 mL/kg predicted body weight) </li></ul><ul><li>Conventional tidal volume -40% </li></ul><ul><li>(12 mL/kg) </li></ul><ul><li>Low TV not improved PaO2 </li></ul><ul><li>Mortality in High TV did not result from hypoxemia but from multiorganfailure. </li></ul>Mortality
    12. 12. Lower PEEP/Higher FiO 2 FiO 2 .3 .4 .4 .5 .5 .6 .7 .7 .7 .8 .9 .9 .9 1.0 PEEP 5 5 8 8 10 10 10 12 14 14 14 16 18 18-24 Higher PEEP/Lower FiO 2 FiO 2 .3 .3 .4 .4 .5 .5 .5-.8 .8 .9 1.0 PEEP 12 14 14 16 16 18 20 22 22 22-24 Target enrollment- 750 ALI, ARDS pts.
    13. 13. Results <ul><li>Trial stopped @ the 2 nd interim analysis after 549 pts. Had been enrolled. </li></ul><ul><li>Stopped based on the specified futility stopping rule. </li></ul><ul><li>Surprising Results </li></ul>ESSENTIALLY NO DIFFERENCE IN OUTCOMES (MORTALITY)
    14. 14. Prone position ventilation <ul><li>Improve oxygenation </li></ul><ul><ul><li>Better FRC </li></ul></ul><ul><ul><li>Recruitment of dorsal lung </li></ul></ul><ul><ul><li>Better clearance of secretion </li></ul></ul><ul><ul><li>Better ventilation-perfusion matching </li></ul></ul><ul><li>Potential problems </li></ul><ul><ul><li>facial oedema, eye damage </li></ul></ul><ul><ul><li>dislodgment of endotracheal tubes and intravascular catheters </li></ul></ul><ul><ul><li>Difficulty in resuscitation </li></ul></ul>No differences in clinical outcome
    15. 16. P aO2 : How Low can You Go ?
    16. 17. Severe hypoxemia without evidence of tissue hypoxia in adult respiratory distress syndrome. Lund T , Koller ME , Kofstad J . A patient with severe arterial hypoxemia in adult respiratory distress syndrome (ARDS) secondary to a fractured femur is reported. A marked discrepancy between the clinical condition and laboratory findings was observed. At one point, PaO2 was below 4 kPa (30 mm Hg) on F1O2 0.21 without signs of tissue hypoxia. This patient illustrates beneficial effects of a leftward shift of the oxyhemoglobin dissociation curve. Crit Care Med. 1984 Jan;12(1):75-6.
    17. 18. How harmful is hypoxemia? <ul><li>Unclear </li></ul><ul><li>Rare cause of death in A RDS </li></ul>Your pO2 and SO2 here is ??
    18. 19. How harmful is hypoxemia? <ul><li>Unclear </li></ul><ul><li>Rare cause of death in ARDS </li></ul>Your pO2 and SO2 here is 30 and 78% <ul><ul><li>↑ FIO2 (but this increases risk of oxygen toxicity). </li></ul></ul><ul><ul><li>Increase PEEP and TV (but this increases risk of barotrauma). </li></ul></ul>
    19. 20. What levels of PaO 2 can be targeted? <ul><li>What specific levels of PaO 2 can be targeted in patients is not known. </li></ul><ul><li>PaO 2 values from 60 to 75 mm Hg could be used in most patients unless they had limited cardiac reserve and/or central nervous system disease. </li></ul><ul><li>Values of PaO 2 between 50 and 60 mm Hg could be contemplated in young patients who were previously healthy and who have relatively normal hemoglobin levels. </li></ul><ul><li>Finally, levels of PaO 2 between 40 and 50 mm Hg may be tolerated in some patients but are clearly not desirable. </li></ul>Suter P. Program and abstracts of the 15th Annual Congress of the European Society of Intensive Care Medicine; September 29-October 2, 2002; Barcelona, Spain.
    20. 21. <ul><li>The key question that has to be asked if one is considering targeting lower levels of PaO 2 is the clinical &quot;price&quot; one has to pay to increase the PaO 2 . </li></ul><ul><li>These include the detrimental effects of high inspired FiO 2 , the potential effects of VILI, and the detrimental hemodynamic consequences of high mean airway pressures. </li></ul><ul><li>T here are no guidelines that are currently available that address the specific low levels of PaO2 that are tolerable . </li></ul>What levels of PaO 2 can be targeted? Suter P. Program and abstracts of the 15th Annual Congress of the European Society of Intensive Care Medicine; September 29-October 2, 2002; Barcelona, Spain.
    21. 22. <ul><li>Most intensive care practitioners aim to maintain PaO2 between 8 and 10kPa (or 60 – 80 mm Hg). Although direct evidence is lacking, these levels do not lead to tissue hypoxia unless tissue perfusion is compromised by hypovolemia or hypotension. </li></ul><ul><li>The only exception to this rule is the management of patients with severe head injuries. For these patients, provided cerebral perfusion is maintained, a PaO2 of 10kPa is sufficient. </li></ul>What levels of PaO 2 can be targeted? ITACCS GUIDELINES FOR MANAGEMENT OF MECHANICAL VENTILATION IN CRITICALLY INJURED PATIENTS
    22. 23. Oxygen Dissociation Curve ARDSnet Study 88-94% PaO2 55-80
    23. 24. Tissue Oxygenation <ul><li>Reflects the balance between DO2 and VO2 </li></ul><ul><li>Determined by : </li></ul><ul><ul><li>CO, Hb, SaO2 </li></ul></ul><ul><ul><li>Oxygen affinity of Hb </li></ul></ul><ul><ul><li>Oxygen demand </li></ul></ul><ul><ul><li>Lactate level </li></ul></ul><ul><ul><li>SvO2 </li></ul></ul><ul><li>Permissive hypoxemia is not accompanied by tissue hypoxia </li></ul>
    24. 25. Maintaining Tissue Oxygenation <ul><li>Normalized Oxygen Delivery : </li></ul><ul><ul><li>Cardiac Output </li></ul></ul><ul><ul><li>Hemoglobin concentration </li></ul></ul><ul><li>Minimized oxygen consumption : </li></ul><ul><ul><li>Sedation </li></ul></ul><ul><ul><li>Analgesia </li></ul></ul><ul><ul><li>Mscle paralysis </li></ul></ul>
    25. 26. OXYGEN EXTRACTION VO 2 = Q x Hb X 13.4 X (SaO 2 - SvO 2 ) Arterial Inflow (Q) capillary O 2 O 2 O 2 O 2 O 2 O 2 O 2 Venous Outflow (Q) C ell O 2 (Adapted from the ICU Book by P. Marino)
    26. 27. OXYGEN DELIVERY DO 2 = Q X CaO 2 DO 2 = Q X (1.34 X Hb X SaO 2 ) X 10 Q = cardiac output CaO 2 = arterial oxygen content Normal DO 2 : 520-570 ml/min/m 2 Oxygen extraction ratio = (SaO 2 -SvO 2 /SaO 2 ) X 100 Normal O 2 ER = 20-30%
    27. 28. HEMODYNAMIC SUPPORT Max O 2 extraction Critical DO 2 Abnormal Flow Dependency DO 2 VO 2 Septic Shock/ARDS Max O 2 extraction Critical DO 2 VO 2 = DO 2 X O 2 ER DO 2 VO 2 Normal
    28. 29. Protective lung ventilation protocol from the ARDSNet study <ul><li>Initial tidal volume – 6ml/kg </li></ul><ul><li>Plat. Pressure <30cm H 2 0 </li></ul><ul><li>Oxygenation goal PaO 2 = 55 - 80 mmHg or pulse oximetry oxygen saturation 88–95% </li></ul><ul><li>I:E ratio 1:1–1:3 </li></ul><ul><li>Goal arterial pH = 7.30–7.40  </li></ul><ul><ul><li>If pH < 7.30, increase respiratory rate up to 35 breaths/min  </li></ul></ul><ul><ul><li>If pH < 7.30 and respiratory rate = 35, consider starting intravenous bicarbonate </li></ul></ul>
    29. 30. Summary <ul><li>Low PaO2 in critically ill patients is frequent. </li></ul><ul><li>A PaO 2 value between 50 and 70 mm Hg is likely appropriate for most patients. </li></ul><ul><li>In ARDS, PaO2 : How low can you go, depend on how to maintaining adequate tissue oxygenation rather than SaO2 and reduced incidence of VILI </li></ul><ul><li>Vital organ function and the patient's clinical course are good indicators of tolerance to hypoxemia. </li></ul>

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