Pa co2 and alveolar dead space are more relevant

1,277 views

Published on

0 Comments
2 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
1,277
On SlideShare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
26
Comments
0
Likes
2
Embeds 0
No embeds

No notes for slide

Pa co2 and alveolar dead space are more relevant

  1. 1. PaCO2 and alveolar dead space are more relevant than PF ratio in monitoring the respiratory response to prone position in ARDS patients 學生: 黃菁鳳 指導老師: 林鳳卿 老師 施玫如 老師 日期: 2014/03/12
  2. 2. Outline  Introduction  Material and Methods  Results and Discussion  Conclusion  Limitation  Q&A
  3. 3. Introduction
  4. 4. Acute respiratory distress syndrome (ARDS)  Baby lung : Since its first description in 1967, it has been accepted that ARDS includes a number of lung injuries of various origins whose consequences are decreased lung capacity and thus limit the ventilation ability.  Positive end-expiratory pressure (PEEP) is to restore the functional residual capacity.  A Considerable progress has been made over the past decade in the ventilatory management of patients with ARDS.
  5. 5. Prone Position  Improve oxygenation by relieving atelectasis and improving perfusion.. Recruitment and restore FRC , and improve diaphragm movement.  Reduction of alveolar dead space.  Improve V/Q Matching  Improve survival in severe ARDS (P/F Ratio <100 mmHg) .Define the outcome by increasing P/F Ratio> 20 mmHg after 1 to 6 hours. (2010 Sud et al)
  6. 6.  Anatomical dead space (In Conducting airways: about 150mL in an average adult or 2.2mLs/kg )  Physiological dead space  Alveolar dead space  Apparatus dead space Dead-space ventilation (VD)
  7. 7. Physiologic dead space  Part of the tidal volume which does not participate in gas exchange.  The quantity of CO2 exhaled from the healthy alveoli will be diluted by anatomical dead space and alveoli with no perfusion.  Measure expiratory mixed gas By collecting the exhaled breath in a gas impermeant bag ( Douglas bag)
  8. 8. Alveolar dead space  When the poorly perfused alveoli empty at the same rate as the normal alveoli, it is possible to measure the alveolar dead space.  ETCO2 represents the partial pressure or maximal concentration of CO2 at the end of exhalation
  9. 9. ETCO2 Monitoring  The end-tidal sample of gas (measured by capnography)  Determinants of ETCO2 are: (1) alveolar ventilation, (2) pulmonary perfusion (cardiac output) and (3) CO2 production. Reference: Paramedicine.com
  10. 10. Reference: Paramedicine.com
  11. 11. Ventilated area which do not participate in gas exchange. Reference: Paramedicine.com
  12. 12. Bohr's equation (Based on :all expired CO2 comes from alveolar gas) PECO2 PetCO2
  13. 13. Objective 1  Prone Position allows recruitment of a slow compartment previously excluded from ventilations.  Associated with a decrease in PaCO2→ an indirect reflection of the reduction of the alveolar dead space (VDalv).  VDalv appears to be an independent risk factor for mortality in patients with ARDS . (Nuckton TJ et al. Pulmonary dead-space fraction as a risk factor for death in the acute respiratory distress syndrome. N Engl J Med 2002. )
  14. 14. Objective 2  Siddiki et al used to evaluate he physiological dead space fraction (VDphysiol/VT) by using a rearranged alveolar gas equation for PaCO2 without any expired CO2 measurement.(2010 ).
  15. 15. Purpose 1) Changes in PaCO2 and VDalv might be more relevant than changes in PaO2 in defining the respiratory response to Prone Postion. 2) To validate the method of evaluation of the estimate VDphysiol/VT .
  16. 16. Material and Methods
  17. 17. Inclusion  15 patients.  January 2008 to March2010  Criteria of Acute Respiratory Distress Syndrome Network.  PaO2/FiO2 ratio < 100mmHg after 24 to 48 hours of mechanical ventilation.  Hemodynamic stability: systolic blood pressure> 90 mmHg with norepinephrine < 0.5 μg/kg/minute. Exclusion  COPD ( 2 patients will be excluded ) Material & Methods
  18. 18. Material & Methods  Ventilated in volume-controlled mode (Servo-i)  Ventilator setting : • VT of 6 to 8 mL/kg IBW • I: E =1:2 (Hypercapnia without generating intrinsic PEEP) • End inspiratory pause of 0.5 seconds. (Pplat < 30 cmH2O)  First session of Prone Position.  Blood gas analysis, Pplat, total PEEP, end-tidal CO2(PetCO2) ,mixed expired CO2 (PECO2) just before turning the patient to the PP, every 3 hours in the PP until 15 hours.
  19. 19.  Expired CO2 was measured by capnometer positioned between the proximal end of the endotracheal tube and the Y piece of the ventilator circuit(COSMO; Novametrix, Wallingford, CT, USA). Material & Methods Reference: Egan’s Ch18
  20. 20. Material & Methods  Bohr's method 1. VDalv/VT = 1 - PetCO2/PaCO2 2. VDphysiol/VT = 1 - PECO2/PaCO2.  The estimated VDphysiol/VT : 1 -[(0.86 × VCO2est)/(VE × PaCO2)] (VCO2est :CO2 production calculated by Harris-Benedict equation.)
  21. 21.  Responders to Prone Position were defined in 1. An increase in PaO2/FiO2 ratio >20 mmHg after 15 hours of Prone Position. 2. A decrease in PaCO2 > 2 mmHg after 15 hours of Prone Position. Material & Methods
  22. 22. Result and Discussion
  23. 23. Table 1 Respiratory parameters and blood gas analysis at inclusion. 15Patients 13Patients APACH II:62 SOFA: 11 H1N1/Pneumonia 2COPD
  24. 24. Table 2 Changes in respiratory mechanics, blood gas analysis and VDalv in PP
  25. 25. Mancebo et al 2006 Charron C et al 2011 This study 76/138 prone patients 57/218 prone patients Over 20 hours/day decrease mortality rate. Over 18 hours / day increase survival rate. The maximum effect of VDalv, PaCO2, Pplat show after 6 to 9 hours. Compare to previous study
  26. 26. Table 3 Changes in respiratory mechanics, blood gas analysis and VDalv in PaO2 responders (n = 7) and PaO2 nonresponders (n = 6)
  27. 27. Figure 1 Alterations during PP in PaO2/FiO2, PaCO2, plateau pressure (Pplat) and alveolar dead space (VDalv/VT) in responders and nonresponders (dotted lines) according to PaO2/FiO2 changes.
  28. 28. Table 4 Changes in respiratory mechanics, blood gas analysis and VDalv in PaCO2 responders (n = 7) and PaCO2 nonresponders (n = 6) Compare to PO2 response group
  29. 29. Figure 2 Alterations during PP in PaO2/FiO2, PaCO2, plateau pressure (Pplat) and alveolar dead space (VDalv/VT) in responders and nonresponders according to PaCO2 changes.
  30. 30.  Correlation between (ΔVDalv/VT) and (ΔCrs)  Correlation between (ΔVDalv/VT) and (ΔPaO2/FiO2) R=o.oo6 p=o.95 R=o.29 p=o.03
  31. 31. Compare to previous study Gattinoni et al 2003 Protti A et al 2009 225Patients 32Patients Result • ↓PaCO2≥1 mmHg is predictive of the patient’s prognosis then ↑P/F Ratio > 20 mmHg . • Study show an increased survival at 28 days. • Reason: Improved the efficiency of alveolar ventilation (decreased physiologic deadspace ratio) PaCO2 variation is associated with lung recruitability instead of PaO2/FiO2. (by CT)
  32. 32. Figure 4: Comparison between measured VDphysiol/VT and estimated VDphysiol/VT Comparison for each paired data set (n = 78) in the supine position and after 3, 6, 9, 12 and 15 hours in the prone position
  33. 33. Figure 4: Comparison between measured VDphysiol/VT and estimated VDphysiol/VT
  34. 34. Based on linear correlation R~0.435 R~0.529  Estimated VDphysiol/VT using the Harris-Benedict equation systematically underestimated measured VDphysiol/VT (B).
  35. 35. Based on Bland and Altman representation  Estimated VDphysiol/VT using the Harris-Benedict equation systematically underestimated measured VDphysiol/VT(B).
  36. 36. Compare to previous study  Pelosi st al ,found not significant decrease in Vdphysiol . Pelosi st al 1998 This study Patients 16 13 Duration 120mins 15hrs. PEEP 12.3 cmH2O 6 cmH2O PaCO2 ↓ ↓ VD physiol x ↓ Did not compare with the measure VDphysicol Did Compare with the measute VDphysicol Protti A et al 2009 PEEP: 13 cmH2O
  37. 37. Conclusion
  38. 38. 2. Defining the respiratory response to prone appeared more relevant when using PaCO2 changes rather than PaO2/FiO2 changes. 3. Estimated VDphysiol/VT ratios systematically underestimated measured VDphysiol/VT ratios. 1. Prone position induced a decrease in VDalv/VT, which was correlated with an improvement in respiratory mechanics.
  39. 39. Limitation  Patients numbers.  The prone duration and initial time relate to the consequence  Is the measurement necessary ? How this may affect management at bedside still remain to be studied.  Define the sensitivity of PaCO2 and PaO2 .  Limited treatments.  The limitation of the sensor: secretions and humidity effect the clearance and the accuracy of the measure value.
  40. 40. Q&A
  41. 41. Thank you.

×