1. Mechanical ventilation in special situations-ARDS
Ashraf Al Tarifi, MD,FCCP
Consultant Intensivist and Pulmonologist
KFSH&RC-Riyadh
Al Khortoum
April 19, 2013

2. Case summary
45 year old male patient admitted with pancreatitis secondary to biliary disease.
C/O SOB one day after admission
Found to have Pulse oximetry of 70% on RA
Placed on NRM –sat improved to 92%

5. HISTORICAL PERSPECTIVES
Described by William Osler in the 1800’s
Ashbaugh, Bigelow and Petty, Lancet – 1967
12 patients
pathology similar to hyaline membrane disease in neonates

6. REVISION OF DEFINITIONS
1988: four-point lung injury score
Level of PEEP
PaO2 / FiO2 ratio
Static lung compliance
Degree of chest infiltrates
1994: consensus conference simplified the definition

7. American-European Consensus Conference (AECC) Definition of ARDS
Risk factors, 3 criteria are required:
Radiological
Exclusion
Oxygenation
Bernard et al. Am J Respir Crit Care Med 1994;149:

8. 1994-ARDS Definition (American European consensus)
ARDS defined as
Acute onset bilateral infiltrates
PaO2:FiO2 < 200
No evidence Left heart failure
Pcwp < 18
Clinical features
Refractory hypoxemia
Reduced compliance

9. The Berlin Definition of ARDS May 2012
Timing
Within 1 week of a known clinical insult or new or worsening respiratory symptoms
Chest imaging
Bilateral opacities—not fully explained by effusions, lobar/lung collapse, or nodules
Origin of edema
Respiratory failure not fully explained by cardiac failure or fluid overload. Need objective assessment (eg, echocardiography) to exclude hydrostatic edema if no risk factor present
Oxygenation (with PEEP > 5 cm H2O)
Mild
PaO2/FIO2
mm Hg
Moderate
mm Hg
Severe
<100 mm Hg
JAMA. 2012;307(23) Published online May 21, 2012

10. The Berlin Definition of ARDS- May 2012
Timing
Within 1 week of a known clinical insult or new or worsening respiratory symptoms
Chest imaging
Bilateral opacities—not fully explained by effusions, lobar/lung collapse, or nodules
Origin of edema
Respiratory failure not fully explained by cardiac failure or fluid overload. Need objective assessment (eg, echocardiography) to exclude hydrostatic edema if no risk factor present
Oxygenation (with PEEP > 5 cm H2O)
Mild
PaO2/FIO2
mm Hg
Moderate
mm Hg
Severe
<100 mm Hg
JAMA. 2012;307(23) Published online May 21, 2012

11. Berlin 2012 Definition of ARDS
Mild 22%
Moderate 50%
Severe 28%
ARDS 4%
14%
29%

12. Case summary
45 year old male patient admitted with pancreatitis secondary to biliary disease.
C/O SOB one day after admission
Found to have Pulse oximetry of 70% on RA
Placed on NRM –sat improved to 92%
Patient intubated and ventilated-sat 88%

14. Pt intubated and mechanically ventilated
Initial settings
PCV
FIO2 100%
Tv 550 ml
RR 20
PEEP 5
Peak airway pressure 36
Initial ABG
PH 7.33
PCO2 40 (5.1 Kpa)
PO2 57 (7.2 Kpa)
HCO3 20
Saturation 88%
What would you do next

15. Factors Influencing Oxygenation
FIO2
Mean Airway pressure
Inspiratory Time (I:E ratio)
PEEP

16. Vent settings to improve oxygenation: FIO2
Always start at 100% even if patient was not hypoxemic prior to intubation
Patient might have Rt mainstem intubation
Pneumothorax secondary to high pressures during bagging
Use continuous pulse oximetry if available or check arterial blood gases
Once ETT position confirmed and oxygenation stable start weaning FIO2 to keep sat > 92-94%

17. Permissive Hypoxemia – How Low Can We Accept?
92-96%
88-92%
86-88%
82-86%
78-82%
Respir Care Nov;55(11):

18. Positive end expiratory pressure -PEEP
reduces shunt by recruiting partially collapsed alveoli

19. PEEP

21. ARDS
-10 10

22. ARDS after PEEP

23. Immediately post intubation

24. PEEP 15

25. The PEEP Effect (recruit-Derecruit)
NEJM 2006;354:

26. Higher Vs lower PEEP in ARDS
ARDSNet ALVEOLI study
Assessment of Low tidal Volume and elevated End-expiratory volume to Obviate Lung Injury
6 ml/kg PBW tidal volumes
Plateau pressure limit of 30 cm H2O
High PEEP/low FiO2 protocol vs. Low PEEP/high FiO2
N = 549 patients with ALI/ARDS
Average PEEP 8.3 Vs 13.3
No survival benefit
The National Heart, Lung, and Blood Institute ARDS Clinical Trials Network. N Engl J Med 2004;351:

27. How much PEEP is enough? ARDSnet protocol: PEEP - FiO2 Combinations
GOAL: PaO mm Hg or SpO %
Use these FiO2/PEEP combinations to achieve oxygenation goal.
FIO2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
PEEP 5 8 10 12 14 16 18
20-24
New Eng J Med. 2000;342(18)

28. So, PEEP titrated to 12 cm H2O
Current settings
PCV
FIO2 100%
Tv 550 ml
RR 24
PEEP 12
Peak airway pressure 35
ABG
PH 7.32
PCO2 48
PO2 75
HCO3 22
Saturation 95%
What would you do next

29. Ventilator-Induced lung injury (VILI)
Volutrauma
Overdistention
Atelectetrauma
Repeated recruitment and collapse
Bio trauma
Inflammatory mediators
Barotrauma
High-pressure induced lung damage
Oxygen toxic effect
FiO2 29

30. The Problem of Heterogeneity in ARDS
-10 10

31. The Problem of Heterogeneity Especially in ARDS
Some lung units may be overstretched while others remain collapsed at the same airway pressure.
Finding the right balance of TV and PEEP to keep the lung open without generating high pressures is the goal.
This presents major difficulty for the clinician, who must apply only a single pressure to ventilate patients

32. Ventilator-induced Lung Injury (VILI)
Collapse
Over
Distension

33. Ventilator-Induced Lung Injury Atelectotrauma Vs Volutrauma
Atelectrauma:
Repetitive alveolar collapse and reopening of the under-recruited alveoli
Volutrauma:
Over-distension of normally aerated alveoli due to excessive volume delivery
Dreyfuss: J Appl Physiol 1992 33

34. Mechanisms of Airspace Injury
Airway Trauma
“Stretch”
“Shear”

35. ARDS
-10 10

36. ARDS after PEEP Preventing Atelectotrauma

37. Ventilator-induced Lung Injury (VILI)
Barotrauma
Volutrauma
Atelectrauma
Biotrauma
Over
Distension
Collapse

38. Baro-trauma Etiology :Directly related to airway pressures/PEEP
Incidence
4% - 15%
Highest in ARDS
Incidence now decreased secondary to lung protective ventilation

39. Barotrauma-Pathophysiology
Some alveoli become more distended than others. Alveolar pressure increases and forms a pressure gradient between the alveoli and adjacent perivascular sheath.
Air dissects into the perivascular sheath leading to perivascular interstitial emphysema (PIE) and further moves into areas of least resistance including subcutaneous tissue and tissue planes.

40. Barotrauma-Complications
Pneumothorax
Interstitial emphysema
Pneumomediastinum-leads to PTX in 42% of patients in one study
Pneumopericardium
Subcutaneous emphysema
Pneumoperitoneum

41. Gas Extravasation

42. Barotrauma

44. Oxygen Toxicity : FIO2 > 60 % for > 24h
Absorptive atelectasis
O2/N2 = 21/79 >>>>>> 50/50
Oxygen
Carbon dioxide
Water Vapour
Nitrogen

45. Hyperoxia toxicity: mechanism
Free radicals: lipid peroxidations, especially in the cell membranes, inhibit nucleic acids and protein synthesis, and inactivate cellular enzymes.
Explosive free radical production leading to swamping of the anti-oxidant enzyme systems and as a result free radicals escape inactivation.

46. ARDSnet
NIH NHLBI ARDS Clinical Trials Network

47. Lung-Protective Ventilation
ARDS Network, 2000: Multicenter, randomized 861 patients
Lung-protective ventilation
Conventional ventilation
Tidal Volume (ml/kg) 6 12
Pplateau
<30
<50
PEEP
Protocol
Actual PEEP
8.1
9.1
Result (p<0.001)
31.0%
39.8%
用的是預期體重
Principle for FiO2 and PEEP Adjustment
FiO2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
PEEP 5
5-8
8-10 10
10-14 14
14-18
18-24
NEJM 2000; 342:

48. Lower Tidal Volume and Pplat < 30 Mortality Before Hospital Discharge10 20 30 40 50
Mortality
(Percent)
P=0.0054
ARDS Network NEJM 342: , 2000
6 ml/kg
12 ml/kg

49. NIH ARDS Network Trial Mechanical Ventilation in ARDS
31% mortality
40% mortality

50. Lung-Protective Ventilation
Result:
Lower 22% mortality (31% vs 39.8%)
Increase ventilator-free days
NEJM 2000; 342:

51. Median # Ventilator-Free Days
ARDSnet

52. Median Organ Failure Free Days
NEJM 2000;342:1301-8
P = 0.004
P = 0.004
P = 0.005
= 6 ml/kg
= 12 ml/kg

53. Effect of 45 cmH2O PIP Control 5 min 20 min
Malhotra A. N Engl J Med 2007;357:

54. Back to our patient
Protective lung strategy applied, so tidal volume was decreased to 420 ml (6ml/kg IBW)
(Height-152 )x males
(Height-152 )x females
Current settings
PCV
FIO2 100%
RR 32
PEEP
PIP 28
ABG
pH 7.21
PCO2 65
PO2 71
HCO3 25
Saturation 92%
What would you do next

55. Permissive Hypercapnia
Low Vt (6ml/kg) to prevent over-distention
Increase respiratory rate to avoid very high level of hypercapnia
PaCO2 allowed to rise
Usually well tolerated-May be beneficial
Potential Problems: tissue acidosis, autonomic dysregulation, CNS effect, and circulatory effects
May need to start Bicarb infusion till the kidney starts to compensate (2-3 days)

56. Permissive Hypercapnia – When would you NOT do it?
Renal failure
High intracranial pressures
Cardiovascular problems/Arrhythmia

57. Back to our patient What would you do next
Protective lung strategy done, so tidal volume was decreased to 420 ml (6ml/kg IBW)
(Height-152 )x males
(Height-152 )x females
Current settings
PCV
FIO2 100%
RR 32
PEEP 12
PIP 28
ABG
pH 7.21
PCO2 65
PO2 57
HCO3 25
Saturation 88%
What would you do next

58. Paralysis improves oxygenation
Critical Care Med Jan;32(1):113-9

59. Paralysis in Early ARDS
Papazian L et al. N Engl J Med 2010;363:

60. Paralysis The reason why is unclear  recruitment  SvO2 by  VO2
 compliance
Anti-inflammatory
The effect is highly variable
Paralytics increase risk for delayed neuromuscular complications especially when given with steroids
- Monitor train-of-4 titrate to avoid over paralysis
Anaesth Intensive Care Apr;30(2):192-7.

61. ARDS Recruitment Maneuvers
Application of high airway pressure (35-40cmH2O) for approximately 40 seconds.
Most common methodology
40 cm H2O CPAP
40 seconds
Employed to open atelectatic alveolar units that occur with ARDS and particularly with any disconnection from ventilator
If successful, PaO2 will increase by 20% or more.
Must use PEEP after procedure to keep recruited alveoli open.

62. ARDSnet protocol Vs open lung protocol
Tv 6 ml/kg
Plateau pressure <30
Conventional PEEP (titrate for FIO2 <0.6)
Experimental protocol
Tv 6 ml/kg
Plateau pressure <40
Recruitment maneuvers
High PEEP (10-15)
JAMA, February 2008

63. ARDSnet protocol Vs open lung protocol

64. ARDSnet protocol Vs open lung protocol
JAMA, February 2008

65. Inhaled Nitric Oxide May be used as “rescue” therapy
Most ARDS/ALI patient may have mild to moderate pulmonary HTN
Improvement in oxygenation was small and not sustained
No change on mortality or duration of mechanical ventilation
Increased renal failure
May be used as “rescue” therapy

66. Fluid management in ARDS

67. Pathogenesis of Pulmonary Edema & ALI/ARDS
Alveolar edema fluid flooding
Alveolar edema fluid clearance

68. Low flow by exam or CI <2.5
MAP < 60
Low flow by exam or CI <2.5
Conservative fluid strategy
Furosemide
UOP < 0.5 ml/kg/h &
CVP or PAOP low
KIDNEY
CVP < 4
PAOP < 8
Favors
Dry
LUNG

69. Liberal fluid strategy
CI > 4.5
FiO2 > 0.7
LUNG
Favors
Perfused
KIDNEY
(organs)
CVP
PAOP 14-18

70. Ventilator free days to day 28
P=0.0002

71. ICU free days to day 28
P<0.001
Days

72. Prone ventilation – Takes the heart off the lungs
Supine
Ppl - - -
+ + +
Prone
Ppl -
Gattinoni L. et al.
Intens Care Med
1986; 92:137 +

73. Proning May Benefit the Most Seriously ill ARDS Subset
Supine
0.5
* p<0.05
Prone *
0.4
0.3
Mortality Rate
0.2
0.1
0.0
> 49
40- 49
31- 40
0 - 31
Quartiles of SAPS II
SAPS II

74. High Frequency Ventilation in ARDS-Harmful
Ferguson ND et al. N Engl J Med 2013;368:

75. Steroids in ARDS
To be answered in Debate session

76. Steroid therapy
Increase the number of ventilator-free and shock-free days during the first 28 day
Improve oxygenation, compliance and blood pressure
No increase in the rate of infectious complications
Higher rate of neuromuscular weakness
Routine use of steroid is not supported
Starting steroid more than 14 days after the onset of ARDS may increase mortality
NEJM 2006;354:

77. The P’s of refractory hypoxemia
PEEP
Pee (diuresis)
Prone
Paralysis
Pleural evacuation
Prostacyclin (or iNO)
More PEEP

78. Take home messages
Take ARDS seriously-it kills about patients per year in the US
Use lower Tv (6ml/kg IBW) to keep plateau pressure <30
Permissive hypercapnea is safe and well tolerated
Use enough PEEP to recruit lungs
Keep lungs dry

79. Use ventilators safely!
normal
lungs
5 min of
45 cm H2O
20 min of
45 cm H2O
Dreyfuss, Am J Respir Crit Care Med 1998;157: