This document provides an overview of acute respiratory distress syndrome (ARDS). It begins with a definition and history of ARDS, describing the criteria and epidemiology. It then discusses the clinical disorders and lung injuries that can cause ARDS in children. The pathogenesis and pathophysiology of ARDS are explained in detail, including the roles of endothelial injury, mediators, diminished surfactant activity, reduced lung volumes, and altered pulmonary hemodynamics. Clinical phases and outcomes of ARDS are reviewed. Various therapies for ARDS are presented, such as mechanical ventilation strategies, prone positioning, high frequency oscillation, extracorporeal membrane oxygenation, surfactant, steroids, inhaled nitric oxide, and partial liquid ventilation.

1. Chapter 7: Acute
Respiratory Distress
Syndrome
James D. Fortenberry, MD, FCCM, FAAP
Medical Director, Critical Care Medicine and
Pediatric/Adult ECMO
Children’s Healthcare of Atlanta at Egleston

2. ARDS: What Is It?
Term first introduced in 1967
Acute respiratory failure with non-cardiogenic
pulmonary edema, capillary leak after diverse insult
Adult RDS defined to differentiate from neonatal
surfactant deficiency
Problems with definition troubled literature
Murray score 1988: CXR, PEEP, Hypoxemia,
Compliance
Synonyms
 Shock lung
 Da Nang Lung
 Traumatic wet lung

3. New and Improved
Adult Respiratory Distress
Syndrome
Acute Respiratory Distress
Syndrome

4. ARDS: New Definition
Criteria
 Acute onset
 Bilateral CXR infiltrates
 PA pressure < 18 mm Hg
 Classification
Acute lung injury - PaO2 : F1O2 < 300
Acute respiratory distress syndrome -
PaO2 : F1O2 < 200
- 1994 American - European
Consensus Conference

5. ARDS - Epidemiology
New criteria allow better estimate of
incidence
• 1994 criteria in Sweden: ALI
17.9/100,000; 13.5/100,000 ARDS
• US: may be closer to 75/1000,000
• Prospective data pending
• Incidence in children appears similar
• 5-9% of PICU admissions

6. Clinical Disorders Associated with ARDS
Direct Lung Injury Indirect Lung Injury
Common causes Common Causes
Pneumonia Sepsis
Aspiration of gastric
contents
Severe trauma with shock ,
multiple transfusions
Less common causes Less common causes
Pulmonary contusion Cardiopulmonary bypass
Fat emboli Drug overdose
Near-Drowning Acute pancreatitis
Inhalational injury Transfusions of blood products
Reperfusion pulmonary
edema

7. The Problem: Lung Injury
Etiology In Children
Other 4%
Hemorrhage 5%
Trauma 5%
Non-infectious Pneumonia
14%
Cardiac Arrest 12%
Septic Syndrome 32%
Infectious Pneumonia 28%
Davis et al., J Peds 1993;123:35

8. ARDS - Pathogenesis
Instigation
• Endothelial injury: increased
permeability of alveolar - capillary
barrier
• Epithelial injury : alveolar flood, loss
of surfactant, barrier vs. infection
• Pro-inflammatory mechanisms

9. ARDS Pathogenesis: Resolution Phase
Equally important
• Alveolar edema - resolved by active
sodium transport
• Alveolar type II cells - re-
epithelialize
• Neutrophil clearance needed

11. ARDS - Pathophysiology
• Capillary leak:non-cardiogenic pulmonary
edema
• Inflammatory mediators
• Diminished surfactant activity and airway
collapse
• Reduced lung volumes
• Heterogeneous
• “Baby Lungs”
• Altered pulmonary hemodynamics

12. ARDS:CT Scan View

13. ARDS - Pathophysiology:
Diminished Surfactant Activity
• Surfactant production and composition
altered in ARDS: low lecithin-sphingomyelin
ratio
• Components of edema fluid may inactivate
surfactant

14. ARDS - Pathophysiology:
Diminished Surfactant Activity
• Surfactant product of Type II pneumocytes
• Importance of surfactant:
 P = 2T/r (Laplace equation; P: trans-
pulmonary pressure, T: surface tension,
r: radius)
• Surfactant proportions surface tension to
surface area: thus

17. ARDS - Pathophysiology: Lung
Volumes
• Reduced lung volumes, primarily reduced FRC
• FRC = ? Nl =
• Low FRC-large intrapulmonary shunt, hypoxemia
• Implies
 lower compliance = flatter PV curve
 marked hysteresis
 PV curve concave above FRC and inflection point
at volume > FRC
 closing volume in range of tidal volume
 resistance increased primarily due to mechanical
unevenness (vs. airway R): high flow rates
helpful

21. ARDS - Pathophysiology: Lung
Volumes
• FRC = Volume of gas in lungs at end of
normal tidal expiration; outward recoil of
chest wall = inward recoil of lungs
• Normal FRC =
• FRC decreased by 20-40% in ARDS
• FRC decreased by 20-30% when supine:
elevate head!

22. ARDS - Pathophysiology:
Mediators
• Massive literature
• Mediators involved but extent of
cause/effect unknown
• Cellular:
 neutrophils-causative: depletion in models
can obliterate lesion; ARDS can occur in
neutropenic patient; direct endothelial
injury, release radicals, proteolytic
enzymes
 macrophages-release cytokines

23. ARDS - Pathophysiology:
Mediators
• Humoral:
 Complement
 Cytokines: TNF, IL-1
 PAF, PGs, leukotrienes
 NO
 Coagulant pathways

24. ARDS - Pathophysiology:Pulmonary
Edema
• Non-cardiogenic pulmonary edema-
Starling formula
• What changes in ARDS?
 Q = K(Pc - Pis) - σ (Πpl - Πis)
Q =
K =
Pc = ; Pis =
σ =
Πpl = ; Πis =

26. Phases of ARDS
• Acute - exudative, inflammatory: capillary
congestion, neutrophil aggregation, capillary
endothelial swelling, epithelial injury; hyaline
membranes by 72 hours
(0 - 3 days)
• Sub-acute - proliferative: proliferation of type II
pneumocytes (abnormal lamellar bodies with
decreased surfactant), fibroblasts-intra-alveolar,
widening of septae
(4 - 10 days)
• Chronic - fibrosing alveolitis: remodeling by
collagenous tissue, arterial thickening, obliteration
of pre-capillary vessels; cystic lesions
( > 10 days)

28. ARDS - Outcomes
• Most studies - mortality 40% to 60%;
similar for children/adults
• Death is usually due to sepsis/MODS
rather than primary respiratory
• Mortality may be decreasing
53/68 % 39/36 %

29. ARDS - Principles of Therapy
• Provide adequate gas
exchange
• Avoid secondary injury

31. Therapies for ARDS
Innovations:
NO
PLV
Proning
Surfactant
Anti-
Inflammatory
Mechanical
Ventilation Gentle ventilation:
Permissive
hypercapnia
Low tidal volume
Open-lung
HFOV
ECMO
IVOX
IV gas
exchange
AVCO2R
Total
Implantable
Artificial Lung
ARDS
Extrapulmonary Gas Exchange

32. The Dangers of Overdistention
• Repetitive shear stress
• Injury to normal alveoli
• inflammatory response
• air trapping
• Phasic volume swings: volume trauma

33. • compliance
• intrapulmonary shunt
• FiO2
• WOB
• inflammatory response
The Dangers of Atelectasis

34. 0
10
20
13 33 38
Airway Pressure (cmH20)
LungVolume(ml/kg)
AtelectasisAtelectasis
““Sweet Spot”Sweet Spot”
OverdistentionOverdistention
Lung Injury Zones

35. ARDS: George H. W. Bush Therapy
“Kinder, gentler” forms of
ventilation:
•Low tidal volumes (6-8 vs.10-15
cc/kg)
•“Open lung”: Higher PEEP, lower
PIP
•Permissive hypercapnia: tolerate
higher pCO2

37. Lower Tidal Volumes for ARDS
• Multi-center trial, 861 adult ARDS
• Randomized:
Tidal volume 12 cc/kg
Plateau pressure < 50 cm H2O
vs
Tidal volume 6 cc/kg
Plateau pressure < 30 cm H2O
ARDS Network,
NEJM, 342: 2000

38. Lower Tidal Volumes for ARDS
0
5
10
15
20
25
30
35
40
Percent
Death
Ventfree
days
Traditional
Lower
*
*
* p < .001
ARDS Network,
NEJM, 342: 2000
22% decrease

39. Is turning the
ARDS patient
“prone” to be
helpful?

40. Prone Positioning in ARDS
• Theory: let gravity improve matching
perfusion to better ventilated areas
• Improvement immediate
• Uncertain effect on outcome

42. Prone Positioning in Adult ARDS
• Randomized trial
• Standard therapy vs. standard +
prone positioning
• Improved oxygenation
• No difference in mortality, time on
ventilator, complications
Gattinoni et al., NEJM, 2001

43. Prone Positioning in Pediatric ARDS:
Longer May Be Better
• Compared 6-10 hrs PP vs. 18-24 hrs
PP
• Overall ARDS survival 79% in 40 pts.
Relvas et al., Chest 2003

44. Brief vs. Prolonged Prone Positioning
in Children
0
5
10
15
20
25
Pre-PP Brief PP Prolonged PP
Oxygenation
Index(OI)
- Relvas et al., Chest 2003
*
*
**

45. High FrequencyHigh Frequency
Oscillation:Oscillation:
A Whole LottaA Whole Lotta
Shakin’ Goin’ OnShakin’ Goin’ On

46. - Reese Clark- Reese Clark
It’s not absolute pressure,
but volume or pressure
swings that promote lung
injury or atelectasis.

47. • Rapid rate
• Low tidal volume
• Maintain open lung
• Minimal volume swings
High Frequency Ventilation

48. High Frequency Oscillatory Ventilation

50. HFOV is the easiest way to
find the ventilation
“sweet spot”

51. HFOV: Benefits Vs. Conventional
Ventilation

52. HFOV vs. CMV in Pediatric
Respiratory Failure: Results
• Greater survival without severe lung
disease
• Greater crossover to HFOV and
improvement
• Failure to respond to HFOV strong
predictor of death
Arnold et al, CCM, 1994

53. 0
20
40
HFOV CV CV to
HFOV
HFOV to
CV
SurvivalwithCLD%
-- Arnold et al,Arnold et al, CCMCCM, 1994, 1994
**
HFOV vs. CMV in Pediatric
Respiratory Failure

54. HFOV
• Reduces need for ECMO, chronic lung
disease in neonates
• Improves survival without CLD in
pediatric ARDS
HFOV: Outcomes of Randomized
Controlled Trials

56. Pediatric ECMO
• Potential candidates
• Neonate - 18 years
• Reversible disease process
• Severe respiratory/cardiac failure
• < 10 days mechanical ventilation
• Acute, life-threatening deterioration

58. Impact of ECMO on Survival in
Pediatric Respiratory Failure
• Retrospective, multi-center cohort analysis
• 331 patients, 32 hospitals
• Use of ECMO associated with survival (p < .
001)
• 53 diagnosis and risk-matched pairs:
ECMO decreased mortality (26% vs 47%,
p < .01)
-Green et al, CCM, 24:1996

59. Impact of ECMO on Survival in
Pediatric Respiratory Failure
0
10
20
30
40
50
60
70
80
90
Mortality %
< 25% 25 - 50
%
50 -
75%
> 75%
ECMO
Non-ECMO
*
p < .05 - Green et al., CCM, 1996

60. Pediatric Respiratory ECMO -
Children’s Healthcare of Atlanta
Diagnosis Number Survival % ELSO Survival
%
ARDS/ARF 38 71 51
Bacterial
Pneumonia
9 85 79
Viral
Pneumonia
24 86 53
Trauma 5 80 63
Burns 4 75 52
TOTAL 86 79% 62%

61. Other Cost Intensive Therapies
Therapy Cost/Patient
Pediatric ECLS $ 232, 941
Pediatric Liver Transplant $ 206, 375
Pediatric Heart Transplant $ 126,695

62. ECMO: Comparison to Other
Expensive Therapies
4.19
43.5
62.5
26.5
16.3
0
10
20
30
40
50
60
70
Cost/Life-Year
(ThousandsofDollars)
ECLS Liver Bone
Marrow
Cardiac Renal
Vats et al., CCM, 1998

63. If you think about ECMO,
it is worth a call to consider
ECMO

64. Surfactant in ARDS
• ARDS:
 surfactant deficiency
 surfactant present is dysfunctional
• Surfactant replacement improves
physiologic function

65. Calf’s Lung Surfactant Extract in
Acute Pediatric Respiratory Failure
• Multi-center trial-uncontrolled,
observational
• Calf lung surfactant (Infasurf) – intra-
tracheal
• Immediate improvement and weaning in
24/29 children with ARDS
• 14% mortality
-Willson et al,CCM, 24:1996

66. Surfactant in Pediatric ARDS
• Current randomized multi-center
trial
• Placebo vs calf lung surfactant
(Infasurf)
• Children’s at Egleston is a
participating center-study closed,
await results

67. Steroids in ARDS
• Theoretical anti-inflammatory, anti-
fibrotic benefit
• Previous studies with acute use (1st 5
days)
No benefit
Increased 2° infection

68. Effects of Prolonged Steroids in
Unresolving ARDS
• Randomized, double-blind, placebo-
controlled trial
• Adult ARDS ventilated for > 7 days without
improvement
• Randomized:
 Placebo
 Methylprednisolone 2 mg/kg/day x 4 days,
tapered over 1 month
Meduri et al, JAMA 280:159, 1998

69. Steroids in Unresolving ARDS
• By day 10, steroids improved:
 PaO2/FiO2 ratios
 Lung injury/MOD scores
 Static lung compliance
• 24 patients enrolled; study stopped
due to survival difference
Meduri et al, JAMA, 1998

70. Steroids in Unresolving ARDS
0
10
20
30
40
50
60
70
80
90
100
ICU
survival
Hospital
survival
Steroid
Placebo
* *
p<.01*- Meduri et al., JAMA, 1998

71. Inhaled Nitric Oxide in
Respiratory Failure
Neonates
 Beneficial in term neonates with PPHN
 Decreased need for ECMO
Adults/Pediatrics
 Benefits - lowers PA pressures,
improves gas exchange
 Randomized trials: No difference in
mortality or days of ventilation

72. ECMO and NO in Neonates
• ECMO improves survival in neonates
with PPHN (UK study)
• NO decreases need for ECMO in
neonates with PPHN: 64% vs 38%
(Clark et
al, NEJM, 2000)

73. Effects of Inhaled Nitric Oxide In
Children with AHRF
• Randomized, controlled, blinded multi-
center trial
• 108 children with OI > 15
• Randomized: Inhaled NO 10 ppm vs.
mechanical ventilation alone
Dobyns, Cornfield, Anas,
Fortenberry et al., J. Peds, 1999

75. Inhaled NO and HFOV In Pediatric
ARDS
58
53
58
71
0
10
20
30
40
50
60
70
80
Survival%
CM
V
CM
V
+
NO
HFOV
HFOV
+
NO
Dobyns et al.,Dobyns et al.,
J PedsJ Peds, 2000, 2000
*

76. Partial Liquid
Ventilation

77. Partial Liquid Ventilation
Mechanisms of action
 oxygen reservoir
 recruitment of lung volume
 alveolar lavage
 redistribution of blood flow
 anti-inflammatory

78. Liquid Ventilation
Pediatric trials started in 1996
 Partial: FRC (15 - 20
cc/kg)
 Study halted 1999 due to
lack of benefit
Adult study (2001): no
effect on outcome

79. ARDS- “Mechanical” Therapies
Prone positioning - Unproven outcome
benefit
Low tidal volumes - Outcome benefit in
large study
Open-lung strategy - Outcome benefit in
small study
HFOV -Outcome benefit in
small study
ECMO - Proven in neonates
unproven in children

80. Pharmacologic Approaches to
ARDS: Randomized Trials
Glucocorticoids
- acute - no benefit
- fibrosing alveolitis - lowered mortality,
small study
Surfactant - possible benefit in
children
Inhaled NO - no benefit
Partial liquid ventilation - no benefit

81. “…We must discard the old approach
and continue to search for ways to
improve mechanical ventilation. In
the meantime, there is no substitute
for the clinician standing by the
ventilator…”
- Martin J. Tobin, MD