This document discusses acute respiratory distress syndrome (ARDS). Key points include:
- ARDS occurs in 1-4% of PICU admissions and has a mortality rate varying between 20-75%.
- It is defined by acute onset pulmonary edema, hypoxemia, and absence of heart failure. Severity is classified by PaO2/FiO2 ratio.
- Causes include direct lung injury from pneumonia/aspiration or indirect injury from sepsis/trauma.
- Management focuses on mechanical ventilation with low tidal volumes, permissive hypercapnia and optimal PEEP to reduce lung injury while improving oxygenation. Prognosis depends on severity of hypoxemia and underlying cause.
Slideshow is from the University of Michigan Medical School's M2 Respiratory sequence
View additional course materials on Open.Michigan:
openmi.ch/med-M2Resp
Updates on Acute respiratory distress syndromeHamdi Turkey
These lecture notes were made by Dr. Hamdi Turkey (Pulmonologist at Taiz university)
** Contents:
- Historical view on ARDS
- New definition of ARDS
- Precipitating risk factors
- Pathophysiology of ARDS
- Clinical picture, Diagnosis, Management and Prognosis
Do Not Forget To Visit Our Pages On Facebook on the following Links:
https://www.facebook.com/groups/569435236444761/
AND
https://www.facebook.com/groups/690331650977113/
Slideshow is from the University of Michigan Medical School's M2 Respiratory sequence
View additional course materials on Open.Michigan:
openmi.ch/med-M2Resp
Updates on Acute respiratory distress syndromeHamdi Turkey
These lecture notes were made by Dr. Hamdi Turkey (Pulmonologist at Taiz university)
** Contents:
- Historical view on ARDS
- New definition of ARDS
- Precipitating risk factors
- Pathophysiology of ARDS
- Clinical picture, Diagnosis, Management and Prognosis
Do Not Forget To Visit Our Pages On Facebook on the following Links:
https://www.facebook.com/groups/569435236444761/
AND
https://www.facebook.com/groups/690331650977113/
2. EPIDEMIOLOGY
• ARDS occurs in 1-4% of PICU admissions
• 10% of PICU patients who receive mechanical ventilation
meet diagnostic criteria for ARDS
• Mortality varies between 20 – 75%
3. • Multicentered, prospective cohort study - Flori et al.
-overall hospital mortality was 22% among children
with a PaO2:FIO2 ratio <300
-ARDS (PaO2: FIO2 <200) had a mortality of 26%
-MC diagnosis associated with ALI and ARDS among
the entire study cohort pneumonia (35%)
4. American-European Consensus Criteria
ALI and ARDS
• Acute onset
• Bilateral pulmonary infiltrates on chest radiography
• Pulmonary artery occlusion pressure >18 mm Hg or
no clinical evidence of left atrial hypertension
• PaO2:FIO2 ratio <300 = ALI
• PaO2:FIO2 ratio <200 = ARDS
• Bernard GR, Artigas A, Brigham KL, et al. The American-European Consensus Conference on
ARDS. Definitions, mechanisms, relevant outcomes, and clinical trial coordination. Am J
Respir Crit Care Med 1994;149:818–24.
5. The Berlin Definition of ARDS
• Respiratory symptoms must have begun within
one week of a known clinical insult, or the patient
must have new or worsening symptoms during
the past week
• Bilateral opacities consistent with pulmonary
edema must be present on a chest radiograph or
computed tomographic (CT) scan
• The patient’s respiratory failure must not be fully
explained by cardiac failure or fluid overload
6. • A moderate to severe impairment of
oxygenation must be present(PaO2/FiO2)
-Mild ARDS – The PaO2/FiO2 is >200 mmHg,
but ≤300 mmHg,
-Moderate ARDS – The PaO2/FiO2 is >100
mmHg, but ≤200 mmHg
-Severe ARDS – The PaO2/FiO2 is ≤100
all accompanied by ventilator setting that
include PEEP ≥5 cm H2O.
7. ETIOLOGY
DIRECT INJURY INDIRECT INJURY
Common Common
-Pneumonia , -Sepsis
-Aspiration of gastric content -Severe trauma
Less common Less common
-Pulmonary concussion -Cardiopulmonary bypass
-Fat embolism -Drug overdose
-Near drowning -Acute pancreatitis
-Inhalational injury, -Blood transfusion
8. Mechanisms preventing alveolar
edema
• Retained intravascular protein
• The interstitial lymphatics
• Tight junctions btw alveolar epithelial cells
9. Injury
• Injury causes release of pro-inflammatory
cytokines
• Damage to the capillary endothelium and
alveolar epithelium
• Functional surfactant is lost
• Ability to upregulate alveolar fluid clearance
may also be lost
10. Consequences
• Impaired gas exchange
- ventilation-perfusion mismatching
-while increased physiologic dead space
impairs carbon dioxide elimination
• Decreased lung compliance
-stiffness of poorly or non-aerated lung
• Pulmonary hypertension
-hypoxic vasoconstriction,
-vascular compression by positive airway pressure,
-parenchymal destruction, airway collapse,
11. Phases of ARDS
Exudative phase
↓pulmonary compliance, arterial hypoxemia, tachypnea, hypocarbia.
,x ray (pulmonary edema)
Fibroproliferative phase
↑ alveolar dead space / refractory pulmonary hypertension due to
chronic inflammation and scarring of the alveolar-capillary unit.
Recovery phase
restoration of alveolar epithelial barrier/ gradual improvement in
pulmonary compliance resolution of arterial hypoxemia/ return to
premorbid pulmonary function in many patients .
12.
13. Clinical features
• Fluid accumulation
• Lung compliance declines and tachypnea ensues
• Regional atelectasis and small-airways closure
• Hypoxia / breathing labored
• Hypocarbia followed by hypercarbia
• Rales over areas of atelectasis or alveolar congestion
and decreased air entry over areas that are largely
consolidated. Occasionally rhonchi
14. Investigations
Chest Xray
• Small volume lungs
• Diffuse infiltrates
• Airbronchograms , atelectasis
• Fibrosis with reticular opacities
CT scan
• Heterogenous opacification in dependent
regions
22. • PEEP
-augment anatomical dead space by distending large
airways
-cardiovascular compromise in high PEEP
• Optimal PEEP
-Improves oxygenation
-Displacement of fluid from alveoli
-Recruitment and opening up of collapsed alveoli
-Improved FRC
• Permissive hypercapnia
-Accept high CO2 till pH 7.2
23. • Most children have concomitant shock
• Aggressive fluid resuscitation till stable
• Excess lung water will decrease saturation
• Adequate sedation and analgesia
• Antibiotic therapy for primary cause
• Early enteral nutrition
24. Prone positioning
• Prone position improves V/Q mismatch
• Recruitment of dependent portions
• Decreases chest wall compliance (transmitting
airway pressure to the alveoli more efficiently
and stabilizing alveolar volume over a larger
portion of previously nonaerated lung units)
• If no deterioration with prone position,
continue for 18-20 hours
26. Predictors of outcome
• Disease-related
-Oxygenation-PaO2/FiO2( mild, moderate, and
severe ARDS had mortality rates of 27, 32, and 45
percent, respectively)
-Pulmonary vascular dysfunction(elevated
transpulmonary gradient (ie, ≥12 mmHg)
-Underlying cause of the ARDS
• Patient related
27. • Treatment related
-Fluid balance-positive fluid balance may be
associated with higher mortality (1)
-Treatment with glucocorticoids
-Packed red blood cell transfusion-increased
likelihood of death (odds ratio 1.10 per unit
transfused, 95% CI 1.04-1.17) (2)
1.Rosenberg AL, Dechert RE, Park PK, et al. Review of a large clinical series: association of cumulative
fluid balance on outcome in acute lung injury: a retrospective review of the ARDSnet tidal volume
study cohort. J Intensive Care Med 2009; 24:35.
2.Gong MN, Thompson BT, Williams P, et al. Clinical predictors of and mortality in acute
respiratory distress syndrome: potential role of red cell transfusion. Crit Care Med 2005;
33:1191.