ARDS
Ruchi Kapoor
April 2015
A 34 year old paraplegic man with history of neurogenic bladder is
admitted to the ICU for septic shock due to UTI. He is given IVF, Zosyn
and intubated for decreased level of consciousness. CXR is normal
with the ETT in the appropriate position.
2 days later he is evaluated for persistent hypoxemia on mechanical
ventilation.
Vital Signs are: T 37.1 °C (98.8 °F), BP 90/50 mm Hg, HR 96/min, RR
26/min.
Oxygen saturation on an FIO2 of 0.8 is 89%.
Pulmonary examination reveals bilateral inspiratory crackles.
Cardiac examination reveals distant, regular heart sounds.
Lab results:
Hgb 13.2 g/dL
WBC 10,000/uL.
ABG on FiO2 80%: pH 7.48, pCO2 30 mm Hg, pO2 60 mmHg
Urine and blood cultures grow E. Coli that is sensitive to Zosyn.
Follow-up CXR shows diffuse bilateral infiltrates without
cardiomegaly. CVP is 8 mm Hg.
Which of the following is the most likely cause of this patient's
hypoxemia?
A.
B.
C.
D.
Acute respiratory distress syndrome
E. coli pneumonia
Heart failure
Idiopathic acute eosinophilic pneumonia
Lab results:
Hgb 13.2 g/dL
WBC 10,000/uL.
ABG on FiO2 80%: pH 7.48, pCO2 30 mm Hg, pO2 60 mmHg
Urine and blood cultures grow E. Coli that is sensitive to Zosyn.
Follow-up CXR shows diffuse bilateral infiltrates without
cardiomegaly. CVP is 8 mm Hg.
Which of the following is the most likely cause of this patient's
hypoxemia?
A.
B.
C.
D.
Acute respiratory distress syndrome
E. coli pneumonia
Heart failure
Idiopathic acute eosinophilic pneumonia
Objectives
 What is ARDS? – The Definition
 Why does it happen? – The Pathophysiology
 How to manage it? – The Basic Ventilation Strategy
What is ARDS?
ARDS is lung injury that leads to:
 Impaired gas exchange
 Decreased lung compliance
 Increased pulmonary arterial pressure
Definition of ARDS
 Acute onset (within 1 week of clinical insult)
 Bilateral pulmonary edema
 PaO2/FiO2 <200 (or <300 if PEEP >5 cmH2O)
 Exclude cardiogenic pulmonary edema
Risk Factors
(i.e. “clinical insult”)
 Sepsis
 TRALI
 Aspiration
 Burns
 Pneumonia
 Drugs and alcohol
 Pancreatitis
 Lung transplant
 Trauma
 Hematopoietic stem cell
transplant
 Massive transfusion
Pathophysiology of ARDS
Starts with capillary endothelium.
Ends with alveolar epithelium.
 Capillary endothelium is activated.
 Endothelium releases pro-inflammatory cytokines
(e.g. TNF, IL-8) that recruit neutrophils to the lungs.
 Neutrophils are activated and release toxic
mediators (e.g. reactive oxygen species, proteases)
 Causes further damage of capillary endothelium,
and now of alveolar epithelium, leading to
pulmonary edema.
Pulmonary Edema
NORMAL ALVEOLI
ALVEOLAR EDEMA
Pulmonary
capillary
Pulmonary
capillary
Interstitial
fluid
Lymphatic
movement
Alveolar
lumen
EMPTY of
fluid
Breakdown
of barriers
Alveola
r lumen
FULL of
fluid
Protein
A 50-year-old previously health man is evaluated in the ICU
for ARDS due to severe community-acquired pneumonia. He
is intubated and placed on mechanical ventilation.
Vital Signs: 38.3 °C (100.9 °F), 120/60 mm Hg, 110 beats/min.
Oxygen saturation by pulse oximetry is 96%.
Physical exam is unremarkable except for bilateral inspiratory
crackles.
Ideal Body weight is 60 kg.
Initial ventilator settings are volume control with
Rate 18 / TV 420 / PEEP 10 / FiO2 0.8
Peak pressure is 34 cm H2O. Plateau pressure is 32 cm H2O.
Which of the following is the most appropriate next step in
management?
A. Decrease respiration rate
B. Decrease tidal volume
C. Increase FIO2
D. Increase PEEP
Ideal Body weight is 60 kg.
Initial ventilator settings are volume control with
Rate 18 / TV 420 / PEEP 10 / FiO2 0.8
Peak pressure is 34 cm H2O. Plateau pressure is 32 cm H2O.
Which of the following is the most appropriate next step in
management?
A. Decrease respiration rate
B. Decrease tidal volume
C. Increase FIO2
D. Increase PEEP
Lung protective ventilation
 Avoid further damage to an already edematous
and injured lung by preventing overdistention of
alveoli
 Use Low Tidal Volume Ventilation (LTVV)
 Based on predicted/ideal body weight, not actual
body weight
 Allow for permissive hypercapnia and respiratory
acidosis.
Step-by-Step approach to
Low Tidal Volume
Ventilation
1. Set mode to volume assist-control
2. Set initial Tidal Volume (TV) to 8 mL/kg
3. Reduce TV to 7 then 6 mL/kg over 1-3 hrs
4. Keep plateau pressure (Pplat) 25 – 30 cm H20
5. Adjust FiO2 and PEEP to keep PaO2 55 – 80
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
A 63-year-old man with ARDS due to aspiration pneumonia is
evaluated in the ICU. He has just been intubated and placed
on mechanical ventilation
Vital signs: 37.0 °C (98.6 °F), 150/90 mm Hg, 108 beats/min.
Height: 150 cm (59 in)
Weight: 70.0 kg (154.3 lb).
Ideal body weight: 52.0 kg (114.6 lb).
Physical exam is only notable for crackles in the lower left
lung field. Patient is sedated.
Mechanical ventilation is on the assist/control mode at a rate
of 18/min. Positive end-expiratory pressure is 8 cm H2O, and
FIO2 is 1.0.
Which of the following is the most appropriate tidal volume?
A. 300 mL
B. 450 mL
C. 700 mL
D. 840 mL
Mechanical ventilation is on the assist/control mode at a rate
of 18/min. Positive end-expiratory pressure is 8 cm H2O, and
FIO2 is 1.0.
Which of the following is the most appropriate tidal volume?
A. 300 mL
B. 450 mL
C. 700 mL
D. 840 mL
Summary
 ARDS is acute lung injury with bilateral pulmonary
edema and hypoxia that is NOT cardiogenic in
origin
 ARDS occurs when capillary endothelium and
alveolar epithelial barriers break down.
 The cornerstone of management in ARDS is lowtidal volume ventilation to prevent overdistention
of alveoli.
References
 The ARDS Definition Task Force*. Acute Respiratory Distress Syndrome: The
Berlin Definition. JAMA. 2012;307(23):2526-2533. doi:10.1001/jama.2012.5669.
 Ferguson et al. The Berlin Definition of ARDS: An Expanded Rationale,
Justification, and Supplementary Material. Intensive Care Med.
2012;38(10):1573-1582. doi:10.1007/s00134-012-2682-1
 Piantadosi CA, Schwartz DA. The Acute Respiratory Distress Syndrome. Ann
Intern Med. 2004;141:460-470. doi:10.7326/0003-4819-141-6-200409210-00012
 The Acute Respiratory Distress Syndrome Network. Ventilation with Lower
Tidal Volumes as Compared with Traditional Tidal Volumes for Acute Lung
Injury and the Acute Respiratory Distress Syndrome. N Engl J Med.
2000;342(18):1301-1308. DOI: 10.1056/NEJM200005043421801
 Uptodate.com