Mechanical Ventilation in Acute Respiratory Distress Syndrome
Case
Male / 65
Severe dyspnea, 3 days
High fever and purulent sputum
WBC: 23,000/mm3
2D-echo: EF 60%
Oxygenation under Mechanical ventilation
Mode: Controlled Mandatory Ventilation
FIO2: 80%
PEEP: 8 cmH 2O
ABGA pH
7.356
PaCO2
42.7 mmHg
PaO2
80.0 mmHg
HCO3-
29.7 mEq/L
SaO2
93.6%
Q1: Which of the following is a correct pathophysiology of hypoxemia in this patient?
1.
Decreased alveolar-capillary barrier permeability
2.
Eosinophil dependent lung injury
3.
A decrease in cytokines
4.
Increased alveolar fluid removal
5.
Heterogeneous acute lung inflammation
Summary of the Case
Acute onset of dyspnea, 3 days
Severe hypoxemia, PaO2/FIO2 = 80 / 0.8 = 100 mmHg
Bilateral opacities in a chest X-ray
Normal cardiac function
What Condition?
ARDS Acute Respiratory Distress Syndrome
RECOMMENDED CRITERIA FOR ACUTE LUNG INJURY (ALI) AND ACUTE RESPIRATORY DISTRESS SYNDROME (ARDS)
Timing
Oxygenation
Chest Radiograph
Pulmonary Artery Wedge Pressure
ALI criteria
Acute onset
PaO2/FIO2 300 mmHg (regardless of PEEP level)
Bilateral infiltrates seen on frontal chest radiograph
18 mmHg when measured or no clinical evidence of left atrial hypertension
ARDS criteria
Acute onset
PaO2/FIO2 200 mmHg (regardless of PEEP level)
Bilateral infiltrates seen on frontal chest radiograph
18 mmHg when measured or no clinical evidence of left atrial hypertension
www.wordle.net
Bernard GR, et al. Am J Respir Crit Care Med 1994;149;818
The New (Berlin) Definition of ARDS Timing Chest imaginga Origin of edema
Within 1 week of a known clinical insult or new or worsening respiratory symptoms Bilateral opacities—not fully explained by effusions, lobar/lung collapse, or nodules 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
Oxygenationb Mild 200 mmHg < PaO2/FIO2 300 mmHg with PEEP or CPAP 5 cmH2Oc Moderate 100 mmHg < PaO2/FIO2 200 mmHg with PEEP 5 cmH2O Severe PaO2/FIO2 100 mmHg with PEEP 5 cm H2O Abbreviations: CPAP, continuous positive airway pressure; FIO2, fraction of inspired oxygen; PaO2, partial pressure of arterial oxygen; PEEP, positive end-expiratory pressure aChest radiograph or computed tomography scan. bIf altitude is higher than 1000 m, the correction factor should be calculated as follows: [Pa /F O2 IO2(barometric pressure/760)]. cThis may be delivered noninvasively in the mild acute respiratory distress syndrome group.
ARDS Definition Task Force, et al. JAMA. 2012;;307:2526
Ware LB, et al. N Engl J Med 2000;342:1334
Increased permeability of the alveolar-capillary barrier Influx of protein-rich edema fluid into the air-space Neutrophil dependent lung injury Cytokines Disrupt normal epithelial fluid transport, impairing the removal of fluid Abnormalities in the production, composition, and function of surfactant Abnormalities of the coagulation system
Q1: Which of the following is a correct pathophysiology of hypoxemia in this patient?
1.
Decreased permeability of the alveolar-capillary barrier
2.
Eosinophil dependent lung injury
3.
Decrease in cytokines
4.
Increased alveolar fluid removal
5.
Heterogeneous acute lung inflammation
Mechanical Ventilation with traditional high tidal volume and zero PEEP
Expiration
Physical stretch
Inspiration
Shearing force
1. Spillover
2. Translocation
Multiple Organ Dysfunction Syndrome
Lung Protective Ventilation Strategies
Heterogeneity Homogeneity Prone Position Ventilation Recruitment Maneuver
High (adequate) PEEP Low Tidal Volume 6~8 mL/Kg of predicted body weight Plateau Pr. < 30 cmH2O Shearing force
Lung protective ventilation strategy
Low tidal volume In a Narrow Sense High-PEEP
In a Broad Sense Prone position
Recruitment maneuver
Q2: Which of the following mechanical ventilation strategies for ARDS is a recommended therapy based on strong clinical evidence?
1.
Low tidal volume
2.
High-PEEP
3.
Prone position
4.
Recruitment maneuver
5.
High frequency ventilation
Evidence based recommendations for LPV strategies
A
recommended therapy based on strong clinical evidence from randomized clinical trials
A
B
C
indeterminate evidence: recommended only as alternative therapy
C
D
Low tidal volume
High PEEP
Prone position ventilation
Recruitment maneuvers
A, recommended therapy based on strong clinical evidence from randomized clinical trials; B, recommended therapy based on supportive but limited clinical data; C, indeterminate evidence: recommended only as alternative therapy; D, not recommended based on clinical evidence against efficacy of therapy.
Q2: Which of the following mechanical ventilation strategies for ARDS is a recommended therapy based on strong clinical evidence?
1.
Low tidal volume
2.
High-PEEP
3.
Prone position
4.
Recruitment maneuver
5.
High frequency ventilation
Review of Evidence
Low Tidal Volume
ARDS Network Trial: Lower Tidal Volume vs. Traditional Tidal Volume
Different ONLY in
Tidal volume Plateau pressure
Traditional tidal volume
Lower tidal volume
12 mL/Kg*
6 mL/Kg*
50 cmH2O
30 cmH2O
*Kg of predicted body weight
Main Outcomes of ARDS Network Trial
VARIABLE
GROUP RECEIVING LOWER TIDAL VOLUMES
GROUP RECEIVING TRADITIONAL TIDAL VOLUMES
P VALUE
DEATH before discharge home and breathing without assistance (%)
