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American-European Consensus ARDS Defination
• An acute condition characterized by bilateral pulmonary
infiltrates and severe hypoxemia in the absence of
evidence for cardiogenic pulmonary edema.
• PaO2/FiO2 <300 = ALI
PaO2/FiO2 <200 = ARDS
• Cardiogenic pulmonary edema must be excluded either
by clinical criteria or by a pulmonary capillary wedge
pressure (PCWP) lower than 18 mm Hg
WHAT IS P/F RATIO…
• PAO2/ FIO2
•Fio2 is 0.5, 0.6, 0.7 etc.
•If pao2 140, fio2 0.7
•p/f ratio will b
•140/ 0.7 = 200
Limitations of Consensus Definitions
•The chest radiograph is subject to variability in
interpretation,,, & acute is ill defined
•PaO2/FiO2 may vary according to ventilator
parameters, e.g., PEEP, and at extremes of FiO2
•Accuracy in excluding the presence of heart
failure may be influenced by measurement
methodology and timing
•PACs are rarely used
•PCWP may oscillate above and below the cut-off
and may be elevated for reasons other than heart
Maintaining a low tidal volume
Monitoring plateau pressure
Setting PEEP based on the FiO2 requirement
TARGETS OF VENTILAION STRATEGY
• Avoid overdistending lung units by
limiting the inflation volume and
• Avoid repetitive opening and
collapse by applying adequate PEEP
• Ideally, ventilation would take place in
a “zone of safety”on the deflation limb
of the PV curve
The “Baby lung”
ARDS Lung has alveoli
partially aerated alveoli
“Normal” segments inflate easily
Unaerated segments distend poorly
Normal lung segments may be over-inflated when
ventilated with traditional tidal volumes
FACE MASK VS HELMET NIV MASK
• In a single-center trial, 83 patients with ARDS who required NIV
using full face mask for at least eight hours were randomly
assigned to continue face mask NIV or switch to helmet-
delivered NIV .
• Helmet-delivered NIV involves the administration of positive
pressure and oxygen through a transparent hood that covers the
entire head and face and is sealed with a rubber collar at the neck.
• Helmet-delivered NIV reduced the need for intubation (18
versus 62 percent) in ARDS patients, most of whom had mild or
moderate disease. In addition,
• it was also associated with a higher rate of ventilator-free days,
shorter ICU stay, and lower 90-day mortality without an
increase in adverse effects
• In 2000, the NIH ARDS Network published the findings of their
first randomized, controlled, multi-center clinical trial in 861
• The trial was designed to compare a lower-tidal-volume
ventilatory strategy (6 mL/kg predicted body weight, plateau
pressure < 30 cm H2O) with a higher tidal volume (12 mL/kg
predicted body weight, plateau pressure <50 cm H2O).
• In this trial, the in-hospital mortality rate was 40% in the 12
mL/kg group and 31% in the 6 mL/kg
• Ventilator-free days and organ failure–free days were also
significantly improved in the low-tidal-volume group. These
findings were truly remarkable, since no prior large randomized
clinical trial of any specific therapy for ALI/ARDS has ever
demonstrated a mortality benefit.
OPEN LUNG VENTILATION
• Open lung ventilation (OLV) is a strategy that combines
low tidal volume ventilation (LTVV) with a
recruitment maneuver and subsequent titration of
applied PEEP to maximize alveolar recruitment.
• The LTVV and set limits on plateau pressure aim to
mitigate alveolar overdistension, while the applied PEEP
seeks to minimize cyclic atelectasis. Together, these
effects are expected to decrease the risk of ventilator-
associated lung injury.
• a supplement to high peep vent mgt.
• Periodically bt briefly raises the transpulmonary pressures to higher levels than used for
• 3 RCTs have tested RMs in ARDS.
• Transient improvement in gas exchange but no apparent sustained benefit.
• Risks –pulmonary / hemodynamic
• 3 negative trials of PEEP has prompted investigators to explore alternative strategies to
guide PEEP titration.
• CT imaging to titrate PEEP risk of pt transfer, cost, radiation exposure
• Electrical impedance tomography(ETT)
• Lung ultrasound
• Pressure-volume relationship analysis—LIP as well as STRESS INDEX.
• Targeted transpulmonary pressure(airway pressure-pleural pressure).
548 ARDS patients
PaO2/FiO2 < 200 cmH20 , Fi02 > 0.5
HFOV 47% vs Control 35%
(RR 1.33; 95% CI 1.09 to 1.64; P = 0.005)
548 ARDS patients
–PaO2/FiO2 < 200 cmH20 –PEEP > 5 cmH20
30 day mortality
•HFOV 41.7% vs Control 41.1%
•Difference 0.6%, 95% CI −6.1 to 7.5
340 ARDS patients
PaO2/FiO2 < 150 mmHg
Adjusted Mortality at Day 90
NMB: 31.6% vs placebo: 40.7%
(95% CI 0.48 to 0.98; P = 0.04)
282 patients with ALI
Aerosolized albuterol vs saline
•albuterol 14.4 vs control 16.6 d
(95% CI difference –4.7 to 0.3 d: P = 0.087)
albuterol 23.0% vs control 17.7%
(95% CI difference –4.0 to 14.7%,P=0.30)
INVERSE RATIO VENTILATION
• PCIRV increases mean airway pressures and improves
• Little benefit
• Auto PEEP
• Haemodynamic instability
PARTIAL LIQUID VENTILATION
•No benefit in mortality