ARDS Guidelines

Dr. George John,

Critical Care,

Christian Medical College,

Vellore

Causative Factors in ARDS

PRIMARY INJURY

HOST RESPONSE

CONSEQUENCES OF THERAPY

SPECTRUM OF LUNG “INJURY”

Cardiogenic pulmonary

oedema

ALI ARDS

Altered Starling’s Forces

P/F RATIO 200 - 300 P/F RATIO < 200

Pulmonary Changes

• Alveolar Flooding

• Interstitial inflammation

• Atelectasis

Early Exudative Phase < 1 week

Late Fibro Proliferative Phase > 1 week

Guidelines

• Oxygenation

• Ventilation

• Position

• Fluid management

• Miscellaneous

Oxygenation

Lowest FiO2

- to keep PaO2 55 – 80mm Hg

Increase Alveolar Recruitment = degree of penetration of gas into poorly / nonaerated lung regions

- PEEP - recruitment manoeuver- inverse ratio ventilation

Prone positioning ( “proning” )NO (Nitric Oxide)

The Pressure Profile

Peak Pressure

Plateau Pressure

Mean Pressure

PEEP

VentilationVENTILATIONVolume Control mode; I:E ratio 1:1 – 1:3

- Tidal Volume 6ml / kg- Plateau Pressure < 30cm H2O - High rate if CO2 high – up to 35 / minute

Measures to decrease CO2 production (sedation, decrease temperature) Permissive hypercapnoeaIf pH < 7.30 – use HCO3 infusionOther techniques:?Tracheal gas insufflation (TGI) / Expiratory washout (EWO)

(use humidified gas only)? Pressure Control Mode with pressure = 30

- many with less pressure needed for ventilation in the study - study done with VC mode

Position“PRONING”

• Ventilation in the prone position improves oxygenation but most clinical studies have not shown that prone ventilation improves outcome. In a study of paediatric patients (2 weeks to 18 years of age) with acute lung injury, prone positioning did not significantly reduce ventilator-free days or improve clinical outcome.

• However, in a study published in 2006, prolonged prone positioning (at least 20 hours a day) in patients greater than 18 years of age showed that it was safe and may reduce mortality.

Fluid ManagementLiberal versus Conservative

Conservative strategy: maintain a low target filling pressure (CVP of less than 4mm Hg or PAOPof less than 8 mm Hg)

versusLiberal strategy: maintain higher filling pressure CVP 10 – 14mm Hg orPAOP 14-18mm Hg. This was achieved by a combination of bolus fluidadministration, use of frusemide or dobutamine, depending on theperfusion, urine output , measured filling pressures and cardiac output (if available).

Result:There was no significant difference in mortality (25.5% in the conservative group vs.

28.4% in the liberal group). However, the conservative strategy improved the oxygenation index, lung injury score, increased the number of ventilator free days and days not spent in ICU. The conservative strategy did not increase the incidence or prevalence of shock during the study. In addition, the conservative strategy did not increase the use of dialysis during the first 60 days.

Monitoring

• In a landmark study published in 2006, the use of PA catheter guided therapy did not improve organ function or survival as compared to CVC guided therapy. The PA catheter was associated with more complications (twice as many catheter related complications, predominantly arrhythmias) than CVC guided therapy.

Cardiovascular

• Haemoglobin 8 – 10 g%

• Maintain Cardiac Output

Judicious fluids

Use inotropes as needed

Other Modalities• SteroidsEarlier study:

Evidence that use of steroids after the first week of ARDS improves prognosis significantly.

In 2006: No benefit in the use of methylprednisolone after the first week of ARDS. Use of sterods after 14 days of ARDS was associated with increased mortality at 60 days. This was in spite of the steroid therapy and improving ventilator free shock free days during the first 28 days. Methyprednisolone did not increase infectious complications but was associated with a higher rate of neuromuscular weakness.

• Nitric OxideNo benefit• Beta agonists:The beta agonist lung injury trial (BALTI) has shown that treatment withintravenous albutamol (15ug / kg / hr) reduces extravascular lung water (EVLW)in patients with ALI / ARDS with a reduction in plateau pressures at Day 7.The effect on EVLW started at 48 hours. Patients receiving intravenoussalbutamol had a higher incidence ofsupraventricular arrhythmias these were notsustained as the dose of salbutamol was modified in these patients. There wasno improvement in mortality with the use of salbutamol – however the study wasnot Powered to detect a difference in mortality.

“Imitators”

• Acute Interstitial Pneumonia (AIP)

• Acute Eosinophilic Pneumonia

• Acute BOOP

• DAH

• Acute HP

Suspecting “ Imitators”

• Common features: fever, cough, myalgia, raised WBC, CRP, LDH

• Distinguishing features: BAL, Lung Biopsy, Response to steroids and prognosis (in some)

Possible Approach• Early BAL – infectious agents, differential WBC count• Serological tests for autoimmune disease, CK (polymyositis)• Haematocrit – serial• Ferritin (increased in adult Still’s)• Renal function• Urine microscopy• Lung biopsy – if BAL is inconclusive, after considering risk vs.

benefit. Specially important in DAH (vasculitis induced) ; necessary for immunofluorecent staing for ABMA.

•  The suggestion to start all these patients initially on steroids for 3 days till the BAL results / other tests are available is controversial and needs to be evaluated in a RCT.

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