Acute Respiratory Distress Syndrome (ARDS) - Standard Treatment Guidelines

The acute respiratory distress syndrome (ARDS) is a sudden, life-threatening lung failure caused by an inflammatory injury to the lung that is characterized clinically by acute hypoxemic respiratory failure accompanied by pulmonary infiltrates.

Clinical disorders associated with the development of ARDS are divided into those associated with direct injury to the lung and those that cause indirect lung injury (summarized in Table 1). Severe sepsis from any cause is a common underlying disease. Falciparum malaria, leptospirosis,H1N1 influenza pneumonia,hantavirus infection, scrub typhus and severe pneumonias due to Legionella and the pneumococcus are common causes of ARDS and multiorgan failure in India.

Table 1. Clinical Disorders Associated with the Development of ARDS

Direct Lung Injury	Indirect Lung Injury
Common causes Pneumonia Aspiration of gastric contents Less common causes Pulmonary contusion Fat emboli Near-drowning Inhalational injury Reperfusion pulmonary edema after lung transplantation or pulmonary embolectomy	Common causes Sepsis Severe trauma with shock and Multiple transfusions Less common causes Cardiopulmonary bypass Drug overdose Acute pancreatitis Transfusion of blood products

Ministry of Health and Family Welfare, Government of India has issued the Standard Treatment Guidelines for Acute Respiratory Distress Syndrome (ARDS). Following are the major recommendations :

Case Definition:

The American–European Consensus Conference Committee definition is commonly used. It defines a spectrum of severity ranging from a milder form of lung injury, Acute Lung Injury (ALI), to a more severe Acute Respiratory Distress Syndrome (ARDS)

Table 2. 1994 American–European Consensus Conference Committee Definitions

Condition	Timing	Oxygenation	Chest Radiograph	Pulmonary Artery Occlusion Pressure
Acute Lung Injury (ALI)	Acute Onset	PaO2/FiO2 <300 torr	Bilateral Infiltrates on Frontal chest radiograph	< 18 mmHg. when measured or no clinical evidence of left atrial hypertension
Acute Respiratory Distress Syndrome (ARDS)	Acute Onset	PaO2/FiO2 <200 torr	Bilateral Infiltrates on Frontal chest radiograph	< 18 mmHg. when measured or no clinical evidence of left atrial hypertension

Incidence of Condition In Our Country

An early estimate by the National Institutes of Health (NIH) suggested that the annual incidence in the United States was 75 per100, 000 population. Most studies report a mortality of 40 %-60% from ARDS with most deaths being attributed to sepsis and multi-organ failure rather than a primary respiratory cause. Recent studies have shown a decreasing mortality from this disease to as low as 36% and 34%. This may be probably related to improved and more effective strategies for ventilation and treatment of sepsis and better supportive care of the critically ill patients.

There are no reliable data from India.

Differential Diagnosis/ Types

• Cardiogenic pulmonary edema


• Fluid overload


• Bronchopneumonia


• Aspiration pneumonia


• Viral pneumonia


• Alveolar hemorrhage


• Pulmonary contusion


• Miliary tuberculosis


• Extensive pulmonary metastases


• Vasculitis

Prevention And Counselling

• Management of the underlying condition


• Early mangement and control of sepsis


• Prognosis is guarded with mortality of about 50%

Optimal Diagnostic Criteria, Investigations, Treatment & Referral Criteria

*Situation 1: At Secondary Hospital/ Non-Metro situation: Optimal Standards of Treatment in Situations where technology and resources are limited

Clinical diagnosis:

• Features of the underlying condition


• Breathlessness, tachypnea, respiratory distress, cyanosis, sweating, mental obtundation


• Pulse oximetry show SpO2 below 90%, or is maintained above 90% only with high flow oxygen

Investigations:

• Blood count, cultures, Ultrasonography and other investigations to diagnose the underlying


• Chest X-ray : Bilateral parenchymal infiltrates


• Arterial blood gases: low PaO2, low PaO2 / FiO2 ratio


• Echocardiography: normal left ventricular function, may show signs of pulmonary hypertension and right ventricular dysfunctionin severe cases

Treatment:

• Treatment of the underlying illness


• ALI / ARDS is not a disease of the lung alone; it is often a part of multiorgan dysfunction in systemic inflammation and sepsis. Thus ventilatory and pulmonary management are part of the overall management of the patient. Identifying and treating the inciting clinical disorder is of utmost importance while supportive therapy with mechanical ventilation gives time for the lungs to heal.


• Oxygen therapy


• Intubation and mechanical ventilation

1. Use tidal volume of 6 ml/kg ideal body weight (approximately 350-400 ml for average height Indian male, and 300ml for average height Indian female), respiratory rate 15-30/min


2. Give 5-10 PEEP

• Increase PEEP and FiO2 to maintain the following goals:

1. Plateau Pressure Pplat< 30 cm H2O


2. pH of 7.25-7.35

• PaO2 55mmHg – 70mmHg, or SpO2 88%-95%


• Avoid ventilator induced lung injury: do not exceed tidal volume and plateau pressure limit


• Supportive care as outlined in Chapter on Respiratory Failure and Mechanical Ventilation


• Avoid fluid overload, use basic hemodynamic monitoring (see chapteron Hemodynamic Monitoring)


• Mechanical Ventilation settings for Protective Lung Ventilation

Variable	Protocol
Ventilator mode	Volume assist-control
Tidal volume	< 6 mL/kg ideal body weight
Plateau pressure	Pplat< 30 cm H2O
Ventilation set rate/min	6–35/min, adjusted to achieve arterial
pH goal	pH of 7.25-7.35 pH of 7.25-7.35 considered acceptable.
Inspiratory flow, I:E	Adjust flow to achieve I:E of 1:1–1:3
Oxygenation goal	PaO255-80mmHg 88% < SpO2 < 95%
Fio2/PEEP (mm Hg) combinations	0.3/5, 0.4/5, 0.4/8, 0.5/8, 0.5/10, 0.6/10, 0.7/10, 0.7/12, 0.7/14, 0.8/14, 0.9/14, 0.9/16, 0.9/18, 1.0/18, 1.0/22, 1.0/24
Weaning	Attempts to wean by pressure support required when FiO2/PEEP are .40/8

Referral criteria:

• Undiagnosed underlying condition


• Severe underlying illness and multiple organ dysfunction (e.g., severe sepsis, renal failure, etc)


• Associated polytrauma with head injury


• High FiO2 and PEEP requirement (FiO2 > 0.5 and PEEP > 10)


• Requirement of deep sedation and neuromuscular blockade to allow smooth mechanical ventilation


• High plateau pressures > 30 cmH2O despite tidal volume of 6 ml/kg


• Development of complications such as pneumothorax, ventilator-associated pneumonia


• Inability to wean patient

*Situation 2: At Super Specialty Facility in Metro location where higher-end technology is available

Clinical diagnosis:

• Features of the underlying condition


• Breathlessness, tachypnea, respiratory distress, cyanosis, sweating, mental obtundation


• Pulse oximetry show SpO2 below 90%, or is maintained above 90% only with high flow oxygen

Investigations:

• Blood count, cultures, Ultrasonography and other investigations to diagnose the underlying


• Chest X-ray : Bilateral parenchymal infiltrates


• Arterial blood gases: low PaO2, low PaO2 / FiO2 ratio


• Echocardiography: normal left ventricular function, may show signs of pulmonary hypertension and right ventricular dysfunctionin severe cases


• Investigations to find the source of sepsis / underlying cause of ARDS


• CT scan of the Chest: alveolar filling, consolidation, and atelectasis occurring predominantly in dependent lung zone. lung injury in ARDS is non-homogeneous, and basal, dependent lung regions are more severely affected by edema and consolidation.

Treatment:

• Treatment of the underlying illness


• ALI / ARDS is not a disease of the lung alone; it is often a part of multiorgan dysfunction in systemic inflammation and sepsis. Thus ventilatory and pulmonary management are part of the overall management of the patient. Identifying and treating the inciting clinical disorder is of utmost importance while supportive therapy with mechanical ventilation gives time for the lungs to heal.


• Oxygen therapy


• Intubation and mechanical ventilation

1. Use tidal volume of 6 ml/kg ideal body weight (approximately 350-400 ml for average height Indian male, and 300ml for average height Indian female), respiratory rate 15-30/min


2. Give 5-10 PEEP

• Increase PEEP and FiO2 to maintain the following goals:

1. Plateau Pressure Pplat< 30 cm H2O


2. pH of 7.25-7.35

• PaO2 55mmHg – 70mmHg, or SpO2 88%-95%


• Avoid ventilator induced lung injury: do not exceed tidal volume and plateau pressure limit


• Supportive care as outlined in Chapter on Respiratory Failure and Mechanical Ventilation


• Avoid fluid overload, use basic hemodynamic monitoring (see chapteron Hemodynamic Monitoring)


• Mechanical Ventilation settings for Protective Lung Ventilation


• Continue protective lung ventilation strategy, high FiO2 and PEEP


• Permissive hypercapnia


• Deep sedation and neuromuscular blockade


• Recruitment manoeuvres


• Prone ventilation


• Nitric oxide


• High frequency oscillation


• Extracorporeal membrane oxygenation


• Steroids may be considered but not recommended for routine use


• Continue supportive Care


• Prevent ventilator induced lung injury and ventilator associated pneumonia


• Start weaning the patient as soon as possible

Variable	Protocol
Ventilator mode	Volume assist-control
Tidal volume	< 6 mL/kg ideal body weight
Plateau pressure	Pplat< 30 cm H2O
Ventilation set rate/min	6–35/min, adjusted to achieve arterial
pH goal	pH of 7.25-7.35 pH of 7.25-7.35 considered acceptable.
Inspiratory flow, I:E	Adjust flow to achieve I:E of 1:1–1:3
Oxygenation goal	PaO255-80mmHg 88% < SpO2 < 95%
Fio2/PEEP (mm Hg) combinations	0.3/5, 0.4/5, 0.4/8, 0.5/8, 0.5/10, 0.6/10, 0.7/10, 0.7/12, 0.7/14, 0.8/14, 0.9/14, 0.9/16, 0.9/18, 1.0/18, 1.0/22, 1.0/24
Weaning	Attempts to wean by pressure support required when FiO2/PEEP are .40/8

Guidelines by The Ministry of Health and Family Welfare :

JV Divatia, Professor & Head, Department of Anaesthesia, Critical Care and Pain, Tata Memorial Hospital, Mumbai