New 2012 Berlin Definition for ARDS

Source:http://emergencymedic.blogspot.com

The new 2012 definition for Acute Respiratory Distress Syndrome (ARDS) (published in JAMA June 2012)

According to the previous definition published in 1994 by the American-European Consensus Conference (AECC), ARDS must have the following 4 criteria:

• the onset must be acute
• there must be hypoxemia with PaO2/FIO2 ratio ≤ 200
• there must be bilateral infiltrates on CXR
• these findings cannot be attributed to other causes

A separate category for acute lung injury (ALI) is defined with PaO2/FIO2 ≤ 300

However, a number of problems are found with the 1994 definition, including:

• term 'acute' was not defined (i.e., how "acute" is acute)
• the category of ratio PaO2/FIO2 between 201-300 is confusing (PaO2/FIO2 ≤ 300 is ALI, PaO2/FIO2  ≤  200 is ARDS, PaO2/FIO2 between 201 - 300 ?ALI/ARDS)
• CXR interpretation has poor inter-observer reliability

With this, the new Berlin 2012 definition of ARDS is published with the following changes:

1. the category of acute lung injury (ALI) with PaO2/FIO2 ≤ 300 is REMOVED
2. instead, ARDS is now divided into three categories based on severity of hypoxemia
1. PaO2/FIO2 between 200–300 is defined as mild
2. PaO2/FIO2 between 101 - 199 is defined as moderate
3. PaO2/FIO2 of less than 100 is defined as severe
3. The term 'acute' now has a specified time frame of symptoms developing within ONE week of a known clinical insult
4. Other changes:
1. the CXR criteria is now more defined with the added phrase "bilateral opacities - not fully explained by effusions, lobar/lung collapse, or nodules"
2. PCWP reading is no longer required as part of the diagnosis as this is increasingly not used. Instead, this new definition requires that the respiratory failure cannot be explained fully by cardiac failure or volume overload.

Editorial comment in JAMA June 2012 points out that this new definition only improves its predictive value of mortality slightly; however, the clarity of the criteria is significantly improved.

Ref:The ARDS Definition Task Force. Acute respiratory distress syndrome: The Berlin definition. JAMA 2012 Jun 20; 307:2526
Abstract: http://jama.jamanetwork.com/article.aspx?articleid=1160659

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Permissive hypercapnic ventilation (PHV)

Source:http://www.uptodate.com/contents/permissive-hypercapnic-ventilation

INTRODUCTION

Permissive hypercapnic ventilation (PHV) is a strategy of mechanical ventilation that accepts deliberate alveolar hypoventilation [1]. Its primary purpose is to allow ventilator changes that reduce alveolar pressure and its associated risks, such as pulmonary barotrauma, ventilator-associated lung injury, and hypotension. Hypercapnic acidosis is a consequence of this strategy and not a goal.

Patient selection, efficacy, and potential harms of PHV are discussed in this topic. In addition, the strategy itself is described. Use of PHV in patients with acute respiratory distress syndrome and asthma is reviewed separately. (See "Mechanical ventilation in acute respiratory distress syndrome" and "Mechanical ventilation in adults with acute exacerbations of asthma".)

PATIENT SELECTION

Selecting patients for PHV requires careful consideration of the indications and contraindications, which are discussed in this section.

Indications — PHV is indicated in situations where decreasing the minute ventilation (ie, lowering the tidal volume or respiratory rate) may be beneficial. It is most commonly utilized in patients with acute lung injury or acute respiratory distress syndrome (collectively referred to as ARDS in this review), an acute exacerbation of asthma, or an acute exacerbation of chronic obstructive pulmonary disease (COPD).

• ARDS — Low tidal volume ventilation improves important clinical outcomes in patients with ARDS. The respiratory rate is routinely increased during low tidal volume ventilation in an effort to maintain an adequate minute ventilation. However, the increased respiratory rate may be insufficient to compensate for the low tidal volumes and hypercapnic acidosis may develop. PHV is indicated in this situation, rather than abandoning low tidal volume ventilation. (See "Mechanical ventilation in acute respiratory distress syndrome", section on 'Low tidal volume ventilation'.)
• Asthma — Widespread bronchoconstriction reduces expiratory airflow during an asthma exacerbation. Auto-PEEP will develop if the expiratory airflow is reduced to such a degree that the next breath is initiated prior to the completion of expiration. The expiratory time should be prolonged in this situation, which can be accomplished by increasing the inspiratory flow rate, decreasing the tidal volume, or decreasing the respiratory rate. Lowering the tidal volume or respiratory rate will decrease the minute ventilation and may result in hypercapnic acidosis. PHV is indicated in this situation, rather than accepting significant auto-PEEP. (See "Mechanical ventilation in adults with acute exacerbations of asthma".)
• COPD — Patients with COPD are similarly at risk for auto-PEEP during mechanical ventilation. PHV is indicated if efforts to reduce auto-PEEP result in hypercapnic acidosis, as described above for patients with an asthma exacerbation. (See "Positive end-expiratory pressure (PEEP)", section on 'Auto (intrinsic) PEEP'.)

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ARDS-Ventilator

new england journal of medicine, 2000. study on ARDS: low tidal volume ventilation vs traditional ventilation in ARDS by ARDS Network group.

- The one strategy that has proven effective in reducing the duration of mechanical ventilation and improving survival is the use of low tidal volume
ventilation.
- This strategy employs ventilator-delivered tidal volumes of 6 mL per kilogram of predicted body weight, with an additional goal of maintaining plateauairway pressures < 30 cm H2O.
- Part of this protocol dictates the use of certain combinations of inspired oxygen (FiO2) and PEEP.
- Because use of this protocol has been shown to improve outcomes for ALI/ARDS patients, it should be employed whenever possible in treating these
patients.- Therefore, these FiO2/PEEP combinations should be used to achieve adequate oxygenation:

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