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JAMA: H1N1, ECMO, and Survivability

 

 

# 5882

 

 

Despite its reputation as a `mild’ pandemic, the 2009 H1N1 `swine flu’ virus produced unusually severe respiratory infections in a very small subset of patients.  Thousands of people ended up in ICUs, with some requiring ventilator assistance for weeks on end.

 

Last month in mBio: Lethal Synergism of H1N1 Pandemic Influenza & Bacterial Pneumonia, we looked at a study that proposed that bacterial co-infections were behind many of these cases of ARDS (Acute Respiratory Distress Syndrome).

 

In late 2009, in Cytokine Storm Warnings I wrote about a study that appeared in the  American Thoracic Society's American Journal of Respiratory and Critical Care Medicine, that looks at the autopsy results of 21 pandemic flu victims.

 

Researchers found three separate types of severe lung damage, and point to signs of a cytokine storm response in some of these cases.

 

But whatever the cause (and there likely were several), many swine flu patients found themselves suffering from serious lung damage (see The View From The ICU).

 

Normally, patients with ARDS are placed on mechanical ventilation, and treated with a variety of pharmacological agents to reduce infection (antibiotics) and lung inflammation (corticosteroids, Nitric Oxide, etc.).

 

Despite these measures, ARDS is generally fatal in 50% of patients.

 

With H1N1-related pneumonia, mechanical ventilation often did not result in adequate oxygenation, as the lungs were too congested to allow oxygen exchange in the alveoli.

 

oxygenation

(Image adapted from Wikipedia)

 

In some hospitals an expensive and controversial treatment called ECMO was tried on some adult and adolescent patients with ARDS, and early reports were encouraging.

 

ECMO or Extracorporeal Membrane Oxygenation is a specialized heart-lung bypass machine used to take over the body’s heart and lung function – for days or weeks if necessary – while the body heals from injury or illness.

 

ECMO is most commonly used in neonatal intensive care units for newborns in respiratory distress, although it is also used for pediatric and adult patients with severe heart or respiratory deficits.

 

In the fall of 2009 we saw a report in The Lancet  where UK researchers determined that ARF (Adult Respiratory Failure) patients that received ECMO support as opposed to conventional ventilation had a greater survivability without disability.

 

 

Yesterday in JAMA (Journal of the American Medical Association) two articles appeared on the use of ECMO during the pandemic; a study and an editorial.

 

Noah MA, et al "Referral to an extracorporeal membrane oxygenation center and mortality among patients with severe 2009 influenza A(H1N1)" JAMA 2011; DOI: 10.1001/jama.2011.1471.


Checkley W "Extracorporeal membrane oxygenation as a first-line treatment strategy for ARDS: Is the evidence sufficiently strong?" JAMA 2011; DOI: 10.1001/jama.2011.1504.

 

 

The study – which was limited to patients at 4 hospitals with ECMO facilities in the UK – used `matched pairs’ of patients with similar history, age, symptoms, and other traits that would be expected to have an effect on outcome.

 

Across the board they found that ECMO patients were twice as likely to survive as were non-ECMO patients.

 

While these findings are both encouraging and intriguing, ECMO is hardly a panacea for a pandemic.

 

Even among those who received ECMO, more than 20% died. And ECMO therapy is invasive, expensive, requires anticoagulant drugs for the duration of treatment, and can result in serious complications. 

 

Furthermore, ECMO units are severely limited in number, with the number reported available in the United States during the pandemic as `a few hundred’.

 

The authors caution that the higher survivability of patients who received ECMO treatment may have been due to other factors, and that these results – while encouraging - should be taken cautiously. Still, they believe their results will help revitalize interest in ECMO as a viable treatment option of ARDS.

 

The accompanying editorial cautioned that randomized controlled trials of ECMO treatment for ARDS would be needed to prove its true value.

 

The JAMA research article, and the editorial are both available online, and worth reading. 

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