National Emphysema Treatment Trial (NETT) 

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Project ended
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Antonello Punturieri, M.D., Ph.D.

What was the goal of the NETT?

The NETT was the first multi-center trial to study whether lung volume reduction surgery (LVRS) was a safe and effective treatment for patients with chronic obstructive pulmonary disease (COPD) of the mainly emphysema type. A secondary objective of the NETT was to identify criteria to select patients who would benefit the most from LVRS.

LVRS was first used to treat emphysema in the 1950s. In LVRS, 20% to 35% of the most damaged regions of each lung is removed on the theory that reducing lung size would pull open the airways and allow the breathing muscles to return to a more normal and comfortable position, making breathing easier and easing symptoms. Although some patients seemed to improve after the surgery, a high risk of death or complications associated with LVRS prevented its widespread use. In the early 1990s, some physicians began using LVRS again.

In response to the community’s concerns about the safety and effectiveness of LVRS, the NHLBI in 1995 convened a workshop of experts in the treatment of emphysema. The experts proposed a systematic scientific study of LVRS. At the same time, an independent study requested and funded by the Health Care Financing Administration, now known as the Centers for Medicare and Medicaid Services (CMS), found that there were not enough data on the risks and benefits of LVRS to justify unrestricted Medicare reimbursement. The CMS also recommended a scientific study of LVRS.


  • The NHLBI, in collaboration with other federal government agencies, launched the NETT in 1996.
  • The 17 NETT clinical centers studied more than 1,200 patients who had severe emphysema.
  • The NETT clarified the short-term and long-term risks and benefits of LVRS as a treatment for severe emphysema.
  • The NETT helped to identify patients who would benefit from LVRS, which led Medicare to cover LVRS treatment for select patients based upon data from the NETT.

What were the key findings of the NETT?

The NETT determined the benefits, risks, and cost-effectiveness of LVRS treatment of COPD with emphysema. The NETT results reported in 2003 led to Medicare coverage of LVRS for patients meeting certain criteria, based on the study results.

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Results of the NETT showed that, on average, patients who received LVRS with medical therapy were more likely to function better after 2 years and did not face an increased risk of death, compared with patients who received medical therapy alone. The effects of LVRS varied widely among patients, however.

Researchers identified two characteristics — emphysema mostly in the upper lobes of the lungs and low exercise capacity — that helped predict which patients would benefit from surgery. Patients with both characteristics were more likely to survive longer and function better after LVRS. Patients with only one of these characteristics received some benefit from the surgery, although surgery did not increase survival time for these patients.


For patients whose emphysema was not in the upper lobes and who had greater exercise capacity, LVRS reduced survival time and failed to improve functional levels. Early in the study, researchers stopped enrolling patients with severe airflow obstruction and either limited ability to exchange oxygen when breathing or widespread damage in the lungs. The researchers determined that these patients received little benefit from LVRS and were at high risk of death from the procedure.

Cost Effectiveness

For the LVRS group, average costs were very high in the first year following surgery. In the third year of follow-up, however, total medical care costs were equivalent in the LVRS group and the group that received medical therapy only.

NETT investigators concluded that if the benefits from LVRS were maintained, the cost effectiveness of surgery added to medical therapy could ultimately approach levels consistent with other treatments that are considered of good value. This outcome would be especially likely for patients found to gain the most from LVRS — those with upper-lobe emphysema and low exercise capacity.

How was the National Emphysema Treatment Trial conducted?

The NETT began in 1996 as a cooperative effort between the NHLBI and CMS to study the risks and benefits of LVRS. In addition, the Agency for Healthcare Research and Quality (AHRQ) contributed support for an analysis of the cost effectiveness of LVRS based on NETT data.

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At the start of the study, participants completed a 6- to 10-week pulmonary rehabilitation program, which included education, counselling, exercise training, and other techniques to help them understand and manage their condition. Patients also received medicines and oxygen as needed. Participants were then randomly assigned either to continue this treatment or to have LVRS in addition to continued medical treatment.

While participants remained under the care of their own physicians, the NETT evaluated participants at 6 months, 1 year, and every year thereafter until the NETT ended. NETT researchers measured lung function, quality-of-life scores, shortness of breath, and exercise capacity, in addition to survival, illness, and hospitalization rates.

NETT investigators monitored participants for an average of 29 months before reporting their findings in 2003. Investigators followed up with participants for 2 additional years and found that, for patients who benefited from LVRS, the benefits continued during that time. The NETT ended in 2005. NETT investigators also conducted a prospective cost-effectiveness analysis over 3 years of follow-up as part of the trial.