To prospectively investigate the association between plasma lactate concentration and short-term adverse outcomes in patients with acute PE.

Pulmonary embolism (PE) represents 0.4% of hospitalizations and is the third leading cause of death due to cardiovascular disease (1). In contrast to stroke and acute coronary syndromes, its mortality has not decreased in recent decades likely due to only minor advances in short-term prognostication and treatment strategies (2).The presence of shock or hypotension remains the principal prognostic clinical marker and,to date, is the only factor that clearly indicates a more aggressive treatment than heparin (3). However, only 5% of patients with acute PE present with shock. The majority of PE patients are normotensive and are usually treated with heparin alone. Several studies have looked for new prognostic indicators in order to better stratify normotensive PE patients. A large body of evidence shows that right ventricular dysfunction/injury markers such as elevation of brain natriuretic peptides, troponins, and echocardiographic evidence of right ventricular dysfunction (RVD) are associated with adverse prognosis (3-8). However, these markers have some important limitations. Echocardiography is usually not available around-the-clock in most clinical settings, moreover it shares with troponins and natriuretic peptides a good negative predictive value (>90%) but a low positive predictive value (about 10%) for short-term mortality, probably precluding these markers' usefulness to target more aggressive treatments (8).

Plasma lactate concentration is a marker of the severity of the tissue oxygen supply-to-demand imbalance. It may reflect tissue hypoperfusion also in the presence of normal blood pressure. Accordingly, in other critical settings such as sepsis,plasma lactate concentration is considered to be an accurate prognostic marker as it rises before hemodynamic impairment is clinically evident (9). Furthermore, plasma lactate concentration can be easily and rapidly assayed on arterial blood samples using a blood gas analyzer, which is usually available in emergency departments (EDs) and intensive care units. Recently, a retrospective study showed that plasma lactate ≥ 2 mmol/L was associated with a high mortality rate in patients with acute PE (10). Moreover a prospective monocentric study confirmed these retrospective results and revealed that plasma lactate has prognostic relevance beyond known clinical and instrumental prognostic markers (TELOS study, Ann Emerg Med, in press, see attached file)

The aim of present study is to prospectively investigate the association between plasma lactate concentration and short-term adverse outcomes in patients with acute PE. In particular, we examine whether high plasma lactate (≥ 2 mmol/L) is associated with a high incidence of PE related major adverse events, defined as PE related death or hemodynamic collapse >10% within 7 days of follow-up. Moreover we investigate whether plasma lactate shows incremental prognostic value to clinically overt hemodynamic impairment and to RVD/injury markers, maintaining prognostic relevance in both hypotensive and normotensive PE patients.

Inclusion Criteria:

• Symptomatic objective pulmonary embolism

Exclusion Criteria:

• life expectancies of less than 3 months
• first symptoms 15 day or more before inclusion.

Consecutive adult patients (minimum age eighteen) who presented to the ED of the hospitals participating in the study with clinical suspicion of PE will be considered for the study. We excluded patients with life expectancies of less than 3 months, and patients with first symptoms 15 day or more before inclusion.

The diagnosis of PE will be established by spiral computed tomography or by lung scan or a selective pulmonary angiogram.

Patients with proven PE who will give written consent to the use of their medical information for research purposes will be enrolled in the study.