Early goal directed therapy has been found to improve prognosis in septic patients, if the therapeutic goal is achieved within the first six hours. The aim of our study is to demonstrate that in patients with acute cardiorespiratory failure, rapid (within 2 hours) lactate clearance can help define patients’ prognosis. 67 consecutive patients, admitted to our 16-bed Emergency Medicine ward for acute cardiorespiratory failure (age 75,9 ± 9,8) (APACHE II score 19,0 ± 4,1), were included in the study. Blood lactate concentration was read at admission and after 2, 6 and 24 hours. We evaluated mortality at seven days and the use of orotracheal intubation (patients with negative outcome) vs. discharge or transfer to a non-emergency ward with subsequent discharge (patients with negative outcome). Lactate concentration at admission was 4,6 ± 2,5 mmol/l; lactate clearance (%) at 2 hours was 40,4 ± 32,1 in patients with a positive outcome and –8,3 ± 5,0 in patients with a negative outcome (p < 0,05). Lactate clearance at 2 hours < 25% is correlated to a negative outcome with an 84,2% sensitivity and a 79,2% specificity. The positive predictive value was 61,5% and the negative predictive value was 92,2%. Systematic lactate clearance monitoring can be used in cases of acute cardiorespiratory insufficiency to identify patients with a high risk of negative outcome. In our study, low clearance at two hours was associated with an increase in mortality and/or the need for orotracheal intubation. Conversely, a clearance at two hours of > 25% in most cases confirms the therapeutic strategy undertaken. Serial evaluation of blood lactate concentration may therefore be useful in guiding treatment strategies.