INFLUENCE OF MECHANICAL VENTILATION ON BLOOD LACTATE IN PATIENTS WITHACUTE RESPIRATORY-FAILURE

Objectives: To determine whether mechanical ventilation (MV) may affec t blood lactate concentration in patients with acute respiratory failu re. Design: Prospective observational study with follow-up to hospital discharge. Setting: A 17-bed medical and coronary intensive care unit in a 650-bed general hospital. Patients: 55 adult patients mechanical ly ventilated for acute respiratory failure between May 1996 and April 1997 were recruited. Measurements and results: Arterial blood samples for determination of plasma lactate and blood gas analysis were taken just before tracheal intubation on spontaneous breathing, and 20 and 60 min after the initiation of controlled MV. Cuff systemic arterial p ressure was measured before tracheal intubation and every 10 min durin g the first h of MV. Hyperlactatemia (arterial blood lactate greater t han or equal to 2 mmol/l) was present in 21 of the 55 patients studied . After 20 min of MV, there was a decrease in blood lactate from 4.74 +/- 1.78 to 3.07 +/- 1.69 mmol/l (p < 0.01); 40 min later there was a further decrease to 2.63 +/- 1.35 mmol/l (p < 0.05). The decrease in b lood lactate was also observed in those patients who after starting MV developed systemic arterial hypotension (p < 0.01). In patients with a normal lactate concentration at the entry to the study, lactate rema ined the same after 60 min on MV (NS). Conclusions. Controlled MV decr eases substantially the severity of hyperlactatemia in patients with a cute respiratory failure, and any adverse circulatory effects of MV do not alter this beneficial outcome.