Poster presentation | Open | Published:
How early is enough in lactate monitoring?
Critical Carevolume 10, Article number: P54 (2006)
In ARF patients treated with non-invasive ventilation (NIV) a low pH value not improving within 2 hours greatly increases the risk of NIV failure. In relation to the high diaphragm lactate production, we tested the hypothesis that the lactate clearance (LC) was more predictive of the risk of NIV failure in comparison with the difference in pH (DpH) in patients with cardiac pulmonary edema (PE) and metabolic or mixed acidosis.
Forty-seven consecutive patients observed in the Emergency Room with PE were treated with pharmacological therapy (FiO2 0.5, morphine, inotropes, diuretics, vasodilators if hypertensive) and CPAP (10 cmH2O) byhelmet if they had metabolic acidosis, or BIPAP (IPAP 14 cmH2O -EPAP 6 cmH2O) by face mask if they had mixed acidosis. The mean inspiratory airway pressure was the same in the two ventilatory treatments. Blood gas analysis were performed at admission and every 30 min for 2 hours. Clearance of lactate was calculated as: lactate start -lactate (30 min, 1 hour, 1.5 hour, 2 hour) / lactate start × 100 (%).
Significant results were obtained after 2 hours of NIV. In Table 1 the pH value at admission and after 2 hours of NIV and lactate clearance at 2 hours are reported in 35 patients responding to NIV and 12 patients who failed NIV. The higher proportions predicted to fail were with DpH < 0.01 and LC < 25% at 2 hours (OR 3.4 and 5.1, respectively). In another 15 similar patients we compared the predicted risk of failure of NIV related to DpH < 0.01 and LC < 25%, selecting an arbitrary probability of failure equal to 50% between expected and observed failures: the C statistics (area under the ROC curve) of LC < 25 and DpH < 0.01 were 0.85 and 0.73, respectively (P < 0.001).
Lactate clearance is a reliable indicator of the response of patients with PE to NIV. LC < 25% is more sensible than DpH < 0.01, perhaps because it does not take into account confounder factors related to previous metabolic acidosis. It could be considered a cost-effective method for early triaging of patients to be admitted to the ICU for invasive ventilation.