Does the arterial-central venous lactate gradient correlate with the P/F ratio in mechanical ventilated critically ill patients?

Introduction

There is evidence about pulmonary production and release of lactate during acute lung injury. The aim of this study was to evaluate whether the arterial-central venous lactate gradient (AVLG) is correlated with the P/F ratio in general ICU patients.

Methods

Twenty-four patients requiring mechanical ventilation for at least 72 hours were enrolled. During the first 72 hours, we prospectively collected and recorded central venous and arterial blood samples to analyse blood gases and serum lactate every 24 hours. Ventilator settings as well as general patient characteristics were also recorded. Data are shown as the median and interquartiles. The Spearman correlation test was used and P < 0.05 was considered significant.

Results

Eleven females and 13 males were evaluated. Median age was 49 (42, 65) years old and the APACHE II score was 23 (19, 33). One-half of patients were admitted with septic shock diagnosis. Four patients had the diagnosis of acute lung injury or acute respiratory distress syndrome at enrollment. The median PEEP was 10 (8, 12) cmH₂O, FiO₂ was 0.4 (0.3, 0.5) and the P/F ratio was 229 (159, 315). The AVLG was evaluated as the variation [(arterial – venous lactate) / arterial lactate] and its median was 0.00 (-0.20, 0.08). In overall group analysis (n = 70), the P/F ratio and AVLG correlation was -0.05 (P = 0.670). In the P/F ≤ 200 subgroup analysis (n = 25), the P/F ratio and AVLG correlation was 0.08 (P = 0.709).

Conclusion

Even though the lungs may produce and release lactate in some patients as sepsis and acute respiratory distress syndrome subjects, we could not find a correlation between the AVLG and the P/F ratio in a general population of critically ill patients. However, our results are probably underpowered.