Pulmonary lactate production in septic patients with and without ARDS

Introduction

The lungs may be a source of lactate in septic patients, specially when severe respiratory failure is present. Furthermore, first-days lactate levels have been related to outcome in those patients.

Objectives

To describe the relationship between pulmonary lactate flux and PaO₂/FiO₂ ratio in septic patients; to verify the relationship between lactate flux and outcome.

Setting

A large general ICU.

Design

Prospective, observational study.

Patients

Thirty-two adult septic patients.

Method

All patients were monitored with pulmonary artery catheter and gastric tonometer. Systemic hemodynamic and oxygen variables, arterial and mixed-venous lactate levels, and gastric mucosal pCO₂ (PgCO₂) were measured every 8 hours for 5 days. PCO₂gap (PCO₂gap = PgCO₂ — PaCO₂) and pulmonary lactate flux [(arterial lactate — mixed venous lactate) × cardiac output] were calculated. Results were expressed as median and inter-quartile 25–75%. The median values at the first day were used to statistical analyzes. Mann–Whitney U-test was used to evaluate of differences between the groups.

Results

Mean age was 57 ± 17 years, being higher among patients with ARDS than the ones without ARDS. Mean APACHE II and SOFA scores were 21.5 ± 6.6 and 9.9 ± 2.5, respectively. The lactate flux showed a trend to be greater in non-survivors than survivors septic patients (P = 0.06).

Conclusion

Despite of respiratory failure severity, all septic patients presented pulmonary lactate production, which was significantly greater in patients with ARDS.

Table 1 The first day data for hemodynamic and oxygenation parameters