0032. Relationship between microcirculatory alterations and venous-to-arterial carbon dioxide differences in patients with septic shock

Introduction

Increased venous to arterial carbon dioxide difference (Pv-aCO₂) have been attributed to low cardiac output states. However, mechanisms conducting to Pv-aCO₂ increases during normal or even high cardiac output conditions as in septic shock are not fully understood. We hypothesized that Pv-aCO₂ could reflect the adequacy of microvascular perfusion during resuscitated septic shock

Objectives

To test the hypothesis that Pv-aCO₂ could reflect the microvascular blood flow during the early phases of resuscitation in septic shock

Methods

We included 80 patients with a first episode of septic shock admitted to a mixed ICU in a University Hospital over a 12-month period. Time 0 (T0) was set at ICU admission when a pulmonary artery catheter was inserted. Arterial and venous gases analyses were performed at T0 and 6 hours after (T6). We defined Pv-aCO₂ as the difference between the mixed venous and arterial CO₂ partial pressures. A Sidestream Dark-Field (SDF) imaging device (Microvision Medical, Amsterdam, the Netherlands) was used to evaluate the sublingual microcirculation both at T0 and T6. At each assessment, 5 sequences of 20 seconds each were recorded and stored under a random number. An investigator blinded to the sequence order and patient's clinical course, analyzed the sequences semi-quantitatively. The vessels were separated into large and small using a cut-off value of 20 µm in diameter. We evaluated the relation between the percentage of small vessels perfused and the Pv-aCO₂ using linear and non-linear regressions and Spearman Rho test. A p< 0.05 was considered as significant.

Results

We found significant but very weak relationships between general hemodynamics or oxygen derived parameters with Pv-CO₂.Pv-aCO₂ was inversely related to the percentage of small vessels perfused both at T0 and T6 (T0: R²:0.515, p< 0.001; T6: R²:0.453, p< 0.001).

Fig. 1

Pv-aCO2 vs. SVP and CO at T0

Fig. 2

Pv-aCO2 vs. SVP and CO at T6

Table 1 General hemodynamics and Oxygen-derived parameters

Conclusions

Microvascular blood flow is a key determinant of Pv-aCO₂ during normodynamic septic shock. Pv-aCO₂ could track microvascular alterations during early phases of septic shock.