Venous-arterial PCO₂ difference as an early predictor of organ dysfunction in the ICU

Introduction

The early identification and scrupulous monitoring of tissue dysoxia can improve the management of critical patient. In this light, the final product of aerobe and anaerobe metabolism (that is, carbon dioxide) can provide useful information on adequacy of tissue perfusion and metabolism [1, 2]. The aim of our study was to evaluate whether the venous-arterial PCO₂ gradient provides useful information on tissue dysfunction in patients admitted to the ICU.

Methods

We retrospectively studied 135 patients admitted to our ICU in 2006 with a length of stay >24 hours and a gas analysis from arterial and central venous blood at admission. Venous-arterial PCO₂ gradient (ΔpCO₂), organ dysfunction in the first 24 hours and ICU mortality were collected. Organ dysfunction was defined as a SOFA score ≥2 for each organ. The patients were subdivided and compared on the basis of ΔpCO₂ value: ΔpCO₂ ≥ 6 mmHg (High group) and ΔpCO₂ <6 mmHg (Normal group).

Results

Thirty-nine patients (29%) showed a ΔpCO₂ ≥ 6 mmHg (ΔpCO₂ 9.6 ± 3.1). In the Normal group the mean ΔpCO₂ value was 1.2 ± 4.1. The High group showed a larger rate (44%) of respiratory failure than the Normal group (25%) Similarly, cardiovascular dysfunction was observed in 49% of the patients of the High group and only in 19% of the Normal group (P < 0.05). Renal failure was also slightly larger in the High group (31%) than in the Normal group (22%) (P > 0.05). As expected, patients of the High group showed an ICU mortality (33%) three times larger (P < 0.05) than patients of the Normal group (12%).

Conclusions

The above data support the hypothesis that ΔpCO₂ can provide useful information on the tissue perfusion and metabolism in ICU patients and can be used as a reliable biomarker for early prediction of organ dysfunction.