Cerebral Arterio-venous pCO₂ Difference, Estimated Respiratory Quotient, and Early Posttraumatic Outcome: Comparison With Arterio-venous Lactate and Oxygen Differences

Abstract

Arterio-venous pCO₂ difference (AVDpCO₂) and estimated respiratory quotient, the ratio between AVDpCO₂ and arterio-venous O₂ difference, may be potentially useful estimators of irreversible posttraumatic global cerebral ischemia. Our aim was to evaluate their relevance, along with arterio-venous lactate difference (AVDL) and lactate oxygen index (LOI), in early outcome prediction. The retrospective study involved 55 patients with severe head injury, admitted consecutively in a multidisciplinary intensive care unit of a general hospital. A retrograde jugular catheter was placed as soon as possible, allowing for 324 simultaneous arterio-jugular samples to be taken throughout the first 48-hour postinjury. Early brain death (within 48 h) was assumed to be due to early global ischemia. A multivariate model including clinical and radiologic descriptors and jugular bulb variables showed that a widening of AVDL and LOI was associated with early brain death. Whereas in the patients who died, a progressive worsening of AVDpCO₂ and estimated respiratory quotient, associated with corresponding changes in AVDL and LOI were observed, in patients who survived the widening of AVDpCO₂ normalized along with that of arterio-venous O₂ difference. These findings suggest that the isolated measurement of widening AVDpCO₂ is not specific for global cerebral ischemia, but its observation over time could be potentially more useful.