van Beest PA, Lont MC, Holman ND, Loef B, Kuiper MA, Boerma EC.; Intensive Care Med. 2013 Jun;39(6):1034-9.
PURPOSE: To investigate the interchangeability of mixed and central venous-arterial carbon dioxide differences and the relation between the central difference (pCO2 gap) and cardiac index (CI). We also investigated the value of the pCO2 gap in outcome prediction.
METHODS: We performed a post hoc analysis of a well-defined population of 53 patients with severe sepsis or septic shock. Mixed and central venous pCO2 were determined earlier at a 6 h interval (T = 0 to T = 4) during the first 24 h after intensive care unit (ICU) admittance. The population was divided into two groups based on pCO2 gap (cut off value 0.8 kPa).
RESULTS: The mixed pCO2 difference underestimated the central pCO2 difference by a mean bias of 0.03± 0.32 kPa (95 % limits of agreement: -0.62-0.58 kPa). We observed a weak relation between pCO2 gap and CI. The in hospital mortality rate was 21 % (6/29) for the low gap group and 29 % (7/24) for the high gap group; the odds ratio was 1.6 (95 % CI 0.5-5.5), p = 0.53. At T = 4 the odds ratio was 5.3 (95 % CI 0.9-30.7); p = 0.08.
CONCLUSIONS: From a practical perspective, the clinical utility of central venous pCO2 values is of potential interest in determining the venous-arterial pCO2 difference. The likelihood of a bad outcome seems to be enhanced when a high pCO2 gap persists after 24 h of therapy.
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