Safety and accuracy of bedside carbon dioxide cavography for insertion of inferior vena cava filters in the intensive care unit.

BACKGROUND: Bedside insertion of inferior vena caval filters (IVCFs) avoids risks associated with transporting these critically ill patients to the operating room or to the radiology suite. But because IVCF insertion requires preinsertion caval imaging, the risk of contrast-induced renal failure remains a concern. Carbon dioxide (CO2) as a contrast agent does not cause renal failure, but its accuracy in determining vena caval diameter (a critical factor in filter selection) and its safety in the critical care population are unknown. This study is designed to assess the safety of using CO2 as a contrast agent in this patient population and to evaluate its accuracy in determining the diameter of the inferior vena cava when used at the bedside.

STUDY DESIGN: A prospective study comparing CO2 with iodinated contrast (IC) material was performed in critically ill patients undergoing vena cavography before bedside IVCF placement. CO2 cavagrams were performed with one or more hand injections of 60 mL of CO2; a single injection of 40 mL of IC material was used. Digital subtraction techniques were used for all of the studies. Blood pressure, pulse rate, and arterial oxygen saturation, end-tidal CO2, and intracranial pressure (when available) were recorded before, during, and after contrast injection. Statistical analysis was performed using the paired t-test, with p < 0.05 being considered significant. Data are expressed as mean +/- SD.

RESULTS: Twenty-three patients were studied. Mean transverse inferior vena cava (IVC) diameters measured 20.4 +/- 0.7mm (IC) and 20.0 +/- 0.7mm (CO2); p = 0.003. The difference in the measurements was 0.4 +/- 0.1 mm, with the largest difference being 1.7mm. In the remaining 10 patients, CO2 differed from IC in determining IVC diameter by only 0.4mm, a statistically significant (p < 0.05) but clinically insignificant difference. No adverse effects on blood pressure, pulse, arterial oxygen saturation, end-tidal CO2, or intracranial pressure were noted with the use of CO2.

CONCLUSIONS: Carbon dioxide as a contrast agent is safe and provides accurate determination of vena caval diameter and anatomy. Carbon dioxide should be considered the contrast agent of choice in critically ill patients.