THE EFFECT OF A VENOUS FILTER ON EMBOLIC LOAD, DURING MEDULLARY CANAL PRESSURIZATION: A CANINIE STUDY.

Abstract

Using an established canine model of fat embolization, the effect of temporary mechanical blockade of embolic load during medullary canal pressurization was studied. Haemodynamic measurements, echocardiography and postmortem histomorphometry were used as outcome measures. There was statistically significant difference between the filter and the control groups, when the pulmonary vascular resistance, the percentage area of lungs occupied by fat and the percentage of pulmonary vasculature occupied by fat were compared. We have shown that mechanical blockade by a filter does stop the adverse effect on the lungs during canal pressurization.

Acute intramedullary stabilization of femoral fractures in multiply injured patients still remains controversial. Intravasation of medullary fat has been suspected to trigger ARDS. This study investigates the effect of a filter placed into the ipsilateral common iliac vein during medullary canal pressurization.

Using an established canine model, twelve mongrel dogs were randomized into two groups. A special filter was inserted percutaneously into the left common iliac vein in half the dogs where as the other half served as controls. In all dogs, the left femora and tibiae were pressurized by injection of bone cement and insertion of intramedullary rods. Hemodynamic measurements and echocardiography images were recorded continuously. After sacrifice, the lungs were harvested for analysis.

The mean pulmonary artery pressure at three minutes of pressurization was 12 mm of Hg in the filter group and 28mm of Hg in the control group. The pulmonary vascular resistance in the control group was increased from the 3^rd minute of pressurization throughout the experiment. This was statistically significant when compared with the baseline. There was no such change seen in the filter group. Transesophageal echocardiography showed less embolic shower in the filter group and histomorphometry demonstrated statistically signifant difference, when the percentage area of lungs and the percentage of pulmonary vasculature occupied by fat in the filter group as compared to the control group.

This canine study has demonstrated that mechanical blockade by a venous filters can significantly reduce the embolic load on the lungs during canal pressurization.