I would be grateful for your advice/opinion regarding the following case.
We admitted a preterm baby 28 weeks gestation with oesophageal atresia and tracheo-oesophageal fistula in our unit in October. The baby was severely IUGR weighted only 600 g at birth. He had a fistula closure on day 1. Due to his cardiovascular and respiratory instability the full correction was delayed. He had a difficult time following the surgery. He was stabilised, weaned of the ventilator and the correction surgery was planned when he developed sepsis. We looked for the source of the infection so among other investigations we did an Echo. His Echo showed a mass in his right ventricle, which we thought to be a thrombosis. We started him on LMWH treatment. He deteriorated couple of days after the treatment was started and required ventilation again. The repeated Echo didn't show the thrombus in the right ventricle anymore. Abdominal Us scan was done, which showed a mass in the inferior v. cava. The mass is about 4 cm long, seems to be attached to the wall of the vein above the renal vein, but in other places it is not connected to the wall of the vein. It didn't cause any disruption in the blood flow. (had good urine output and he was not oedematous). The most likely diagnosis was the thrombosis (as a consequence of previous umbilical/femoral catheter or longline) so I continued the LMWH. The correction surgery was done and he came off the ventilator and reached full feeds. On the repeated scans the inferior v. cava mass didn't show any change (not even attachment to the wall), according to the Chest guideline on thrombosis we should discontinue the treatment with LMWH after 3 month. Would you recommend to stop the treatment even if the mass didn't change? Can we give aspirin to an ex-preterm as a prophylaxis? Is it necessary? Do you have experience with a thrombus which didn't show any change? Can you think of anything else as a differential?