Discussion

Venous thromboembolism (VTE), comprising deep venous thrombosis (DVT) and pulmonary embolism (PE), is a common and serious complication predominantly occurring in hospitalized patients. The estimated incidence of a first acute VTE is 0.7 to 1.4 per 1000 person-years and is mostly observed in patients older than 55 years8. Marik et al. reported an 11.7% incidence of DVT in a group of medical ICU patients9. The lack of resources limited our ability to systematically perform US screening for each COVID-19 patient with a VTE risk factor. The real morbidity and mortality of VTE in COVID-19 patients needs to be investigated further.
The treatment of DVT and PE is nonspecific. Anticoagulant and thrombolytic therapies are essential strategies. However, for hemorrhagic or preoperative patients who are suffering from DVT simultaneously, IVC filter insertion could be an effective intervention for preventing lethal PE.
Our report describes three severe COVID-19 patients also presenting with DVT disease. All of them had reached IVCF implantation intervention criteria to prevent acute PE. There are however no recommendations on the best IVCF implantation strategy in the latest COVID-19 practice guidelines. ICVF implantation is normally performed under digital subtraction angiography (DSA) guidance, as presented in case 1. Severe COVID-19 patients however often present with hypoxaemia, requiring continuous HFNC and ECG monitoring. These unstable features would not allow transfer of these patients to the DSA room. Transferring patients from isolation wards would also increase the likelihood of cross-infection in the hospital. Disinfection of the DSA room would have a significant impact on medical and non-medical resources, together with manpower. The team thus opted for US guided IVCF implantation for both remaining cases.
Up to the point of submission, we believe that this is the first bedside US-guided IVCF implantation reported case in severe COVID-19 patients on the isolation ward. We would like to summarise our experience pertaining to thrombosis prevention and treatment in severe and critical COVID-19 patients as follows:
1. More attention should be paid to the prevention and treatment of DVT and PE, in spite of the current shortage of critical medical resources;
2. For severe and critically ill patients, primary preventive strategies with stockings and/or drugs should be encouraged. Physicians should closely monitor biomarkers of hypercoagulation. There should also be increased awareness about the possibility of neurovascular compromise in the extremities. Routine colour US scans may be necessary for COVID-19 inpatients;
3. During the current COVID-19 epidemic, an US-guided IVCF implantation on the isolation ward may be considered in patients who fulfil criteria for implantation;
4. Full preparation is needed to achieve bedside IVCF implantation: pre-assessment of the feasibility of a percutaneous approach via the femoral vein; assessment of whether the inferior vena cava is unobstructed; evaluation of whether there is vena cava variation; fasting for 12 hours before surgery (giving an ordinary enema 1 hour before surgery is another alternative choice). Vascular surgeons need to take level 3 protective measures before entering the isolation ward and strictly follow protective protocol to avoid contamination.
In conclusion, COVID-19 positive patients with abnormal signs and symptoms in the extremities should be monitored closely. A colour US scan is recommended for severe and critical COVID-19 patients with a high PADUA index and/or Caprini index. If the patients have reached an IVCF implantation indication, we strongly recommend opting for an US-guided bedside IVCF implantation strategy on the isolation ward instead of the conventional DSA method.