Phlegmasia After Caesarean Section With a Falling Platelet Count

Diagnosis. Phlegmasia cerulea dolens - extensive iliofemoral and popliteal venous thrombosis causing such high venous and compartment pressure that arterial inflow is compromised (ABI 0.7, dusky, painful, petechiae). Untreated it progresses to venous gangrene and amputation. Superimposed is a high-probability heparin-induced thrombocytopenia: platelet fall from 242 to 78 ×10⁹/L at day 5–6 of unfractionated heparin, with a new massive thrombosis. Her 4T score is high (thrombocytopenia, typical timing, new thrombosis, and few competing causes beyond the postpartum state).

Immediate actions.

• Stop every heparin exposure - unfractionated heparin, low-molecular-weight heparin, line flushes, and heparin-bonded catheters, which should be exchanged if practical.
• Start a non-heparin parenteral anticoagulant immediately, without waiting for the PF4 result. Argatroban (hepatic dosing, no renal adjustment) or bivalirudin (renal adjustment) are the standard choices. Anticoagulation is not optional here; it is the baseline treatment for both the HIT and the thrombosis.
• Send PF4 antibody (ELISA) and, if positive, a functional confirmatory assay. Send baseline coagulation studies.
• Do not give platelet transfusions - they can precipitate arterial thrombosis in HIT.
• Do not start warfarin in isolation. Starting a vitamin K antagonist before the platelets recover can cause venous limb gangrene through transient protein C depletion; warfarin is only introduced once platelets exceed about 150 ×10⁹/L, with at least 5 days of overlap with a parenteral agent.
• Do not give fondaparinux; data in HIT are limited and cross-reactivity is a concern.
• Elevate the limb, give adequate analgesia, and document a lifelong heparin allergy prominently.

Then the question of the threatened limb still has to be answered - anticoagulation alone is not obviously enough with an ABI of 0.7.

The problem. Anticoagulation alone resolves most phlegmasia over days, but with arterial compromise and a dusky tense limb, waiting risks venous gangrene, compartment syndrome and amputation. Every interventional option has a specific problem in this patient.

• Catheter-directed thrombolysis is the usual first-line intervention for phlegmasia, and would be my choice in an ordinary patient. Here it is relatively contraindicated: platelets of 78 ×10⁹/L are below the usual threshold (roughly 100 ×10⁹/L) for lytic therapy, and HIT itself is a prothrombotic state in which lytic therapy has been associated with paradoxical propagation. Major bleeding risk in a 6-day postpartum woman is also not trivial.
• Pharmacomechanical thrombectomy - mechanical debulking with a rheolytic or aspiration device, with no or minimal lytic - is the most attractive option. It restores outflow quickly without depending on a lytic, and can be combined with a retrievable device only if needed. Risks are haemolysis, haemoglobinuria, contrast nephropathy (check renal function first, which is not yet known) and venous valve injury.
• Open surgical venous thrombectomy with an arteriovenous fistula is a legitimate option for a threatened limb, but it is a major operation in a fresh postpartum patient.
• IVC filter is not indicated here. Anticoagulation is not contraindicated - she is on argatroban - and a filter does nothing for the obstructed iliac vein. Reserve it for the rare case where anticoagulation must be interrupted for surgery.

Plan. Multidisciplinary discussion with haematology and interventional radiology, then proceed to pharmacomechanical thrombectomy with minimal or no lytic agent, continuing argatroban throughout. Platelets of 78 are borderline, not prohibitive; a further fall below about 50 would push me back toward elevation, anticoagulation and close observation with a low threshold for fasciotomy if compartment pressures rise. Consent her explicitly that amputation remains a possibility.

Transition. Once platelets recover above about 150 ×10⁹/L, start warfarin with at least 5 days of overlap with argatroban, targeting an INR of 2–3, then stop the parenteral agent. Do not use a direct oral anticoagulant during the acute phase of HIT; evidence is limited and the acute prothrombotic state is not the setting to experiment.

Duration. Heparin-induced thrombocytopenia with thrombosis is treated for a minimum of 3 months. She has a strong provoking factor (pregnancy and caesarean delivery), so 3 months is defensible, but many would extend to 6 months given the extent of thrombosis and the illofemoral involvement, and some would continue indefinitely if there is residual thrombus or ongoing risk. Reassess at 3 months with duplex and a clinical assessment of post-thrombotic symptoms.

Lifelong heparin avoidance. Document it as an allergy with the specific reaction, give her a medical-alert card and a letter, and warn her that heparin hides in catheter locks, dialysis circuits, heparin-bonded lines and surgical prophylaxis. Any future procedure requiring parenteral anticoagulation should use argatroban or bivalirudin, and her obstetric and anaesthetic teams must be told before any future delivery.

Breastfeeding. Warfarin is compatible with breastfeeding. Argatroban has limited data, so transitioning to warfarin as soon as the platelets allow is desirable.

Follow-up. Compression stockings (30–40 mmHg) for symptom control and to reduce post-thrombotic syndrome; duplex at 3–6 months to assess iliac and femoral patency; advice on long-haul travel, hydration, and weight management; and a plan for thromboprophylaxis in any future pregnancy using a non-heparin agent, decided before conception.