Nonthrombotic Embolism

Nonthrombotic embolism is obstruction of the circulation by material other than blood clot. The main forms are:

• Gas: venous or arterial air embolism, and decompression gas.
• Fat and marrow: fat embolism and fat embolism syndrome.
• Cellular: tumour embolism.
• Infective: septic emboli.
• Particulate and foreign material: talc, cellulose and starch from injected crushed tablets, bone cement, mercury, retained catheter or guidewire fragments.

Air embolism

• Venous entry occurs through central venous catheter insertion, use, disconnection or removal, haemodialysis circuits, neurosurgery in the sitting position, laparoscopy with CO2 insufflation, caesarean section, major trauma, lung biopsy, and positive pressure barotrauma.
• Rapid entry of 3 to 5 mL/kg (roughly 200 to 300 mL in an adult) can be fatal. The gas forms an air lock in the right ventricular outflow tract and causes acute right heart failure.
• Arterial air embolism arises from paradoxical passage through a patent foramen ovale (present in about 25%), pulmonary barotrauma, cardiopulmonary bypass, and lung biopsy. Small volumes in the cerebral or coronary circulation cause stroke or myocardial infarction.

Fat embolism

• It follows fractures of long bones and pelvis, especially closed femoral shaft fractures, intramedullary reaming and nailing, joint arthroplasty, liposuction, bone marrow transplant, sickle cell crisis, pancreatitis and burns.
• Embolisation is common, but the clinical fat embolism syndrome occurs in roughly 1 to 5% of long bone fractures.
• Mechanical obstruction is followed by biochemical injury from free fatty acids, with endothelial damage, inflammation and increased capillary permeability.

Tumour embolism

• Tumour cells lodge in pulmonary arterioles and provoke fibrocellular intimal proliferation and thrombosis, causing pulmonary hypertension.
• Primaries are most often gastric, breast, hepatocellular, renal and choriocarcinoma.

Septic embolism arises from right-sided endocarditis (injection drug use, indwelling catheters, pacemaker leads), septic thrombophlebitis, and Lemierre syndrome.

Bone cement implantation syndrome is hypoxia, hypotension and arrhythmia at the time of cementing, most often in hemiarthroplasty of the hip in elderly patients.

Decompression sickness results from nitrogen bubbles after rapid ascent in divers, aviators and compressed air workers.

Venous air embolism

• Sudden dyspnoea, cough, chest pain, tachycardia, hypotension, light-headedness and sense of impending doom.
• Millwheel murmur, wheeze, and gasping respiration.
• In anaesthetised patients, the earliest sign is a fall in end-tidal CO2 with hypoxaemia, then hypotension and arrhythmia.

Arterial air embolism

• Focal neurological deficit, seizure, loss of consciousness, ST elevation and arrhythmia, and marbling of the tongue or retinal arterial gas bubbles.

Fat embolism syndrome

• Onset 12 to 72 hours after injury, with a classic triad:
• Respiratory: hypoxaemia, tachypnoea, and bilateral infiltrates.
• Neurological: confusion, drowsiness, focal signs or coma, out of proportion to the pulmonary findings.
• Petechial rash: conjunctivae, axillae, neck and upper chest, present in 20 to 50% and transient.
• Fever, tachycardia, retinal exudates, jaundice, renal impairment, anaemia and thrombocytopenia may occur.

Tumour embolism

• Progressive dyspnoea over days to weeks, cough, hypoxaemia, right heart failure and haemoptysis, which may be rapidly fatal. It can mimic recurrent pulmonary thromboembolism.

Septic embolism

• Fever, pleuritic pain, haemoptysis and multiple peripheral nodules, many cavitating, with signs of the infected source.

Decompression sickness

• Joint pain ("bends"), skin itching or marbling, paraesthesia, paraparesis, vertigo, and chest symptoms ("chokes"), appearing within 6 hours of surfacing in most cases.

Red flags are sudden cardiovascular collapse during central line manipulation, neurological deterioration after fracture without head injury, and hypotension at the moment of cement pressurisation.

Air embolism

• Diagnosis is clinical and based on context. Transoesophageal echocardiography is the most sensitive detector, showing bubbles in the right heart. Precordial Doppler and end-tidal CO2 monitoring are used intraoperatively.
• CT shows gas in vessels or cardiac chambers. Aspiration of gas through a central catheter confirms the diagnosis.
• Perform ECG, troponin and arterial blood gas. Echocardiography with bubble study identifies a right to left shunt.

Fat embolism syndrome

• The diagnosis is clinical, requiring supportive major and minor features and exclusion of pulmonary embolism, sepsis and head injury.
• Chest CT shows patchy ground glass opacities and septal thickening.
• MRI brain shows multiple small hyperintense lesions on T2 and diffusion sequences in a "starfield" pattern.
• Laboratory features include falling haemoglobin and platelets, raised ESR, and lipuria. Fat-laden macrophages on lavage lack specificity.

Tumour embolism

• CT pulmonary angiography may be normal or show tree-in-bud nodularity and peripheral vessel beading. Echocardiography shows right ventricular strain.
• Diagnosis is by cytology from blood aspirated through a wedged pulmonary artery catheter, or by lung biopsy, and is frequently made post mortem.

Septic embolism

• At least three sets of blood cultures before antibiotics, echocardiography (transthoracic then transoesophageal), and CT chest showing multiple peripheral cavitating nodules and feeding vessel sign.

Other tests

• Foreign body emboli from retained catheter fragments: chest radiograph and fluoroscopy.
• Decompression sickness: clinical diagnosis, with MRI of the spinal cord and brain to document injury.

Venous air embolism

• Stop further entry: occlude the site, flood the surgical field with saline, clamp or pinch the catheter, and place an occlusive dressing.
• Give 100% oxygen and discontinue nitrous oxide.
• Position left lateral decubitus with head down to trap air in the right ventricular apex away from the outflow tract.
• Aspirate air from the right atrium through a multi-orifice central catheter whose tip lies at the superior vena cava and right atrial junction.
• Support the circulation with fluids and norepinephrine 0.05 to 0.5 micrograms/kg/min. Chest compressions in cardiac arrest may break the air lock.
• Prevention: place the patient supine or head down during line insertion and removal, use air-eliminating filters and Luer-lock connections, and keep infusion bags from running dry.

Arterial and cerebral air embolism

• 100% oxygen immediately, supine positioning, fluid resuscitation, and benzodiazepines for seizures.
• Hyperbaric oxygen recompression to 2.8 atmospheres absolute using the standard 6 hour schedule as early as possible. Benefit persists even with delays of many hours.

Decompression sickness

• 100% oxygen by tight mask, isotonic IV fluids 1 to 2 L, recompression therapy at 2.8 atmospheres absolute, and avoidance of aspirin and alcohol.
• Aeromedical transfer at cabin pressure of 1 atmosphere or low altitude.

Fat embolism syndrome

• Prevention: early stabilisation of long bone fractures within 24 hours, careful reaming and venting during intramedullary nailing, and adequate resuscitation.
• Treatment is supportive: oxygen or ventilation with lung protective settings (tidal volume 6 mL/kg predicted body weight, PEEP titrated to oxygenation), euvolaemia, haemodynamic support, and treatment of coagulopathy.
• Corticosteroids (methylprednisolone 1.5 mg/kg every 8 hours for 3 doses) reduced incidence when given prophylactically in small studies, but are not routine. Heparin, alcohol and albumin are not recommended.
• Most patients recover within 3 to 7 days, with mortality of 5 to 15% in severe cases.

Tumour embolism

• Treat the primary cancer with systemic therapy. Anticoagulation does not help. Supportive care with oxygen, and palliative planning, since prognosis is measured in weeks in most.

Septic embolism

• Start empirical IV therapy covering Staphylococcus aureus after cultures: flucloxacillin 2 g IV every 4 to 6 hours for methicillin-sensitive disease, or vancomycin 15 to 20 mg/kg IV every 8 to 12 hours (or daptomycin 8 to 10 mg/kg daily) when MRSA is a risk.
• Remove infected catheters and leads. Continue 4 to 6 weeks for endocarditis. Surgery for large vegetations, persistent bacteraemia and valve dysfunction.

Bone cement implantation syndrome

• Prevention: 100% oxygen during cementing, euvolaemia, medullary lavage and venting, and cement in the doughy phase.
• Treatment: fluids, vasopressors (phenylephrine or norepinephrine) and cardiopulmonary resuscitation if needed.

Retained intravascular fragments

• Retrieve percutaneously with a snare under fluoroscopy.

Particulate (talc, cellulose) embolism from intravenous misuse

• Supportive care, oxygen, and treatment of pulmonary hypertension. Corticosteroids are sometimes used. Drug use counselling.