4.4 Nonthrombotic Embolism (Air, Fat, Amniotic Fluid, Tumor, Septic) & Acute Chest Syndrome

Venous and Arterial Air Embolism

Sources include:

• Central venous catheter insertion or removal, especially with the patient upright or inspiring.
• Disconnected lines.
• Pressurized infusions and hemodialysis circuits.
• Sitting-position neurosurgery, laparoscopy, and penetrating chest trauma.
• Barotrauma during mechanical ventilation.

Rapid entry of a few milliliters per kilogram of air can obstruct the right ventricular outflow tract (an "air lock").

Presentation: sudden dyspnea, hypoxemia, hypotension, a sudden fall in end-tidal CO2 (dead space), a "mill-wheel" murmur, and acute right ventricular strain. Arterial gas embolism reaches the brain or coronaries through a patent foramen ovale or across the pulmonary bed. It presents with stroke-like deficits, seizures, or myocardial ischemia.

Management:

1. Stop the entry: clamp or occlude the line, cover the site with an occlusive dressing, and flood the field with saline.
2. Give 100% oxygen to wash out nitrogen and shrink the bubbles.
3. Position: left lateral decubitus with head down (the Durant maneuver) for venous air embolism, to keep air in the right atrial apex away from the outflow tract. The evidence is limited, and positioning must not delay resuscitation.
4. Aspirate through a catheter already positioned in the right atrium, if one is present.
5. Start CPR if the patient arrests; chest compressions can break up an air lock.
6. Arrange hyperbaric oxygen for arterial gas embolism with neurological or cardiac deficits.

Prevention: place jugular and subclavian catheters with the patient head down, remove them supine or head down during exhalation or Valsalva, apply an occlusive dressing, and keep the patient supine briefly afterward.

Fat Embolism Syndrome

Fat embolism syndrome follows long-bone (especially femoral) or pelvic fractures and intramedullary reaming. Less common causes are orthopedic surgery, liposuction, pancreatitis, and bone marrow necrosis in sickle cell disease. Fat globules lodge in capillaries and release free fatty acids that cause endothelial injury.

• Timing: 24 to 72 hours after the injury.
• Classic triad:
  • Respiratory distress with hypoxemia (often an ARDS-like picture).
  • Neurological changes, from confusion to coma.
  • A petechial rash over the axillae, conjunctivae, oral mucosa, and upper chest (present in a minority).
• Supporting findings: thrombocytopenia, anemia, retinal hemorrhages, fat globules in urine or sputum, and a "starfield" pattern of diffuse punctate diffusion restriction on brain MRI. Diagnosis is clinical (Gurd and Wilson criteria).
• Management: supportive, with lung-protective ventilation and hemodynamic support. Early fracture fixation, within about 24 hours, lowers the incidence. Routine corticosteroids are not recommended for treatment.

Amniotic Fluid Embolism

Amniotic fluid embolism occurs during labor, cesarean delivery, or within about 30 minutes after delivery. It presents with:

• Sudden hypoxemia, hypotension, or cardiac arrest.
• Often seizures or altered mental status.
• Disseminated intravascular coagulation with massive hemorrhage.

The mechanism is an anaphylactoid reaction with acute pulmonary hypertension and right ventricular failure, followed by left ventricular failure. There is no confirmatory test; it is a clinical diagnosis of exclusion.

Management:

• High-quality CPR with manual left uterine displacement.
• Perimortem (resuscitative) cesarean delivery if there is no return of circulation by about 4 minutes, aiming to deliver within 5 minutes. This also improves maternal hemodynamics.
• A massive transfusion protocol with early fibrinogen replacement (cryoprecipitate or concentrate).
• Right ventricular support with inhaled pulmonary vasodilators, dobutamine or milrinone, and norepinephrine.
• VA-ECMO at capable centers.

Tumor Embolism

Microscopic tumor emboli most often come from:

• Breast, gastric, lung, and prostate cancer.
• Hepatocellular and renal cell carcinoma.

They cause subacute, progressive dyspnea and pulmonary hypertension with right heart failure, while CT pulmonary angiography is often normal or shows only subtle peripheral changes. Pulmonary tumor thrombotic microangiopathy, classically from gastric adenocarcinoma, adds fibrocellular intimal proliferation and rapid deterioration. Cytology of blood aspirated through a wedged pulmonary artery catheter can show malignant cells. The prognosis is poor. Large tumor emboli can arise from renal cell carcinoma extending up the IVC, or from atrial myxoma.

Septic Pulmonary Emboli

• Sources:
  • Right-sided endocarditis (people who inject drugs, typically S. aureus).
  • Infected central catheters or pacemaker leads.
  • Pelvic septic thrombophlebitis.
  • Lemierre syndrome: septic thrombophlebitis of the internal jugular vein after pharyngitis or a peritonsillar abscess, usually from Fusobacterium necrophorum. It presents with neck pain and swelling, persistent fever, and septic emboli.
• Imaging: multiple peripheral nodules of varying age that cavitate, often with a feeding-vessel sign.
• Treatment:
  • Prolonged antibiotics; for Lemierre syndrome, a beta-lactam such as ampicillin-sulbactam or a carbapenem, or metronidazole combined with a cephalosporin.
  • Source control (catheter removal, drainage, or valve surgery when indicated).
  • Anticoagulation for Lemierre thrombus is individualized.

Acute Chest Syndrome in Sickle Cell Disease

Definition: a new pulmonary infiltrate involving at least one complete lung segment, plus fever, chest pain, tachypnea, wheezing, cough, or hypoxemia.

Triggers:

• Infection (atypical bacteria and respiratory viruses).
• Fat embolism from bone marrow infarction.
• Hypoventilation from rib infarction or opioids.
• Surgery and anesthesia.

The syndrome can progress within hours to severe respiratory failure.

Management:

• Oxygen for hypoxemia.

• Analgesia balanced against hypoventilation.

• Incentive spirometry, which also prevents the syndrome during vaso-occlusive crises.

• Empiric cephalosporin plus macrolide.

• Bronchodilators for wheeze.

• Avoid fluid overload.

• Simple transfusion when the hemoglobin has fallen about 1 g/dL or more below baseline.

• Exchange transfusion for rapid progression:

  • Oxygen saturation below 90% despite supplemental oxygen.
  • Increasing respiratory distress.
  • Spreading infiltrates.
  • A falling hemoglobin despite simple transfusion.

  The aim is to reduce hemoglobin S to below about 30% without raising total hemoglobin above about 10 g/dL, which increases viscosity.