Fat Embolism Syndrome

History
In 1861, Zenker described fat droplets in the lung capillaries of a railroad worker who sustained a fatal thoracoabdominal crush injury.
In 1873, Bergmann was first to establish the clinical diagnosis of fat embolism syndrome.

What is it ??
complex with potentially catastrophic cardiopulmonary and cerebral dysfunction
Three problems :
dyspnoea, petechiae and mental confusion

Definitions
Fat Emboli: Fat particles or droplets travel through the circulation
Fat Embolism: fat emboli passes into the bloodstream and lodges within a blood vessel.
Fat Embolism Syndrome (FES): serious manifestation of fat embolism occasionally causes multi system dysfunction, the lungs are always involved and next is brain

Fulminant fat embolism
sudden intravascular liberation of a large amount of fat causing pulmonary vascular obstruction, severe right heart failure, shock and often death within the first 1-12 h of injury

Etiology

Trauma related (95 %)
Long bone fractures
Pelvic fractures
Fractures of other marrow-containing bones
Orthopaedic procedures
Soft tissue injuries (e.g. chest compression with or without rib fractures)
Burns
Liposuction
Bone marrow harvesting and transplant

Non-trauma related
Pancreatitis
Diabetes mellitus
Osteomyelitis and panniculitis
Bone tumour lysis
Steroid therapy
Sickle cell haemoglobinopathies
Alcoholic (fatty) liver disease
Lipid infusion
LAST OPD – pneumonic

fat emboli also can arise from circulating lipoproteins

What is frequent ??
lower extremity and pelvic trauma,
intramedullary nailing of long-bone fractures,
hip arthroplasty, and knee arthroplasty

Incidence ??
incidence of FES was 1 %
But multiple fractures, adults, high velocity injuries, cementing, hypovolumia
It can be upto 33 %

Lethal dose
The acute lethal dose of fat ranges from 20-50 ml.
The volume of marrow fat from a femur is approximately 70-100 ml.
Mortality – 10 – 20 %

Pathophysiology ??
The Mechanical theory (Gauss)
Biochemical theory (Lehmann and Moore)
Coagulation theory

The Mechanical theory (Gauss)
Trauma to long bones releases fat droplets
(10-40 μm in diameter)
fat droplets enter the torn veins near long bone ( intramedullary pressure is higher than the venous pressure)
They enter lungs
perivascular hemorhage and edema- picture of ARDS
but smaller ones ( 7- 10 mic.) travel to systemic circulation via ? Patent foramen ovale -

Prevalence of PFO = 25 %

Biochemical theory
Embolized fat is degraded in plasma to free fatty acids.
FFA can cause lung injury, cardiac contractile dysfunction
CRP appears to be responsible for lipid agglutination and may also participate in the mechanism of non-traumatic FES.

Coagulation theory
Tissue thromboplastin is released with marrow elements following long bone fractures.
Activates intravascular coagulation
fibrin and fibrin degradation products, leukocytes, platelets and fat globules combine to increase pulmonary vascular permeability
Catecholamines are involved

Can it happen in sickle cell disease ??

Sickling
Bone marrow necrosis
as a result of hypoxia
may release fat

Number of theories means
Poorly understood ??

Clinical Features
12-72 hrs after the initial injury
Rarely two weeks

Features
Respiratory changes – 95 %
Cerebral changes – 60 %
petechiae (33% - 60 %).
Not necessary to follow one by one

Respiratory changes
Dyspnoea, tachypnoea and hypoxaemia are the most frequent early findings.
Respiratory failure as ARDS

Cerebral
The more common presentation is with an acute confusional state
but focal neurological signs including hemiplegia, aphasia, apraxia, visual field disturbances have been described.
Seizures and decorticate posturing have also been seen.
Fortunately, almost all neurological deficits are transient and fully reversible.

Petechiae
Embolization of small dermal capillaries leading to extravasation of erythrocytes. This produces a petechial rash in the conjunctiva, oral mucous membrane and skin folds of the upper body especially the neck and axilla
No relation to platelets
Self limiting (36 hours to seven days)

Petechiae
Neck

Petechiae
Petechiae only rarely appear on the legs and they are never seen on the face or the posterior aspect of the body. WHY ??
May be –
fat globules float and therefore distribute to branches of the aorta that arise from the top of the arch, and to the side of the body that is uppermost

Gurd – 1 major + 4 minor
Major –
Axillary or subconjuctival petechiae
PaO2 < 60 with FiO2 of > 40
CNS depression disproportionate to hypoxemia
Pulmonary edema ( PODE – Pneumonic)
Minor
tachycardia, pyrexia, retinal fat emboli, (Purtscher’s retinopathy )urine or sputum fat, Increased ESR, Decreased platelet/ hematocrit.
exclusion of other posttraumatic causes of hypoxemia
Beware a lung injury

Lindeque’s criteria- # femur , #tibia + 1 feature

Schonfeld’s criteria- fat embolism index- 5 or more

The features are acute, but not abrupt

How to confirm ??
High index of suspicion and some investigations

CXR usually normal early on, later may show ‘snowstorm’ pattern- diffuse bilateral infiltrates

Lab values
Arterial blood gases :
This reveals a low partial pressure of oxygen and a low partial pressure of CO2 with respiratory alkalosis.
An unexplained anemia (70% of patients) and thrombocytopenia (platelet count <1,50,000 mm-3 in up to 50% of patients.
Hypocalcemia (due to binding of free fatty acids to
calcium) and elevated serum lipase have also been
Reported
Hypofibrinogenemia

CVS
ECG : sinus tachycardia ; Non specific ST T changes, RBBB,
Lung scan : ? V/Q mismatch.
Transesophageal echocardiography : Fat droplets. PFO, Rt sided dilatation if present

Broncho alveolar lavage
BAL : fat droplets.
The staining of cells with oil red O after recovery by a standard 150- to 200-mL lavage can identify intracellular fat droplets.
Can be there in minimal fat embolism – but!!
quantitative count of lavage cells containing fat of greater than 30% being significant of fat embolism syndrome

CT Brain
White matter petechiae
Cerebral edema
Rarely cerebral atrophy due to
full embolisation

MRI brain – increased signal intensities

Treatment
Prevention and supportive
adequate oxygenation and ventilation,
stable haemodynamics,
blood products as clinically indicated, hydration,
prophylaxis of deep venous thrombosis and stress-related gastrointestinal bleeding,
Nutrition care

Prevention
Hole and drill the long bones
Early immobilization of fractures
Cementless prostheses or
bone-vacuum cementing technique
Less reaming
Albumin also binds fatty acids and may decrease the extent of lung injury
Methylprednisolone 1.5 to 7.5 mg / kg IV 6 to 12 doses (depending on the risk) ?? Advantage

Prevention
during cementing
Hydration
Oxygenation
No nitrous

Treatment
Aspirin
Heparin
N acetyl cysteine
Other speculated therapies such as glucose and insulin, alcohol infusion therapy have theoretical benefit
Details of mechanical ventilation, Inhaled nitric oxide, inhaled prostacyclins – not covered

Prognosis who survived
The prognosis for patients who survive fat embolism is good, with recovery from the fat embolism syndrome usually being complete within 2-4 weeks.
neurological signs may remain for up to 3 months

Summary
Definitions
Incidence
Etiology
lethal dose
Theories
Prevention
Treatment