With regard to fat embolism syndrome (FES), outline the precipitants, clinical features, diagnosis and management

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College answer

Precipitants:                                               
Trauma-related 
Orthopaedic (most common) 
Long bone fracture (esp femur) 
Pelvic fracture 
Elective Orthopaedic surgery 
Non-orthopaedic 
Liposuction 
BM harvest/transplant 
Nontrauma-related 
Acute pancreatitis  
Sickle cell disease 
 
Clinical features                                              
Typically develops 24-72 hours following insult. 
Classic clinical triad (neurological, respiratory, cutaneous), none of which is specific for FES. 
•    Respiratory – the most common presenting feature. Dyspnoea, hypoxia, ARDS  
•    Neurological – confusion, reduced level of consciousness, seizure, focal deficit, retinal changes (petechiae) 
•    Petechial rash – usually in non-dependent areas, including neck, axillae, anterior chest, head, subconjunctiva. Only in 1/3 of cases, and often not until 3-5 days after insult. 
Other – fever, thrombocytopenia, coagulation abnormalities (incl DIC), anaemia, tachycardia, myocardial depression, renal/liver dysfunction, high ESR 
 
Diagnosis 
Based on the clinical features in the setting of known precipitant 
CXR may reveal bilateral patchy infiltrates 
No single diagnostic test – BAL sampling for lipids has been described – no other tests shown to be useful 
Several sets of diagnostic criteria proposed 
 
Management                                               
Prevention clearly preferable if possible – e.g. surgical timing (following fracture) and technique Fixation of fracture 
No specific therapy. Supportive only. 
Steroids controversial – proposed anti-inflammatory effect but limited data to support 
 

Discussion

Precipitants

Conditions Associated with Fat Embolism
(from Jain et al, 2008 )
Traumatic Unrelated to trauma
  • 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
  • Pancreatitis
  • Diabetes mellitus
  • Osteomyelitis and panniculitis
  • Bone tumour lysis
  • Steroid therapy
  • Sickle cell haemoglobinopathies
  • Alcoholic (fatty) liver disease
  • Lipid infusion (TPN or propofol)
  • Cyclosporine A solvent
  • Lymphography
  • Altitude sickness
  • One long bone fracture: 1-3% chance
  • Chance increases in proportion of number of fractures, and size of involved bones
  • 33% with bilateral femoral fractures

Clinical features

Symptoms of fat embolism

  • Confusion is usually the earliest symptom (60%), but seizures and focal neurological signs have also been reported (all resolve completely)
  • Dyspnoea
  • Tachypnoea
  • Haemoptysis
  • Usually, with a latent period (say, some days after the manipulation of a fracture).

Signs of fat embolism

  • Respiratory features are present in 95%: moist crepitations over all lung fields, hypoxia, cyanosis. ARDS-like picture develops
  • Fat globules may be seen in the sputum!
  • Petechial rash (in 30-60%) - alone, enough to make the diagnosis according to Schonfelds criteria.
  • Fever
  • Tachycardia
  • Purtscher’s retinopathy: 
    • cotton wool exudates
    • macular oedema
    • macular haemorrhage
    • retinal haemorrhages
    • visible fat droplets on ophthalmoscopy
  • Jaundice
  • Renal impairment
  • Anaesthetists often note a sudden drop in end-tidal CO2 concentration during a stable steady state.

Diagnosis

Diagnostic Criteria for  Fat Embolism

Gurd's Criteria

Major criteria

  • Axillary or subconjunctival petechiae
  • Hypoxaemia PaO2 <60 mm Hg, FIO2=0.4
  • Central nervous system depression disproportionate to hypoxaemia
  • Pulmonary oedema

Minor criteria

  • Tachycardia <110 bpm
  • Pyrexia <38.5°C
  • Emboli present in the retina on fundoscopy
  • Fat globules present in urine
  • A sudden inexplicable drop in haematocrit or platelet values
  • Increasing ESR
  • Fat globules present in the sputum

Lindeque's criteria

  • Sustained PaO2 <8 kPa
  • Sustained PCO2of >7.3 kPa or a pH <7.3
  • Sustained respiratory rate >35 breaths min-1 despite sedation
  • Increased work of breathing: dyspnoea, accessory muscle use,tachycardia, and anxiety

Schonfeld criteria

  • Petechiae = 5
  • Chest X-ray changes (diffuse alveolar infiltrates)= 4
  • Hypoxaemia (PaO2 < 9.3 kPa) = 3
  • Fever (>38°C) = 1
  • Tachycardia (>120 beats min–1) = 1
  • Tachypnoea (>30 bpm) = 1
  • Confusion = 1
  • Cumulative score >5 required for diagnosis

Laboratory features:

  • Thrombocytopenia
  • Anaemia (sudden decrease) -70% of patients
  • High ESR
  • Fat macroglobulinaemia
  • Hypocalcemia (due to free fatty acids binding calcium)
  • Elevated serum lipase
  • DIC-like coagulopathy
  • ABG: respiratory alkalosis with hypoxia and an unexplained shunt
  • ECG: right heart strain, RBBB

Characteristic imaging:

  • CXR: florid embolism may develop into a "flocculent" patchy widespread opacities, "snowstorm appearance".
  • CT chest: non specific; focal areas of ground glass opacification
  • CT brain: diffuse white-matter petechial hemorrhages consistent with microvascular injury.
  • TOE: may actually catch the passing of fatty globules within the heart, but afterwards - useless.

Management:

  • Specific management not supported by very strong evidence:
    • Corticosteroids
    • Aspirin
    • Heparin infusion (which supposedly encourage lipase activity and discourages the formation of platelet aggregates).
    • N-acetylcysteine (based on rat studies only)
  • Boring, non-specific treatment:
    • O2 supplementation
    • Positive pressure ventilation
    • Correction of coagulopathy
    • Replacement of platelets
    • Correction of the source problem (i.e. reduction of fractures)

References

References

Mellor, A., and N. Soni. "Fat embolism." Anaesthesia 56.2 (2001): 145-154.

Gurd, Alan R., and R. I. Wilson. "The fat embolism syndrome." Journal of Bone & Joint Surgery, British Volume 56.3 (1974): 408-416.

Myers, R., and J. J. Taljaard. "Blood alcohol and fat embolism syndrome." J Bone Joint Surg Am 59.7 (1977): 878-880.

Hofmann, S., G. Huemer, and M. Salzer. "Pathophysiology and management of the fat embolism syndrome." Anaesthesia 53.S2 (1998): 35-37.

Kosova, Ethan, Brian Bergmark, and Gregory Piazza. "Fat Embolism Syndrome." Circulation 131.3 (2015): 317-320.

Jain, S., et al. "Fat embolism syndrome." JAPI 56 (2008): 245-249.

Gupta, Amandeep, and Charles S. Reilly. "Fat embolism." Continuing education in anaesthesia, critical Care & pain 7.5 (2007): 148-151.