This entity is poorly understood produces important intraoperative mortality and morbidity especially in patients undergoing cemented hip arthroplasty.  Here are the short review about the definition, incidence, clinical features, risk factors, etiology, Patho physiology, risk reduction and management of BCIS.  
DEFINITION:
It is agreed that BCIS is characterized by hypoxia, hypotension, pulmonary arterial hypertension, cardiac arrhythmias and cardiac arrest.  It is most often seen with hip arthoplasty during any one of these steps, femoral reaming, acetabular or femoral cement implantation or insertion of the prosthesis or joint reduction. 
CLASSIFICATION BASED ON THE SEVERITY:

• Grade I:  Moderate hypoxia Spo2 less than 94% or hypotension SBP > 20% of the basal value. 
• Grade II:  Severe hypoxia Spo2 < 88% or hypotension SBP > 40% or unexpected loss of consciousness.
• Grade III: Cardio vascular collapse requiring CPR.

INCIDENCE:
According to many large studies incidence varies from 0.43% to 1.6%.

CLINICAL FEATURES:

• Hypoxaemia
• Hypotension
• Sudden loss of consciousness
• Increased PVR
• Increased PAP
• Systemic vascular resistance reduced
• Reduced Stroke volume
• Reduced cardiac output.

Because of marrow and fat embolisation in the pulmonary radicles the pulmonary vascular resistance increased leading on to pulmonary arterial hypertension, right ventricular distension failure and bulging of right ventricle into left producing reduced left ventricular filling and stroke volume.  If the embolisation occurs in the brain due to persistent foramen ovale it will lead to cerebral fat emboli evidenced by serum S-100B protein concentration.  (a marker of cerebral injury).
Aetiology and Patho Physiology:

• MMA  (Mono Methyl Methacrylate) mediated hypotension
• Embolic model:

This is more acceptable as evidenced by trans oesophageal echo

• The link between the intramedullary pressure and embolisation
• Haemo dyanamic effects of embolisation and mediator release due to fat emboli.
• Histamine release and hypersensitivity
• Complement activation C3a  and C5a are  potent   mediators of vasoconstriction and broncho constriction.

PATIENT RISK FACTORS:
Pre-existing cardio pulmonary disease with increased PVP, secondary fractures due to metastatic diseases are more prone for BCIS. 
SURGICAL RISK FACTORS:
Pre-existing uninstrumented femoral canal is prone for BCIS or marrow is vascularised and debris can enter venules and produce BCIS.
ANAESTHETIC RISK REDUCTION:

• General anaesthesia with volatile agents the risk of hypotension and BCIS is high.
• Uncemented prosthesis insertion without undue intramedullary pressure can reduce BCIS.
• Regular use of vasopressores (Low dose epinephrine) during cementing and prosthesis insertion and reduction.

SURGICAL RISK REDUCTION:

• Low viscosity cement definitely reduces increased intramedullary pressure.
• Cement fat to be disposed off as it produces more intramedullary pressure.
• Uncemented prosthesis
• Lavage to reduce the debris.
• Venting at the shaft to reduce the pressure.
• Preparing cement in vaccum reduces the BCIS

MANAGEMENT:

• Release of tourniquet during knee arthroplasty produces high incidence of BCIS.
• TOE
• Use of Vaso pressors
• Fluid resuscitation.