How to prevent fat embolism?

Fat embolus is a very serious and known complication of fat transfer. The probability of embolus is much higher in the setting of fat transfer than for liposuction alone.
A fat embolus occurs when injected fat is inadvertently introduced into a vessel and travels centrally within the vasculature. The hallmark triad of symptoms include neurologic changes, a petechial rash, and respiratory changes. The treatment is typically supportive in nature. While it is a very serious complication, if diagnosed early it can be managed. Mortality rates are quoted as low as 5%.
While it is true, injection of donor fat into the infra-muscular plane (within the muscle) increases fat viability this does come with a significant increase in risk. There are large vessels deep to and within the muscle which can be inadvertently injected while grafting leading to a fat embolus. The consequences of such a complication are very serious and life threatening.

At the recent American Society of Plastic Surgeons Hot Topics, data from AAAASF (ambulatory surgical certifying body) was presented, suggesting that BBL /gluteal lipoaugmentation demonstrates a dramatically higher risk profile than other surgeries. The Aesthetic Surgery and Educational and Research Fund is convening a task force as well. The hope is that we will have more concrete guidelines for addressing these very serious complications.
That being said, the safest way to avoid fat emboli is to stay in the subcutaneous plane (at the expense of fat viability)and avoid the deeper muscular plane. If grafting of the deep plane is planned, surgeons should consider blunt cannulas, aspiration prior to injection. Using a supra-gluteal approach to minimize the risk of inadvertent intravascular injection has also been proposed.Unfortunately, even when undertaking the maximal precautions, complications can occur.  They can occur to any physician irrespective of training, location etc. Thus it is very important to be followed closely by your physician. This will ensure that in the unlikely event of a problem, diagnosis can be made promptly and treatment started immediately. 
As always, discuss your concerns with a board certified plastic surgeon (ABPS).

The risk will not be zero with any technique or instrument but superficial injections with larger blunt cannula will have the lowest risk.

Hello dear!Thanks for the question, and sorry to hear about that.The first thing is to look for a board certified plastic surgeon for a good evaluation. Make sure to fallow all the doctor's instructions, be healthy and don't hide anything if you have a condition, take the medications, hydration, and everything else depend on your evolution and body response to surgery.Hope this could help. Good luck :)