An anaesthesiologist at the centre of a legal battle over Joan Rivers' death has insisted she did everything she could to save the star's life when the funnywoman flatlined on the operating table.

The veteran comedienne passed away aged 81 in September (14), a week after she suffered a cardiac arrest during a routine throat procedure at the Yorkville Endoscopy clinic in New York City.

A medical examiner concluded Rivers' death was caused by hypoxic arrest, when the supply of oxygen to her brain was cut off during the medical procedure, and the star's daughter Melissa later filed a lawsuit targeting the clinic and Dr. Renuka Bankulla, the anaesthesiologist who oversaw the operation, among others.

Bankulla has now filed legal papers hitting back at claims she failed to demand a "crash cart" when Rivers' breathing and heart rate plummeted, insisting she took every step necessary to save the star's life, according to the New York Post.

In the documents, which were filed at Manhattan Supreme Court, Bankulla denies claims of malpractice and insists she could not have done any more to help Rivers.

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NY Times: At Surgery Clinic, Rush to Save Joan Rivers's Life -