Comedian Joan Rivers was admitted to Mount Sinai Hospital in New York City Thursday in critical condition, after reportedly undergoing a minor endoscopic procedure at a medical clinic.
The 81-year-old host of E!’s “Fashion Police” was rushed to the hospital after she “stopped breathing,” an unnamed source told E! News.
The same source told the network doctors were “putting a scope down her throat to check her vocal chords.”
While authorities would not identify Rivers as the patient transferred to Mount Sinai, the New York City Fire Department told FOX411 the person transported was in cardiac arrest.
Rivers was sedated while undergoing the procedure, which is common for patients undergoing endoscopic procedures to assure maximal patient comfort, according to the American Society for Gastrointestinal Endoscopy (ASGE).
Upper endoscopies allow a doctor to examine the lining of the upper gastrointestinal tract, which includes the esophagus, stomach and part of the small intestine.
Doctors may use the procedure to obtain a biopsy or to treat any abnormalities.
While complications from an upper endoscopy are uncommon, bleeding can occur at a biopsy site or where a polyp was removed, but it is usually minimal and does not require a follow-up, according to the ASGE.
Gastroenterologist Dr. Anish Sheth, who is not treating Rivers, told FoxNews.com that the procedures are safe, but risks can include perforation, bleeding, aspiration and side effects from the anesthesia.
There is usually a small risk for complications when healthy patients are administered general anesthesia. In some rare cases, general anesthesia can cause lung infections, stroke, heart attack or death, according to The Mayo Clinic.
Existing heart conditions or factors that can increase the risk of complications include smoking, obesity, diabetes, high blood pressure, drug allergies, alcohol abuse or sleep apnea, The Mayo Clinic reports.
A hospital spokesman confirmed Rivers was being treated at the Mount Sinai, and said they will "provide an update on her condition as it becomes available."
Rivers was diagnosed with osteoporosis in 2002.