Russian doctors said Sunday that they learned just a few minutes before evacuating hostages from a Moscow theater held by Chechen terrorists that special forces had pumped an anesthetic gas into the auditorium.

Not knowing what gas was used, medical personnel were left scrambling in confusion about how to treat the rescued captives.

They still have not been told what the gas was.

One day after special forces liberated the theater, killing 50 Chechens who held more than 750 people hostage, criticism mounted over the number of dead hostages — 116 — and the way they died.

A trio of doctors from the Moscow medical service said that only one hostage had been killed by gunfire. The remaining 116 were felled by the gas, they told a news conference.

"In standard situations, the compound that was used on people does not act as aggressively as it turned out to do," said Andrei Seltsovsky, Moscow's chief physician. "But it was used on people who were in a specific [extreme] situation for more than 50 hours. ... All of this naturally made the situation more difficult."

Seltsovsky said medical personnel are familar with the general category of the gas, which makes recipients unconscious, and is used to anesthetize surgical patients.

But many questions remain about the gas used in Saturday's assault.

Doctors know the gas can stop people from breathing, hinder the circulation of blood and paralyze the heart and liver, even in controlled situations.

But the situation was not normal for the hostages — nearly no movement, a lack of water, food and sleep, and pyschological stress.

"For us, there was nothing surprising in the toxicological composition itself," said Yevgeny Luzhnikov, the head of the city health service's Department of Severe Poisoning. "What was unusual was its use in extraordinary circumstances."

He said that the main causes of death among the 116 dead hostages included respiratory failure, heart attack and circulatory failure.

The doctors said that as of Sunday afternoon, there were 646 patients in 14 hospitals, including 150 in intensive care.

Lev Fedorov, an independent chemist and environmental activist, asserted that medical teams and rescue services weren't told enough beforehand to help evacuate and treat the hostages. That, he said, led to so many of their deaths.

He speculated that the special forces troops were treated with an antidote to the gas, but none was provided for the hostages.

"Instead of wasting time when taking hostages out from the hall, emergency workers and doctors should have given them the antidote right in the hall," Fedorov said.

But Seltsovsky and the other doctors said there was no antidote. They also defended the actions of the medical personnel at the theater, calling the the first aid provided outside the theater and modern intensive care methods sufficient to counter the effects of the gas on people in normal health.