Police said 28 of those injured at the party of friends and family were sent to hospitals after inhaling the gas, while others were treated outside the building.
As of Sunday evening 12 remained in hospital care, Le Matin reported online.
The party, attracting about 100 people, was held to celebrate the 38th birthday of a man called Sergej in the Flon neighbourhood of the Vaud capital, the newspaper said.
Meat was cooked on a gas barbecue in a poorly ventilated room and some of the revellers began to feel sick around 11 pm on Saturday.
“Between the emission of smoke and the fact that oxygen started to become less available, people started to feel bad,” one of the party organizers told Le Matin
Several of those affected lost consciousness.
Rescue officials treated more than half the people suffering from the gas on site.
Smoke in the room where the party was held was found to have levels of carbon monoxide at five times the maximum level permitted, Michel Gandillon, of Lausanne’s rescue and protection service said.
More than 50 officials from the fire department, rescue service, ambulance brigade and police department were called to the scene.