Post-moem purge is associated with the following:

During putrefaction, discoloured natural fluids and liquified tissues are made frothy by gas. Due to the presence of gas in the abdomen, the diaphragm is forced upwards compressing the lungs and hea, and blood stained froth exudes from the mouth and nostrils which is known as post-paum purge. Ref: The Essentials of Forensic Medicine and Toxicology by K S Narayan Reddy, 27th edition, Page 146.