A hypobaric wound space is provided for prophylactic and diagnostic purposes in surgical wounds of the abdomen deliberately left open. The hypobaric wound space provided is established by a combination of an impermeable folio sheet or thin flexible membrane, tissue fluid absorbing gauze or sponge, a drain tube, and a suction device to create hypobaric conditions and prevent wound contamination and infection, and to collect wound fluid to diagnose protein, fluid and other substrate losses on a quantity and quality basis. More specifically the invention provided relates to postoperatively applying negative pressure to the wound space of any surgical wound that was deliberately left open by filling the wound space with medical gauze or any material that is capable of absorbing tissue fluid, sealing the wound space with an impermeable folio or flexible membrane by engaging the folio to the skin of surrounding wound edges, and evacuating air and tissue fluid from the wound space by continuous suction through a drain tube to protect the wound from contamination and infection, and to diagnose fluid and losses substrate losses on a quantity and quality basis.