The following formula can be used to quickly calculate the severity of a patient's oxygen deficit:
PaO2 ÷ FiO2
= 90 ÷ .21
Acute Lung Injury (inflammatory response, increased capillary leak) is defined as non-cardiac pulmonary edema with a PaO2/FiO2 ratio < 300. Acute Respiratory Distress Syndrome (ARDS) is defined as non-cardiac pulmonary edema with a PaO2/FiO2 ratio < 200. NOTE: This is based on a patient without PEEP. If PEEP requirements are > 5, consider the actual PaO2/FiO2 to be lower than the calculated value (i.e., the patient's oxygenation is actually worse).
Clinical Nurse Specialist,CCTC
February 16, 2007