An oxygenation index is an assessment of how much oxygen diffuses across the membranes of the lungs and into the blood when a patient inhales. This index can be useful in the management of patients who require mechanical ventilation to breathe. Higher levels can be a sign of concern, as they may indicate an increased risk of a poor patient outcome because the patient cannot get as much oxygen out of each breath. Doctors work to lower the oxygenation index and increase the movement of oxygen from the lungs into the bloodstream.
To calculate the oxygenation index, the doctor multiplies the fraction of inspired oxygen by mean airway pressure, and divides this number by the arterial oxygen pressure. The fraction of inspired oxygen refers to how much oxygen is present in an inhaled gas mixture. Patients very rarely inhale 100% oxygen, unless they are severely ill. The mean airway pressure can be measured by checking ventilator settings to determine what the ventilator delivers to the pressure. Arterial oxygen pressure is measurable with an arterial blood gas test.
Patients on ventilators usually need constant monitoring, as they are at risk of health complications and the settings typically need recurrent adjustment. A doctor may request a regular oxygenation index check to assess the patient's performance on the ventilator. This information goes into the patient's chart along with vital signs and other observations. Reviewing the chart can provide a doctor with important information about the case, including how well the patient is responding to treatment.
Studies on the use of mechanical ventilation in patients of all ages have provided important information about the connection between oxygenation index and patient outcomes. Numerous health care facilities use a ventilator triage protocol to determine how long to keep patients on ventilators, and how to adjust the settings as patients improve or get worse. These protocols include evidence-based medicine from research, like charts showing what kinds of outcomes to expect with different oxygenation index values.
This can also be important for making long term decisions about patient care. The longer a patient stays on a ventilator, the greater the risk of pneumonia and other complications. In cases where a patient begins to deteriorate on a ventilator and appears to be fatally ill, the doctor may advise family members that the patient is unlikely to recover, and may not be able to breathe independently ever again. Family members may opt to take such patients off mechanical ventilation.