O2 Related Outcomes

O2 Modes

O2 Modes refers to the way in which patients receive supplemental oxygen:

• RA = room air
• NC = nasal cannula
• HFNC = high-flow nasal cannula
• CPAP = continuous positive airway pressure, a form of non-invasive mechanical ventilation
• BIPAP = bilevel positive airway pressure, a form of non-invasive mechanical ventilation
• ETT = endotracheal tube, a form of invasive mechanical ventilation
• TRACH = tracheostomy, patients may or may not be mechanically ventilated at the same time

FiO2 (Fraction of inspired oxygen)

FiO2 refers to the %age of oxygen in the air that the patient breathes. FiO2 values can be obtained from multiple sources

• Lab results
• Flowsheet measurements
• Estimated values based on O2 Mode and O2 flow rate

Estimated FiO2

• FiO2 values of patients on Room Air (RA) are estimated at 21%.
• FiO2 values of patients assisted via high flow nasal cannula (HFNC) or nasal cannula (NC) are estimated with the following formula:
  
  FiO2 = 0.21 + (0.03 * [O2 liters/min])
  
  
• Note that this equation should only be used when O2 flow rate <= 15 LPM.

If both estimated and measured FiO2 values are present for a given timestamp, FiO2 measured values will take precedence over estimated values.

AA Gradient (Alveolar–arterial gradient)

AA gradient refers to the difference in O2 concentration between a patient's alveoli and arteries. A higher AA gradient indicates that oxygen is not being transferred to the blood adequately.

The AA gradient is calculated from the following formula:

AA gradient = (FiO2*(P_atm - P_H2O) - PaCO2/0.8) - PaO2

• PaO2 = arterial PO2 (measured in arterial blood)
• PaCO2 = partial pressure of CO2 in arterial blood; currently only using PaCO2 values measured from same sample as PaO2
• FiO2 = closest FiO2 prior to PaO2 and PaCO2 measurements
• P_atm = at sea level = 760 mmHg
• P_H2O = assuming 100% humidity in the alveoli = 47 mmHg