Nitric Oxide, Inhaled — Criteria for Initiating iNO — Clinical Pathway: ICU and Inpatient

Inhaled Nitric Oxide for Acute Hypoxemic Respiratory Failure Clinical Pathway — PICU

Criteria for Initiating iNO

Indications

For the majority of patients with hypoxemic respiratory failure, the literature does not support its use. It is indicated for:

  • Persistent or presumed neonatal pulmonary hypertension

Criteria for Initiating iNO

Criteria
Oxygen Index (OI) > 15
AND/OR
P/F Ratio ≤ 100

OI and P/F Ratio are often used interchangeably.
If the patient does not have an arterial line, neither value is appropriate (a venous gas is not sufficient). SpO2 should be used as the criteria for initiation.

Indicators of Hypoxemia:

P/F Ratio: The ratio of arterial oxygen concentration to the fraction of inspired oxygen—scales the arterial oxygen concentration for the FiO2 required to achieve it.

  • P/F Ratio = PaO2/FiO2
  • For example, with normal oxygenation in air
    • PaO2 =100 torr, FiO2 = 0.21
    • P/F Ratio = 100/0.21 = 476
  • ‘Normal’ P/F ratio is around 500
  • ARDS classification:
    • Mild ARDS – P/F ratio 201-300 on CPAP/PEEP ≥ 5
    • Moderate ARDS – P/F 101-200 on PEEP ≥ 5
    • Severe ARDS – P/F ≤ 100 on PEEP ≥ 5

Oxygen Index (OI): This is similar to the P/F ratio but also accounts for the fact that oxygenation is influenced by mean airway pressure (MAP):

  • OI = FiO2 x MAP x 100/PaO2 = MAP x 100/(P/F ratio)
  • With normal oxygenation with natural airway:
    • PaO2 = 100, FiO2 = 0.21, ‘natural’ MAP = 3 cm H2O
    • OI = 3 cm H2O x 100/476 = 0.63
  • The higher the OI, the more severe the lung dysfunction.

Note: For patients whose iNO is being weaned, repeat OI and P/F values should be correlated with the most recent ABG (within the q2 hour ventilator check timeframe).