INHALED NITRIC OXIDE
Nitric Oxide, iNO
Reviewed by Dr David Knight
Nitric oxide (NO) is a gas that is
given into the ventilator circuit. It is a potent vasodilator. When given into
the ventilator circuit, it dilates the pulmonary vasculature. It is inactivated
instantly in blood, by reacting with haemoglobin. Therefore it has no action on
the systemic vasculature and therefore (theoretically) on systemic blood
Dose and Administration
- Cylinder has 880 parts per million (ppm) in nitrogen
- Add to ventilator circuit between humidifier and baby.
- Start on 20ppm (approximately 200ml/min, and increase according to measurement on Nitric Oxide Monitor)
- Start on 0.2 litres per minute in 10 litres of 100% O2 = 17.4 ppm
- Reduce to 0.1 litres per minute: = 8.7 ppm
- Reduce according to response
- Doses above 20ppm are not indicated as generally a response is obtained prior to this.
Persistent pulmonary hypertension of the newborn (proven on clinical
grounds or by
- Severe respiratory failure
Contraindications and Precautions
- None in term infants. This is now considered a recognised practice.
- Caution in preterm infants. Benefit in preterm infants has not be proven by randomised studies.
Nitric oxide is endothelial derived
relaxing factor (EDRF). It is produced in the endothelium of blood vessels and
diffuses out of the cells. It then enters vascular smooth muscle cells and
activates guanalate cyclase which forms cyclic guanosine monophosphate (cGMP).
This is a smooth muscle relaxer. cGMP is inactivated by cGMP phosphodiesterase.
The half life of NO is 3-6 seconds.
NO is bound to haemoglobin and
inactivated to nitosylhaemoglobins and methaemoglobin.
Possible Adverse Effects
- Combines with haemoglobin to
form methaemoglobin. At clinically used doses high methaemoglobin levels
have not been reported. In overdose, it may be fatal. If
methaemoglobinaemia occurs, check the ventilator circuit, particularly the
delivery and measuring points of iNO.
- Is a toxic free radical and causes tissue damage. NO is used by macrophages to kill bacteria. It can
theoretically damage the lung through lipid peroxidation. The precise
importance of this has not been elucidated. Produces peroxynitrates which
are toxic to tissue.
- NO converts to nitrogen dioxide NO2) spontaneously when mixed with oxygen. High concentration of
NO in O2 lasts 6 seconds! At clinical doses (<20 ppm), the half-life is much
longer. NO2 is very toxic.
- NO is an inhibitor of platelet function. Caution when
thrombocytopenia or bleeding problem.