A 40 year old woman requires a trial of inhaled nitric oxide for severe pulmonary hypertension with right ventricular failure following a mitral valve replacement.  She is intubated and ventilated.  Describe how you would provide this, including the safeguards that are required.

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College Answer

Treatment should only be provided where forethought as to the key elements of safety and proper equipment are provided. Inhaled nitric oxide is still an investigational drug in Australia, and is not currently approved by TGA. Dose selection and titration should be done carefully observing effects by commencing at 5-10ppm and dialling up gradually increasing as necessary up to possibly 160 ppm. Monitoring of efficacy should be performed such as with PAP/PaO2 and/or Pulmonary Vascular Resistance (via pulmonary artery catheter or TOE).
Monitoring toxicity with NO2 and possibly methaemoglobin levels. Monitor also for risk of pulmonary haemorrhage.
Safe management of the cylinder is essential including knowledge of spill emergency procedure. Attention should be paid to waste gas evacuation, including at the least adequate air conditioning and possibly passive and active scavenging.

Discussion

The scope for the use of nitric oxide, and the number of people familiar with the practice, grows more and more slender with each passing day. Still it has applications in paediatric ICU, and there are still some staunch believers in its benefits. And one will note the vintage of the question (the drug has long since been approved, found good use, and subsequently has fallen out of favour).

A thorough (albeit amateurish) discussion of its various marvels can be found elsewhere.

Arguments for and against the use of nitric oxide:

  • NO is a potent pulmonary vasodilator
  • it improves ventilation-perfusion matching
  • it improves pulmonary pressures and oxygenation, but this effect is not sustained, nor is it associated with an improved outcome.
    • good Cochrane analysis demonstrated no benefit in mortality in ARDS
    • Oxygenation improves only for the first 24 hours of therapy.
  • It requires specialised equipment and its use is associated with complications eg. pulmonary haemorrhage, nitrogen dioxide toxicity and methaemoglobinaemia.
  • Thus, nitric oxide these days is seldom used.
  • In the manufacturers brochure, it is recommended for use only in the neonatal population.

Administration

  • via uniquely designed gas mixer
  • from its own tank
  • start at 5-10 ppm, go up to 160ppm as needed

Monitoring

  • Monitor PA pressures with PAC
  • monitor response with arterial oxygenation
  • regular CXR, watch for pulmonary haemorrhage
  • Monitor for toxicity, particularly methaemoglobin levels
  • Observe strict handling sfaeguards, including gas scavenging and ventilation precautions

References

References

Ikaria, the only company which produces this stuff in Australia, has an excellent product information pamphlet.

 

Afshari, Arash, et al. "Inhaled nitric oxide for acute respiratory distress syndrome (ARDS) and acute lung injury in children and adults." Cochrane Database Syst Rev 7 (2010).