This has come up once, in  Question 28.3 from the first paper of 2011. The marvels and wonder of nitric oxide are discussed elsewhere. This question refers specifically to the the nitric oxide cylinder, which is the form this gas is usually found in.

The gas tank itself

  • The gas comes in a pressurised cylinder, under a brand name "INOmax".
  • It contains 99.92% nitrogen and only 0.08% nitric oxide, or 800 parts per million (ppm).
  • Well, it needs to be dilute, for convenience of administration.
  • The highest concentration you would ever use is about 80ppm, which corresponds to a gas mixture of 90% whatever, and 10% Inomax.
  • The INOmax delivery system procedure guide is an excellent source of detailed gas-cylinder-related information.

Things to worry about while using nitric oxide

The following adverse effects have been reported with its use:

  • Methemoglobinaemia, as abundantly discussed already
  • Hypotension (maybe some of it does leak into the systemic circulation, or maybe this the effect of depressed LV function
  • Rebound hypoxia after abrupt withdrawal
  • Thrombocytopenia (in as many as 10% of patients)
  • Increased susceptibility to pulmonary infections probably due to NO2 formation and associated lung injury

There are also several contraindications.

  • Left ventricular failure: NO seems to cause lots of adverse effects in this group of patients- particularly, pulmonary oedema. In fact, halfway through one study, the investigators had to start excluding CCF patients from the trial because of these effects.
  • Left to right shunting: NO will decrease the pulmonary (and thus the RV) pressure, increasing the amount of blood shunted via a septal defect.
  • Uncontrolled haemorrhage: Though there is no human evidence, in animal studies NO had been shown to increase bleeding times.
  • Existing methaemoglobinaemia: obviously, it will get worse.

References

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

Barker, Steven J., and John J. Badal. "The measurement of dyshemoglobins and total hemoglobin by pulse oximetry." Current Opinion in Anesthesiology21.6 (2008): 805-810.

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).