Nitric oxide and its role in the management of hypoxaemia in the anaesthetised horse—a narrative review

Objective: To outline historical aspects of nitric oxide, including its discovery and biological effects, to describe the current use of inhaled nitric oxide (iNO) in human healthcare, and to review the available evidence on the use of pulsed iNO (PiNO) for the management of hypoxaemia in anaesthetised horses. Databases used: Google Scholar and PubMed databases were searched using the search terms nitric oxide, PiNO, environment, discovery, acute respiratory distress syndrome, COVID-19, SARS-CoV-2, horse, pony, hypoxaemia, and anaesthesia. Conclusions: Inhaled NO is licensed in the management of hypoxic respiratory failure in human neonates and has also been used to treat refractory hypoxaemia in humans fulfilling certain criteria. There is now a substantial body of evidence demonstrating that PiNO is an effective treatment option for managing hypoxaemia during general anaesthesia in horses. The administration of PiNO to well-ventilated alveoli leads to a redistribution of pulmonary blood flow from dependent, nonventilated regions to nondependent, better ventilated regions of the lung. This reduces intrapulmonary shunting and improves indices of oxygenation and oxygen delivery. Whilst much of the evidence is experimental, there are some descriptions of its successful use in client-owned horses undergoing surgery for colic and arthroscopic procedures. As the prototypical delivery device (the NOrse, Datex-Ohmeda Research Department, Helsinki, Finland) has been redeveloped, the use of PiNO in clinical equine anaesthesia may offer a realistic treatment option for the management of hypoxaemia in anaesthetised horses in the near future.