According to a new study led by Klaus Hopster, Assistant Professor of Large Animal Anaesthesiology at Pennsylvania’s School of Veterinary Medicine, Heliox – a breathing gas composed of a mixture of helium (He) and oxygen (O2) – when used under higher pressure ventilation, could achieve better results for horses under anaesthesia.
A horse in general surgery is an awkward sight. For the best access, the animals may be placed on their sides or even their backs, a position that puts considerable pressure on their internal organs, often leading to partial lung collapse. Despite using oxygen-rich ventilation, blood oxygen levels can fall to dangerous levels during lengthy procedures.
Veterinarians have employed a variety of strategies to mitigate these respiratory challenges, including using O2 delivered under high pressure to ensure the alveoli – the small sacs in the lungs where gas exchange takes place – are opened, or “recruited.” Others had used heliox, with mixed results.
Researchers at the University of Pennsylvania wanted to get more clarity on the best approach for ventilating horses. Hopster led the study from the school’s new Bolton Centre and found that horses receiving heliox while under anesthesia did better than those receiving pure O2. Adjusting the pressure of the ventilation the horses received, also improved overall oxygenation, the study found.
“Our paper showed that when you use high pressure ventilation using heliox, you’re able to achieve better results,” says Hopster. “The results are clear in healthy horses; what we’d like to do in the near future is see if we can extend this to other species or compromised animals.”
Hopster collaborated on the work, which appears in the American Journal of Veterinary Research, with Pennsylvania’s School of Veterinary Medicine’s Lauren Duffee, Charlotte Hopster-Iversen and Bernd Driessen.
Hopster and colleagues observed that horses ventilated with heliox rated better for two measures of respiratory mechanical function – low peak inspiratory pressure and higher lung compliance – compared to those breathing pure O2.
“With He, you get a more unturbulent flow, so you need a lower pressure to the end of the lungs,” Hopster says. “You can get the same result in terms of pulmonary function with lower pressures.”
In future work, Hopster and colleagues would like to examine whether a mixture of O2 and nitrogen (N2) might also be effective for horses, or whether this result is particular to the heliox mixture. They would also like to extend their studies to sheep, whose respiratory systems provide a good model for humans. That could help shed light on good strategies to ventilate people who already have compromised respiratory systems, such as individuals with asthma.
The research was supported by Pennsylvania’s School of Veterinary Medicine Department of Clinical Studies at New Bolton Centre.