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Oxygen: when less may be more
  1. Federico Corletto, PhD, CertVA, DipECVAA, MRCVS
  1. Dick White Referrals, Statin Farm, London Road, Six Mile Bottom, Cambridgeshire CB8 0UH, UK
  1. e-mail: fc{at}

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UNDERSTANDING the implications related to the administration of a high oxygen concentration (FiO2) in anaesthetised and critically ill animals has challenged the common belief that ‘the more, the better’ rule applies to oxygen administration.

The mechanisms underlying the short- and long-term complications related to the administration of a high oxygen concentration are considerably different: while oxidative injury plays an important role when a high oxygen concentration is administered for a long period of time, absorption atelectasis seems more relevant in anaesthetised subjects receiving 100 per cent oxygen for a shorter period of time (Lumb 2007). Furthermore, the presence of lung pathology and concurrent administration of chemotherapy agents may increase the sensitivity of the lung to the risk of oxidative injury induced by the administration of a high FiO2, such that balancing the risks and benefits of oxygen supplementation can be particularly difficult in critically ill subjects (Mathes 1995, Knight and others 2000).

Absorption atelectasis is a well-described problem in anaesthetised horses breathing high FiO2 (Marntell and others 2005). The reduced muscular tone and the cranial displacement of the diaphragm that result from anaesthesia give rise to compression of the lung and consequent reduction of functional residual capacity, both of which predispose to small airway closure. When such airway …

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