Oxygen reserve index as a noninvasive indicator of arterial partial pressure of oxygen in anaesthetized donkeys: a preliminary study.

OBJECTIVE

To evaluate the oxygen reserve index (ORI) as a noninvasive estimate of the PaO during moderate hyperoxaemia [100-200 mmHg (13.3-26.6 kPa)], and to determine ORI values identifying PaO > 100, > 150 (20.0 kPa) and > 200 mmHg in anaesthetized donkeys with an inspired fraction of oxygen (FiO) > 0.95.

STUDY DESIGN

Prospective observational study.

ANIMALS

A group of 28 adult standard donkeys aged (mean ± standard deviation) 4 ± 2 years and weighing 135 ± 15 kg.

METHODS

Donkeys were sedated intramuscularly with xylazine and butorphanol; anaesthesia was induced with ketamine and diazepam and maintained with isoflurane in oxygen. An adhesive sensor probe was applied to the donkey's tongue and connected to a Masimo pulse co-oximeter to determine ORI values. An arterial catheter was inserted into an auricular artery. After ORI signal stabilization, the value was noted and PaO determined by blood gas analysis. The Pearson correlation coefficient was used to assess the relationship between ORI and PaO for oxygen tension < 200 mmHg (< 26.6 kPa). The Youden index was used to identify the value of ORI that detected PaO > 150 and 200 mmHg (20.0 and 26.6 kPa) with the highest sensitivity and specificity.

RESULTS

A total of 106 paired measurements were collected. A mild positive correlation was observed between ORI and PaO for values < 200 mmHg (26.6 kPa; r = 0.52). An ORI > 0.0, > 0.1 and > 0.3 indicated a PaO > 100, > 150 and > 200 mmHg (13.3, 20.0 and 26.6 kPa) with negative predictive values > 94%.

CONCLUSIONS AND CLINICAL RELEVANCE

ORI may provide a noninvasive indication of PaO > 100, > 150 and > 200 mmHg (13.3, 20.0 and 26.6 kPa) in anaesthetized donkeys with an FiO > 0.95, although it does not replace blood gas analysis for assessment of oxygenation.