Oxygen Reserve Index as a Tool to Monitor Four Techniques of Oxygen Supplementation at Different Flow Rates in Dogs...

Respiratory dysfunction often decreases arterial oxygen content. Four common oxygen delivery techniques-flow-by, nasal prongs, a tight-vented mask, and a tight mask connected to a Venturi valve-were evaluated for their effectiveness in increasing the oxygen reserve index (ORi), a dimensionless index of oxygen content that provides additional information compared to traditional pulse oximetry (SpO₂) during hyperoxia (PaO₂ 100-200 mmHg), and that ranges from 0 to 1. Thirty-two dogs sedated with dexmedetomidine and an opioid were evenly divided into four groups based on the technique for oxygen administration. Each dog received oxygen at 1, 2, and 3 L/min by a single technique, and the amount of inhaled oxygen (FiO₂) was measured at the level of the cervical trachea. At each flow rate, ORi and SpO₂ were recorded. The flow-by method minimally increased the FiO₂, and ORi reached its highest value only in 3 out of 8 dogs at the maximum flow rate. Other methods exhibited direct correlations between the oxygen flow rate and ORi (p < 0.001). These methods effectively increased FiO₂ and ORi, with over half of the values exceeding 40% and 0.4, respectively. The tight-vented mask showed variable increases in FiO₂, ranging between 22 and 90%. Despite method-dependent variations, all devices increased SpO₂ > 98% as the FiO₂ increased (p = 0.002). In conclusion, nasal prongs and the mask connected to the Venturi valve showed the highest correlation between the oxygen flow rate and the ORi. These results suggest that using these two techniques in conjunction with ORI can help in optimizing oxygen therapy.