Oxygen Reserve Index as a Tool to Monitor Four Techniques of Oxygen Supplementation at Different Flow Rates in Dogs Sedated with Dexmedetomidine and an Opioid

SIMPLE SUMMARY: Oxygen is a valuable resource, and its responsible use in veterinary medicine for treating dogs that require supplementation is of utmost importance. However, the effectiveness of various devices in enhancing arterial oxygen content during therapy remains inadequately explored. In patients breathing room air, pulse oximetry (SpO(2)) assesses arterial oxygen content based on its binding with hemoglobin, represented as a percentage. SpO(2) is considered accurate in estimating arterial oxygenation for values between 100% and 80%. Physiologically, SpO(2) is >98% when breathing room air and the device can also monitor the effectiveness of oxygen therapy. When the oxygen content in the blood rises above physiologic levels, the SpO(2) remains constant. To address this, a new parameter, the oxygen reserve index, aids in estimating the animal’s arterial oxygen levels. Our study has determined that when compared with a vented face mask or flow-by methods, nasal prongs and Venturi valves, with the latter delivering a fixed oxygen amount, are the most effective methods for enriching inhaled oxygen flow. By employing these devices, coupled with the guidance of the oxygen reserve index, it becomes possible to optimize the minimum required oxygen flow rate for supplementation. This approach not only improves the efficacy of oxygen administration but also reduces wastage concurrently. ABSTRACT: 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 (SpO(2)) during hyperoxia (PaO(2) 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 (FiO(2)) was measured at the level of the cervical trachea. At each flow rate, ORi and SpO(2) were recorded. The flow-by method minimally increased the FiO(2), 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 FiO(2) and ORi, with over half of the values exceeding 40% and 0.4, respectively. The tight-vented mask showed variable increases in FiO(2), ranging between 22 and 90%. Despite method-dependent variations, all devices increased SpO(2) > 98% as the FiO(2) 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.