Early warning for SpO₂ decrease by the oxygen reserve index in neonates and small infants

Continuously assessing the oxygenation levels of patients to detect and prevent hypoxemia can be advantageous for safe anesthesia, especially in neonates and small infants. The oxygen reserve index (ORI) is a new parameter that can assess oxygenation through a relationship with arterial oxygen partial pressure (PaO₂ ). The aim of this study was to examine whether the ORI provides a clinically relevant warning time for an impending SpO₂ (pulse oximetry hemoglobin saturation) reduction in neonates and small infants.

ORI and SpO₂ were measured continuously in infants aged <2 years during general anesthesia. The warning time and sensitivity of different ORI alarms for detecting impending SpO₂ decrease were calculated. Subsequently, the agreement of the ORI and PaO₂ with blood gas analyses was assessed.

The ORI of 100 small infants and neonates with a median age of 9 months (min-max, 0-21 months) and weight of 8.35 kg (min-max, 2-13 kg) were measured. For the ORI/PaO₂ correlation, 54 blood gas analyses were performed. The warning time and sensitivity of the preset ORI alarm during the entire duration of anesthesia were 84 s (25th-75th percentile, 56-102 s) and 55% (95% CI 52%-58%), and those during anesthesia induction were 63 s (40-82 s) and 56% (44%-68%), respectively. The positive predictive value of the preset ORI alarm were 18% (95% CI 17%-20%; entire duration of anesthesia) and 27% (95% CI 21%-35%; during anesthesia induction). The agreement of PaO₂ intervals with the ORI intervals was poor, with a kappa of 0.00 (95% CI = [-0.18; 0.18]). The weight (p = .0129) and height (p = .0376) of the infants and neonates were correlated to the correct classification of the PaO₂ interval with the ORI interval.

The ORI provided an early warning time for detecting an impending SpO₂ decrease in small infants and neonates in the defined interval in this study. However, the sensitivity of ORI to forewarn a SpO₂ decrease and the agreement of the ORI with PaO₂ intervals in this real-life scenario were too poor to recommend the ORI as a useful early warning indicator for this age group.