Abstract
Oxygenation index (OI), an invasive measurement, is routinely used as a marker of severity of hypoxemic respiratory failure in neonates. Oxygen saturation index (OSI) is a noninvasive measurement and has been shown to be a reliable surrogate marker of OI in children and adults with respiratory failure. To evaluate the correlation of OI with OSI and to derive and validate predictive OI from noninvasive OSI measurements for clinically relevant OI values. For this retrospective cohort study, 220 neonates requiring invasive mechanical ventilation for hypoxic respiratory failure during the first 3 days of admission were recruited from a level III neonatal intensive care unit during a 6-year period, from January 1, 2012, to December 31, 2017. Data were analyzed from January 2017 to December 2017. The primary outcome was correlation of OI with OSI, analyzed using Pearson correlation coefficient. The secondary outcome was derivation and validation of OI from OSI. The data were split into derivative samples, from which a predictive equation for OI was derived using generalized linear model, and a validation sample was used to assess the predictive ability of the derived OI. Bland-Altman plot was used to assess agreement between derived OI and measured OI. A total of 1442 paired OI and OSI measurements from 220 infants (190 preterm and 30 term; median [interquartile range] gestational age, 29 [26-33] weeks; mean [SD] birth weight, 1602 [1092] g) were recorded during the study. The median (interquartile range) number of samples was 5 (3-9) per patient. Overall, OI and OSI showed strong correlation (r = 0.89). The correlation was stronger in preterm infants (<28 weeks, r = 0.93; 28-33 weeks, r = 0.93) and within an oxygen saturation range of 85% to 95% (r = 0.94). The predictive derivative equation showed a strong linear association and good agreement in both derivation and validation data sets, with strong accuracy measures of derived OI for OI cutoffs of 5, 10, 15, 20, and 25. A strong correlation of OI with OSI was found. Derived OI from OSI was in good agreement and strongly predictive of clinically relevant OI cutoffs from 5 to 25. Oxygenation index derived from noninvasive sources may be useful to reliably assess severity of respiratory failure and response to therapy on a continuous basis.
Highlights
Hypoxemic respiratory failure (HRF) is one of the common reasons in neonates for admission to neonatal intensive care units in the United States
Derived Oxygenation index (OI) from Oxygen saturation index (OSI) was in good agreement and strongly predictive of clinically relevant OI cutoffs from 5 to 25
Oxygenation index calculated from peripheral arterial line sources correlated strongly with OSI derived from both preductal SpO2 (n = 45; r = 0.86) and postductal SpO2 (n = 154; r = 0.94) sources
Summary
Hypoxemic respiratory failure (HRF) is one of the common reasons in neonates for admission to neonatal intensive care units in the United States. Estimated incidence of neonates with respiratory failure requiring mechanical ventilation is approximately 18 per 1000 live births.[1,2] Hypoxemic respiratory failure is associated with increased risk of mortality, morbidity, and worse neurological outcomes.[3,4] Oxygenation index (OI) is routinely used as an indicator of severity of HRF in neonates, with an arbitrary cutoff of or less for mild HRF, between and for moderate HRF, between and 40 for severe HRF, and more than 40 for very severe HRF.[5] Oxygenation index is calculated as OI = MAP × FIO2 × 100 / PaO2, where MAP indicates mean airway pressure and FIO2 indicates fraction of inspired oxygen.[5] Oxygenation index has been used as a marker in clinical management and clinical trials for initiating therapies including inhaled nitric oxide in infants with HRF and pulmonary hypertension[6,7,8,9] and for administering and evaluating response to surfactant therapy.[10,11] Oxygenation index higher than 40 is used as a criterion for consideration of extracorporeal membrane oxygenation.[12,13] Oxygenation index has been proposed as a predictive marker for neonatal outcomes, including mortality.[14] Limitations of OI include the need for an indwelling arterial catheter for frequent sampling and that it is an intermittent measurement of oxygenation status by nature. Oxygen saturation index has been validated in pediatric intensive care unit patients as a reliable index for assessing severity of respiratory failure and lung injury.[15,16] to our knowledge, studies on the use of OSI in neonates with HRF are very limited.[17,18]
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