Oxygen saturation targeting by pulse oximetry in the extremely low gestational age neonate: a quixotic quest

A Bayesian Reanalysis of the Overall and Sex-Disaggregated Results of the Neonatal Oxygenation Prospective Meta-Analysis (NeOProM)

Data from the Neonatal Oxygenation Prospective Meta-analysis (NeOProM) indicate that targeting a higher (91-95%) versus lower (85-89%) pulse oximeter saturation (SpO2) range may reduce mortality and necrotizing enterocolitis (NEC) and increase retinopathy of prematurity (ROP). Aiming to re-evaluate the strength of this evidence, we conducted a Bayesian reanalysis of the NeOProM data. We used Bayes factors (BFs) to evaluate the likelihood of the data under the combination of models assuming the presence vs. absence of effect, heterogeneity, and moderation by sex. The Bayesian reanalysis showed moderate evidence in favor of no differences between SpO2 targets (BF10 = 0.30) in death or major disability, but moderate evidence (BF10 = 3.60) in favor of a lower mortality in the higher SpO2 group. Evidence in favor of differences was observed for bronchopulmonary dysplasia (BPD) (BF10 = 14.44, lower rate with lower SpO2), severe NEC (BF10 = 9.94), and treated ROP (BF10 = 3.36). The only outcome with moderate evidence in favor of sex differences was BPD. This reanalysis of the NeOProM trials confirmed that exposure to a lower versus higher SpO2 range is associated with a higher mortality and risk of NEC, but a lower risk of ROP and BPD. The Bayesian approach can help in assessing the strength of evidence supporting clinical decisions.

The Association Between Pregnancy-Induced Hypertension and Neonatal Cerebral Metabolism, Hemodynamics, and Brain Injury as Determined by Physiological Imaging

Pregnancy-induced hypertension (PIH) is common and may affect maternal and children’s healthcare. However, the neurobiological status of neonates born from mothers with PIH has yet to be elucidated. The present study employed physiological imaging to investigate the association between maternal PIH and a number of neonatal health parameters, including cerebral metabolism, hemodynamics, and pathophysiological vulnerabilities. Following the acquisition of ethical approval, we recruited 16 neonates with maternal PIH and 22 normal neonates (non-PIH) as controls. All neonates underwent magnetic resonance imaging (MRI) of the brain. Phase-contrast (PC) MRI and T2-relaxation-under-spin-tagging (TRUST) MRI were performed to determine global cerebral blood flow, oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen (CMRO₂). These physiological parameters were then compared between PIH neonates and controls. Linear regression analysis was performed to investigate the associations between maternal PIH and each of the physiological parameters. Receiver operating characteristic curves (ROCs) were used to determine whether maternal systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) which could facilitate the diagnosis of neonatal brain injuries. PIH neonates showed significantly lower OEF (25.5 ± 8.8% vs. 32.6 ± 7.3%, P = 0.01) and CMRO₂ (29.7 ± 9.4 vs. 40.9 ± 15.0 μmol/100 g/min, P = 0.01) compared to the controls. Maternal blood pressure levels [PIH or non-PIH groups, each one standard deviation (SD) increase in SBP, DBP, and MAP, respectively] were negatively associated with OEF [regression coefficient (β) = −7.9, P = 0.007; β = −4.2, P = 0.004; β = −3.6, P = 0.02; β = −4.0, P = 0.008, respectively). Furthermore, each one SD increase in maternal DBP and MAP was negatively associated with CMRO₂ (β = −4.7, P = 0.03; β = −4.4, P = 0.04, respectively). The areas under the curves (AUCs) with 95% confidence intervals (CIs) for maternal SBP, DBP, and MAP were 0.90 (0.80–0.97), 0.85 (0.73–0.97), and 0.89 (0.76–0.99), respectively. The AUC values for maternal SBP, DBP, and MAP indicated good diagnostic ability for identifying neonatal brain injuries. The present study demonstrated that maternal PIH may be associated with a lower oxygen extraction and lower cerebral metabolism in neonates.

Thresholds for oximetry alarms and target range in the NICU: an observational assessment based on likely oxygen tension and maturity

BACKGROUND

Continuous monitoring of SpO2 in the neonatal ICU is the standard of care. Changes in SpO2 exposure have been shown to markedly impact outcome, but limiting extreme episodes is an arduous task. Much more complicated than setting alarm policy, it is fraught with balancing alarm fatigue and compliance. Information on optimum strategies is limited.

METHODS

This is a retrospective observational study intended to describe the relative chance of normoxemia, and risks of hypoxemia and hyperoxemia at relevant SpO2 levels in the neonatal ICU. The data, paired SpO2-PaO2 and post-menstrual age, are from a single tertiary care unit. They reflect all infants receiving supplemental oxygen and mechanical ventilation during a 3-year period. The primary measures were the chance of normoxemia (PaO2 50-80 mmHg), risks of severe hypoxemia (PaO2 ≤ 40 mmHg), and of severe hyperoxemia (PaO2 ≥ 100 mmHg) at relevant SpO2 levels.

RESULTS

Neonates were categorized by postmenstrual age: < 33 (n = 155), 33-36 (n = 192) and > 36 (n = 1031) weeks. From these infants, 26,162 SpO2-PaO2 pairs were evaluated. The post-menstrual weeks (median and IQR) of the three groups were: 26 (24-28) n = 2603; 34 (33-35) n = 2501; and 38 (37-39) n = 21,058. The chance of normoxemia (65, 95%-CI 64-67%) was similar across the SpO2 range of 88-95%, and independent of PMA. The increasing risk of severe hypoxemia became marked at a SpO2 of 85% (25, 95%-CI 21-29%), and was independent of PMA. The risk of severe hyperoxemia was dependent on PMA. For infants < 33 weeks it was marked at 98% SpO2 (25, 95%-CI 18-33%), for infants 33-36 weeks at 97% SpO2 (24, 95%-CI 14-25%) and for those > 36 weeks at 96% SpO2 (20, 95%-CI 17-22%).

CONCLUSIONS

The risk of hyperoxemia and hypoxemia increases exponentially as SpO2 moves towards extremes. Postmenstrual age influences the threshold at which the risk of hyperoxemia became pronounced, but not the thresholds of hypoxemia or normoxemia. The thresholds at which a marked change in the risk of hyperoxemia and hypoxemia occur can be used to guide the setting of alarm thresholds. Optimal management of neonatal oxygen saturation must take into account concerns of alarm fatigue, staffing levels, and FiO2 titration practices.

Evaluation of two SpO2 alarm strategies during automated FiO2 control in the NICU: a randomized crossover study

Background

Changes in oxygen saturation (SpO₂) exposure have been shown to have a marked impact on neonatal outcomes and therefore careful titration of inspired oxygen is essential. In routine use, however, the frequency of SpO₂ alarms not requiring intervention results in alarm fatigue and its corresponding risk. SpO₂ control systems that automate oxygen adjustments (Auto-FiO₂) have been shown to be safe and effective. We speculated that when using Auto-FiO₂, alarm settings could be refined to reduce unnecessary alarms, without compromising safety.

Methods

An unblinded randomized crossover study was conducted in a single NICU among infants routinely managed with Auto-FiO₂. During the first 6 days of respiratory support a tight and a loose alarm strategy were switched each 24 h. A balanced block randomization was used. The tight strategy set the alarms at the prescribed SpO₂ target range, with a 30-s delay. The loose strategy set the alarms 2 wider, with a 90-s delay. The effectiveness outcome was the frequency of SpO₂ alarms, and the safety outcomes were time at SpO₂ extremes (< 80, > 98%). We hypothesized that the loose strategy would result in a marked decrease in the frequency of SpO₂ alarms, and no increases at SpO₂ extremes with 20 subjects. Within subject differences between alarm strategies for the primary outcomes were evaluated with Wilcoxon signed-rank test.

Results

During a 13-month period 26 neonates were randomized. The analysis included 21 subjects with 49 days of both tight and loose intervention. The loose alarm strategy resulted in a reduction in the median rate of SpO₂ alarms from 5.2 to 1.6 per hour (p <  0.001, 95%-CI difference 1.6–3.7). The incidence of hypoxemia and hyperoxemia were very low (less than 0.1%-time) with no difference associated with the alarm strategy (95%-CI difference less than 0.0–0.2%).

Conclusions

In this group of infants we found a marked advantage of the looser alarm strategy. We conclude that the paradigms of alarm strategies used for manual titration of oxygen need to be reconsidered when using Auto-FiO₂. We speculate that with optimal settings false positive SpO₂ alarms can be minimized, with better vigilance of clinically relevant alarms.

Trial registration

Retrospectively registered 15 May 2018 at ISRCTN (49239883).

Electronic supplementary material

The online version of this article (10.1186/s12887-019-1496-5) contains supplementary material, which is available to authorized users.

Hypoxemic and hyperoxemic likelihood in pulse oximetry ranges: NICU observational study

OBJECTIVE

Describe the likelihood of hypoxemia and hyperoxemia across ranges of oxygen saturation (SpO₂), during mechanical ventilation with supplemental oxygenation.

DESIGN

Retrospective observational study.

SETTING

University affiliated tertiary care neonatal intensive care unit.

PATIENTS

Two groups of neonates based on postmenstrual age (PMA): <32 weeks (n=104) and >36 weeks (n=709).

MAIN MEASURES

Hypoxemia was defined as a PaO₂ <40 mm Hg, hyperoxemia as a PaO₂ of >99 mm Hg and normoxemia as a PaO₂ of 50-80 mm Hg. Twenty-five per cent was defined as marked likelihood of hypoxemia or hyperoxemia.

RESULTS

From these infants, 18 034 SpO₂-PaO₂ pairs were evaluated of which 10% were preterm. The PMA (median and IQR) of the two groups were: 28 weeks (27-30) and 40 weeks (38-41). With SpO₂ levels between 90% and 95%, the likelihoods of hypoxemia and hyperoxemia were low and balanced. With increasing levels of SpO₂, the likelihood of hyperoxemia increased. It became marked in the preterm group when SpO₂ was 99%-100% (95% CI 29% to 41%) and in the term group with SpO₂ levels of 96%-98% (95% CI 29% to 32%). The likelihood of hypoxemia increased as SpO₂ decreased. It became marked in both with SpO₂ levels of 80%-85% (95% CI 20% to 31%, 24% to 28%, respectively).

CONCLUSIONS

The likelihood of a PaO₂ <40 mm Hg is marked with SpO₂ below 86%. The likelihood of a PaO₂ >99 mm Hg is marked in term infants with SpO₂ above 95% and above 98% in preterm infants. SpO₂ levels between 90% and 95% are appropriate targets for term and preterm infants.

Optimal oxygen saturation in extremely premature neonates

So far, great efforts have been made to understand the demands of extremely premature neonates (EPNs´; born before the 28(th) week of gestation) on postnatal care, including optimal oxygen saturation, that will allow them to survive without disability. A major yet unresolved problem is to find an "optimal range" of their oxygen saturation and to maintain it without drops or increases, i.e., without hypoxia or hyperoxia. The individual sections of this paper deal with the changes of SpO(2) (an estimate of SaO(2) measured by pulse oximetry) that occur before, during, and after premature labor, postnatal factors affecting SpO(2), and especially how to find an acceptable compromise in choosing the most effective and minimally harmful range of SpO(2) for EPNs' with the careful FiO(2) adjustment and continually monitored SpO(2). At present, the two SpO(2) ranges, narrow (90-94%) vs. wider (88-94%), are most discussed. However, the question of how much oxygen is too much or little remains unanswered. There is even a view that there is no uniform optimal SpO(2) range for EPNs, and that each newborn has its own, individually specific range that changes due to its intrinsic and/or extrinsic factors.