A conversion formula for comparing pulse oximeter desaturation rates obtained with different averaging times

Longitudinal pilot study of oxygen saturation indices in healthy preterm infants

BACKGROUND

This study aimed to determine patterns of nocturnal pulse oximetry indices in moderate to late preterm infants, and investigate the relationship between oxygen desaturations, the apnoea hypopnoea index, and both corrected gestational and postnatal age.

METHODS

21 healthy infants born at 32 + 0 - 36 + 6 weeks gestation underwent serial nocturnal pulse oximetry studies and respiratory polygraphy studies until 40 weeks corrected gestational age (CGA). The main outcome measures were number of >3% oxygen desaturations/hour (ODI3), mean oxygen saturations, and number of apnoeas and hypopnoeas/hour.

RESULTS

Median ODI3 increased between weeks 1 and 3 from 49.9 to 85.4/hour (p = 0.017). Mean oxygen saturations reached a corresponding nadir of 96.0% in week 3, then increased to 96.8% in week 6 (p = 0.019). Mixed effects modelling demonstrated that ODI3 and mean saturations were influenced by postnatal age but not CGA (p < 0.05). Desaturations frequently occurred without an apnoea or hypopnoea.

CONCLUSION

ODI3 rises then falls during the first 8 weeks of life in moderate to late preterm infants, independently of CGA. These interesting preliminary results highlight the importance of further serial data collection to generate age-specific normal ranges, and develop a better understanding of respiratory control in preterm infants.

IMPACT

The frequency of >3% oxygen desaturations (ODI3) in healthy moderate to late preterm infants rises then falls after birth, peaking in postnatal week 3. There is a corresponding nadir in mean saturations. There were significant non-linear relationships between ODI3/mean saturations and postnatal age, but not corrected gestational age. The majority of brief oxygen desaturations occurred without an apnoea or hypopnoea. Normal ranges for oxygen saturation indices are not known in this population. These results demonstrate the need for further serial data collection to generate age-specific normal ranges and inform oxygen prescribing guidelines.

Use of pulse oximetry as an investigative test for paediatric respiratory sleep disorders

The article covers the following elements: practical and technological considerations for optimising data collection and output; reference ranges for oximetry parameters across the ages; things to consider when interpreting a pulse oximetry study (eg, sleep/wake times); the ability of pulse oximetry to predict obstructive sleep apnoea; using oximetry as a screening tool for sleep disordered breathing in children with Down syndrome; things to consider when setting up a home oximetry service; and a case of an infant being weaned from oxygen using pulse oximetry studies.

Evaluation of the impact of oximeter averaging times on automated FiO2 control in routine NICU care: a randomized cross-over study

Objective

Changes in oximeter averaging times have been noted to affect alarm settings. Automated algorithms (A-FiO2) assess FiO2 faster than oximeter averaging, potentially impacting their effectiveness.

Methods

In a single NICU routinely using 15 fabian-PRICO A-FiO2 systems, neonates were randomly exposed to SpO2 averaging time settings switched every 12 h among short (2-4 s), medium (10 s), and long (16 s) oximeter averaging times for the entire duration of their A-FiO2 exposure. Primary endpoints were the percent time in the set SpO2 target range (dependent on PMA), SpO2 < 80%, and SpO2 > 98%, excluding FiO2 = 0.21.

Results

Ten VLBW neonates were enrolled over 11 months. At entry, they were 17 days old (IQR: 14-19), with an adjusted gestational age of 29 weeks (IQR: 27-30). The study included data from 272 days of A-FiO2 control (34% short, 32% medium, and 34% long). Respiratory support was predominantly non-invasive (53% NCPAP, 40% HFNC, and 6% NIPPV). The aggregate SpO2 exposure levels were 67% (IQR: 55-82) in the target range, 5.4% (IQR: 2.0-10) with SpO2 < 80%, and 1.2% (IQR: 0.4-3.1) with SpO2 > 98%. There were no differences in the target range time between the SpO2 averaging time settings. There were differences at the SpO2 extremes (p ≤ 0.001). The medium and long averaging were both lower than the short, with the difference larger than predicted. Multivariate analysis revealed that these findings were independent of subject, ventilation mode, target range, and overall stability.

Conclusions

This A-FiO2 algorithm is effective regardless of the SpO2 averaging time setting. There is an advantage to the longer settings, which suggest an interaction with the controller.

Pulse Oximeter Performance during Rapid Desaturation

The reliability of pulse oximetry is crucial, especially in cases of rapid changes in body oxygenation. In order to evaluate the performance of pulse oximeters during rapidly developing short periods of concurrent hypoxemia and hypercapnia, 13 healthy volunteers underwent 3 breathing phases during outdoor experiments (39 phases in total), monitored simultaneously by five different pulse oximeters. A significant incongruity in values displayed by the tested pulse oximeters was observed, even when the accuracy declared by the manufacturers were considered. In 28.2% of breathing phases, the five used devices did not show any congruent values. The longest uninterrupted congruent period formed 74.4% of total recorded time. Moreover, the congruent periods were rarely observed during the critical desaturation phase of the experiment. The time difference between the moments when the first and the last pulse oximeter showed the typical study endpoint values of SpO₂ 85% and 75% was 32.1 ± 23.6 s and 24.7 ± 19.3 s, respectively. These results suggest that SpO₂ might not be a reliable parameter as a study endpoint, or more importantly as a safety limit in outdoor experiments. In the design of future studies, more parameters and continuous clinical assessment should be included.

Weaning oxygen in infants with bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a form of chronic lung disease commonly seen in preterm infants as the sequelae following respiratory distress syndrome. The management of evolving BPD aims to minimise lung injury and prevent the impact of hypoxia and hyperoxia. Proposed morbidities include respiratory instability, pulmonary hypertension, suboptimal growth, altered cerebral oxygenation and long-term neurodevelopmental impairment. The ongoing management and associated morbidity present a significant burden for carers and healthcare systems. Long-term oxygen therapy may be required for variable duration, though there is a lack of consensus and wide variation in practise when weaning supplemental oxygen. Furthermore, a shift in care towards earlier discharge and community care underlines the importance of a structured discharge and weaning process that eliminates the potential risks associated with hypoxia and hyperoxia. This review article describes recent evidence outlining oxygen saturation reference ranges in young infants, on which structured guidance can be based.

Observational study on the influence of averaging time on oximetry results in infants and children

AIM

Oximetry values are influenced by the averaging time (AT) used. We aimed to evaluate the effect of different ATs on number, duration, mean single event and total integral of desaturations in preterm infants and children to convert between parameters obtained with different ATs.

METHODS

In a prospective observational study, 49 children underwent sleep laboratory-based polysomnography and 15 preterm infants were studied in the intensive care unit. Their raw red-to-infrared-saturation-data were reprocessed using seven different ATs (3-16 seconds). Desaturation thresholds were <80% (infants) and <90% (children), conversion formulas and their median percentage errors were calculated.

RESULTS

We found a linear relationship between the logarithms of the ATs and those of the desaturation parameters, leading to a conversion formula with different exponents. Based on this relationship, the number of desaturations decreased from AT = 3s to AT = 16s by factor 0.28 (children) and 0.18 (infants); total oxygen saturation integral decreased by factor 0.72 (children) and 0.48 (infants). The desaturation duration increased by factor 1.89 (children) and 3.34 (infants).

CONCLUSION

The number and total integral decreased, but the duration and mean single event integral increased with increasing AT. These changes were stronger in infants. Conversion formulas may facilitate comparisons between studies using different averaging times.

Noninvasive Monitoring and Assessment of Oxygenation in Infants

Formerly, assessing oxygenation relied on recognizing cyanosis; however, this is unreliable. Also, in neonates, a pink color, suggesting absence of severe hypoxemia, is difficult to assess. An objective and continuous assessment of oxygenation is necessary. Currently, this is best achieved noninvasively by transcutaneous partial pressure of oxygen (PTcO₂) monitoring or pulse oximetry. Because both PTcO₂ and oxygen saturation monitors (pulse oximeters) may display erroneous measurements, thorough understanding of their operating principles is required. Also, clinicians must recognize the range of values expected in healthy neonates. In this article, data on these issues are reviewed.

Oximetry use in obstructive sleep apnea

INTRODUCTION

Overnight oximetry has been proposed as an accessible, simple, and reliable technique for obstructive sleep apnea syndrome (OSAS) diagnosis. From visual inspection to advanced signal processing, several studies have demonstrated the usefulness of oximetry as a screening tool. However, there is still controversy regarding the general application of oximetry as a single screening methodology for OSAS. Areas covered: Currently, high-resolution portable devices combined with pattern recognition-based applications are able to achieve high performance in the detection of this disease. In this review, recent studies involving automated analysis of oximetry by means of advanced signal processing and machine learning algorithms are analyzed. Advantages and limitations are highlighted and novel research lines aimed at improving the screening ability of oximetry are proposed. Expert commentary: Oximetry is a cost-effective tool for OSAS screening in patients showing high pretest probability for the disease. Nevertheless, exhaustive analyses are still needed to further assess unattended oximetry monitoring as a single diagnostic test for sleep apnea, particularly in the pediatric population and in populations with significant comorbidities. In the following years, communication technologies and big data analyses will overcome current limitations of simplified sleep testing approaches, changing the detection and management of OSAS.

Alarms, oxygen saturations, and SpO2 averaging time in the NICU

BACKGROUND

Alarm overload is a significant concern in the Neonatal Intensive Care Unit (NICU). Selecting a longer oxygen saturation (SpO2) averaging time will reduce the number of alarms but may mask fluctuations in oxygenation.

OBJECTIVE

Characterize bedside monitor alarms in the NICU and estimate the impact of longer SpO2 averaging time and alarm delay.

METHODS

All bedside monitor alarms were analyzed over a 12-month period in the University of Virginia NICU, using the default averaging time (8 seconds) and SpO2 alarm limits set at 88-95% for infants on supplemental oxygen. In 10 VLBW infants, SpO2 averaging time was lowered to 2 seconds for 24 hours and events of SpO2 out of the target range were estimated with 2-, 8-, or 16-second averaging time, with and without a 15-second alarm delay.

RESULTS

There were 3,263,590 alarms in the unit over 12 months. Low or high SpO2 alarms constituted 79% of the total, and 55% of these events lasted <15 seconds. In 10 infants we estimated that increasing SpO2 averaging time from 2 to 16 seconds would have led to 53% fewer SpO2 alarms but the mean duration of alarms would have been 2.15-fold longer. Adding a 15-second alarm delay to 2-second SpO2 averaging in this analysis decreased SpO2 alarms by 67%.

CONCLUSION

Longer SpO2 averaging times mask the number and severity of events of aberrant oxygenation in preterm infants without decreasing total alarm time. Incorporating an alarm delay with shorter SpO2 averaging times can reduce alarm number and duration, and allow more accurate assessment of oxygenation, which may be important for research into consequences of aberrant oxygenation in this vulnerable population.

The Impact of Averaging Window Length on the"Desaturation Indexes during Overnight Pulse Oximetry at High-Altitude"

STUDY OBJECTIVES

To determine the impact of averaging window-length on the "desaturation" indexes (DIs) obtained via overnight pulse oximetry (SpO2) at high altitude.

DESIGN

Overnight SpO2 data were collected during a 10-day sojourn at high altitude. SpO2 was obtained using a commercial wrist-worn finger oximeter whose firmware was modified to store unaveraged beat-to-beat data. Simple moving averages of window lengths spanning 2 to 20 cardiac beats were retrospectively applied to beat-to-beat SpO2 datasets. After SpO2 artifacts were removed, the following DIs were then calculated for each of the averaged datasets: oxygen desaturation index (ODI); total sleep time with SpO2 < 80% (TST < 80), and the lowest SpO2 observed during sleep (SpO2 low).

SETTING

South Base Camp, Mt. Everest (5,364 m elevation).

PARTICIPANTS

Five healthy, adult males (35 ± 5 y; 180 ± 1 cm; 85 ± 4 kg).

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

49 datasets were obtained from the 5 participants, totalling 239 hours of data. For all window lengths ≥ 2 beats, ODI and TST < 80 were lower, and SpO2 low was higher than those values obtained from the beat-to-beat SpO2 time series data (P < 0.05).

CONCLUSIONS

Our findings indicate that increasing oximeter averaging window length progressively underestimates the frequency and magnitude of sleep disordered breathing events at high altitude, as indirectly assessed via the desaturation indexes.