Evaluation of a new end-tidal carbon monoxide monitor from the bench to the bedside

A "Gold Standard" Test for Diagnosing and Quantifying Hemolysis in Neonates and Infants

Identifying "gold standard" diagnostic tests can promote evidence-based neonatology practice. Hemolysis is a pathological shortening of the erythrocyte lifespan, differing from erythrocyte senescence in responsible mechanisms and clinical implications. Diagnosing hemolysis goes beyond a binary (yes vs. no) determination. It is characterized according to magnitude, and as acute vs. chronic, and genetically based vs. not. For neonates with significant hyperbilirubinemia or anemia, detecting hemolysis and quantifying its magnitude provides diagnostic clarity. The 2022 American Academy of Pediatrics (AAP) Clinical Practice Guideline on management of hyperbilirubinemia in the newborn states that hemolysis is a risk factor for developing significant hyperbilirubinemia and neurotoxicity. The guideline recommends identifying hemolysis from any cause, but specific guidance is not provided. A spectrum of laboratory tests has been endorsed as diagnostic methods for hemolysis. Herein we examine these laboratory tests and recommend one as the "gold standard" for diagnosing and quantifying hemolysis in neonates and infants.

Higher ETCOc predicts longer phototherapy treatment in neonatal hyperbilirubinemia

Objective

This study aimed to evaluate the predictive performance of end-tidal carbon monoxide corrected to ambient carbon monoxide (ETCOc) values phototherapy in neonates with significant hyperbilirubinemia.

Methods

A prospective study was conducted on neonates with significant hyperbilirubinemia who received phototherapy between 3 and 7 days of life. The breath ETCOc and serum total bilirubin of the recruited infants were measured on admission.

Results

The mean ETCOc at admission in 103 neonates with significant hyperbilirubinemia was 1.70 ppm. The neonates were categorized into two groups: phototherapy duration ≤72 h (n = 87) and >72 h (n = 16) groups. Infants who received phototherapy for >72 h had significantly higher ETCOc (2.45 vs. 1.60, P = 0.001). The cutoff value of ETCOc on admission for predicting longer phototherapy duration was 2.4 ppm, with a sensitivity of 62.5% and specificity of 88.5%, yielding a 50% positive predictive value and a 92.7% negative predictive value.

Conclusion

ETCOc on admission can help predict the duration of phototherapy in neonates with hyperbilirubinemia, facilitate clinicians to judge disease severity, and make clinical communication easier and more efficient.

An End-Tidal Carbon Monoxide Nomogram for Term and Late-Preterm Chinese Newborns

OBJECTIVE

To establish a reference nomogram for end-tidal CO corrected for ambient CO (ETCOc) levels in term and late-preterm Chinese newborns and then assess its efficacy to identify hemolytic hyperbilirubinemia.

STUDY DESIGN

We conducted a prospective study by measuring concurrent ETCOc and total serum bilirubin (TSB) or transcutaneous bilirubin (TcB) levels collected postnatally at 12, 24, 48, 72, 96, and 120 hours of age. ETCOc at the 25th, 50th, 75th, and 95th percentiles at each epoch were used to construct the reference nomogram. We then explored the ability of predischarge ETCOc and TSB/TcB metrics to predict the development of hyperbilirubinemia requiring phototherapy in early postnatal period and jaundice readmission in late postnatal period.

RESULTS

Our nomogram, based on 990 measurements from 455 infants who were not nonhemolytic, displayed a steady line within 3 postnatal days, followed by a subsequent decline. From a cohort of infants with a serial ETCOc measurements (n = 130) and those readmitted (n = 21), we found that ETCOc and TSB/TcB ≥75th percentile can identify most hemolytic hyperbilirubinemia between 12 and 72 hours after birth with an area under the curve (AUC) of 0.741. An ETCOc ≥1.7 ppm alone between 96 and 120 hours after birth can identify most hemolytic hyperbilirubinemia with an AUC of 0.816. In addition, 90.5% of readmitted infants had an ETCOc ≥75th percentile.

CONCLUSIONS

An ETCOc reference nomogram during the first 5 postnatal days in nonhemolytic term and late-preterm newborns can be used to identify hemolytic hyperbilirubinemia requiring phototherapy in the early postnatal period and readmission in the late postnatal period.

Role of Cord Blood Carboxyhemoglobin in Detecting Significant Hyperbilirubinemia in Term Neonates with ABO Alloimmunization

OBJECTIVE

This study aimed to assess whether cord blood carboxyhemoglobin (COHb) levels in jaundiced term neonates with and without a positive direct Coombs test (DCT) and in healthy controls could be used as a predictor of severe hyperbilirubinemia. The percentage of cord blood COHb should be higher among neonates with Coombs-positive ABO hemolytic disease than among those with Coombs-negative ABO incompatibility and higher than that of ABO-compatible control neonates.

STUDY DESIGN

This cross-sectional descriptive study of 198 term neonates comprised three subgroups: group I featured 68 DCT-positive ABO-incompatible neonates (ABO + DCT), group II featured 60 DCT-negative ABO-incompatible neonates with hyperbilirubinemia (ABO-DCT), and group III featured 70 healthy controls. COHb was determined by an OSM3 hemoximeter.

RESULTS

Group I differed from groups II and III for cord blood bilirubin, cord blood hemoglobin, and cord blood hematocrit. Groups I and II had higher mean total serum bilirubin (TSB) levels than group III, while there was no difference in the mean TSB levels between groups I and II. There was no significant difference between the COHb group means for groups I, II, and III (p = 0.98). The area under the receiver operating characteristic curve calculated for group I/group III and group II/group III were found to be 0.62 and 0.54, respectively.

CONCLUSION

COHb levels did not prove to be superior to the DCT for predicting the risk of developing severe hyperbilirubinemia in term neonates.

KEY POINTS

· COHb levels do not predict the risk of developing severe hyperbilirubinemia in term neonates.. · COHb levels may predict that ABO incompatibility in early life.. · COHb levels did not prove to be superior to the direct coombs test..

Reference intervals for end-tidal carbon monoxide of preterm neonates

OBJECTIVES

We constructed reference intervals for end-tidal carbon monoxide (ETCOc) levels of neonates 28 ^0/7 to 34 ^6/7 weeks gestation in order to assess hemolytic rate.

STUDY DESIGN

This is a prospective four-NICU study in Bangkok, Thailand, and Utah, USA.

RESULTS

Of 226 attempted measurements, 92% were successful. Values from day 1 through 28 were charted and upper (>95th percentile) reference interval limits calculated. During the entire 28 days, the ETCOc upper reference intervals from babies in Bangkok were higher than those in Utah (p < 0.01). No differences were found due to sex, or earliest vs. latest gestation at birth (both p > 0.1). Similar to term neonates, preterm neonates in Bangkok and Utah had higher ETCOc values during the first 48 h after birth than thereafter (p < 0.01).

CONCLUSIONS

Using this methodology, and the reference interval chart, the hemolytic rate of preterm infants ≥28 weeks can be assessed.

Breath Biomarkers in Diagnostic Applications

The detection of chemical compounds in exhaled human breath presents an opportunity to determine physiological state, diagnose disease or assess environmental exposure. Recent advancements in metabolomics research have led to improved capabilities to explore human metabolic profiles in breath. Despite some notable challenges in sampling and analysis, exhaled breath represents a desirable medium for metabolomics applications, foremost due to its non-invasive, convenient and practically limitless availability. Several breath-based tests that target either endogenous or exogenous gas-phase compounds are currently established and are in practical and/or clinical use. This review outlines the concept of breath analysis in the context of these unique tests and their applications. The respective breath biomarkers targeted in each test are discussed in relation to their physiological production in the human body and the development and implementation of the associated tests. The paper concludes with a brief insight into prospective tests and an outlook of the future direction of breath research.

Measuring Human Hemolysis Clinically and in Extreme Environments Using Endogenous Carbon Monoxide Elimination

The measure of hemolysis in humans is clinically important. Here we describe methods using a gas chromatograph equipped with a reduction gas detector to detect the human analyte carbon monoxide (CO) that were developed for the extreme environment of the International Space Station. These methods can be adapted to in-hospital use for clinical care with characteristics that may surpass existing measures of hemolysis. We demonstrate improved performance over previous-generation methods in terms of reproducibility, accuracy, control for physical and intervening factors to quantitatively assess hemolysis rates at unprecedented levels. The presented measure of hemolysis using CO elimination is based on a different physiological approach that can complement and augment existing detection tools. In addition to their suitability for extreme environments, the methods present distinctive advantages over existing markers for the diagnosis, monitoring and response to treatment of hemolytic anemia. These methods have the potential to fulfill a wide range of research and clinical applications.

Noninvasive Detection of Hemolysis with ETCOc Measurement in Neonates at Risk for Significant Hyperbilirubinemia

BACKGROUND

Hemolytic hyperbilirubinemia due to blood group incompatibility or glucose-6-phosphate dehydrogenase deficiency (G6PD) is a common cause of significant hyperbilirubinemia. Hemolysis in a hyperbilirubinemic infant increases the risk of bilirubin neurotoxicity. A new portable device (CoSense) can rapidly detect breath end-tidal carbon monoxide corrected to ambient carbon monoxide (ETCOc). ETCOc levels are surrogate markers of hemoglobin breakdown and bilirubin production.

OBJECTIVE

The aim was to evaluate the association between ETCOc values and hemolysis and its relevance in neonates at risk for significant hyperbilirubinemia.

METHODS

A prospective study was conducted among newborn infants born at more than 35 weeks and with a birth weight greater than 2,000 g with a G6PD deficiency, blood group incompatibility, or clinical jaundice needing phototherapy during the first 7 days of life. The recruited infants had their breath ETCOc measured twice, first on the day of recruitment and then again on the following day.

RESULTS

Fifty infants completed this study. Their mean ETCOc was 1.61 (±0.56) ppm. There was a linear correlation (r = 0.89) between increasing ETCOc values and reticulocyte counts (RC). Sixteen newborns with ABO incompatibility had a significantly higher mean ETCOc of 1.98 ppm (±0.71) as compared to 1.43 (±0.38) ppm in the nonhemolytic hyperbilirubinemia (NHH) group (n = 25) (p = 0.002). This was suggestive of hemolysis as shown by the significantly higher RC of 6.90% (±3.38) compared to 4.68 (±1.26) in the NHH group (p <0.005). Neonates with an ETCOc level ≥1.8 ppm had a higher RC, a lower hemoglobin level, higher serum bilirubin levels, and a rapid rise in serum bilirubin and needed a longer duration of phototherapy. ETCOc values ≥1.8 ppm were suggestive of hemolysis (RC ≥6%), with a sensitivity of 90% and a specificity of 83%.

CONCLUSION

Higher ETCOc values ≥1.8 ppm are suggestive of hemolysis and they are associated with significant hyperbilirubinemia.

Identification of risk for neonatal haemolysis

AIM

To identify neonates at risk of haemolytic hyperbilirubinaemia through near-concurrent measurements of total serum/plasma bilirubin (TB) or transcutaneous bilirubin (TcB) and end-tidal breath carbon monoxide (CO), corrected for ambient CO (ETCOc), an index of bilirubin production and haemolysis.

METHODS

Paired TB/TcB (mg/dL) and ETCOc (ppm) measurements were obtained in newborns (n = 283) at 20 to <60 hours of age in five nurseries. TB/TcB values were assigned TB/TcB percentile risk values using the Bhutani hour-specific nomogram. In infants having two serial TB/TcB measurements (n = 76), TB rate of rise (ROR, mg/dL/h) was calculated.

RESULTS

For the entire cohort (n = 283), 67.1% and 32.9% had TB/TcB<75th and ≥75th percentile, respectively. TB/TcB (5.79 ± 1.84 vs 9.14 ± 2.25 mg/dL) and ETCOc (1.61 ± 0.45 vs 2.02 ± 1.35 ppm, p = 0.0002) were different between the groups. About 36.6% of infants with TB/TcB ≥75th percentile had ETCOc ≥ 2.0 ppm. In the subcohort of infants with serial TB/TcB measurements (n = 76), 44.7% and 55.3% had TB/TcB<75th and ≥75th percentile, respectively. TB/TcB (5.28 ± 1.97 vs 9.53 ± 2.78 mg/dL), ETCOc (1.72 ± 0.48 vs 2.38 ± 1.89 ppm, p = 0.05) and TB ROR (0.011 ± 0.440 vs 0.172 ± 0.471 mg/dL/h) were different between the groups.

CONCLUSION

The combined use of TB/TcB percentile risk assessments and ETCOc measurements can identify infants with haemolytic hyperbilirubinaemia. The addition of TB ROR can identify those infants with elimination disorders.

Identification of neonatal haemolysis: an approach to predischarge management of neonatal hyperbilirubinemia

AIM

Relative contributions of increased production [by end-tidal carbon monoxide concentrations (ETCOc)] and decreased elimination of bilirubin to predischarge hour-specific total bilirubin (TB) levels were assessed in healthy late-preterm and term newborns. Secondly, we report predischarge ETCOc ranges to guide clinical management of hyperbilirubinemia.

METHODS

TB and ETCOc (≤3 timepoints) determinations of newborns aged between six hours and <6 days (n = 79) were stratified by postnatal age epochs. Hyperbilirubinemia risk was assessed by plotting TB values as a function of ETCOc.

RESULTS

Stratifications of ETCOc (in ppm, mean, median and interquartile ranges) by postnatal age epochs (0-24, 24-48 and 48-72) were as follows: 2.0, 1.9, 1.8-2.2 (n = 11); 1.6, 1.5, 1.1-2.0 (n = 58); and 2.0, 1.8, 1.6-2.3 (n = 9), respectively. Infants with ETCOc ≥ 2.5 were at high risk, between 1.5 and 2.5 at moderate risk and ≤1.5 were at low risk. Risk due to haemolysis alone was not independent (p < 0.01). For infants with TB >75th percentile (n = 31), 23% had ETCO ≤1.5, and 77% had ETCOc > 1.5 (p < 0.00003).

CONCLUSION

Near-simultaneous ETCOc and TB measurements in infants with TB >75th percentile accurately identify haemolytic hyperbilirubinemia.