Carbon monoxide concentrations in paediatric sepsis syndrome

Carboxyhemoglobin as biomarker of late-onset sepsis in preterm infants

Carboxyhemoglobin (COHb) is considered a biomarker of oxidative stress and previous studies reported an increase in COHb levels in preterm infants who develop late-onset sepsis (LOS). Our aim was to assess the correlation between COHb levels and the risk for LOS development. We retrospectively studied 100 preterm infants, 50 in the LOS and 50 in the no LOS group. COHb levels were measured on the day of diagnosis of the first episode of LOS, 3, 2, and 1 days before and 1 and 4 days after the onset of LOS. Logistic regression analysis showed that a higher level of COHb 2 days before the diagnosis of LOS increases the risk for LOS development (OR 12.150, 95% Cl 1.311-12.605; P = 0.028). A COHb level of 1.55% measured 2 days before the diagnosis of LOS is the best predictive threshold for LOS with a sensitivity of 70% and a specificity of 70%.    Conclusion: Increased levels of COHb may predict the diagnosis of LOS in very preterm infants with a good accuracy. If further studies confirm our findings, this easy-to-measure biomarker could provide neonatologists with another tool for monitoring and early diagnosis of sepsis in high-risk patients. What is Known: • Carboxyhemoglobin (COHb) is a biomarker of oxidative stress. • Previous studies reported an increase in COHb levels in preterm infants who develop late-onset sepsis (LOS). What is New: • COHb levels increased two days before the diagnosis of LOS and this increase was associated with the risk for developing LOS. • ROC curve analysis for COHb measured two days before the diagnosis of LOS showed that 1.55% is the best predictive threshold for LOS with a sensitivity of 70% and a specificity of 70%.

Local delivery of gaseous signaling molecules for orthopedic disease therapy

Over the past decade, a proliferation of research has used nanoparticles to deliver gaseous signaling molecules for medical purposes. The discovery and revelation of the role of gaseous signaling molecules have been accompanied by nanoparticle therapies for their local delivery. While most of them have been applied in oncology, recent advances have demonstrated their considerable potential in diagnosing and treating orthopedic diseases. Three of the currently recognized gaseous signaling molecules, nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), are highlighted in this review along with their distinctive biological functions and roles in orthopedic diseases. Moreover, this review summarizes the progress in therapeutic development over the past ten years with a deeper discussion of unresolved issues and potential clinical applications.

Carboxyhemoglobin as biomarker of prematurity complications

BACKGROUND

Carboxyhemoglobin (COHb) is considered a biomarker of oxidative stress and previous studies suggest a correlation between its blood level and prematurity complications. Our aim in this study was to assess the correlation between COHb levels and the risk for bronchopulmonary dysplasia (BPD), intraventricular hemorrhage (IVH), and retinopathy of prematurity (ROP).

METHODS

We retrospectively studied 178 preterm infants with gestational age of 27.0 ± 1.5 weeks, among which 121 (68 %) had BPD, 43 (24 %) IVH, and 33 (19 %) ROP. COHb levels measured during the first seven days of life were recorded.

RESULTS

Logistic regression analysis showed that higher levels of COHb on the seventh day of life increases the risk for moderate-to-severe BPD (OR 4.552, 95 % Cl 1.220-16.997; P = 0.024), while higher levels of COHb on the fourth day of life increases the risk for grade 2-4 IVH (OR 5.537, 95 % Cl 1.602-19.134; P = 0.007).

CONCLUSIONS

COHb measured in the first week of life can contribute to predicting the risk for BPD and IVH, but not for ROP, in very preterm infants. Since COHb can be readily measured, its assessment can be useful in clinical practice for early identification of preterm infants at high risk for oxidative stress related complications.

Carboxyhemoglobin Levels in Preterm Neonatal Late-Onset Sepsis: to Predict or not to Predict

Background

In this study, we aimed to evaluate carboxyhemoglobin (COHb) levels in diagnosing late-onset sepsis (LOS) in preterm neonates.

Methods

The records of culture-positive LOS in preterm neonates hospitalized in NICU from January 2017 to July 2022 were reviewed. COHb levels, C-reactive protein, procalcitonin, and neutrophil to lymphocyte ratio of septic preterm infants were compared to controls. In addition, serial COHb levels measured within six hours before or 24h after blood culture sampling, three to seven days prior, and three to five days after starting antimicrobial therapy were retrieved from patient records.

Results

The study included 77 blood-culture-positive preterm infants and 77 non-septic controls. During the LOS episode, the COHb values were found to be significantly increased (median: 1.8, IQR: 1.4-2.5) when compared to the control group (median: 1.2, IQR: 0.8-1.6) (p < 0.001). ROC analysis yielded an AUC of 0.714 for COHb (95% CI: 0.631-0.796, p<0.001). At an optimal cut-off of >1.5%, the test's sensitivity was 64.94%, the specificity was 72.73%, the positive predictive value was 70.42%, and the negative predictive value was 67.47%. LOS led to a dramatic rise followed by a decrease after the initiation of the antimicrobial therapy [1.8 (1.4-2.5)] vs. [1.45 (0.2-4)] p<0.001.

Conclusion

COHb levels increased at the beginning of LOS, decreasing in response to antibiotics. When used in conjunction with other sepsis biomarkers, the variation of COHb can be important in evaluating late-onset sepsis episodes in preterm infants.

Serial Carboxyhemoglobin Levels and Its Relationship with Late Onset Sepsis in Preterm Infants: An Observational Cohort Study

Objective: This study aimed at assessing the serial carboxyhemoglobin (COHb) levels in preterm infants during the first week of life and their variation with late-onset sepsis (LOS). Study Design: Infants with <37 gestational weeks were categorized into two groups according to the presence of culture proven LOS. Serial COHb levels were obtained during the first week of life, at the onset of the LOS episode, and upon blood culture negativity with response to antibiotics. Result: Overall 207 infants were enrolled. A LOS episode resulted in a significant increase in COHb levels (p < 0.001), which decreased to normal levels when the blood cultures were sterile (p < 0.001). At a cut of level of 1.35% COHb had a sensitivity of 56% and a specificity of 90% to confirm LOS (p < 0.001). Conclusion: In this study, we demonstrated an increase in COHb levels at the onset of LOS and a decrease with response to antibiotherapy.

Pathological Impact of the Interaction of NO and CO with Mitochondria in Critical Care Diseases

The outcome of patients with critical care diseases (CCD) such as sepsis, hemorrhagic shock, or trauma is often associated with mitochondrial dysfunction. In turn, mitochondrial dysfunction is frequently induced upon interaction with nitric oxide (NO) and carbon monoxide (CO), two gaseous messengers formed in the body by NO synthase (NOS) and heme oxygenase (HO), respectively. Both, NOS and HO are upregulated in the majority of CCD. A multitude of factors that are associated with the pathology of CCD exert a potential to interfere with mitochondrial function or the effects of the gaseous messengers. From these, four major factors can be identified that directly influence the effects of NO and CO on mitochondria and which are defined by (i) local concentration of NO and/or CO, (ii) tissue oxygenation, (iii) redox status of cells in terms of facilitating or inhibiting reactive oxygen species formation, and (iv) the degree of tissue acidosis. The combination of these four factors in specific pathological situations defines whether effects of NO and CO are beneficial or deleterious.

Determinants of Carboxyhemoglobin Levels and Relationship with Sepsis in a Retrospective Cohort of Preterm Neonates

Carboxyhemoglobin levels in blood reflect endogenous carbon monoxide production and are often measured during routine blood gas analysis. Endogenous carbon monoxide production has been reported to be increased during sepsis, but carboxyhemoglobin levels have not been thoroughly evaluated as a biomarker of sepsis. We sought to determine whether carboxyhemoglobin levels were elevated during sepsis in a high risk population of premature neonates. We conducted a retrospective cohort study of 30 infants in two neonatal intensive care units using electronic medical and laboratory records. The majority of infants were extremely premature and extremely low birth weight, and 25 had at least one episode of sepsis. We collected all carboxyhemoglobin measurements during their in-patient stay and examined the relationship between carboxyhemoglobin and a variety of clinical and laboratory parameters, in addition to the presence or absence of sepsis, using linear mixed-effect models. We found that postnatal age had the most significant effect on carboxyhemoglobin levels, and other significant associations were identified with gestational age, hemoglobin concentration, oxyhemoglobin saturation, and blood pH. Accounting for these covariates, there was no significant relationship between the onset of sepsis and carboxyhemoglobin levels. Our results show that carboxyhemoglobin is unlikely to be a clinically useful biomarker of sepsis in premature infants, and raise a note of caution about factors which may confound the use of carbon monoxide as a clinical biomarker for other disease processes such as hemolysis.

Unmyelinated white matter loss in the preterm brain is associated with early increased levels of end-tidal carbon monoxide

Objective

Increased levels of end-tidal carbon monoxide (ETCOc) in preterm infants during the first day of life are associated with oxidative stress, inflammatory processes and adverse neurodevelopmental outcome at 2 years of age. Therefore, we hypothesized that early ETCOc levels may also be associated with impaired growth of unmyelinated cerebral white matter.

Methods

From a cohort of 156 extremely and very preterm infants in which ETCOc was determined within 24 h after birth, in 36 infants 3D-MRI was performed at term-equivalent age to assess cerebral tissue volumes of important brain regions.

Results

Linear regression analysis between cerebral ventricular volume, unmyelinated white matter/total brain volume-, and cortical grey matter/total brain volume-ratio and ETCOc showed a positive, negative and positive correlation, respectively. Multivariable analyses showed that solely ETCOc was positively related to cerebral ventricular volume and cortical grey matter/total brain volume ratio, and that solely ETCOc was inversely related to the unmyelinated white matter/total brain volume ratio, suggesting that increased levels of ETCOc, associated with oxidative stress and inflammation, were related with impaired growth of unmyelinated white matter.

Conclusion

Increased values of ETCOc, measured within the first 24 hours of life may be indicative of oxidative stress and inflammation in the immediate perinatal period, resulting in impaired growth of the vulnerable unmyelinated white matter of the preterm brain.

Carbon monoxide is a poison... to microbes! CO as a bactericidal molecule

Inflammation and immunity result in a wide range of disease processes, including chronic obstructive pulmonary disease, ischemia-reperfusion injury, atherosclerosis, vascular thrombosis and sepsis. Heme oxygenase-1 (HO-1) is a key enzyme that is indispensable for the temporal and spatial regulation of host response and, together with its essential metabolite carbon monoxide (CO), is crucial for maintaining homeostasis, inhibition of inflammation and the preservation of function and life. The biology of HO-1 is being discussed in this review series by Soares and colleagues and thus will not be reviewed here. Rather we will complement the HO-1 overview with a comprehensive discussion of CO as perhaps the one product of HO-1 that has been most studied. Of the numerous physiologic effects observed with CO, in the past five years it has become apparent that CO has been ascribed an additional novel role as a 'bactericidal agent'. Its role in the maintenance of homeostasis remains intact; however, the designation necessitates the paradoxical induction of the inflammatory response and binding to hemoproteins in order to restore homeostasis and sustain life. In this article, we review and discuss reports that have propelled and challenged the paradoxical use of CO, once viewed as a toxic molecule, now as a host defense molecule agent against microbes.

Carbon monoxide is a significant mediator of cardiovascular status following preterm birth

OBJECTIVE

With male gender as a strong predictor of cardiovascular instability, we hypothesized that gender-specific differences in circulating carbon monoxide levels contributed to dysregulated microvascular function in preterm male infants.

METHODS

Infants born at 24 to 34 weeks of gestation (N = 84) were studied in a regional tertiary neonatal unit. Carboxyhemoglobin levels were measured through spectrophotometry in umbilical arterial blood and at 24, 72, and 120 hours after birth. Microvascular blood flow was determined through laser Doppler flowmetry.

RESULTS

Carboxyhemoglobin levels demonstrated a strong inverse relationship with gestational age (r = -0.636; P < .001) and were higher in boys (P = .032). Repeated-measures analysis of variance showed a significant decrease in arterial carboxyhemoglobin levels over time (P < .001), with significant between-subjects effects for gestational age (P = .011) and gender (P = .025). Positive correlations with microvascular blood flow at 24 hours of age (r = 0.495; P < .001) and 120 hours of age (r = 0.548; P < .001) were observed. With controlling for gestational age, carboxyhemoglobin levels at 72 hours were greater for infants who died in the first week of life (P = .035).

CONCLUSIONS

The gestational age- and gender-specific differences in carboxyhemoglobin levels and the relationship with dysregulated microvascular blood flow, a state related to greater illness severity and hypotension, are novel findings not confined solely to sick preterm infants. Both inducible heme oxygenase-dependent and non-heme oxygenase-dependent pathways may initially play a central role in carbon monoxide production, inducing pathophysiologic processes in a gender-specific manner.

Arterial carboxyhemoglobin level and outcome in critically ill patients

OBJECTIVE

Arterial carboxyhemoglobin is elevated in patients with critical illness. It is an indicator of the endogenous production of carbon monoxide by the enzyme heme oxygenase, which modulates the response to oxidant stress. The objective was to explore the hypothesis that arterial carboxyhemoglobin level is associated with inflammation and survival in patients requiring cardiothoracic intensive care.

DESIGN

Prospective, observational study.

SETTING

A cardiothoracic intensive care unit.

PATIENTS

All patients admitted over a 15-month period.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Arterial carboxyhemoglobin, bilirubin, and standard biochemical, hematologic, and physiologic markers of inflammation were measured in 1,267 patients. Associations were sought between levels of arterial carboxyhemoglobin, markers of the inflammatory response, and clinical outcome. Intensive care unit mortality was associated with lower minimum and greater maximal carboxyhemoglobin levels (p < .0001 and p < .001, respectively). After adjustment for age, gender, illness severity, and other relevant variables, a lower minimum arterial carboxyhemoglobin was associated with an increased risk of death from all causes (odds risk of death, 0.391; 95% confidence interval, 0.190-0.807; p = .011). Arterial carboxyhemoglobin correlated with markers of the inflammatory response.

CONCLUSIONS

Both low minimum and high maximum levels of arterial carboxyhemoglobin were associated with increased intensive care mortality. Although the heme oxygenase system is protective, excessive induction may be deleterious. This suggests that there may be an optimal range for heme oxygenase-1 induction.

Carbon monoxide in sepsis

Despite modern practices in critical care medicine, sepsis or systemic inflammatory response syndrome remains a leading cause of morbidity and mortality in the intensive care unit. Thus, the need to identify new therapeutic tools for the treatment of sepsis is urgent. In this context, carbon monoxide has become a promising therapeutic molecule that can potentially prevent uncontrolled inflammation in sepsis. In humans, carbon monoxide arises endogenously from the degradation of heme by heme oxygenase enzymes. Both endogenously synthesized and exogenously applied carbon monoxide can exert antiinflammatory and antiapoptotic effects in cells and tissues. Based on these properties, carbon monoxide, when applied at low concentration, conferred protection in a variety of cellular and rodent models of sepsis, and furthermore reduced morbidity and mortality in vivo. Therefore, application of carbon monoxide may have a major impact on the future of sepsis treatment. This review summarizes evidence for salutary effects of carbon monoxide in sepsis of various organs, including lung, heart, kidney, liver, and intestine, and discusses the potential translation of the data into human clinical trials.

[Carbon monoxide--poison or potential therapeutic?]

Carbon monoxide (CO) is much more than just a toxic gas. Carbon monoxide is produced endogenously by the enzyme heme oxygenase and has important functions under physiological and pathophysiological conditions. Recent studies suggested antioxidative, anti-inflammatory, antiproliferative, anti-apoptotic, and vasodilating characteristics. Regarding clinically-relevant diseases in anesthesiology and critical care medicine, such as adult respiratory distress syndrome (ARDS), sepsis, or during organ transplantation, cytoprotective properties have been demonstrated by low-dose CO in experimental models. In view of a potential CO application in future human studies, this review discusses what is known to date about CO as it relates to functional, protective and toxic aspects.

Hemophagocytic macrophages constitute a major compartment of heme oxygenase expression in sepsis

Schaer DJ, Schaer CA, Schoedon G, Imhof A, Kurrer MO.

Hemophagocytic macrophages constitute a major compartment of heme oxygenase expression in sepsis.

Objectives: Uncontrolled macrophage activation with hemophagocytosis is a distinctive feature of hemophagocytic syndromes (HPS). We examined whether lympho-histiocytic infiltration of the bone marrow and liver, as well as hemo-/erythrophagocytosis also occurs during sepsis and whether this process could account for the increased production of anti-inflammatory heme-oxygenase (HO-1) products observed during sepsis. Methods: Hemophagocytosis and expression of CD163, HO-1, ferritin as well as CD8 and granzyme-B were examined in post-mortem bone marrow samples from 28 patients with sepsis and from eight control patients. Results: Comparison of samples from non-septic patients with samples from patients with fatal sepsis revealed that the latter group displayed dense lympho-histiocytic bone marrow infiltration with CD163⁺/HO-1⁺/ferritin⁺ macrophages as well as with CD8⁺ and granzyme-B⁺ T-cells. Hemophagocytosis with prominent phagocytosis of erythroid cells was readily apparent in septic patients, implying that this process is a likely stimulus for the up-regulation of macrophage HO-1 expression. Conclusions: Lympho-histiocytic activation with hemophagocytosis is a shared pathophysiologic mechanism in HPS and sepsis. Furthermore, the association of hemophagocytosis with an increase in HO-1 expression may indicate a novel role for this apparently futile process as a negative regulator of inflammation.

Glucose intolerance modifies the inflammatory response after intestinal ischemia-reperfusion

Streptozotocin administration in newborn rats (nSTZ-rats) leads to adults with mild insulin deficiency and normoglycemia, and is accepted as a model of type 2 diabetes. We examined possible differences in the production of inflammatory mediators between healthy and nSTZ-rats after ischemia-reperfusion (I-R). Two-month-old control and nSTZ-rats were randomly separated into control and intestinal I-R groups. After reperfusion, samples were obtained from the portal vein (PV) infrahepatic cava vein (ICV), suprahepatic cava vein (SCV), jejunal wall, and pancreas. Nitric oxide (NO), lipid hydroperoxides (LPO), tumor necrosis factor alpha (TNF-alpha), 60 kDa receptor (sTNF-R1), 80 kDa (sTNF-R2), and intercellular adhesion molecule-1 (ICAM-1), were determined. After I-R, nSTZ-rats showed increased plasma concentrations of LPO, NO, ICAM-1 (0.5141 +/- 0.083 vs 0.024 +/- 0.003, ICV; 0.574 +/- 0.075 vs 0.023 +/- 0.003, SCV; 0.528 +/- 0.067 vs 0.027 +/- 0.003 PV; ng/ml), TNF-alpha (42.4 +/- 5.7 ICV, 248.4 +/- 28.2 SCV, and 33.6 +/- 4.0 PV. In n STZ-rats, vs 4.36 +/- 0.57, 4.74 +/- 0.77, and 3.16 +/- 0.32, respectively, in control rats; pg/ml), and sTNF-R1. Both TNF-alpha and NO plasma levels were higher in SCV than in ICV and PV after I-R. In addition, after I-R, jejunal wall of nSTZ-rats showed an increase of TNF-alpha IL-1, and IL-10 levels. A pre-existing state of glucose intolerance intensifies the inflammatory response after intestinal I-R.

Exhaled breath measures of inflammation: are they useful in neonatal chronic lung disease?

Neonatal chronic lung disease is a common problem for surviving infants of extreme prematurity. Although the precise pathophysiology is still not known, it is clear that inflammation provides a common link that amplifies the injury to the premature lung. Current invasive measures of pulmonary inflammation include markers in blood and airway effluent, with the cellular composition of tracheal fluid being the "gold standard". In this article available exhaled breath measures, particularly nitric oxide, carbon monoxide, volatile hydrocarbons, and exhaled breath condensate, are reviewed with particular reference to sample collection, analysis, and common pitfalls as they apply to the ventilated premature newborn at risk of chronic lung disease. Although they have great potential, all measures require thorough validation before being used clinically.