An increase in exhaled CO concentration in systemic inflammation/sepsis

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.

An adaptive Kalman filtering algorithm based on back-propagation (BP) neural network applied for simultaneously detection of exhaled CO and N2O

A compact high-resolution spectroscopic sensor using a thermoelectrically (TE) cooled continuous-wave (CW) room temperature (RT) quantum cascade laser (QCL) was demonstrated for simultaneous measurements of exhaled carbon monoxide (CO) and nitrous oxide (N₂O). The sampling pressure was optimized to improve the sensitivity, the optimal pressure was determined to be 150 mbar based on an optical density analysis of simulated and measured absorption spectra. An adaptive Kalman filtering algorithm based on back-propagation (BP) neural network was developed and proposed for real-time exhaled breath analysis in order to perform fast and high precision on-line measurements. The detection limits (1σ) of 1.14 ppb and 1.12 ppb were experimentally achieved for CO and N₂O detection, respectively. Typical concentrations of exhaled CO and N₂O from smokers and non-smokers were analyzed. The experimental results indicated that the state-of-the-art CW-QCL based sensor has a great potential for non-invasive, on-line identification and quantification of biomarkers in human breath.

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.

Exhaled nitric oxide and carbon monoxide in mechanically ventilated brain-injured patients

The inflammatory influence and biological markers of prolonged mechanical-ventilation in uninjured human lungs remains controversial. We investigated exhaled nitric oxide (NO) and carbon monoxide (CO) in mechanically-ventilated, brain-injured patients in the absence of lung injury or sepsis at two different levels of positive end-expiratory pressure (PEEP). Exhaled NO and CO were assessed in 27 patients, without lung injury or sepsis, who were ventilated with 8 ml kg(-1) tidal volumes under zero end-expiratory pressure (ZEEP group, n  =  12) or 8 cm H2O PEEP (PEEP group, n  =  15). Exhaled NO and CO was analysed on days 1, 3 and 5 of mechanical ventilation and correlated with previously reported markers of inflammation and gas exchange. Exhaled NO was higher on day 3 and 5 in both patient groups compared to day 1: (PEEP group: 5.8 (4.4-9.7) versus 11.7 (6.9-13.9) versus 10.7 (5.6-16.6) ppb (p  <  0.05); ZEEP group: 5.3 (3.8-8.8) versus 9.8 (5.3-12.4) versus 9.6 (6.2-13.5) ppb NO peak levels for days 1, 3 and 5, respectively, p  <  0.05). Exhaled CO remained stable on day 3 but significantly decreased by day 5 in the ZEEP group only (6.3 (4.3-9.0) versus 8.1 (5.8-12.1) ppm CO peak levels for day 5 versus 1, p  <  0.05). The change scores for peak exhaled CO over day 1 and 5 showed significant correlations with arterial blood pH and plasma TNF levels (r s  =  0.49, p  =  0.02 and r s  =  -0.51 p  =  0.02, respectively). Exhaled NO correlated with blood pH in the ZEEP group and with plasma levels of IL-6 in the PEEP group. We observed differential changes in exhaled NO and CO in mechanically-ventilated patients even in the absence of manifest lung injury or sepsis. These may suggest subtle pulmonary inflammation and support application of real time breath analysis for molecular monitoring in critically ill patients.

ANALYSIS OF AGREEMENT BETWEEN EXPIRED-AIR CARBON MONOXIDE MONITORS

Introduction

The current study examined the level of agreement in expired-air carbon monoxide (CO) values, focusing especially on those confirming abstinence, between the two most commonly used CO monitors, the Vitalograph BreathCO and the Bedfont piCO+ Smokerlyzer.

Methods

Expired-air samples were collected via both monitors from adult dependent smokers (44 M, 34 F) participating in studies using CO values to confirm abstinence durations of: 24 hours, 12 hours, or no abstinence. All met DSM-IV nicotine dependence criteria and had a mean (SD) Fagerström Test of Cigarette Dependence score of 5.1 (1.8). Paired data collected across multiple visits were analyzed by regression-based Bland-Altman method of Limits of Agreement.

Findings

Analysis indicated a lack of agreement in CO measurement between monitors. Overall, the Bedfont monitor gave mean (±SEM) readings 3.83 (±.23) ppm higher than the Vitalograph monitor. Mean differences between monitors were larger for those ad lib smoking (5.65±.38 ppm) than those abstaining 12-24 hours (1.71±.13 ppm). Yet, there also was not consistent agreement in classification of 24 hour abstinence between monitors.

Conclusions

Systematic differences in CO readings demonstrate these two very common monitors may not result in interchangeable values, and reported outcomes in smoking research based on CO values may depend on the monitor used.

Normal values of exhaled carbon monoxide in healthy subjects: comparison between two methods of assessment

Background

In a previous study, exhaled carbon monoxide (eCO) has been assessed in healthy non-smokers with a photo acoustic spectrometer Brüel&Kjær 1312. Unexpectedly, values were higher than those reported in literature, which were mostly obtained with electrochemical analysers. This study was aimed to compare eCO values obtained with Brüel&Kjær 1312 and PiCO + Smokerlyzer, a largely utilized electrochemical analyser.

Methods

Thirty-four healthy subjects, 15 non-smokers and 19 smokers, underwent eCO assessment with Brüel&Kjær 1312 and PiCO + Smokerlyzer during a prolonged expiration (15 seconds). Brüel&Kjær 1312 assessed CO concentration 7 and 12 seconds after the beginning of expiration and displayed the mean value. PiCO + Smokerlyzer was utilized according to the manufacturer’s recommendations. In vitro, the two devices were tested with standard concentrations of CO in nitrogen (5, 9.9, 20, and 50 ppm), and the time needed by PiCO + Smokerlyzer readings to stabilize was assessed at different gas flows.

Results

Both Brüel&Kjær 1312 and PiCO + Smokerlyzer presented very good internal consistency. The values provided were strictly correlated, but at low test concentrations, the Brüel&Kjær 1312 readings were greater than the PiCO + Smokerlyzer, and vice versa. PiCO + Smokerlyzer overestimated the CO standard concentrations at 5 and 9.9 ppm by 20%, while Brüel&Kjær 1312 measures were correct. PiCO + Smokerlyzer readings stabilized in 12 seconds during in vitro tests and in 15 seconds during in vivo measurements, suggesting that the values displayed corresponded to the initial phase of expiration.

Conclusions

Differences between Brüel&Kjær 1312 and PiCO + Smokerlyzer may be explained because Brüel&Kjær 1312 measured CO levels in the middle and at the end of expiration while PiCO + Smokerlyzer assessed them in the initial part of expiration.

Carbon monoxide in exhaled breath testing and therapeutics

Carbon monoxide (CO), a low molecular weight gas, is a ubiquitous environmental product of organic combustion, which is also produced endogenously in the body, as the byproduct of heme metabolism. CO binds to hemoglobin, resulting in decreased oxygen delivery to bodily tissues at toxicological concentrations. At physiological concentrations, CO may have endogenous roles as a potential signaling mediator in vascular function and cellular homeostasis. Exhaled CO (eCO), similar to exhaled nitric oxide (eNO), has been evaluated as a candidate breath biomarker of pathophysiological states, including smoking status, and inflammatory diseases of the lung and other organs. eCO values have been evaluated as potential indicators of inflammation in asthma, stable COPD and exacerbations, cystic fibrosis, lung cancer, or during surgery or critical care. The utility of eCO as a marker of inflammation and its potential diagnostic value remain incompletely characterized. Among other candidate 'medicinal gases' with therapeutic potential, (e.g., NO and H2S), CO has been shown to act as an effective anti-inflammatory agent in preclinical animal models of inflammatory disease, acute lung injury, sepsis, ischemia/reperfusion injury and organ graft rejection. Current and future clinical trials will evaluate the clinical applicability of this gas as a biomarker and/or therapeutic in human disease.