Carboxyhemoglobin levels in medical intensive care patients: a retrospective, observational study

Association of blood carboxyhemoglobin levels with mortality and neurological outcomes in out-of-hospital cardiac arrest

Background

Carbon monoxide (CO), produced endogenously by heme oxygenase-1, plays a crucial role in the immune system by mitigating cellular damage under stress. However, the significance of carboxyhemoglobin (COHb) levels after out-of-hospital cardiac arrest (OHCA) is not well understood. This study aimed to explore the association between COHb levels at hospital arrival and within the first 24 h post-arrival with 30-day mortality and neurological outcomes in patients who experienced OHCA.

Methods

This single-center, retrospective study analyzed data from adult patients who experienced OHCA seen at Okayama University Hospital from 2019 to 2023. The patients were assigned to one of two study groups based on COHb levels (0.0% or ≥0.1%) upon hospital arrival. The primary outcome was 30-day mortality.

Results

Among the 560 eligible patients who experienced OHCA, 284 (50.7%) were in the COHb 0.0% group and 276 (49.3%) were in the COHb ≥ 0.1% group. The 30-day mortality was significantly higher in the COHb 0.0% group compared to the COHb ≥ 0.1% group (264 [92.9%] vs. 233 [84.4%]). Multivariable logistic regression showed that the COHb 0.0% group was associated with 30-day mortality (adjusted ORs: 2.24, 95% CIs: 1.10-4.56). Non-survivors at 30 days who were admitted to the intensive care unit had lower COHb levels at hospital arrival (0.0% vs. 0.2%) and lower mean COHb levels during the first 24 h post-arrival (0.7% vs. 0.9%) compared to survivors.

Conclusions

COHb levels of 0.0% were linked to worse outcomes in patients experiencing OHCA, warranting further research on the prognostic implications of COHb in this context.

Carboxyhemoglobin predicts oxygenator performance and imminent oxygenator change in extracorporeal membrane oxygenation

BACKGROUND

The continuous exposure of blood to a non-biological surface during extracorporeal membrane oxygenation (ECMO) may lead to progressive thrombus formation in the oxygenator, hemolysis and consequently impaired gas exchange. In most centers oxygenator performance is monitored only on a once daily basis. Carboxyhemoglobin (COHb) is generated upon red cell lysis and is routinely measured with any co-oximetry performed to surveille gas exchange and acid-base homeostasis every couple of hours. This retrospective cohort study aims to evaluate COHb in the arterial blood gas as a novel marker of oxygenator dysfunction and its predictive value for imminent oxygenator change.

RESULTS

Out of the 484 screened patients on ECMO 89, cumulatively requiring 116 oxygenator changes within 1833 patient days, including 19,692 arterial COHb measurements were analyzed. Higher COHb levels were associated with lower post-oxygenator pO2 (estimate for log(COHb): - 2.176 [95% CI - 2.927, - 1.427], p < 0.0001) and with a shorter time to oxygenator change (estimate for log(COHb): - 67.895 [95% CI - 74.209, - 61.542] hours, p < 0.0001). COHb was predictive of oxygenator change within 6 h (estimate for log(COHb): 5.027 [95% CI 1.670, 15.126], p = 0.004).

CONCLUSION

COHb correlates with oxygenator performance and can be predictive of imminent oxygenator change. Therefore, longitudinal measurements of COHb in clinical routine might be a cheap and more granular candidate for ECMO surveillance that should be further analyzed in a controlled prospective trial design.

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%.

U-Shaped Association Between Carboxyhemoglobin and Mortality in Patients With Acute Respiratory Distress Syndrome on Venovenous Extracorporeal Membrane Oxygenation

Background

Carbon monoxide (CO) is an endogenous signaling molecule that activates cytoprotective programs implicated in the resolution of acute respiratory distress syndrome (ARDS) and survival of critical illness. Because CO levels can be measured in blood as carboxyhemoglobin, we hypothesized that carboxyhemoglobin percent (COHb%) may associate with mortality.

OBJECTIVES

To examine the relationship between COHb% and outcomes in patients with ARDS requiring venovenous extracorporeal membrane oxygenation (ECMO), a condition where elevated COHb% is commonly observed.

DESIGN

Retrospective cohort study.

SETTING

Academic medical center ICU.

PATIENTS

Patients were included that had ARDS on venovenous ECMO.

MEASUREMENTS AND MAIN RESULTS

We examined the association between COHb% and mortality using a Cox proportional hazards model. Secondary outcomes including ECMO duration, ventilator weaning, and hospital and ICU length of stay were examined using both subdistribution and causal-specific hazard models for competing risks. We identified 109 consecutive patients for analysis. Mortality significantly decreased per 1 U increase in COHb% below 3.25% (hazard ratio [HR], 0.35; 95% CI, 0.15-0.80; p = 0.013) and increased per 1 U increase above 3.25% (HR, 4.7; 95% CI, 1.5-14.7; p = 0.007) reflecting a nonlinear association (p = 0.006). Each unit increase in COHb% was associated with reduced likelihood of liberation from ECMO and mechanical ventilation, and increased time to hospital and ICU discharge (all p < 0.05). COHb% was significantly associated with hemolysis but not with initiation of hemodialysis or blood transfusions.

CONCLUSIONS

In patients with ARDS on venovenous ECMO, COHb% is a novel biomarker for mortality exhibiting a U-shaped pattern. Our findings suggest that too little CO (perhaps due to impaired host signaling) or excess CO (perhaps due to hemolysis) is associated with higher mortality. Patients with low COHb% may exhibit the most benefit from future therapies targeting anti-oxidant and anti-inflammatory pathways such as low-dose inhaled CO gas.

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.

Predictive markers related to local and systemic inflammation in severe COVID-19-associated ARDS: a prospective single-center analysis

BACKGROUND

As the COVID-19 pandemic strains healthcare systems worldwide, finding predictive markers of severe courses remains urgent. Most research so far was limited to selective questions hindering general assumptions for short- and long-term outcome.

METHODS

In this prospective single-center biomarker study, 47 blood- and 21 bronchoalveolar lavage (BAL) samples were collected from 47 COVID-19 intensive care unit (ICU) patients upon admission. Expression of inflammatory markers toll-like receptor 3 (TLR3), heme oxygenase-1 (HO-1), interleukin (IL)-6, IL-8, leukocyte counts, procalcitonin (PCT) and carboxyhemoglobin (CO-Hb) was compared to clinical course. Clinical assessment comprised acute local organ damage, acute systemic damage, mortality and outcome after 6 months.

RESULTS

PCT correlated with acute systemic damage and was the best predictor for quality of life (QoL) after 6 months (r = - 0.4647, p = 0.0338). Systemic TLR3 negatively correlated with impaired lung function (ECMO/ECLS: r = - 0.3810, p = 0.0107) and neurological short- (RASS mean: r = 0.4474, p = 0.0023) and long-term outcome (mRS after 6 m: r = - 0.3184, p = 0.0352). Systemic IL-8 correlated with impaired lung function (ECMO/ECLS: r = 0.3784, p = 0.0161) and neurological involvement (RASS mean: r = - 0.5132, p = 0.0007). IL-6 in BAL correlated better to the clinical course than systemic IL-6. Using three multivariate regression models, we describe prediction models for local and systemic damage as well as QoL. CO-Hb mean and max were associated with higher mortality.

CONCLUSIONS

Our predictive models using the combination of Charlson Comorbidity Index, sex, procalcitonin, systemic TLR3 expression and IL-6 and IL-8 in BAL were able to describe a broad range of clinically relevant outcomes in patients with severe COVID-19-associated ARDS. Using these models might proof useful in risk stratification and predicting disease course in the future. Trial registration The trial was registered with the German Clinical Trials Register (Trial-ID DRKS00021522, registered 22/04/2020).

Carboxyhemoglobin as a diagnostic and prognostic biomarker of hemolytic anemias in dogs

BACKGROUND

Endogenous production of carbon monoxide during hemoglobin metabolism leads to the formation of carboxyhemoglobin. Carboxyhemoglobin concentration is abnormally high in humans with hemolytic anemia (HA).

HYPOTHESIS

Measurement of carboxyhemoglobin concentration can discriminate HA from other forms of anemia.

ANIMALS

Twenty-seven dogs with HA (immune-mediated HA, n = 22; microangiopathic HA, n = 5), 27 dogs with non-HA (kidney disease, n = 14; immune-mediated thrombocytopenia, [n = 6]; miscellaneous, n = 7) and 24 nonanemic control dogs.

METHODS

Prospective cohort study. Carboxyhemoglobin quantification, a CBC and biochemistry profile were performed upon admission, and survival to hospital discharge and at 30 days were the measured outcomes. Groups were compared by the Mann-Whitney and Kruskal-Wallis tests. Receiver-operator characteristic (ROC) analyses were used to examine the predictive utility of carboxyhemoglobin for the diagnosis of HA in anemic dogs.

RESULTS

Carboxyhemoglobin (median [interquartile range]) differed between dogs with HA (7.7% [2.5%]) and non-HA (3.6% [1.05]; P < .001) and dogs with HA and nonanemic dogs (3.5% [0.65%]; P < .001). No difference was detected between nonHA and nonanemic dogs. The area under the ROC curve for carboxyhemoglobin as predictor of HA in anemic dogs was 0.997 (95% CI, 0.99-1.00). Three optimal cut-off points were identified, including 5.05%, 4.55% and 4.85%, with corresponding sensitivity/specificity of 92.6%/100%, 100%/92.6% and 96.3%/96.3%, respectively. Neither carboxyhemoglobin nor any of the CBC or chemistry analytes were associated with survival.

CONCLUSIONS AND CLINICAL IMPORTANCE

Carboxyhemoglobin proved an excellent predictor of HA in dogs and might constitute a useful, ancillary tool for diagnosing and monitoring hemolytic anemias.

Carboxyhemoglobin (CO-Hb) Correlates with Hemolysis and Hospital Mortality in Extracorporeal Membrane Oxygenation: A Retrospective Registry

Background: Patients supported with extracorporeal membrane oxygenation (ECMO) may develop elevated carboxyhemoglobin (CO-Hb), a finding described in the context of hemolysis. Clinical relevance of elevated CO-Hb in ECMO is unclear. We therefore investigated the prognostic relevance of CO-Hb during ECMO support. Methods: Data derives from a retrospective single-center registry study. All ECMO patients in a medical ICU from October 2010 through December 2019 were considered. Peak arterial CO-Hb value during ECMO support and median CO-Hb values determined by point-of-care testing for distinct time intervals were determined. Groups were divided by CO-Hb (<2% or ≥2%). The primary endpoint was hospital survival. Results: A total of 729 patients with 59,694 CO-Hb values met the inclusion criteria. Median age (IQR) was 59 (48−68) years, 221/729 (30.3%) were female, and 278/729 (38.1%) survived until hospital discharge. Initial ECMO configuration was veno-arterial in 431/729 (59.1%) patients and veno-venous in 298/729 (40.9%) patients. Markers for hemolysis (lactate dehydrogenase, bilirubin, hemolysis index, and haptoglobin) all correlated significantly with higher CO-Hb (p < 0.001, respectively). Hospital survival was significantly higher in patients with CO-Hb < 2% compared to CO-Hb ≥ 2%, evaluating time periods 24−48 h (48.6% vs. 35.2%, p = 0.003), 48−72 h (51.5% vs. 36.8%, p = 0.003), or >72 h (56.9% vs. 31.1%, p < 0.001) after ECMO cannulation. Peak CO-Hb was independently associated with lower hospital survival after adjustment for confounders. Conclusions: In ECMO, CO-Hb correlates with hemolysis and hospital survival. If high CO-Hb measured should trigger a therapeutic intervention in order to reduce hemolysis has to be investigated in prospective trials.

Carbon Monoxide Signaling: Examining Its Engagement with Various Molecular Targets in the Context of Binding Affinity, Concentration, and Biologic Response

Carbon monoxide (CO) has been firmly established as an endogenous signaling molecule with a variety of pathophysiological and pharmacological functions, including immunomodulation, organ protection, and circadian clock regulation, among many others. In terms of its molecular mechanism(s) of action, CO is known to bind to a large number of hemoproteins with at least 25 identified targets, including hemoglobin, myoglobin, neuroglobin, cytochrome c oxidase, cytochrome P450, soluble guanylyl cyclase, myeloperoxidase, and some ion channels with dissociation constant values spanning the range of sub-nM to high μM. Although CO's binding affinity with a large number of targets has been extensively studied and firmly established, there is a pressing need to incorporate such binding information into the analysis of CO's biologic response in the context of affinity and dosage. Especially important is to understand the reservoir role of hemoglobin in CO storage, transport, distribution, and transfer. We critically review the literature and inject a sense of quantitative assessment into our analyses of the various relationships among binding affinity, CO concentration, target occupancy level, and anticipated pharmacological actions. We hope that this review presents a picture of the overall landscape of CO's engagement with various targets, stimulates additional research, and helps to move the CO field in the direction of examining individual targets in the context of all of the targets and the concentration of available CO. We believe that such work will help the further understanding of the relationship of CO concentration and its pathophysiological functions and the eventual development of CO-based therapeutics. SIGNIFICANCE STATEMENT: The further development of carbon monoxide (CO) as a therapeutic agent will significantly rely on the understanding of CO's engagement with therapeutically relevant targets of varying affinity. This review critically examines the literature by quantitatively analyzing the intricate relationships among targets, target affinity for CO, CO level, and the affinity state of carboxyhemoglobin and provide a holistic approach to examining the molecular mechanism(s) of action for CO.

Carboxyhemoglobin Does Not Predict the Need of Mechanical Ventilation and Prognosis during COPD Exacerbation

Background

Carboxyhemoglobin (COHb) is a complex formed by the binding of carbon monoxide to hemoglobin in blood. Higher COHb levels have been associated with poor prognosis in a variety of pulmonary disorders. However, little is known regarding the prognostic significance of COHb among individuals with chronic obstructive pulmonary disease (COPD) exacerbation.

Methods

In a retrospective study, we evaluated associations of venous COHb levels on hospital admission with the need for invasive mechanical ventilation, in-hospital mortality, and rehospitalization, among 300 patients hospitalized for COPD exacerbation in internal medical wards.

Results

Rates of in-hospital death and 1-year recurrent hospitalizations were 11.0% and 59.6%, respectively. COHb levels were not significantly associated with in-hospital mortality (OR = 0.82, P=0.25, 95% CI 0.59–1.15) or with 1-year rehospitalizations (OR = 0.91, P=0.18, 95% CI 0.79–1.04). The mean COHb level did not differ significantly between patients who needed invasive mechanical ventilation and those who were not invasively mechanically ventilated during the current hospitalization (2.01 ± 1.42% vs. 2.19 ± 1.68%, P=0.49).

Conclusions

Among patients hospitalized with COPD exacerbation in internal medicine wards, COHb levels on admission were not associated with invasive mechanical ventilation treatment, rehospitalizations, or mortality.

Association of COVID-19 with Intracranial Hemorrhage during Extracorporeal Membrane Oxygenation for Acute Respiratory Distress Syndrome: A 10-Year Retrospective Observational Study

Extracorporeal membrane oxygenation (ECMO) is potentially lifesaving for patients with acute respiratory distress syndrome (ARDS) but may be accompanied by serious adverse events, including intracranial hemorrhage (ICRH). We hypothesized that ICRH occurs more frequently in patients with COVID-19 than in patients with ARDS of other etiologies. We performed a single-center retrospective analysis of adult patients treated with venovenous (vv-) ECMO for ARDS between January 2011 and April 2021. Patients were included if they had received a cranial computed tomography (cCT) scan during vv-ECMO support or within 72 h after ECMO removal. Cox regression analysis was used to identify factors associated with ICRH. During the study period, we identified 204 patients with vv-ECMO for ARDS, for whom a cCT scan was available. We observed ICRH in 35.4% (n = 17/48) of patients with COVID-19 and in 16.7% (n = 26/156) of patients with ARDS attributable to factors other than COVID-19. COVID-19 (HR: 2.945; 95%; CI: 1.079–8.038; p = 0.035) and carboxyhemoglobin (HR: 0.330; 95%; CI: 0.135–0.806; p = 0.015) were associated with ICRH during vv-ECMO. In patients receiving vv-ECMO, the incidence of ICRH is doubled in patients with COVID-19 compared to patients suffering from ARDS attributable to other causes. More studies on the association between COVID-19 and ICRH during vv-ECMO are urgently needed to identify risk patterns and targets for potential therapeutic interventions.

Repeated unconsciousness due to chronic carbon monoxide poisoning in an older patient: a case report

Objective: Although much is known about acute carbon monoxide (CO) poisoning, little is known about chronic CO poisoning. Chronic CO poisoning is often diagnosed based on the patient's living environment and medical history. Herein, we report the case of an older patient who presented with repeated unconsciousness due to chronic CO poisoning. Case presentation: A 90-year-old man was brought to the emergency department after being found at home with a disturbance of consciousness. Arterial blood gas measurements in room air revealed a carboxyhemoglobin level of 18.0%. Impaired consciousness was caused by chronic CO poisoning. The patient received high-flow oxygen therapy, which promptly improved his condition. According to his family, briquette kotatsu was the cause of chronic CO poisoning. Conclusion: Although high-flow oxygen therapy has been said to be less effective than hyperbaric oxygen therapy in CO poisoning treatment, recent studies have demonstrated that high-flow oxygen has similar effects and benefits. Thus, in institutions that do not have hyperbaric oxygen, high-flow oxygen may be sufficient to treat patients with CO poisoning, as seen in the present case. It should be noted that briquette kotatsu can lead to CO poisoning. This case highlights the need for clinicians to consider patients' living conditions.

Do carboxyhaemoglobin and methaemoglobin levels predict the return of spontaneous circulation and prognosis of cardiac arrest patients?

BACKGROUND

Early prediction of return of spontaneous circulation (ROSC) for cardiac arrest (CA) patients is a major challenge. Different biomarkers have been studied as an early predictor for ROSC, but a consensus has not been achieved in this regard. This study's goal was to investigate the value of the carboxyhaemoglobin (COHb) and methaemoglobin (MetHb) levels as a predictive marker for ROSC and prognostic marker for patients who achieve ROSC.

METHODS

A total of 241 adult patients (109 female, 132 male) diagnosed as non-traumatic CA were included in the study. The patients were divided into two groups based on whether they achieved ROSC. The ROSC group was divided into two sub-groups: survivors and non-survivors. Complete blood count parameters, routine biochemistry measurements, coagulation parameters, and blood gas analysis, and cardiac markers values were compared between the groups.

RESULTS

COHb levels were significantly lower in the non-ROSC group than in the ROSC group (P = .002). Urea, creatinine, potassium and cTn (cardiac troponin) levels in the non-ROSC group were significantly higher than in the ROSC group (P < .001, .001, .014, and .005, respectively). COHb levels were significantly lower in the non-survivor group than in the survivor group (P = .022). Urea, creatinine, potassium, lactate dehydrogenase, and cTn levels were significantly higher in the non-survivor group than the survivor group (P = .001, .005, .001, .010 and .008, respectively). There was no significant difference between the ROSC and non-ROSC groups and survivor group and non-survivor groups in terms of MetHb levels (P = .769 and .668, respectively). Moreover, CPR duration is significantly shorter in the survivor group than the non-survivor group (P ˂ .001).

CONCLUSION

COHb levels in the blood gas analysis at the time of admission could be used as a predictive marker for ROSC and prognostic marker for the patients who achieved ROSC.

Pulse Oximetry Is Unreliable in Patients on Veno-Venous Extracorporeal Membrane Oxygenation Caused by Unrecognized Carboxyhemoglobinemia

Continuous bedside pulse oximetry (SpO2) is universally used to monitor oxygenation for patients supported on veno-venous extracorporeal membrane oxygenation (VV-ECMO). Yet, elevated carboxyhemoglobin (COHb), a known event in VV-ECMO, diminishes the reliability of SpO2. This retrospective cohort study aims to assess the accuracy of SpO2 compared with oxyhemoglobin (SaO2) and quantify COHb levels by co-oximetry in the VV-ECMO population. Forty patients on VV_ECMO from 2012 to 2017 underwent 1,119 simultaneous SaO2 and SpO2 measurements. Most patients were male (60%) with average age of 46 years. SpO2 overestimated SaO2 values by 2.35% at time of cannulation and 0.0061% for each additional hour on VV-ECMO (p < 0.0001). Twenty-nine (72.5%) patients developed elevated COHb (>3% of hemoglobin saturation) at least once during VV-ECMO support and 602 (40.2%) arterial blood gases yielded elevated COHb levels. Mean duration for ECMO with elevated COHb was 244 hours compared with 98 hours in patients without (p < 0.0048). Patients who developed COHb were younger (mean age 40 vs. 55 years, p < 0.024) and had single-site double-lumen cannulation (odds ratio = 4.5, p = 0.23). At time of cannulation, mean COHb was 2.18% and increased by 0.0054% for each additional hour (p < 0.0001). For every 1% increase in COHb, SaO2 decreased by 1.1% (p < 0.0001). During VV-ECMO, SpO2 often overestimates SaO2 by substantial margins. This is attributable to rising COHb levels proportional to duration on VV-ECMO. In this population where adequate oxygen delivery is often marginal, clinicians should be wary of the reliability of continuous pulse oximetry to assess oxygenation.

The Role of Methemoglobin and Carboxyhemoglobin in COVID-19: A Review

Following the outbreak of a novel coronavirus (SARS-CoV-2) associated with pneumonia in China (Corona Virus Disease 2019, COVID-19) at the end of 2019, the world is currently facing a global pandemic of infections with SARS-CoV-2 and cases of COVID-19. Since severely ill patients often show elevated methemoglobin (MetHb) and carboxyhemoglobin (COHb) concentrations in their blood as a marker of disease severity, we aimed to summarize the currently available published study results (case reports and cross-sectional studies) on MetHb and COHb concentrations in the blood of COVID-19 patients. To this end, a systematic literature research was performed. For the case of MetHb, seven publications were identified (five case reports and two cross-sectional studies), and for the case of COHb, three studies were found (two cross-sectional studies and one case report). The findings reported in the publications show that an increase in MetHb and COHb can happen in COVID-19 patients, especially in critically ill ones, and that MetHb and COHb can increase to dangerously high levels during the course of the disease in some patients. The medications given to the patient and the patient’s glucose-6-phospate dehydrogenase (G6PD) status seem to be important factors determining the severity of the methemoglobinemia and carboxyhemoglobinemia. Therefore, G6PD status should be determined before medications such as hydroxychloroquine are administered. In conclusion, MetHb and COHb can be elevated in COVID-19 patients and should be checked routinely in order to provide adequate medical treatment as well as to avoid misinterpretation of fingertip pulse oximetry readings, which can be inaccurate and unreliable in case of elevated MetHb and COHb levels in the blood.

Arterial carboxyhaemoglobin levels in children admitted to PICU: A retrospective observational study

While carbon monoxide (CO) is considered toxic, low levels of endogenously produced CO are protective against cellular injury induced by oxidative stress. Carboxyhaemoglobin (COHb) levels have been associated with outcomes in critically ill adults. We aimed to describe the distribution of carboxyhaemoglobin in critically ill children and the relationship of these levels with clinical outcomes. This retrospective observational study was conducted at a large tertiary paediatric intensive care unit (PICU). We included all children admitted to the PICU over a two-year period who underwent arterial blood gas analysis. We measured the following: (i) Population and age-related differences in COHb distribution; (ii) Change in COHb over the first week of admission using a multi-level linear regression analysis; (iii) Uni- and multivariable relationships between COHb and length of ventilation and PICU survival. Arterial COHb levels were available for 559/2029 admissions. The median COHb level was 1.20% (IQR 1.00-1.60%). Younger children had significantly higher COHb levels (p-value <2 x 10-16). Maximum Carboxyhaemoglobin was associated with survival 1.67 (95% CI: 1.01-2.57; p-value = 0.02) and length of ventilation (OR 5.20, 95% CI: 3.07-7.30; p-value = 1.8 x 10-6) following multi-variable analysis. First measured and minimum COHb values were weakly associated with length of ventilation, but not survival. In conclusion, children have increased COHb levels in critical illness, which are greater in younger children. Higher COHb levels are associated with longer length of ventilation and death in PICU. This may reflect increased oxidative stress in these children.

Endogenous carbon monoxide production in extracorporeal membrane oxygenation-related hemolysis: potential use of point-of-care CO-oximetry carboxyhemoglobin to detect hemolysis

Extracorporeal membrane oxygenation (ECMO)‐related hemolysis is a rare but devastating condition. Death is inevitable without early recognition and prompt management. Endogenous carbon monoxide production, as an epiphenomenon of hemolysis, potentially allows rapid detection of such condition by use of point‐of‐care CO‐oximetry carboxyhemoglobin.

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.

Induction of heme oxygenase-1 by hemin protects lung against orthotopic autologous liver transplantation-induced acute lung injury in rats

BACKGROUND

Post-liver transplantation acute lung injury (ALI) severely affects patients' survival, whereas the mechanism is unclear and effective therapy is lacking. The authors postulated that reperfusion-induced increased oxidative stress plays a critical role in mediating post-liver transplantation ALI and that induction of heme oxgenase-1 (HO-1), an enzyme with anti-oxidative stress properties, can confer effective protection of lung against ALI.

METHODS

Male Sprague-Dawley rats underwent autologous orthotopic liver transplantation (OALT) in the absence or presence of treatments with the selective HO-1 inducer (Hemin) or HO-1 inhibitor (ZnPP). Lung tissues were collected at 8 h after OALT, pathological scores and lung water content were evaluated; survival rate of rats was analyzed; protein expression of HO-1 was determined by western blotting, and nuclear translocation of Nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor(NF)-κB p65 were detected by Immunofluorescence staining. The inflammatory cytokines and oxidative indexes of lung tissue were determined.

RESULTS

In lungs harvested at the early stage i.e. 8 h after OALT, Hemin treatment significantly increased superoxide dismutase activities, and reduced malondialdehyde, hydrogen peroxide, interleukin-6, myeloperoxidase, and tumor necrosis factor-α production,which were associated with increased HO-1 protein expression and lower pathological scores and increased survival rate of rats. The underline mechanisms might associate with activation of Nrf2 and inhibition of NF-κB p65 nuclear translocation. However, these changes were aggravated by ZnPP.

CONCLUSIONS

Hemin pretreatment, by enhancing HO-1 induction, increased lung antioxidant capacity and reduced inflammatory stress,protected the lung from OALT-induced ALI at early stage of reperfusion.

Effects of Two Different Exogenous Surfactant Preparations on Serial Peripheral Perfusion Index and Tissue Carbon Monoxide Measurements in Preterm Infants with Severe Respiratory Distress Syndrome

BACKGROUND

Administration of an exogenous surfactant may affect both ventilatory and hemodynamic parameters in preterm infants with respiratory distress syndrome (RDS). Peripheral perfusion may be expected to be influenced, and serial perfusion index (PI) values may show this effect. Noninvasive transcutaneous carbon monoxide (TCO) monitoring may show RDS severity, oxidative and inflammatory stress, and response to surfactant treatment.

METHODS

This randomized controlled nonblinded study was performed in 30 preterm infants with RDS, treated with poractant alfa (n = 15) or beractant (n = 15); 18 preterm infants without RDS served as a control group. Oxygenation and hemodynamic parameters were recorded and compared through the first 6 hours of treatment. PI and TCO values were measured prior to (Tp), immediately after (T0), and at 5 minutes (T5), 30 minutes (T30), 60 minutes (T60), and 360 minutes (T360) after the bolus surfactant administration. The mean arterial pressure, oxygenation index, pH, and lactate levels were recorded simultaneously.

RESULTS

Both study groups had lower Tp PI and higher Tp TCO levels than controls. Both surfactant preparations improved the PI, TCO, mean arterial pressure, oxygenation index, pH, and lactate levels at the end point of T360. However, the median Tp PI value of 1.3 first decreased to 0.86 at T0 (P < 0.001), and then it increased to 0.99 at T5 (p < 0.001) and to 1.25 at T30 (p = 0.037). The median Tp TCO value of 3 decreased to 2, 1.5, 0, and 0 at T0, T5, T30, and T60, respectively (p < 0.001). PI more quickly recovered to Tp values (30 minutes vs. 60 minutes) and reached the control group values (30 minutes vs. 360 minutes) with beractant compared to that with poractant alfa. TCO recovered to Tp values in both groups at the same time (5 minutes vs. 5 minutes), but reached the control group values more quickly (5 minutes vs. 30 minutes) with poractant alfa than with beractant.

CONCLUSION

Patients with RDS had poor perfusion, and PI improved with both surfactant preparations only following a short decline in the 1(st) minute. The expected improvement of PI occurred earlier in the beractant subgroup. TCO declined in both groups, showing lung improvement and decreased oxidative/inflammatory stress, and it was normalized earlier with poractant alfa.

Year in review 2012: Critical Care--Cardiology

In this review I discuss key research papers in cardiology and intensive care published in Critical Care during 2012 with related studies published in other journals quoted whenever appropriate. These studies are grouped into the following categories: cardiovascular therapies, mechanical therapies, pathophysiologic mechanisms, hemodynamic monitoring, ultrasound in respiratory failure, microcirculation, and miscellaneous.