Determination of carboxyhemoglobin half-life in patients with carbon monoxide toxicity treated with high flow nasal cannula oxygen therapy

Tools used to assess comfort among patients undergoing high flow nasal cannula: A scoping review

OBJECTIVE

The aims were twofold: (a) to map tools documented in the literature to evaluate comfort among patients undergoing high flow nasal cannula (HFNC) treatment; and (b) to assess if the retrieved tools have been validated for this purpose.

METHODS

A scoping review, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for scoping reviews (PRISMA-ScR). In July 2023, PubMed, Scopus, CINAHL and Cochrane Library were consulted. Studies assessing comfort in adult, paediatric, and neonatal patients undergoing HFNC were included.

RESULTS

Seventy-four articles were included, among which nine (12.2 %) investigated comfort as the primary aim. Twenty-five different tools were found, classifiable into 14 types, mostly unidimensional and originating from those measuring pain. The most widely used was the Visual Analogic Scale (n = 27, 35.6 %) followed by the Numerical Rating Scale (n = 11, 14.5 %) and less defined generic tools (n = 10, 13.2 %) with different metrics (e.g. 0-5, 0-10, 0-100). Only the General Comfort Questionnaire and the Comfort Scale were specifically validated for the assessment of comfort among adults and children, respectively.

CONCLUSION

Although the comfort of patients undergoing HFNC is widely investigated in the literature, there is a scarcity of tools specifically validated in this field. Those used have been validated mainly to assess pain, suggesting the need to inform patients to prevent confusion while measuring comfort during HFNC and to develop more research in the field.

IMPLICATIONS FOR CLINICAL PRACTICE

Comfort assessment is an important aspect of nursing care. Given the lack of validation studies in the field, efforts in research are recommended.

Comparing high-flow nasal oxygen therapy and normobaric oxygen therapy on the treatment of carbon monoxide poisoning

AIM

We aimed to investigate whether there is a difference in the rate of decrease in carboxyhemoglobin (COHB) values between high-flow nasal oxygen (HFNO) and normobaric oxygen (NBO) therapy.

MATERIAL AND METHOD

This retrospective observational study included patients with carbon monoxide poisoning who were treated with HFNO or NBO (control group). All patients were started on NBO therapy with a non-rebreather face mask at a rate of 15 L/min. In the NBO group, NBO treatment was continued until the COHB value fell below 10%. In the HFNO group, as soon as the preparation of the HFNO device was completed, NBO treatment was terminated and HFNO treatment was started and continued until the COHB value fell below 10%. The primary outcome of the study was the difference between HFNO and NBO in terms of COHB half-life rates.

RESULTS

A total of 81 patients were included in the study, 44 in the HFNO group and 37 in the NBO group. The median of COHB t1/2 values between HFNO and the NBO treatment groups were 47.3 (IQR: 25-75%: 31.5-65.4) and 46 (IQR: 25-75%: 32.3-56.2), respectively, but this difference was not statistically significant (p = 0.81).

CONCLUSION

The results of this study suggest that HFNO treatment does not have a significant advantage over NBO treatment in the carbon monoxide elimination rate within the first 60 min of treatment.

Clinical review of high-flow nasal oxygen therapy in human and veterinary patients

Oxygen therapy is the first-line treatment for hypoxemic acute respiratory failure. In veterinary medicine this has traditionally been provided via mask, low-flow nasal oxygen cannulas, oxygen cages and invasive positive pressure ventilation. Traditional non-invasive modalities are limited by the maximum flow rate and fraction of inspired oxygen (FiO₂) that can be delivered, variability in oxygen delivery and patient compliance. The invasive techniques are able to provide higher FiO₂ in a more predictable manner but are limited by sedation/anesthesia requirements, potential complications and cost. High-flow nasal oxygen therapy (HFNOT) represents an alternative to conventional oxygen therapy. This modality delivers heated and humidified medical gas at adjustable flow rates, up to 60 L/min, and FiO₂, up to 100%, via nasal cannulas. It has been proposed that HFNOT improves pulmonary mechanics and reduces respiratory fatigue via reduction of anatomical dead space, provision of low-level positive end-expiratory pressure (PEEP), provision of constant FiO₂ at rates corresponding to patient requirements and through improved patient tolerance. Investigations into the use of HFNOT in veterinary patients have increased in frequency since its clinical use was first reported in dogs with acute respiratory failure in 2016. Current indications in dogs include acute respiratory failure associated with pulmonary parenchymal disease, upper airway obstruction and carbon monoxide intoxication. The use of HFNOT has also been advocated in certain conditions in cats and foals. HFNOT is also being used with increasing frequency in the treatment of a widening range of conditions in humans. Although there remains conflict regarding its use and efficacy in some patient groups, overall these reports indicate that HFNOT decreases breathing frequency and work of breathing and reduces the need for escalation of respiratory support. In addition, they provide insight into potential future veterinary applications. Complications of HFNOT have been rarely reported in humans and animals. These are usually self-limiting and typically result in lower morbidity and mortality than those associated with invasive ventilation techniques.

[Carbon monoxide intoxication-New aspects and current guideline-based recommendations]

Carbon monoxide poisoning is a common and potentially life-threatening intoxication, showing an interindividual variety of unspecific symptoms as well as late neurological and other sequelae. Two new German guidelines (S2k guidelines diagnosis and treatment of carbon monoxide poisoning as well as S3 guidelines oxygen therapy in the acute care of adult patients) focus on current evidence-based information on diagnostics as well as therapeutic options with considerable uncertainty remaining. This review summarizes current information and presents a flow scheme for daily practical use.

Can Exhaled Carbon Monoxide Be Used as a Marker of Exposure? A Cross-Sectional Study in Young Adults

Carbon monoxide (CO) poisoning is a major public health issue worldwide. People are exposed to CO in their daily lives, with one of the common sources of CO being cigarette smoking. Inhalation of CO leads to elevated carboxyhaemoglobin (COHb) levels in the blood and also in exhaled CO concentration. Several factors have been shown to affect COHb concentration and COHb half-life. However, factors affecting exhaled CO concentration and exhaled CO half-life are not well understood. The present study aimed to investigate the potential factors related to baseline exhaled CO concentration and exhaled CO half-life among smokers. A cross-sectional study was conducted between 26 January and 30 June 2019, and young adults were recruited into the study. A total of 74 participants (mean age: 27.1 years, 71.6% males and 28.4% females) attended the study. They were invited to complete a questionnaire, including demographic, physiological, and behavioural factors. Then, exhaled CO measurements were taken. These measurements were taken before and after smoking a single cigarette for smokers and only once for non-smokers. The average baseline exhaled CO concentration was 6.9 ± 4.9 ppm for smokers and 1.9 ± 0.5 ppm for non-smokers. The mean of exhaled CO half-life was around 273.3 min (4.6 h) for smokers. No difference was seen in exhaled CO half-life between light smokers and heavy smokers in the smoking group. Gender and cigarettes smoked weekly affected baseline exhaled CO in smokers. Even though height seemed to positively associate with exhaled CO half-life, the relationship disappeared when adjusting by gender and weight. Therefore, exhaled CO could be used as a marker of CO exposure, but we cannot ignore the factors mentioned in the study. For future study, considering factors related to smoking habits and smoking style are recommended as these may affect total inhaled CO.

High flow nasal cannula for adult acute hypoxemic respiratory failure in the ED setting: A narrative review

Introduction

High flow nasal cannula (HFNC) is a noninvasive ventilation (NIV) system that has demonstrated promise in the emergency department (ED) setting.

Objective

This narrative review evaluates the utility of HFNC in adult patients with acute hypoxemic respiratory failure in the ED setting.

Discussion

HFNC provides warm (37 °C), humidified (100% relative humidity) oxygen at high flows with a reliable fraction of inspired oxygen (FiO₂). HFNC can improve oxygenation, reduce airway resistance, provide humidified flow that can flush anatomical dead space, and provide a low amount of positive end expiratory pressure. Recent literature has demonstrated efficacy in acute hypoxemic respiratory failure, including pneumonia, acute respiratory distress syndrome (ARDS), coronavirus disease 2019 (COVID-19), interstitial lung disease, immunocompromised states, the peri-intubation state, and palliative care, with reduced need for intubation, length of stay, and mortality in some of these conditions. Individual patient factors play an important role in infection control risks with respect to the use of HFNC in patients with COVID-19. Appropriate personal protective equipment, adherence to hand hygiene, surgical mask placement over the HFNC device, and environmental controls promoting adequate room ventilation are the foundation for protecting healthcare personnel. Frequent reassessment of the patient placed on HFNC is necessary; those with severe end organ dysfunction, thoracoabdominal asynchrony, significantly increased respiratory rate, poor oxygenation despite HFNC, and tachycardia are at increased risk of HFNC failure and need for further intervention.

Conclusions

HFNC demonstrates promise in several conditions requiring respiratory support. Further randomized trials are needed in the ED setting.

Treatment of carbon monoxide poisoning: high-flow nasal cannula versus non-rebreather face mask

OBJECTIVE

In this study, the aim was to compare the rate of decrease in carboxyhemoglobin (COHb) values at consecutive time points and calculate the half-life of COHb (COHb t½) in patients admitted to the emergency department (ED) with carbon monoxide (CO) poisoning and treated with either high flow nasal cannula oxygen therapy (HFNC) or non-rebreather face mask (NRFM).

METHODS

This retrospective, cohort study with historical controls was performed over a 2-year period and included adult patients with CO poisoning, whose COHb values were checked. The HFNC group consisted of patients admitted to the ED with CO poisoning when HFNC was available in the hospital, while the NRFM group consisted of patients who presented to the ED with CO poisoning before the availability of HFNC. The primary outcome of the study was to detect the COHb t½.

RESULTS

A total of 71 patients were enrolled in the study. While 35 patients received oxygen with NRFM, 36 patients received HFNC. The mean COHb t½ in the HFNC group was 41.1 min (95% CI: 31.0-58.4) and 64.0 min (95% CI: 43.5-114.4) in the NRFM group. We did not find a significant difference in the COHb t½ between the HFNC group and NRFM group (p = 0.099). COHb levels between treatment arms at serial time points showed a statistically significant difference at 60 min (p = 0.048). We compared the decay constant and half-life of COHb between groups according to gender. In both genders, COHb t½ was significantly different between groups, and COHb t½ was lower in the patients treated with HFNC.

CONCLUSION

HFNC was effective in reducing the half-life of COHb values in patients with carbon monoxide poisoning. Prospective studies to be conducted in larger groups are needed to fully understand the effect of HFNC on carbon monoxide poisoning.

Blood carboxyhemoglobin elimination curve, half-lifetime, and arterial-venous differences in acute phase of carbon monoxide poisoning in ovine smoke inhalation injury model

Smoke inhalation injury (SII) affects more than 50,000 people annually causing carbon monoxide (CO) poisoning. Although the increased blood level of carboxyhemoglobin (CO-Hb) is frequently used to confirm the diagnosis of SII, knowledge of its elimination in the acute phase is still limited. The aim of this study is to determine CO-Hb elimination rates and their differences in arterial (aCO-Hb) and mixed-venous (vCO-Hb) blood following severe SII in a clinically relevant ovine model. Forty-three chronically instrumented female sheep were subjected to SII (12 breaths, 4 sets) through tracheostomy tube under anesthesia and analgesia. After the SII, sheep were awakened and placed on a mechanical ventilator (FiO₂ = 1.0, tidal volume 12 mL/kg, and PEEP = 5cmH₂O) and monitored. Arterial and mixed-venous blood samples were withdrawn simultaneously for blood gas analysis at various time points to determine CO-HB half-lifetime and an elimination curve. The mean of highest aCO-Hb level during SII was 70.8 ± 13.9%. The aCO-Hb elimination curve showed an approximated exponential decay during the first 60 min. Per mixed linear regression model analysis, aCO-Hb significantly (p < 0.001) declined (4.3%/minute) with a decay constant lambda of 0.044. With this lambda, mean lifetime and half-lifetime of aCO-Hb were 22.7 and 15.7 min, respectively. The aCO-Hb was significantly lower compared to vCO-Hb at all-time points (0-180 min). To our knowledge, this is the first report describing CO-Hb elimination curve in the acute phase after severe SII in the clinically relevant ovine model. Our data shows that CO-Hb is decreasing in linear manner with supportive mechanical ventilation (0-60 min). The results may help to understand CO-Hb elimination curve in the acute phase and improvement of pre-hospital and initial clinical care in patients with CO poisoning.

Factors Contributing to CO Uptake and Elimination in the Body: A Critical Review

BACKGROUND

Carbon monoxide (CO) poisoning is an important public health issue around the world. Research indicates that many factors may be related to the rate of CO uptake and elimination in the human body. However, some factors related to CO uptake and elimination are considered controversial. Relatively little attention has been devoted to review and synthesis of factors affecting CO uptake and elimination.

PURPOSE

This paper provides a critical scoping review of the factors and divides them into four aspects, including environmental, demographic, physiological and treatment factors.

METHODS

We searched the scientific databases for research that has proposed a mathematical equation as a synthesis of quantities related to CO poisoning, CO elimination, CO uptake, CO half-life, CO uptake and elimination and their relationships. After excluding the studies that did not meet the study criteria, there were 39 studies included in the review and the search was completed before 16 December 2019.

RESULTS AND CONCLUSION

This review discusses most of the factors that impact the rate of CO uptake and elimination. Several factors may be related to CO uptake and elimination, such as CO concentration, the duration of exposure to CO, age, sex, exercise, minute ventilation, alveolar ventilation, total haemoglobin mass and different treatments for CO poisoning. Although some potential factors were not included in the review, the findings are useful by presenting an overview for discussing factors affecting CO uptake and elimination and provide a starting point for further study regarding strategies for CO poisoning and the environmental standard of CO.

Carbon Monoxide Poisoning Effectively Treated with High-flow Nasal Cannula

Carbon monoxide (CO) poisoning is typically treated by administration of oxygen via non-rebreather mask (NRB). High-flow nasal cannula (HFNC) is an alternative to NRB in a variety of disease states. We report a case of the novel use of HFNC in the treatment of acute CO poisoning. A 29-year-old man presented with a carboxyhemoglobin (COHb) level of 29.8%. He was treated with HFNC, and COHb levels declined to 5.4% in 230 minutes. Given several theoretical advantages of HFNC relative to NRB, HFNC is a potential option for use in the treatment of CO poisoning.

Effect of Hyperbaric Oxygen on Neurologic Sequelae and All-Cause Mortality in Patients with Carbon Monoxide Poisoning: A Meta-Analysis of Randomized Controlled Trials

Background

Hyperbaric oxygen (HBO) is used in patients with carbon monoxide (CO) poisoning to prevent the occurrence of delayed neurological sequelae. However, inconsistent results were obtained regarding the treatment effects of HBO. Therefore, the current meta-analysis was conducted based on published randomized controlled trials (RCTs) to determine the effect of HBO on neurologic sequelae and all-cause mortality in patients with CO poisoning.

Material/Methods

Electronic databases MedLine, EmBase, and the Cochrane Library were searched for relevant RCTs from inception to March 1, 2019. The pooled relative risks (RRs) and weighted mean differences (WMDs) with corresponding 95% confidence intervals (CIs) were calculated to evaluate the outcomes by using a random-effects model. Sensitivity, subgroup, and publication bias analyses were also conducted.

Results

Seven RCTs, including 9 cohorts and a total of 2023 patients with CO poisoning, were enrolled in this study. The summary results revealed that HBO showed an association with lower risk of memory impairment compared to patients receiving normobaric oxygen (NBO), whereas 2 sessions of HBO showed an association with higher risk of memory impairment compared to those who received 1 session of HBO. Moreover, HBO was associated with increased neuropsychologic scores of block design and trail making when compared with NBO. No other significant differences regarding the treatment effects of HBO were observed.

Conclusions

These results indicate that HBO therapy significantly reduces the risk of memory impairment compared to NBO, but 2 sessions of HBO might not be better for memory impairment than 1 session of HBO.