Capnography in the Emergency Department: A Review of Uses, Waveforms, and Limitations

End-Tidal Carbon Dioxide Measurement in Out-of-Hospital Cardiac Arrest as a Predictor of Return of Spontaneous Circulation: A Literature Review

INTRODUCTION

One of the leading causes of morbidity and mortality worldwide is out-of-hospital cardiac arrest. Early defibrillation and high-quality cardiopulmonary resuscitation (CPR) have improved survival. The main goal of CPR is to achieve return of spontaneous circulation (ROSC), which is assessed by looking for a pulse, analyzing the heart rhythm, and assessing carbon dioxide levels. The use of cartography during CPR to confirm the correct position of the endotracheal tube during intubation or to assess the effectiveness of chest compressions has increased significantly in the last years. The aim of this review was to identify correlations between end-tidal carbon dioxide levels and the likelihood of ROSC in patients with out-of-hospital cardiac arrest.

METHODS

A literature search was performed in MEDLINE (via Pubmed), Scopus, Web of Science, and Google Scholar databases from September to November 2022. Keywords combined with the Boolean operators (AND/OR) were used in both free text and Medical Subject Headings. Studies on adult patients published between 01/01/2016 and 28/09/2022 were searched, with no geographical restrictions.

RESULTS

At the end of the selection process, 14 studies were included that investigated capnography in out-of-hospital CPR and reported at least 1 outcome between end-tidal carbon dioxide and ROSC or survival.

DISCUSSION

Capnography is an advantageous tool due to its noninvasive characteristics, ease of use, and immediacy of data. In out-of-hospital cardiac arrest, the use of the end-tidal carbon dioxide appears to be an appropriate complementary tool to support clinical decisions, such as correct positioning of the endotracheal tube, optimizing ventilation in CPR, and as a predictor of ROSC.

Can end-tidal CO2 measurement replace arterial partial CO2 in emergency department respiratory distress management?

OBJECTIVE

To assess the feasibility of using end-tidal carbon dioxide (EtCO2) as a non-invasive substitute for partial pressure of arterial carbon dioxide (PaCO2) in emergency department (ED) triage and follow-up, and to explore the potential of partial pressure of venous carbon dioxide (PvCO2) as an alternative to PaCO2.

DESIGN

Prospective cross-sectional study.

SETTING

Tertiary university hospital.

PATIENTS OR PARTICIPANTS

97 patients presenting with acute respiratory distress to the ED.

INTERVENTIONS

EtCO2, arterial blood gases, and venous blood gases measured at admission (0 min), 60 min, and 120 min.

MAIN VARIABLES OF INTEREST

CO2 levels.

RESULTS

Among 97 patients (mean age: 70.93 ± 9.6 years; 60.8% male), EtCO2 > 45 mmHg at admission showed strong positive correlations with PaCO2 and PvCO2 (r = 0.844, r = 0.803; p < 0.001, respectively). Significant positive correlation was observed between 60-min EtCO2 and PaCO2 (r = 0.729; p < 0.001). Strong correlation between PaCO2 and PvCO2 at 120 min when EtCO2 > 45 mmHg (r = 0.870; p < 0.001). EtCO2 was higher in hospitalized patients compared to discharged ones.

CONCLUSIONS

EtCO2 appears promising as a substitute for PaCO2 in ED patients with acute respiratory distress within the initial two hours of treatment. Venous blood gas sampling offers a less invasive alternative to arterial sampling, facilitating simultaneous blood tests.

Diagnostic utility of capnography in emergency department triage for screening acidemia: a pilot study

BACKGROUND

Capnography is a quantitative and reliable method of determining the ventilatory status of patients. We describe the test characteristics of capnography obtained during Emergency Department triage for screening acidemia.

RESULTS

We performed an observational, pilot study of adult patients presenting to Emergency Department (ED) triage. The primary outcome was acidemia, as determined by the basic metabolic panel and/or blood gas during the ED visit. Secondary outcomes include comparison of estimated and measured respiratory rates (RR), relationships between end-tidal CO2 (EtCO2) and venous partial pressure of CO2, admission disposition, in-hospital mortality during admission, and capnogram waveform analysis. A total of 100 adult ED encounters were included in the study and acidemia ([Formula: see text] or [Formula: see text]) was identified in 28 patients. The measured respiratory rate (20.3 ± 6.4 breaths/min) was significantly different from the estimated rate (18.4 ± 1.6 breaths/min), and its area under the receiver operating curve (c-statistic) to predict acidemia was only 0.60 (95% CI 0.51-0.75, p = 0.03). A low end-tidal CO2 (EtCO2 < 32 mmHg) had positive (LR+) and negative (LR-) likelihood ratios of 4.68 (95% CI 2.59-8.45) and 0.34 (95% CI 0.19-0.61) for acidemia, respectively-corresponding to sensitivity 71.4% (95% CI 51.3-86.8) and specificity 84.7% (95% CI 74.3-92.1). The c-statistic for EtCO2 was 0.849 (95% CI 0.76-0.94, p = 0.00). Waveform analysis further revealed characteristically abnormal capnograms that were associated with underlying pathophysiology.

CONCLUSIONS

Capnography is a quantitative method of screening acidemia in patients and can be implemented feasibly in Emergency Department triage as an adjunct to vital signs. While it was shown to have only modest ability to predict acidemia, triage capnography has wide generalizability to screen other life-threatening disease processes such as sepsis or can serve as an early indicator of clinical deterioration.

Application of End-Tidal CO2 Monitoring to ICU Management

Waveform capnography is a noninvasive measurement of ventilation and perfusion commonly employed in the prehospital setting. It is easy to apply, and modern cardiac monitors are equipped with the necessary ports and capability to display results. Despite its ease of use, end-tidal CO2 monitoring has not yet achieved widespread adoption within the hospital setting. It is routinely used in the emergency department and by anesthesiologists, but its application could support ICU management in critically ill patients. Its use is routinely supported by multiple professional societies, and it has been recommended as a requirement in all cardiac arrests. Careful analysis of the waveform and expired carbon dioxide can guide therapy for patients experiencing respiratory emergencies, hemodynamic compromise, metabolic acidosis, and shock due to trauma, hypovolemia, or sepsis. Use of capnography throughout the hospital could improve patient outcomes and prevent unidentified deterioration.

Comb spectroscopy of CO2 produced from microbial metabolism

We have developed a direct frequency comb spectroscopy instrument, which we have tested on Saccharomyces cerevisiae (baker's yeast) by measuring its CO2 output and production rate as we varied the environmental conditions, including the amount and type of feed sugar, the temperature, and the amount of yeast. By feeding isotopically-enhanced sugar to the yeast, we demonstrate the capability of our device to differentiate between two isotopologues of CO2, with a concentration measurement precision of 260 ppm for 12C16O2 and 175 ppm for 13C16O2. We also demonstrate the ability of our spectrometer to measure the proportion of carbon in the feed sugar converted to CO2, and estimate the amount incorporated into the yeast biomass.

Capnography access and use in Kenya and Ethiopia

PURPOSE

Lack of access to safe and affordable anesthesia and monitoring equipment may contribute to higher rates of morbidity and mortality in low- and middle-income countries (LMICs). While capnography is standard in high-income countries, use in LMICs is not well studied. We evaluated the association of capnography use with patient and procedure-related characteristics, as well as the association of capnography use and mortality in a cohort of patients from Kenya and Ethiopia.

METHODS

For this retrospective observational study, we used historical cohort data from Kenya and Ethiopia from 2014 to 2020. Logistic regression was used to study the association of capnography use (primary outcome) with patient/procedure factors, and the adjusted association of intraoperative, 24-hr, and seven-day mortality (secondary outcomes) with capnography use.

RESULTS

A total of 61,792 anesthetic cases were included in this study. Tertiary or secondary hospital type (compared with primary) was strongly associated with use of capnography (odds ratio [OR], 6.27; 95% confidence interval [CI], 5.67 to 6.93 and OR, 6.88; 95% CI, 6.40 to 7.40, respectively), as was general (vs regional) anesthesia (OR, 4.83; 95% CI, 4.41 to 5.28). Capnography use was significantly associated with lower odds of intraoperative mortality in patients who underwent general anesthesia (OR, 0.31; 95% CI, 0.17 to 0.48). Nevertheless, fully-adjusted models for 24-hr and seven-day mortality showed no evidence of association with capnography.

CONCLUSION

Capnography use in LMICs is substantially lower compared with other standard anesthesia monitors. Capnography was used at higher rates in tertiary centres and with patients undergoing general anesthesia. While this study revealed decreased odds of intraoperative mortality with capnography use, further studies need to confirm these findings.

Cardiopulmonary Resuscitation: The Importance of the Basics

Cardiac arrest is the loss of organized cardiac activity. Unfortunately, survival to hospital discharge is poor, despite recent scientific advances. The goals of cardiopulmonary resuscitation (CPR) are to restore circulation and identify and correct an underlying etiology. High-quality compressions remain the foundation of CPR, optimizing coronary and cerebral perfusion pressure. High-quality compressions must be performed at the appropriate rate and depth. Interruptions in compressions are detrimental to management. Mechanical compression devices are not associated with improved outcomes but can assist in several situations.

Preventing unrecognized esophageal intubation in the emergency department

Tracheal intubation is a commonly performed procedure on critically ill patients in the emergency department. It is associated with many serious complications, one of the most dangerous being unrecognized esophageal intubation, which can result in anoxic brain injury, cardiac arrest, or death. It is the responsibility of the emergency physician to do everything possible to avoid this devastating complication. Preventing unrecognized esophageal intubation requires a two-pronged approach. First, the inadvertent placement of intended tracheal tubes into the esophagus must be reduced as much as is humanly possible. This can be achieved with the routine use of video laryngoscopes for emergency department intubations. Numerous studies have demonstrated that use of video laryngoscopes can significantly reduce the occurrence of esophageal intubation, presumably by providing an improved view of the larynx. Second, if an esophageal intubation inadvertently occurs, it must be rapidly identified and appropriately addressed. The cornerstone of rapid identification is the use of continuous waveform capnography to detect exhaled carbon dioxide. Capnography has been shown to be the most accurate method to determine tube placement after intubation. Standard clinical examinations, for example, auscultation of breath sounds, visualization of chest excursion, and observation of condensation in the tube, have all been demonstrated in studies to be unreliable and thus should not be used to exclude esophageal intubation. Recently, the Project for Universal Management of Airways, an international collaborative of airway experts from anesthesiology, critical care and emergency medicine, published evidence-based guidelines to specifically address the issue of preventing unrecognized esophageal intubation. These guidelines, which have received endorsement from several prominent airway societies, including the Society for Airway Management, the Difficult Airway Society, and the European Airway Management Society, will be briefly discussed in this review.

Doppler ultrasound peak systolic velocity versus end tidal carbon dioxide during pulse checks in cardiac arrest

BACKGROUND

An accurate, non-invasive measure of return of spontaneous circulation (ROSC) is needed to improve management of cardiac arrest patients.

OBJECTIVES

During a pulse check in Emergency Department (ED) cardiac arrest patients, we compared the correlation between 1) end tidal carbon dioxide (ETCO₂) and systolic blood pressure (SBP), and 2) Doppler ultrasound peak systolic velocity (PSV) and SBP. Additionally, we assessed the accuracy of PSV ≥ 20 cm/sec in comparison to previously suggested ETCO₂ ≥ 20 or ≥ 25 mmHg thresholds to predict ROSC with SBP ≥ 60 mmHg.

METHODS

This was a secondary analysis of a previously published prospective observational study of ED cardiac arrest patients with an advanced airway and femoral arterial line in place. During each pulse check, highest SBP, highest PSV, and ETCO₂ at the end of the pulse check were recorded. Spearman correlation coefficients were calculated and compared using a Fisher Z-transformation. Accuracy of previously determined PSV and ETCO₂ thresholds for detecting ROSC with SBP ≥ 60 mmHg were compared using McNemar's tests.

RESULTS

Based on data from 35 patients with 111 pulse checks, we found a higher correlation between PSV and SBP than ETCO₂ and SBP (0.71 vs 0.31; p < 0.001). Diagnostic accuracy of PSV ≥ 20 cm/sec for detecting ROSC with SBP ≥ 60 mmHg was 89% (95% CI: 82%-94%) versus 59% (95% CI: 49%-68%) and 58% (95% CI: 48%-67%) for ETCO₂ ≥ 20 and ≥ 25 mmHg, respectively.

CONCLUSIONS

During a pulse check, Doppler ultrasound PSV outperformed ETCO₂ for correlation with SBP and accuracy in detecting ROSC with SBP ≥ 60 mmHg.

Clinical usefulness of end-tidal CO2 measured using a portable capnometer in patients with respiratory disease

INTRODUCTION

This study aimed to evaluate the correlation and agreement between end-tidal CO₂ (EtCO₂ ) measured with the novel portable capnometer (CapnoEye®) and partial pressure of arterial carbon dioxide (PaCO₂ ) levels in patients with respiratory diseases and to compare the efficacy of EtCO₂ and PvCO₂ in predicting PaCO₂ levels.

METHODS

We analyzed the correlation and the agreement between EtCO₂ and PaCO₂ and between PvCO₂ and PaCO₂ using Pearson's moment correlation coefficient in patients with type 1 and type 2 respiratory failure and both groups overall.

RESULTS

A total of 100 samples were included that comprised 67 men (67%). The mean age of the subjects was 77 ± 13 years. Chronic obstructive pulmonary disease (COPD) (43%) was the most common disease. There was a high correlation between EtCO₂ and PaCO₂ (r = 0.88; p < 0.0001). Sixty-six PvCO₂ samples were obtained, and there was a high correlation between PvCO₂ and PaCO₂ (r = 0.81; p < 0.0001). Regarding type 2 respiratory failure, there was a high correlation between EtCO₂ and PaCO₂ (r = 0.81). The Bland-Altman analysis between PaCO₂ and EtCO₂ revealed a bias of 5.7 mmHg, with limits of agreement ranging from -5.1 mmHg to 16.5 mmHg. In contrast, the analysis between PaCO₂ and PvCO₂ revealed a bias of -6.8 mmHg, and the limits of agreement ranged from -22.13 mmHg to 8.53 mmHg.

CONCLUSION

EtCO₂ measured by CapnoEye® was significantly correlated to PaCO₂ levels in patients with respiratory diseases. Moreover, CapnoEye® may be more useful for predicting hypercapnia conditions in which respiratory diseases are compared with measure PvCO₂ .

An Educational Intervention to Improve Comfort with Applying and Interpreting Transcutaneous CO2 and End-tidal CO2 Monitoring in the PACU

PURPOSE

The purpose of this study was to assess the effectiveness of an educational program about measuring ventilation using devices that assess carbon dioxide levels in patients recovering from a surgical procedure.

DESIGN

A pre-post survey of knowledge attainment from an educational intervention about measuring ventilation using end-tidal carbon dioxide (EtCO₂) and transcutaneous carbon dioxide (tcPCO₂) devices in the postanesthesia care unit (PACU) was distributed to current members of the American Society of PeriAnesthesia Nurses.

METHODS

Participants received a 12-question pre-intervention (five were related to demographics) and a five-question post-intervention survey. Non-demographic survey questions used a one to five Likert scale to assess comfortability or confidence. The intervention created was a voice-over presentation designed to improve PACU RN's comfort and confidence with using and interpreting tcPCO₂ or EtCO₂ in the PACU.

FINDINGS

PACU RNs (N = 108) reported they 'never' or 'rarely' used EtCO₂ (n = 57, 52.7%) monitoring or tcPCO₂ (n = 93, 86.1%) monitoring in the PACU. A paired t test revealed statistically significant differences in the PACU RN's pre-survey and posttest comfortability of applying and interpreting EtCO₂ or tcPCO₂ monitors (P < .05).

CONCLUSIONS

Capnography monitoring should be considered a standard of care for PACU patients. Education of registered nurses working in the PACU is critical before implementing EtCO₂ or tcPCO₂ monitoring.

Capnography and Pulse Oximetry Improve Fast Track Extubation in Patients Undergoing Coronary Artery Bypass Graft Surgery: A Randomized Clinical Trial

Background

Use of capnography as a non-invasive method during the weaning process for fast track extubation (FTE) is controversial. We conducted the present study to determine whether pulse oximetry and capnography could be utilized as alternatives to arterial blood gas (ABG) measurements in patients under mechanical ventilation (MV) following coronary artery bypass graft (CABG) surgery.

Methods

In this randomized clinical trial, 70 patients, who were candidates for CABG surgery, were randomly assigned into two equal groups (n = 35), intervention and control group. In the intervention group, the ventilator management and weaning from MV was done using Etco2 from capnography and SpO2 from pulse oximetry. Meanwhile, in the control group, weaning was done based on ABG analysis. The length of intensive care unit (ICU) stay, time to extubation, number of manual ventilators setting changes, and alarms were compared between the groups.

Results

The end-tidal carbon dioxide (ETCO2) levels in the intervention group were completely similar to the partial pressure of carbon dioxide (PaCo2) in the control group (39.5 ± 3.1 vs. 39.4 ± 4.32, p > 0.05). The mean extubation times were significantly shorter in the intervention group compared to those in the control patients (212.2 ± 80.6 vs. 342.7 ± 110.7, p < 0.001). Moreover, the number of changes in the manual ventilator setting and the number of alarms were significantly lower in the intervention group. However, the differences in the length of stay in ICU between the two groups were not significant (p = 0.219).

Conclusion

Our results suggests that capnography can be used as an alternative to ABG. Furthermore, it is a safe and valuable monitor that could be a good alternative for ABG in this population. Further studies with larger sample sizes and on different disease states and populations are required to assess the accuracy of our findings.

Clinical Trial Registration

Current Controlled Trials, IRCT, IRCT201701016778N6, Registered 3 March 2017, https://www.irct.ir/trial/7192.

Respiratory rate monitoring in healthy volunteers by central photoplethysmography compared to capnography

Monitoring of respiration is a central task in clinical medicine, crucial to patient safety. Despite the uncontroversial role of altered respiratory frequency as an important sign of impending or manifest deterioration, reliable measurement methods are mostly lacking outside of intensive care units and operating theaters. Photoplethysmography targeting the central blood circulation in the sternum could offer accurate and inexpensive monitoring of respiration. Changes in blood flow related to the different parts of the respiratory cycle are used to identify the respiratory pattern. The aim of this observational study was to compare photoplethysmography at the sternum to standard capnography in healthy volunteers. Bland Altman analysis showed good agreement (bias -0.21, SD 1.6, 95% limits of agreement -3.4 to 2.9) in respiratory rate values. Photoplethysmography provided high-quality measurements of respiratory rate comparable to capnographic measurements. This suggests that photoplethysmography may become a precise, cost-effective alternative for respiratory monitoring.

Carbon Dioxide Sensing-Biomedical Applications to Human Subjects

Carbon dioxide (CO2) monitoring in human subjects is of crucial importance in medical practice. Transcutaneous monitors based on the Stow-Severinghaus electrode make a good alternative to the painful and risky arterial "blood gases" sampling. Yet, such monitors are not only expensive, but also bulky and continuously drifting, requiring frequent recalibrations by trained medical staff. Aiming at finding alternatives, the full panel of CO2 measurement techniques is thoroughly reviewed. The physicochemical working principle of each sensing technique is given, as well as some typical merit criteria, advantages, and drawbacks. An overview of the main CO2 monitoring methods and sites routinely used in clinical practice is also provided, revealing their constraints and specificities. The reviewed CO2 sensing techniques are then evaluated in view of the latter clinical constraints and transcutaneous sensing coupled to a dye-based fluorescence CO2 sensing seems to offer the best potential for the development of a future non-invasive clinical CO2 monitor.

Screening Performance Characteristics of Ultrasonography in Confirmation of Endotracheal Intubation; a Systematic Review and Meta-analysis

Introduction:

Recent studies have suggested that point-of-care ultrasonography can be used for confirming the placement of endotracheal tube. This systematic review and meta-analysis aimed to investigate the sensitivity and specificity of ultrasonography for confirming endotracheal tube placement.

Methods:

In this meta-analysis, systematic search of the previous published papers investigating the diagnostic accuracy of ultrasonography for confirmation of endotracheal tube placement was performed. Seven electronic databases, including PubMed, Scopus, Google Scholar, EBSCO, EMBASE, Web of Science, and Cochrane Database were searched up to July 2021, for all relevant articles published in English on this topic. Meta-DiSc version 1.4 software was used for statistical analysis.

Results:

The estimated pooled sensitivity and specificity of ultrasonography for confirmation of endotracheal tube location were 0.98 (95% CI: 0.98–0.99) and 0.94 (95% CI 0.91–0.96), respectively. The pooled positive likelihood ratio and negative likelihood ratio were 5.94 (95% CI 4.41–7.98) and 0.03 (95% CI: 0.02-0.04), respectively. The diagnostic odds ratio of ultrasonography was 281.47 and the area under hierarchical summary receiver operating characteristic (HSROC) revealed an appropriate accuracy of 0.98.

Conclusion:

Ultrasonography has high diagnostic accuracy and can be used as a promising tool for confirmation of endotracheal tube placement, especially in critically ill patients or when capnography is not available, or its result is equivocal.

End-Tidal Carbon Dioxide Pressure Measurement after Prolonged Inspiratory Time Gives a Good Estimation of the Arterial Carbon Dioxide Pressure in Mechanically Ventilated Patients

Background: End-tidal carbon dioxide pressure (PetCO₂) is unreliable for monitoring PaCO₂ in several conditions because of the unpredictable value of the PaCO₂–PetCO₂ gradient. We hypothesised that increasing both the end-inspiratory pause and the expiratory time would reduce this gradient in patients ventilated for COVID-19 with Acute Respiratory Distress Syndrome and in patients anaesthetised for surgery. Methods: On the occasion of an arterial blood gas sample, an extension in inspiratory pause was carried out either by recruitment manoeuvre or by extending the end-inspiratory pause to 10 s. The end-expired PCO₂ was measured (expiratory time: 4 s) after this manoeuvre (PACO₂) in comparison with the PetCO₂ measured by the monitor. We analysed 67 Δ(a-et)CO₂, Δ(a-A)CO₂ pairs for 7 patients in the COVID group and for 27 patients in the anaesthesia group. Results are expressed as mean ± standard deviation. Results: Prolongation of the inspiratory pause significantly reduced PaCO₂–PetCO₂ gradients from 11 ± 5.7 and 5.7 ± 3.4 mm Hg (p < 0.001) to PaCO₂–PACO₂ gradients of −1.2 ± 3.3 (p = 0.043) and −1.9 ± 3.3 mm Hg (p < 0.003) in the COVID and anaesthesia groups, respectively. In the COVID group, PACO₂ showed the lowest dispersion (−7 to +6 mm Hg) and better correlation with PaCO₂ (R² = 0.92). The PACO₂ had a sensitivity of 0.81 and a specificity of 0.93 for identifying hypercapnic patients (PaCO₂ > 50 mm Hg). Conclusions: Measuring end-tidal PCO₂ after prolonged inspiratory time reduced the PaCO₂–PetCO₂ gradient to the point of obtaining values close to PaCO₂. This measure identified hypercapnic patients in both intensive care and during anaesthesia.

Digitization and Analysis of Capnography Using Image Processing Technique

The study of carbon dioxide expiration is called capnometry. The graphical representation of capnometry is called capnography. There is a growing interest in the usage of capnography as the usage has expanded toward the study of metabolism, circulation, lung perfusion and diffusion, quality of spontaneous respiration, and patency of airways outside of its typical usage in the anesthetic and emergency medicine field. The parameters of the capnograph could be classified as carbon dioxide (CO₂) concentration and time points and coordinates, slopes angle, volumetric studies, and functional transformation of wave data. Up to date, there is no gold standard device for the calculation of the capnographic parameters. Capnography digitization using the image processing technique could serve as an option. From the algorithm we developed, eight identical breath waves were tested by four investigators. The values of the parameters chosen showed no significant difference between investigators. Although there were no significant differences between any of the parameters tested, there were a few related parameters that were not calculable. Further testing after refinement of the algorithm could be done. As more capnographic parameters are being derived and rediscovered by clinicians and researchers alike for both lung and non-lung-related diseases, there is a dire need for data analysis and interpretation. Although the proposed algorithm still needs minor refinements and further large-scale testing, we proposed that the digitization of the capnograph via image processing technique could serve as an intellectual option as it is fast, convenient, easy to use, and efficient.

On Analyzing Capnogram as a Novel Method for Screening COVID-19: A Review on Assessment Methods for COVID-19

In November 2019, the novel coronavirus disease COVID-19 was reported in Wuhan city, China, and was reported in other countries around the globe. COVID-19 is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Strategies such as contact tracing and a vaccination program have been imposed to keep COVID-19 under control. Furthermore, a fast, noninvasive and reliable testing device is needed urgently to detect COVID-19, so that contact can be isolated and ringfenced before the virus spreads. Although the reverse transcription polymerase chain reaction (RT-PCR) test is considered the gold standard method for the diagnosis of SARS-CoV-2 infection, this test presents some limitations which cause delays in detecting the disease. The antigen rapid test (ART) test, on the other hand, is faster and cheaper than PCR, but is less sensitive, and may limit SARS-CoV-2 detection. While other tests are being developed, accurate, noninvasive and easy-to-use testing tools are in high demand for the rapid and extensive diagnosis of the disease. Therefore, this paper reviews current diagnostic methods for COVID-19. Following this, we propose the use of expired carbon dioxide (CO2) as an early screening tool for SARS-CoV-2 infection. This system has already been developed and has been tested on asthmatic patients. It has been proven that expired CO2, also known as capnogram, can help differentiate between respiratory conditions and, therefore, could be used to detect SARS-CoV-2 infection, as it causes respiratory tract-related diseases.

The safety and efficacy of high-speed train transport for critical children: a retrospective propensity score matching cohort study

It is widely acknowledged that efficiency of pediatric critical care transport plays a vital role in treatment of critically-ill children. In developing countries, most critically-ill children were transported by ambulance, and a few by air, such as a helicopter or fixed airplane. High-speed train (HST) transport may be a potential choice for critically-ill children to a tertiary medical center for further therapy. This is a single-center, retrospective cohort study from June 01, 2016 to June 30, 2019. All the patients transported to the Pediatric Intensive Care Unit (PICU) of PLA general hospital were divided into two groups, HST group and ambulance group. The propensity score matching method was performed for the comparison between the two groups. Finally, a 2:1 patient matching was performed using the nearest-neighbor matching method without replacement. The primary outcome was hospital mortality. Secondary outcomes included duration of transport, transport cost, hospital stay, and hospitalization cost. A total of 509 critically-ill children were transported and admitted. Of them, 40 patients were transported by HST, and 469 by ambulance. The hospital mortality showed no difference between the two groups (p > 0.05). The transport distance in the HST group was longer than that in the ambulance group (1894.5 ± 907.09 vs. 902.66 ± 735.74, p < 0.001). However, compared to the HST group, the duration of transport time by ambulance was significantly longer (p < 0.001). No difference in vital signs, blood gas analysis, and critical illness score between groups at admission was noted (p > 0.05). There was no death during the transport. There was no difference between groups regarding the transport cost, hospital stays, and hospitalization cost (p > 0.05). High-quality tertiary medical centers are usually located in megacities. HST transport network for critically-ill children could be established to cover most regions of the country. Without increasing financial burden, HST medical transport can be a potentially promising option to improve the outcomes of critically-ill children in developing countries with developed HST network.

Clinical Trial Registration: This study was registered at http://www.chictr.org.cn/index.aspx (chiCTR.gov; Identifier: ChiCTR2000032306).

Can Non-Invasive Capnography and Integrated Pulmonary Index Contribute to Patient Monitoring in the Pediatric Emergency Department?

OBJECTIVES

Noninvasive capnography (NICG) devices can measure oxygen saturation, end-tidal carbon dioxide (EtCO2), respiratory rate, heart rate values and integrated pulmonary index (IPI). This study aimed to evaluate patients who were monitored using NICG for various indications in a pediatric emergency department and to determine its contribution to patient management in the pediatric emergency department (PED).

METHODS

In this study, children aged <18 years who had been monitored with a NICG at the PED in our university between August 2018-May 2019 were evaluated. Of them 48 patients' file records and monitored capnography parameters such as heart rate, respiratory rate, blood pressure, capillary refill time, Glasgow Coma Score, SpO2, EtCO2, IPI recorded in the forms were reviewed.

RESULTS

Patients most often presented to the emergency room due to seizures (35.4%), change in consciousness (22.9%), other neurological reasons (18.8%) with %50 were female. Seizure treatment(16.7%), circulatory-respiratory support(16.7%), and antiedema treatments(6.3%) were required for 39.5% patients as life-saving interventions, and 72.9% patients were hospitalized. Patients with low IPI(<8) values at the beginning and decreasing IPI (<8) measurements within monitoring period needed more life-saving treatments(p=0.005 and p=0.001, respectively). Low IPI values of the patients during monitoring showed a significant difference in the decision to be hospitalized(p=0.048).

CONCLUSIONS

The results of the present study indicate that monitoring with NICG in the pediatric emergency room can be an important early indicator in establishing clinical prediction. The study particularly points out that the IPI value can be a guide in decisions regarding life-saving treatment and hospitalization. Among the capnographic data of these patients who had a change in consciousness IPI values those measured at the beginning and within the monitorizarion period showed a significant correlation with low GCS (<8) (r=0.478, p=0.001 and r=0.456, p=0.02, respectively). Prospective comprehensive large scale studies are needed to examine the use of NICG and IPI in routine PED practice for various indications.

Use of capnography for prediction of obstruction severity in non-intubated COPD and asthma patients

BACKGROUND

Capnography waveform contains essential information regarding physiological characteristics of the airway and thus indicative of the level of airway obstruction. Our aim was to develop a capnography-based, point-of-care tool that can estimate the level of obstruction in patients with asthma and COPD.

METHODS

Two prospective observational studies conducted between September 2016 and May 2018 at Rabin Medical Center, Israel, included healthy, asthma and COPD patient groups. Each patient underwent spirometry test and continuous capnography, as part of, either methacholine challenge test for asthma diagnosis or bronchodilator reversibility test for asthma and COPD routine evaluation. Continuous capnography signal, divided into single breaths waveforms, were analyzed to identify waveform features, to create a predictive model for FEV1 using an artificial neural network. The gold standard for comparison was FEV1 measured with spirometry.

MEASUREMENTS AND MAIN RESULTS

Overall 160 patients analyzed. Model prediction included 32/88 waveform features and three demographic features (age, gender and height). The model showed excellent correlation with FEV1 (R = 0.84), R² achieved was 0.7 with mean square error of 0.13.

CONCLUSION

In this study we have developed a model to evaluate FEV1 in asthma and COPD patients. Using this model, as a point-of-care tool, we can evaluate the airway obstruction level without reliance on patient cooperation. Moreover, continuous FEV1 monitoring can identify disease fluctuations, response to treatment and guide therapy.

TRIAL REGISTRATION

clinical trials.gov, NCT02805114. Registered 17 June 2016, https://clinicaltrials.gov/ct2/show/NCT02805114.

Capillary blood gas in infants with bronchiolitis: Can end-tidal capnography replace it?

OBJECTIVES

To explore the predictive ability of capillary blood gas (CBG) pCO₂ for respiratory decompensation in infants aged ≤6 months with bronchiolitis admitted from the emergency department; to determine whether end-tidal CO₂ (etCO₂) capnography can serve as a less invasive substitute for CBG pCO₂.

STUDY DESIGN

This was a prospective cohort study of previously healthy infants aged ≤6 months admitted for bronchiolitis from the emergency department (ED). Initial CBG pCO₂ and etCO₂ capnography were obtained in the ED prior to inpatient admission. Simple logistic regression modeling was used to examine the associations of CBG pCO₂ and etCO₂ capnography with respiratory decompensation. Pearson's correlation measured the relationship between CBG pCO₂ and etCO₂ capnography.

RESULTS

Of 134 patients, 61 had respiratory decompensation. There was a significant association between CBG pCO₂ and respiratory decompensation (OR = 1.07, p = 0.003), even after outlying values were excluded (OR = 1.06, p = 0.005). End tidal CO₂ capnography was not significantly associated with decompensation (OR = 1.02, p = 0.17), even after outlying values were excluded (OR = 1.02, p = 0.24). There was a moderate correlation between etCO₂ capnography and CBG pCO₂ (r = 0.39, p < 0.001).

CONCLUSION

In infants with bronchiolitis, CBG pCO₂ provides an objective measure for predicting respiratory decompensation, and a single etCO₂ measurement should not replace its use.

Comparison of ETCO2 Value and Blood Gas PCO2 Value of Patients Receiving Non-invasive Mechanical Ventilation Treatment in Emergency Department

Capnography is the non-invasive measurement and graphic representation of the partial pressure of CO2 in expiration. Although there are many studies in the literature comparing the partial pressure of carbon dioxide (pCO2) and end-tidal CO2 (ETCO2) values in patients who underwent IMV (invasive mechanical ventilation), there are no studies showing their interchangeable applicability in patients who received NIMV (non-IMV). We aimed to evaluate whether the use of ETCO2 in the treatment process can replace pCO2 use in patients scheduled for NIMV treatment in the emergency department. Patients who applied to the emergency department with respiratory distress between March 2019 and January 2020, who were diagnosed with acute cardiogenic edema or acute chronic obstructive pulmonary disease (COPD) exacerbation, and who needed NIMV were included in the study. General characteristics of the patients and the pCO2 and ETCO2 values were measured in the blood gas 1 h after the NIMV application was started. 64.2% (99 patients) of the patients included in the study were male, and 35.8% (55 patients) were female. The mean age of the patients included in the study was 69.1 ± 12.2 years. The mean pCO2 values ​​were measured as 52.6 ± 13.2. The mean of ETCO2 values ​​measured simultaneously was 33.6 ± 10.1. There was a significant difference between the controlled pCO2 values ​​and ETCO2 values ​​at the first hour of NIMV treatment (Z: - 10.640, p < 0.001). The ETCO2 level was found to be different in our patients who received NIMV treatment, which could not be used instead of the pCO2 level.

Randomized Double-blind Trial of Intramuscular Droperidol, Ziprasidone, and Lorazepam for Acute Undifferentiated Agitation in the Emergency Department

BACKGROUND

The optimal agent to treat acute agitation in the emergency department (ED) has not been determined. The objective of this study was to compare the effectiveness and safety of intramuscular droperidol, ziprasidone, and lorazepam for acute agitation in the ED.

METHODS

This was a randomized, double-blind trial of ED patients with acute agitation requiring parenteral sedation. The study was conducted under exception from informed consent (21 CFR 50.24) from July 2004 to March 2005. Patients were randomized to receive 5 mg of droperidol, 10 mg of ziprasidone, 20 mg of ziprasidone, or 2 mg of lorazepam intramuscularly. We recorded Altered Mental Status Scale (AMSS) scores, nasal end-tidal carbon dioxide (ETCO₂ ), and pulse oximetry (SpO₂ ) at 0, 15, 30, 45, 60, 90, and 120 minutes as well as QTc durations and dysrhythmias. Respiratory depression was defined as a change in ETCO₂ consistent with respiratory depression or SpO₂  < 90%. The primary outcome was the proportion of patients adequately sedated (AMSS ≤ 0) at 15 minutes.

RESULTS

We enrolled 115 patients. Baseline AMSS scores were similar between groups. For the primary outcome, adequate sedation at 15 minutes, droperidol administration was effective in 16 of 25 (64%) patients, compared to seven of 28 (25%) for 10 mg of ziprasidone, 11 of 31 (35%) for 20 mg of ziprasidone, and nine of 31 (29%) for lorazepam. Pairwise comparisons revealed that droperidol was more effective that the other medications, with 39% (95% confidence interval [CI] = 3% to 54%) more compared to 20 mg of ziprasidone and 33% (95% CI = 8% to 58%) more compared to lorazepam. There was no significant difference between groups in need of additional rescue sedation. Numerically, respiratory depression was lower with droperidol (3/25 [12%]) compared to 10 mg of ziprasidone (10/28 [36%]), 20 mg of ziprasidone (12/31 [39%]), or lorazepam (15/31 [48%]). One patient receiving 20 mg of ziprasidone required intubation to manage an acute subdural hematoma. No patients had ventricular dysrhythmias. QTc durations were similar in all groups.

CONCLUSIONS

Droperidol was more effective than lorazepam or either dose of ziprasidone for the treatment of acute agitation in the ED and caused fewer episodes of respiratory depression.

Automatic classification of regular and irregular capnogram segments using time- and frequency-domain features: A machine learning-based approach

BACKGROUND

The quantitative features of a capnogram signal are important clinical metrics in assessing pulmonary function. However, these features should be quantified from the regular (artefact-free) segments of the capnogram waveform.

OBJECTIVE

This paper presents a machine learning-based approach for the automatic classification of regular and irregular capnogram segments.

METHODS

Herein, we proposed four time- and two frequency-domain features experimented with the support vector machine classifier through ten-fold cross-validation. MATLAB simulation was conducted on 100 regular and 100 irregular 15 s capnogram segments. Analysis of variance was performed to investigate the significance of the proposed features. Pearson's correlation was utilized to select the relatively most substantial ones, namely variance and the area under normalized magnitude spectrum. Classification performance, using these features, was evaluated against two feature sets in which either time- or frequency-domain features only were employed.

RESULTS

Results showed a classification accuracy of 86.5%, which outperformed the other cases by an average of 5.5%. The achieved specificity, sensitivity, and precision were 84%, 89% and 86.51%, respectively. The average execution time for feature extraction and classification per segment is only 36 ms.

CONCLUSION

The proposed approach can be integrated with capnography devices for real-time capnogram-based respiratory assessment. However, further research is recommended to enhance the classification performance.

A review of ventilation in adult out-of-hospital cardiac arrest

Out-of-hospital cardiac arrest continues to be a devastating condition despite advances in resuscitation care. Ensuring effective gas exchange must be weighed against the negative impact hyperventilation can have on cardiac physiology and survival. The goals of this narrative review are to evaluate the available evidence regarding the role of ventilation in out-of-hospital cardiac arrest resuscitation and to provide recommendations for future directions. Ensuring successful airway patency is fundamental for effective ventilation. The airway management approach should be based on professional skill level and the situation faced by rescuers. Evidence has explored the influence of different ventilation rates, tidal volumes, and strategies during out-of-hospital cardiac arrest; however, other modifiable factors affecting out-of-hospital cardiac arrest ventilation have limited supporting data. Researchers have begun to explore the impact of ventilation in adult out-of-hospital cardiac arrest outcomes, further stressing its importance in cardiac arrest resuscitation management. Capnography and thoracic impedance signals are used to measure ventilation rate, although these strategies have limitations. Existing technology fails to reliably measure real-time clinical ventilation data, thereby limiting the ability to investigate optimal ventilation management. An essential step in advancing cardiac arrest care will be to develop techniques to accurately and reliably measure ventilation parameters. These devices should allow for immediate feedback for out-of-hospital practitioners, in a similar way to chest compression feedback. Once developed, new strategies can be established to guide out-of-hospital personnel on optimal ventilation practices.

Development of a severity scoring system for acute haemorrhage in anaesthetized domestic cats: the CABSS score

OBJECTIVE

To determine whether physiological, haematological, biochemical or electrolyte variables can predict severe haemorrhage in cats.

STUDY DESIGN

Randomized crossover study whereby each cat underwent mild and severe haemorrhage, with a 2 month period between events.

ANIMALS

A group of six domestic cats aged 21 ± 1 months and weighing 4.9 ± 1.2 kg, mean ± standard deviation.

METHODS

Cats were anaesthetized (buprenorphine, alfaxalone, isoflurane in oxygen at a fixed end-tidal concentration of 1.7%) before the haemorrhage event. In total, 34 variables were measured twice (prehaemorrhage and posthaemorrhage). The difference and percent change for each variable were compared between haemorrhage events (paired t test). Significant variables were placed into 13 different ratios (posthaemorrhage value of one variable divided by a posthaemorrhage value of a second variable) and compared (paired t test), and Cohen's d (d) was calculated. Receiver operating characteristic curves were plotted and cut-off values for weak, moderate and strong indicators of severe haemorrhage were obtained.

RESULTS

The blood loss was 4.5 ± 1.1 mL kg^-1 and 26.8 ± 5.5 mL kg^-1 for mild and severe haemorrhage events, respectively. The most significant variables with large effect sizes were heart rate (HR), systolic arterial blood pressure (SAP), end-tidal carbon dioxide (Pe'CO₂), serum albumin, haematocrit and actual bicarbonate ion concentration [HCO₃^-(act)]. The most robust ratios were: 1) shock index (d = -2.8; HR:SAP); 2) HR:Pe'CO₂ (d = -2.9); 3) serum albumin: haematocrit (d = 1.5); and 4) HR:HCO₃^-(act) (d = -1.6). These ratios were included in the final proposed Cat Acute Bleeding Scoring System (CABSS).

CONCLUSIONS

and clinical relevance Cats subjected to mild and severe haemorrhage demonstrated statistically and clinically relevant changes whereby four ratios could be created to make up the CABSS. The ratios detected and quantified the presence of severe haemorrhage in anaesthetized cats.

Association of End-Tidal Carbon Dioxide Monitoring With Nurses' Confidence in Patient Readiness for Postanesthesia Discharge

PURPOSE

To determine if end-tidal carbon dioxide (etCO₂) value increased nurses' perceptions of confidence in patients' readiness for postanesthesia care unit (PACU) discharge.

DESIGN

Prospective, cross-sectional, comparative, one-group (pre-post) design.

METHODS

Nurses completed 2 assessments of confidence in readiness for discharge, before and after etCO₂ monitoring. Patient (discharge pain level, body mass index, sleep apnea history, and opioid use) and nurse factors were assessed. Analyses included descriptive and comparative statistics.

FINDINGS

Of 133 patients, mean (standard deviation) etCO₂ was 36.1 (5.7) mm Hg. Nurses' confidence in readiness for discharge differed before and after etCO₂ assessment. Confidence score decreased when etCO₂ was low (P = .003) or high (P = .005), compared with normal values. In linear regression, etCO₂ remained a factor in nurses' confidence in readiness for discharge (P < .001).

CONCLUSIONS

In a PACU, etCO₂ monitoring changed nurses' perceptions of confidence in patients' readiness for discharge.

Invasive mechanical ventilation in the emergency department

Emergency department (ED) lenght of stay of the patients requiring admission to the intensive care units has increased gradually in recent years. Mechanical ventilation is an integral part of critical care and mechanically ventilated patients have to be managed and monitored by emergency physicians for longer than expected in EDs. This early period of care has significant impact on the outcomes of these patients. Therefore, emergency physicians should have comprehensive knowledge of mechanical ventilation. This review will summarize the current literature of the basic concepts, appropriate clinical applications, monitoring parameters, components and mechanisms of mechanical ventilation in the ED.

Different strategies to initiate and maintain hyperventilation: their effect on continuous estimates of dynamic cerebral autoregulation

OBJECTIVE

Capnography is a key monitoring intervention in several neurologically vulnerable clinical states. Cerebral autoregulation (CA) describes the ability of the cerebrovascular system to maintain a near constant cerebral blood flow throughout fluctuations in systemic arterial blood pressure, with the partial pressure of arterial carbon dioxide known to directly influence CA. Previous work has demonstrated dysautoregulation lasting around 30 s prior to the anticipated augmentation of hyperventilation-associated hypocapnia. In order assess to potential benefit of hypocapnic interventions in an acute stroke setting, minimisation of dysregulation is paramount.

APPROACH

Hyperventilation strategies to induce and maintain hypocapnia were performed in 61 healthy participants, effects on temporal estimates of dynamic cerebral autoregulation (autoregulation index, ARI) were assessed to validate the most effective strategy for inducing and maintaining hypocapnia.

MAIN RESULTS

The extent of initial decrease was significantly smaller in the continuous metronome strategy compared to the delayed metronome and voluntary strategies (▵ARI 0.33  ±  1.18, 2.80  ±  3.33 and 3.69  ±  2.79 respectively, p   <  0.017).

SIGNIFICANCE

The use of a continuous metronome to induce hypocapnia rather than the sudden inception of an auditory stimulus appears to reduce the initial decrease in autoregulatory capacity seen in previous studies. Dysautoregulation can be minimised by continuous metronome use during hyperventilation-induced hypocapnia. This advancement in understanding of the behaviour of CA during hypocapnia permits safer delivery of CA targeted interventions, particularly in neurologically vulnerable patient populations.

Retrospective validation of a new volumetric capnography parameter for the exclusion of pulmonary embolism at the emergency department

Volumetric capnography might be used to exclude pulmonary embolism (PE) without the need for computed tomography pulmonary angiography. In a pilot study, a new parameter (CapNoPE) combining the amount of carbon dioxide exhaled per breath (carbon dioxide production (V_CO2)), the slope of phase 3 of the volumetric capnogram (slope 3) and respiratory rate (RR) showed promising diagnostic accuracy (where CapNoPE=(V_CO2×slope 3)/RR).

To retrospectively validate CapNoPE for the exclusion of PE, the volumetric capnograms of 205 subjects (68 with PE) were analysed, based on a large multicentre dataset of volumetric capnograms from subjects with suspected PE at the emergency department. The area under the curve (AUC) of the receiver operating characteristic (ROC) curve and diagnostic accuracy of the in-pilot established threshold (1.90 Pa·min) were calculated. CapNoPE was 1.56±0.97 Pa·min in subjects with PE versus 2.51±1.67 Pa·min in those without PE (p<0.001). The AUC of the ROC curve was 0.714 (95% CI 0.64–0.79). For the cut-off of ≥1.90 Pa·min, sensitivity was 64.7%, specificity was 59.9%, the negative predictive value was 77.4% and the positive predictive value was 44.4%.

The CapNoPE parameter is decreased in patients with PE but its diagnostic accuracy seems too low to use in clinical practice.

Retrospective validation in a large multicentre dataset shows that a novel volumetric capnography derived parameter (CapNoPE) is decreased in patients with PE but its diagnostic accuracy seems too low to use in clinical practicehttp://ow.ly/Ogpg30m0HuU