Utility of non-invasive monitoring of exhaled carbon dioxide and perfusion index in adult patients in the emergency department

BACKGROUND

Several noninvasive solutions are available for the assessment of patients at risk of deterioration. Capnography, in the form of end-tidal exhaled CO2 (ETCO2) and perfusion index (PI), could provide relevant information about patient prognosis. The aim of the present project was to determine the association of ETCO2 and PI with mortality of patients admitted to the emergency department (ED).

METHODS

Multicenter, prospective, cohort study of adult patients with acute disease who needed continuous monitoring in the ED. The study included two tertiary hospitals in Spain between October 2022 and June 2023. The primary outcome of the study was in-hospital mortality (all-cause). Demographics, vital signs, ETCO2 and PI were collected.

RESULTS

A total of 687 patients were included in the study. The in-hospital mortality rate was 6.8%. The median age was 79 years (IQR: 69-86), and 63.3% were males. The median ETCO2 value was 30 mmHg (26-35) in survivors and 23 mmHg (16-30) in nonsurvivors (p = 0.001). For the PI, the medians were 4.7% (2.8-8.1) for survivors and 2.5% (0.98-4-4) for nonsurvivors (p < 0.001). The model that presented the best AUC was age (odds ratio (OR): 1.02 (1.00-1.05)), the respiratory rate (OR: 1.06 (1.02-1.11)), and the PI (OR: 0.83 (0.75-0.91)), with a result of 0.840 (95% CI: 0.795-0.886); the model with the respiratory rate (OR: 1.05 (1.01-1.10)), the PI (OR: 0.84 (0.76-0.93)), and the ETCO2 (no statistically significant OR), with an AUC of 0.838 (95% CI: 0.787-0.889).

CONCLUSIONS

The present study showed that the PI and respiratory rate are independently associated with in-hospital mortality. Both the PI and ETCO2 are predictive parameters with improved prognostic performance compared with that of standard vital signs.

Monitoring persistent pulmonary hypertension of the newborn using the arterial to end tidal carbon dioxide gradient

Persistent pulmonary hypertension of the newborn (PPHN) can be monitored theoretically by the difference of the partial pressure of arterial (PaCO2) to end-tidal CO2 (EtCO2). We aimed to test the hypothesis that the PaCO2-EtCO2 gradient in infants with PPHN would be higher compared to infants without PPHN. Prospective, observational study of term-born ventilated infants with echocardiographically-confirmed PPHN with right-to-left shunting and term-born control infants without respiratory disease. The PaCO2-EtCO2 gradient was calculated as the difference between the PaCO2 measured from indwelling arterial sample lines and EtCO2 measured by continuous Microstream sidestream capnography. Twenty infants (9 with PPHN and 11 controls) were studied with a median (IQR) gestational age of 39.5 (38.7-40.4) weeks, a birthweight of 3.56 (3.15-3.93) kg and a birthweight z-score of 0.03 (- 0.91 to 1.08). The PaCO2-EtCO2 gradient was larger in the infants with PPHN compared to those without PPHN after adjusting for differences in the mean airway pressure and fraction of inspired oxygen (adjusted p = 0.037). In the infants with PPHN the median PaCO2-EtCO2 gradient decreased from 10.7 mmHg during the acute illness to 3.3 mmHg pre-extubation. The median difference in the gradient was significantly higher in infants with PPHN (6.2 mmHg) compared to infants without PPHN (-3.2 mmHg, p = 0.022). The PaCO2-EtCO2 gradient was higher in infants with PPHN compared to term born infants without PPHN and decreased over the first week of life in infants with PPHN. The gradient might be utilised to monitor the evolution and resolution of PPHN.

The utility of capnography in determining the risk of major cardiac adverse events in patients with atypical chest pain

INTRODUCTION

Various scoring systems have been developed to safely rule out the diagnosis of acute coronary syndrome. Furthermore, the efficacy of these scoring systems in predicting the risk of major adverse cardiac events (MACE) is debated. Our aim was to compare parameters such as Integrated Pulmonary Index (IPI) and End Tidal Carbon Dioxide (etCO2) measured in the emergency department with the HEART score in terms of its success in predicting the risk of major adverse cardiac events.

METHOD

Patients with atypical chest pain were registered for the study by the emergency room physician. The patients were investigated regarding gender, age, background characteristics, prognostic accuracy of etCO2, IPI, MACE, and HEART scores.

RESULTS

As a result of the analysis, higher HEART Score and lower etCO2 values were determined in the MACE group compared to the group without MACE. ROC analysis was performed to determine the power of IPI, HEART Score, and etCO2 to predict MACE. The findings revealed that IPI significantly predicted MACE with an AUC value of 0.737.

CONCLUSION

In our study, although the highest sensitivity values in determining the risk of 30-day MACE belonged to the HEART score, etCO2 and IPI might be other parameters that could be used to determine the risk of 30-day MACE.

Indirect cardiac output assessment in a swine pediatric acute respiratory distress syndrome model

PURPOSE

To investigate the correlation between volume of carbon dioxide elimination (V̇CO2) and end-tidal carbon dioxide (PETCO2) with cardiac output (CO) in a swine pediatric acute respiratory distress syndrome (ARDS) model.

METHODS

Respiratory and hemodynamic variables were collected from twenty-six mechanically ventilated juvenile pigs under general anesthesia before and after inducing ARDS, using oleic acid infusion.

RESULTS

Prior to ARDS induction, mean (SD) CO, V̇CO2, PETCO2, and dead space to tidal volume ratio (Vd/Vt) were 4.16 (1.10) L/min, 103.69 (18.06) ml/min, 40.72 (3.88) mmHg and 0.25 (0.09) respectively. Partial correlation coefficients between average CO, V̇CO2, and PETCO2 were 0.44 (95% confidence interval: 0.18-0.69) and 0.50 (0.18-0.74), respectively. After ARDS induction, mean CO, V̇CO2, PETCO2, and Vd/Vt were 3.33 (0.97) L/min, 113.71 (22.97) ml/min, 50.17 (9.73) mmHg and 0.40 (0.08). Partial correlations between CO and V̇CO2 was 0.01 (-0.31 to 0.37) and between CO and PETCO2 was 0.35 (-0.002 to 0.65).

CONCLUSION

ARDS may limit the utility of volumetric capnography to monitor CO.

Prehospital ETCO2 is predictive of death in intubated and non-intubated patients

BACKGROUND

Prehospital identification of shock in trauma patients lacks accurate markers. Low end tidal carbon dioxide (ETCO2) correlates with mortality in intubated patients. The predictive value of ETCO2 obtained by nasal capnography cannula (NCC) is unknown. We hypothesized that prehospital ETCO2 values obtained by NCC and in-line ventilator circuit (ILVC) would be predictive of mortality.

METHODS

This was a prospective, observational, multicenter study. ETCO2 values were collected by a NCC or through ILVC. AUROCs were compared with prehospital systolic blood pressure (SBP) and shock index (SI). The Youden index defined optimal cutoffs.

RESULTS

Of 550 enrolled patients, 487 (88.5%) had ETCO2 measured through an NCC. Median age was 37 (27-52) years; 76.5% were male; median ISS was 13 (5-22). Mortality was 10.4%. Minimum prehospital ETCO2 significantly predicted mortality with an AUROC of 0.76 (CI 0.69-0.84; Youden index ​= ​22 ​mmHg), outperforming SBP with an AUROC of 0.68; (CI 0.62-0.74, p ​= ​0.04) and shock index with an AUROC of 0.67 (CI 0.59-0.74, p ​= ​0.03).

CONCLUSION

Prehospital ETCO2 measured by non-invasive NCC or ILVC may be predictive of mortality in injured patients.

Capnography-Assisted Learned, Monitored (CALM) breathing therapy for dysfunctional breathing in COPD: A bridge to pulmonary rehabilitation

BACKGROUND

Although dyspnea is a primary symptom of chronic obstructive pulmonary disease (COPD), its treatment is suboptimal. In both COPD and acute anxiety, breathing patterns become dysregulated, contributing to abnormal CO2, dyspnea, and inefficient recovery from breathing challenges. While pulmonary rehabilitation (PR) improves dyspnea, only 1-2% of patients access it. Individuals with anxiety who use PR have worse outcomes.

METHODS

We present the protocol of a randomized controlled trial designed to determine the feasibility and acceptability of a new, four-week mind-body intervention that we developed, called "Capnography-Assisted Learned, Monitored (CALM) Breathing," as an adjunct to PR. Eligible participants are randomized in a 1:1 ratio to either CALM Breathing program or Usual Care. CALM Breathing consists of 10 core, slow breathing exercises combined with real time biofeedback (of end-tidal CO2, respiratory rate, and airflow) and motivational interviewing. CALM Breathing promotes self-regulated breathing, linking CO2 changes to dyspnea and anxiety symptoms and targeting breathing efficiency and self-efficacy in COPD. Participants are randomized to CALM Breathing or a Usual Care control group.

RESULTS

Primary outcomes include feasibility and acceptability metrics of recruitment efficiency, participant retention, intervention adherence and fidelity, PR facilitation, patient satisfaction, and favorable themes from interviews. Secondary outcomes include breathing biomarkers, symptoms, health-related quality of life, six-minute walk distance, lung function, mood, physical activity, and PR utilization and engagement.

CONCLUSION

By disrupting the cycle of dyspnea and anxiety, and providing a needed bridge to PR, CALM Breathing may address a substantive gap in healthcare and optimize treatment for patients with COPD.

Effects of apparatus dead space on volumetric capnograms in neonates with healthy lungs: a simulation study

BACKGROUND

Volumetric capnography in healthy ventilated neonates showed deformed waveforms, which are supposedly due to technological limitations of flow and carbon dioxide sensors.

AIMS

This bench study analyzed the role of apparatus dead space on the shape of capnograms in simulated neonates with healthy lungs.

METHODS

We simulated mechanical breaths in neonates of 2, 2.5, and 3 kg of body weight using a neonatal volumetric capnography simulator. The simulator was fed by a fixed amount of carbon dioxide of 6 mL/kg/min. Such simulator was ventilated in a volume control mode using fixed ventilatory settings with a tidal volume of 8 mL/kg and respiratory rates of 40, 35, and 30 breaths per minute for the 2, 2.5 and 3 kg neonates, respectively. We tested the above baseline ventilation with and without an additional apparatus dead space of 4 mL.

RESULTS

Simulations showed that adding the apparatus dead space to baseline ventilation increased the amount of re-inhaled carbon dioxide in all neonates: 0.16 ± 0.01 to 0.32 ± 0.03 mL (2 kg), 0.14 ± 0.02 to 0.39 ± 0.05 mL (2.5 kg), and 0.13 ± 0.01 to 0.36 ± 0.05 mL (3 kg); (p < .001). Apparatus dead space was computed as part of the airway dead space, and therefore, the ratio of airway dead space to tidal volume increased from 0.51 ± 0.04 to 0.68 ± 0.06, from 0.43 ± 0.04 to 0.62 ± 0.01 and from 0.38 ± 0.01 to 0.60 ± 0.02 in the 2, 2.5 and 3 kg simulated neonates, respectively (p < .001). Compared to baseline ventilation, adding apparatus dead space decreased the ratio of the volume of phase III to VT size from 31% to 11% (2 kg), from 40% to 16% (2.5 kg) and from 50% to 18% (3 kg); (p < .001).

CONCLUSIONS

The addition of a small apparatus dead space artificially deformed the volumetric capnograms in simulated neonates with healthy lungs.

Capnography-An Essential Monitor, Everywhere: A Narrative Review

Capnography is now recognized as an indispensable patient safety monitor. Evidence suggests that its use improves outcomes in operating rooms, intensive care units, and emergency departments, as well as in sedation suites, in postanesthesia recovery units, and on general postsurgical wards. Capnography can accurately and rapidly detect respiratory, circulatory, and metabolic derangements. In addition to being useful for diagnosing and managing esophageal intubation, capnography provides crucial information when used for monitoring airway patency and hypoventilation in patients without instrumented airways. Despite its ubiquitous use in high-income-country operating rooms, deaths from esophageal intubations continue to occur in these contexts due to incorrect use or interpretation of capnography. National and international society guidelines on airway management mandate capnography's use during intubations across all hospital areas, and recommend it when ventilation may be impaired, such as during procedural sedation. Nevertheless, capnography's use across high-income-country intensive care units, emergency departments, and postanesthesia recovery units remains inconsistent. While capnography is universally used in high-income-country operating rooms, it remains largely unavailable to anesthesia providers in low- and middle-income countries. This lack of access to capnography likely contributes to more frequent and serious airway events and higher rates of perioperative mortality in low- and middle-income countries. New capnography equipment, which overcomes cost and context barriers, has recently been developed. Increasing access to capnography in low- and middle-income countries must occur to improve patient outcomes and expand universal health care. It is time to extend capnography's safety benefits to all patients, everywhere.

The Capnography Project

Capnography is an essential tool used in the monitoring of patients during anesthesia and in critical care which, while required in most high-income countries, is unavailable in many low- and middle-income countries. Launched in 2020, the Smile Train-Lifebox Capnography Project aimed to find a "capnography solution" for resource-poor settings. The project was specifically interested in a capnography device that would meet the needs of the Smile Train partner hospitals to help monitor children requiring airway or cleft surgery. Project advisory and technical groups were formed and included representation from anesthesia practitioners from a balanced representation from all level of income countries, technical experts in capnography, and representatives from the Global Capnography Project (GCAP), the University of California at San Francisco Center for Health Equity in Surgery & Anesthesia (CHESA), and the World Federation of Societies of Anaesthesiologists (WFSA). Built upon the WFSA minimum capnometer specifications, a human centered design approach was used to develop a Target Product Profile. Seven manufacturers submitted 13 devices for consideration and 3 devices were selected for the testing phase. Each of these devices was evaluated for build quality, and clinical and usability performance. Based on the findings from the overall testing process, a combined capnography and pulse oximetry device by Zug Medical Systems was chosen. To accompany the new Smile Train-Lifebox capnograph, an international team of experienced anesthesiologists and educators came together to develop the necessary education materials. These materials were piloted in Ethiopia, subsequently modified, and endorsed by the education team. The device is now ready for distribution, with the accompanying education package, to the Smile Train network and beyond. In addition, a study is being planned to measure the impact of capnography introduction into operating rooms in resource-constrained settings.

Incidence of postoperative opioid-induced respiratory depression episodes in patients on room air or supplemental oxygen: a post-hoc analysis of the PRODIGY trial

BACKGROUND

Supplemental oxygen (SO) potentiates opioid-induced respiratory depression (OIRD) in experiments on healthy volunteers. Our objective was to examine the relationship between SO and OIRD in patients on surgical units.

METHODS

This post-hoc analysis utilized a portion of the observational PRediction of Opioid-induced respiratory Depression In patients monitored by capnoGraphY (PRODIGY) trial dataset (202 patients, two trial sites), which involved blinded continuous pulse oximetry and capnography monitoring of postsurgical patients on surgical units. OIRD incidence was determined for patients receiving room air (RA), intermittent SO, or continuous SO. Generalized estimating equation (GEE) models, with a Poisson distribution, a log-link function and time of exposure as offset, were used to compare the incidence of OIRD when patients were receiving SO vs RA.

RESULTS

Within the analysis cohort, 74 patients were always on RA, 88 on intermittent and 40 on continuous SO. Compared with when on RA, when receiving SO patients had a higher risk for all OIRD episodes (incidence rate ratio [IRR] 2.7, 95% confidence interval [CI] 1.4-5.1), apnea episodes (IRR 2.8, 95% CI 1.5-5.2), and bradypnea episodes (IRR 3.0, 95% CI 1.2-7.9). Patients with high or intermediate PRODIGY scores had higher IRRs of OIRD episodes when receiving SO, compared with RA (IRR 4.5, 95% CI 2.2-9.6 and IRR 2.3, 95% CI 1.1-4.9, for high and intermediate scores, respectively).

CONCLUSIONS

Despite oxygen desaturation events not differing between SO and RA, SO may clinically promote OIRD. Clinicians should be aware that postoperative patients receiving SO therapy remain at increased risk for apnea and bradypnea.

TRIAL REGISTRATION

Clinicaltrials.gov: NCT02811302, registered June 23, 2016.

Single-FiO2 lung modelling with machine learning: a computer simulation incorporating volumetric capnography

We investigated whether machine learning (ML) analysis of ICU monitoring data incorporating volumetric capnography measurements of mean alveolar PCO2 can partition venous admixture (VenAd) into its shunt and low V/Q components without manipulating the inspired oxygen fraction (FiO2). From a 21-compartment ventilation / perfusion (V/Q) model of pulmonary blood flow we generated blood gas and mean alveolar PCO2 data in simulated scenarios with shunt values from 7.3% to 36.5% and a range of FiO2 settings, indirect calorimetry and cardiac output measurements and acid- base and hemoglobin oxygen affinity conditions. A 'deep learning' ML application, trained and validated solely on single FiO2 bedside monitoring data from 14,736 scenarios, then recovered shunt values in 500 test scenarios with true shunt values 'held back'. ML shunt estimates versus true values (n = 500) produced a linear regression model with slope = 0.987, intercept = -0.001 and R2 = 0.999. Kernel density estimate and error plots confirmed close agreement. With corresponding VenAd values calculated from the same bedside data, low V/Q flow can be reported as VenAd-shunt. ML analysis of blood gas, indirect calorimetry, volumetric capnography and cardiac output measurements can quantify pulmonary oxygenation deficits as percentage shunt flow (V/Q = 0) versus percentage low V/Q flow (V/Q > 0). High fidelity reports are possible from analysis of data collected solely at the operating FiO2.

Deep learning classification of capnography waveforms: secondary analysis of the PRODIGY study

Capnography monitors trigger high priority 'no breath' alarms when CO2 measurements do not exceed a given threshold over a specified time-period. False alarms occur when the underlying breathing pattern is stable, but the alarm is triggered when the CO2 value reduces even slightly below the threshold. True 'no breath' events can be falsely classified as breathing if waveform artifact causes an aberrant spike in CO2 values above the threshold. The aim of this study was to determine the accuracy of a deep learning approach to classifying segments of capnography waveforms as either 'breath' or 'no breath'. A post hoc secondary analysis of data from 9 North American sites included in the PRediction of Opioid-induced Respiratory Depression In Patients Monitored by capnoGraphY (PRODIGY) study was conducted. We used a convolutional neural network to classify 15 s capnography waveform segments drawn from a random sample of 400 participants. Loss was calculated over batches of 32 using the binary cross-entropy loss function with weights updated using the Adam optimizer. Internal-external validation was performed by iteratively fitting the model using data from all but one hospital and then assessing its performance in the remaining hospital. The labelled dataset consisted of 10,391 capnography waveform segments. The neural network's accuracy was 0.97, precision was 0.97 and recall was 0.96. Performance was consistent across hospitals in internal-external validation. The neural network could reduce false capnography alarms. Further research is needed to compare the frequency of alarms derived from the neural network with the standard approach.

Low-Order Mechanistic Models for Volumetric and Temporal Capnography: Development, Validation, and Application

OBJECTIVE

Develop low-order mechanistic models accounting quantitatively for, and identifiable from, the capnogram - the CO 2 concentration in exhaled breath, recorded over time (Tcap) or exhaled volume (Vcap).

METHODS

The airflow model's single "alveolar" compartment has compliance and inertance, and feeds a resistive unperfused airway comprising a laminar-flow region followed by a turbulent-mixing region. The gas-mixing model tracks mixing-region CO 2 concentration, fitted breath-by-breath to the measured capnogram, yielding estimates of model parameters that characterize the capnogram.

RESULTS

For the 17 examined records (310 breaths) of airflow, airway pressure and Tcap from ventilated adult patients, the models fit closely (mean rmse 1% of end-tidal CO 2 concentration on Vcap; 1.7% on Tcap). The associated parameters (4 for Vcap, 5 for Tcap) for each exhalation, and airflow parameters for the corresponding forced inhalation, are robustly estimated, and consonant with literature values. The models also allow, using Tcap alone, estimation of the entire exhaled airflow waveform to within a scaling. This suggests new Tcap-based tests, analogous to spirometry but with normal breathing, for discriminating chronic obstructive pulmonary disease (COPD) from congestive heart failure (CHF). A version trained on 15 exhalations from each of 24 COPD/24 CHF Tcap records from one hospital, then tested 100 times with 15 random exhalations from each of 27 COPD/31 CHF Tcap records at another, gave mean accuracy 80.6% (stdev 2.1%). Another version, tested on 29 COPD/32 CHF, yielded AUROC 0.84.

CONCLUSION

Our mechanistic models closely fit Tcap and Vcap measurements, and yield subject-specific parameter estimates.

SIGNIFICANCE

This can inform cardiorespiratory care.

Closed-Loop ventilation using sidestream versus mainstream capnography for automated adjustments of minute ventilation-A randomized clinical trial in cardiac surgery patients

BACKGROUND

INTELLiVENT-Adaptive Support Ventilation (ASV) is a closed-loop ventilation mode that uses capnography to adjust tidal volume (VT) and respiratory rate according to a user-set end-tidal CO2 (etCO2) target range. We compared sidestream versus mainstream capnography with this ventilation mode with respect to the quality of breathing in patients after cardiac surgery.

METHODS

Single-center, single-blinded, non-inferiority, randomized clinical trial in adult patients scheduled for elective cardiac surgery that were expected to receive at least two hours of postoperative ventilation in the ICU. Patients were randomized 1:1 to closed-loop ventilation with sidestream or mainstream capnography. Each breath was classified into a zone based on the measured VT, maximum airway pressure, etCO2 and pulse oximetry. The primary outcome was the proportion of breaths spent in a predefined 'optimal' zone of ventilation during the first three hours of postoperative ventilation, with a non-inferiority margin for the difference in the proportions set at -20%. Secondary endpoints included the proportion of breaths in predefined 'acceptable' and 'critical' zones of ventilation, and the proportion of breaths with hypoxemia.

RESULTS

Of 80 randomized subjects, 78 were included in the intention-to-treat analysis. We could not confirm the non-inferiority of closed-loop ventilation using sidestream with respect to the proportion of breaths in the 'optimal' zone (mean ratio 0.87 [0.77 to ∞]; P = 0.116 for non-inferiority). The proportion of breaths with hypoxemia was higher in the sidestream capnography group versus the mainstream capnography group.

CONCLUSIONS

We could not confirm that INTELLiVENT-ASV using sidestream capnography is non-inferior to INTELLiVENT-ASV using mainstream capnography with respect to the quality of breathing in subjects receiving postoperative ventilation after cardiac surgery.

TRIAL REGISTRATION

NCT04599491 (clinicaltrials.gov).

Clinical tests for confirming tracheal intubation or excluding oesophageal intubation: a diagnostic test accuracy systematic review and meta-analysis

Unrecognised oesophageal intubation causes preventable serious harm to patients undergoing tracheal intubation. When capnography is unavailable or doubted, clinicians still use clinical findings to confirm tracheal intubation, or exclude oesophageal intubation, and false reassurance from clinical examination is a recurring theme in fatal cases of unrecognised oesophageal intubation. We conducted a systematic review and meta-analysis of the diagnostic accuracy of five clinical examination tests and the oesophageal detector device when used to confirm tracheal intubation. We searched four databases for studies reporting index clinical tests against a reference standard, from inception to 28 February 2023. We included 49 studies involving 10,654 participants. Methodological quality was overall moderate to high. We looked at misting (three studies, 115 participants); lung auscultation (three studies, 217 participants); combined lung and epigastric auscultation (four studies, 506 participants); the oesophageal detector device (25 studies, 3024 participants); 'hang-up' (two non-human studies); and chest rise (one non-human study). The reference standards used were capnography (22 studies); direct vision (10 studies); and bronchoscopy (three studies). When used to confirm tracheal intubation, misting has a false positive rate (95%CI) of 0.69 (0.43-0.87); lung auscultation 0.14 (0.08-0.23); five-point auscultation 0.18 (0.08-0.36); and the oesophageal detector device 0.05 (0.02-0.09). Tests to exclude events that invariably lead to severe damage or death must have a negligible false positive rate. Misting or auscultation have too high a false positive rate to reliably exclude oesophageal intubation and there is insufficient evidence to support the use of 'hang-up' or chest rise. The oesophageal detector device may be considered where other more reliable means are not available, though waveform capnography remains the reference standard for confirmation of tracheal intubation.

Volumetric capnography and return of spontaneous circulation in an experimental model of pediatric asphyxial cardiac arrest

A secondary analysis of a randomized study was performed to study the relationship between volumetric capnography (VCAP) and arterial CO2 partial pressure (PCO2) during cardiopulmonary resuscitation (CPR) and to analyze the ability of these parameters to predict the return of spontaneous circulation (ROSC) in a pediatric animal model of asphyxial cardiac arrest (CA). Asphyxial CA was induced by sedation, muscle relaxation and extubation. CPR was started 2 min after CA occurred. Airway management was performed with early endotracheal intubation or bag-mask ventilation, according to randomization group. CPR was continued until ROSC or 24 min of resuscitation. End-tidal carbon dioxide (EtCO2), CO2 production (VCO2), and EtCO2/VCO2/kg ratio were continuously recorded. Seventy-nine piglets were included, 26 (32.9%) of whom achieved ROSC. EtCO2 was the best predictor of ROSC (AUC 0.72, p < 0.01 and optimal cutoff point of 21.6 mmHg). No statistical differences were obtained regarding VCO2, VCO2/kg and EtCO2/VCO2/kg ratios. VCO2 and VCO2/kg showed an inverse correlation with PCO2, with a higher correlation coefficient as resuscitation progressed. EtCO2 also had an inverse correlation with PCO2 from minute 18 to 24 of resuscitation. Our findings suggest that EtCO2 is the best VCAP-derived parameter for predicting ROSC. EtCO2 and VCO2 showed an inverse correlation with PCO2. Therefore, these parameters are not adequate to measure ventilation during CPR.

Technical validation of the EMMA capnometer under hyperbaric conditions

INTRODUCTION

End-tidal carbon dioxide (ETCO2) monitoring is essential for monitoring intubated critical care patients, yet its use in hyperbaric environments can be problematic. We postulated that the EMMA mainstream capnometer may function accurately under hyperbaric conditions.

METHODS

Stage 1. The EMMA mainstream capnometer was tested at 101 kPa against a reference side-stream capnometer, Philips IntelliVue M3015B microstream, using 10 customised reference gases of various carbon dioxide (CO₂) concentrations (2.47%-8.09%, or 18.5-60.7 mmHg at 101 kPa) in either air or oxygen. Stage 2. The functionality and accuracy of the EMMA capnometer was tested under hyperbaric conditions, 121-281 kPa, using the same test gases.

RESULTS

At 101 kPa, the EMMA capnometer measured CO₂ at levels lower than expected (mean of differences = -2.5 mmHg (95% CI -2.1 to -2.9, P < 0.001)). The Philips capnometer measured CO₂ more closely to expected CO₂ (mean of differences = -1.1 mmHg (95% CI -0.69 to -1.4, P < 0.001). Both devices demonstrated a significant linear relationship with expected CO₂. The EMMA capnometer functioned up to the maximum test pressure (281 kPa). The device over-read CO₂ measurements at pressures > 141 kPa. Although variance increased at pressures in the therapeutic range for hyperbaric treatments, a significant linear relationship between expected and EMMA measured CO₂ was demonstrated. The EMMA capnometer tolerated pressures to 281 kPa, but its display was limited to CO₂ < 99 mmHg.

CONCLUSIONS

This study validated EMMA capnometer function to 281 kPa in the hyperbaric environment. The device over-read CO₂ measurements at pressures >141 kPa, however there was a linear relationship between expected and measured CO₂. The EMMA capnometer may be clinically useful for monitoring expired CO₂ in patients undergoing hyperbaric oxygen treatment.

Nocturnal respiratory abnormalities among ward-level postoperative patients as detected by the Capnostream 20p monitor: A blinded observational study

PURPOSE

This prospective observational study aimed to establish the frequency of postoperative nocturnal respiratory abnormalities among patients undergoing major surgery who received ward-level care. These abnormalities may have implications for postoperative pulmonary complications (PPCs).

METHODS

Eligible patients underwent blinded noninvasive continuous capnography with pulse oximetry using the Capnostream™ 20p monitor over the first postoperative night. All patients received oxygen supplementation and patient-controlled opioid analgesia. The primary outcome was the number of prolonged apnea events (PAEs), defined as end-tidal carbon dioxide (EtCO2) ≤5 mmHg for 30-120 seconds or EtCO2 ≤5 mmHg for >120 seconds with oxygen saturation (SpO2) <85%. Secondary outcomes were the proportion of recorded time that physiological indices were aberrant, including the apnea index (AI), oxygen desaturation index (ODI), integrated pulmonary index (IPI), and SpO2. Exploratory analysis was conducted to assess the associations between PAEs, PPCs, and pre-defined factors.

RESULTS

Among 125 patients who had sufficient data for analysis, a total of 1800 PAEs occurred in 67 (53.4%) patients. The highest quartile accounted for 89.1% of all events. Amongst patients who experienced any PAEs, the median (IQR) number of PAE/patient was four (2-12). As proportions of recorded time (median (IQR)), AI, ODI, and IPI were aberrant for 12.4% (0-43.2%), 19.1% (2.0-57.1%), and 11.5% (3.1-33.3%) respectively. Only age, ARISCAT, and opioid consumption/kg were associated with PPCs.

CONCLUSIONS

PAE and aberrant indices were frequently detected on the first postoperative night. However, they did not correlate with PPCs. Future research should investigate the significance of detected aberrations.

Continuous Monitoring Detected Respiratory Depressive Episodes in Proximity to Adverse Respiratory Events During the PRODIGY Trial

PURPOSE

The PRediction of Opioid-induced respiratory Depression In patients monitored by capnoGraphY (PRODIGY) trial was a multicenter prospective trial conducted to develop a risk prediction score for opioid-induced respiratory depressive (OIRD) episodes. Several subjects in the PRODIGY trial developed critical respiratory depressive events, which were qualified as reportable adverse events (AEs). In this study, we determine whether those patients also had an episode of OIRD as detected by continuous capnography and pulse oximetry leading up to the critical clinical event.

METHODS

Blinded capnography and pulse oximetry data from PRODIGY patients who had critical respiratory depressive AE were reviewed. The occurrence and timing of OIRD episodes were recorded in relationship to the AE.

RESULTS

Of the 1335 subjects in PRODIGY, 7 patients had 8 reportable pulmonary AE and 187 OIRDs (150 apnea episodes, 14 bradypnea episodes, 23 hypoxic episodes) with median 12 (5-19.5) OIRDs per patient. Five patients were monitored before the AE, and multiple preceding OIRD episodes were detected. One patient had 2 AE, the first (hypoxemia) was recognized upon application of pulse oximetry. This patient subsequently had multiple OIRDs until the second AE occurred (somnolence requiring naloxone administration). Another patient's AE (hypotension and bradypnea) was recognized upon monitor application and subsequently had many OIRD episodes.

CONCLUSIONS

In the PRODIGY trial, patients who had a pulmonary AE had multiple preceding OIRDs detected by continuous capnography and pulse oximetry. When monitoring was initiated before the AE, numerous OIRDs, mostly apneic episodes preceded AE, suggesting continuous monitoring of both ventilation and oxygenation may allow for early detection and possible prediction of future clinical decompensation.

Respiratory monitoring of nonintubated patients in nonoperating room settings: old and new technologies

PURPOSE OF REVIEW

Postoperative mortality in the 30 days after surgery remains disturbingly high. Inadequate, intermittent and incomplete monitoring of vital signs in the nonoperating room environment is common practice. The rise of nonoperating room anaesthesia and sedation outside the operating room has highlighted the need to develop new and robust methods of portable continuous respiratory monitoring. This review provides a summary of old and new technologies in this environment.

RECENT FINDINGS

Technical advances have made possible the utilization of established monitoring to extrapolate respiratory rate, the increased availability and user friendliness of side stream capnography and the advent of other innovative systems. The use of aggregate signals wherein different modalities compensate for individual shortcomings seem to provide a reliable and artefact-free system.

SUMMARY

Respiratory monitoring is required in several situations and patient categories outside the operating room. The chosen modality must be able to detect respiratory compromise in a timely and accurate manner. Combing several modalities in a nonobtrusive, nontethered system and having an integrated output seems to give a reliable and responsive signal.

VOLUMETRIC CAPNOGRAPHY FOR RESPIRATORY MONITORING OF PATIENTS DURING ROUTINE COLONOSCOPY WITH ROOM-AIR AND CARBON DIOXIDE INSUFFLATION

BACKGROUND

Capnography and carbon dioxide (CO2) insufflation during gastrointestinal endoscopy under sedation are associated with safety and comfort improvements, respectively. Capnography can provide early detection of apnea and hypoxemia, whereas CO2 insufflation causes lower periprocedural discomfort. This is the first study to report the application of volumetric capnography in colonoscopy.

OBJECTIVE

This study aimed to evaluate the use of volumetric capnography with room air (RA) and CO2 insufflation during routine colonoscopy.

METHODS

In this prospective cohort study, 101 patients who underwent routine colonoscopy under sedation with volumetric capnography monitoring were included. Insufflation with RA was used to distend the intestinal lumen in group 1 (n=51), while group 2 (n=50) used CO2 insufflation. The primary endpoints were episodes of hypoxia, alveolar hypoventilation, and end-tidal CO2 (EtCO2). The secondary endpoints were tidal volume per minute, consumption of sedation medications, and post-procedure pain using the Gloucester modified pain scale.

RESULTS

The number of episodes of hypoxia (SpO2<90%) was similar between the groups: four episodes in Group 1 and two episodes in Group 2. The duration of hypoxia was significantly longer in group 2 (P=0.02). Hypoalveolar ventilation (EtCO2) occurred more frequently in Group 2 than in Group 1 (27 vs 18 episodes, P=0.05). Regarding EtCO2, Group 2 showed higher values in cecal evaluation (28.94±4.68 mmHg vs 26.65±6.12 mmHg, P=0.04). Regarding tidal volume per minute, Group 2 had significantly lower values at the cecal interval compared to Group 1 (2027.53±2818.89 vs 970.88±1840.25 L/min, P=0.009). No episodes of hypercapnia (EtCO2 > 60 mmHg) occurred during the study. There was no difference in the consumption of sedation medications between the groups. Immediately after colonoscopy, Group 2 reported significantly less pain than Group 1 (P=0.05).

CONCLUSION

In our study, volumetric capnography during colonoscopy was feasible and effective for monitoring ventilatory parameters and detecting respiratory complications. CO2 insufflation was safe and associated with less pain immediately after colonoscopy.

CapNet: A Deep Learning-based Framework for Estimation of Capnograph Signal from PPG

Ambulatory respiration signal extraction system is required to maintain continuous surveillance of a patient with respiratory deficiency. The capnograph signal has received a lot of attention in recent years as a valuable indicator of respiratory conditions. However, the typical capnograph signal extraction method is quite expensive and also unpleasant to the patient due to the involvement of a nasal cannula. With the advent of wearable sensor technology, there has been significant research on the use of photoplethysmogram (PPG) signals as a less expensive alternative to extract respiratory information. In this paper, we propose CapNet, a novel deep learning-based framework which takes the regular PPG signal as input, and estimates the capnograph signal as output. Training, validation and testing of the proposed networks in CapNet is done using the IEEE TMBE Respiratory Rate Benchmark dataset by utilizing reference capnograph respiration signals. With a lower MSE and higher cross-correlation values, CapNet outperforms two traditional signal processing algorithms and another recently proposed deep neural network, RespNet. The proposed framework expectantly can be implementable and feasible for constant supervising of patients undergoing respiratory ailments.

Assessment of a new volumetric capnography-derived parameter to reflect compression quality and to predict return of spontaneous circulation during cardiopulmonary resuscitation in a porcine model

We aimed to evaluate a volumetric capnography (Vcap)-derived parameter, the volume of CO2 eliminated per minute and per kg body weight (VCO2/kg), as an indicator of the quality of chest compression (CC) and to predict the return to spontaneous circulation (ROSC) under stable ventilation status. Twelve male domestic pigs were utilized for the randomized crossover study. After 4 min of untreated ventricular fibrillation (VF), mechanical cardiopulmonary resuscitation and ventilation were administered. Following 5-min washout periods, each animal underwent two sessions of experiments: three types of CC quality for 5 min stages in the first session, followed by advanced life support, consecutively in two sessions. Different CC quality had a significant effect on the partial pressure of end-tidal carbon dioxide (PetCO2), VCO2/kg, aortic pressure (mean), aortic systolic pressure, aortic diastolic pressure, right atrial pressure (mean), and carotid blood flow (P < 0.05). With the improvement in CC quality, the values of PetCO2 and VCO2/kg also increased, and the difference between the groups was statistically significant (P < 0.05). The Spearman rank test revealed a significant correlation between the Vcap-derived parameters and hemodynamics. PetCO2 and VCO2/kg have similar capabilities for discriminating survivors from non-survivors, and the area under the curve for both was 0.97. VCO2/kg had similar performance as PetCO2 in reflecting the quality of CC and prediction of achieving ROSC under stable ventilation status in a porcine model of VF-related cardiac arrest. However, VCO2/kg requires a longer time to achieve a stable state after adjusting for quality of CC than PetCO2.

Improving Capnography Use for Critically Ill Emergency Patients: An Implementation Study

OBJECTIVES

Capnography has established benefit during intubation and cardiopulmonary resuscitation (CPR). Implementation within emergency departments (EDs) has lagged. We sought to address barriers to improve documented capnography use for patients requiring intubation or CPR.

METHODS

A controlled before- and after-implementation study was performed in 2 urban EDs. The control site had an existing policy for capnography use. Interventions for the experimental site included a 5-minute informational video, placement of capnography monitors with a shortened warm-up period in all resuscitation rooms, laminated reminder cards, and feedback during staff meetings. Staff members were surveyed about knowledge before and after the intervention. Records were reviewed for documented capnography use for 3 months before and 6 months after the intervention. Change in documented use at the experimental site was compared with the control site.

RESULTS

At the experimental site, 118 providers participated and 190 records were reviewed; 544 records were reviewed from the control site. There was a significant increase in the proportion of documented capnography use at the experimental site (8% versus 19%, P = 0.04) compared with the control site (64% versus 71%, P = 0.10). However, there was no significant trend over time at the experimental site after the intervention (P = 0.86). Despite high baseline knowledge about capnography, providers had improvements in survey responses regarding indications for intubation and CPR, normal values, and minimum effective values during CPR.

CONCLUSIONS

Documented capnography use increased with simple interventions but with no positive trend. Additional work is needed to improve use, including further evaluation of capnography's implementation in the ED.

Preventing Postoperative Opioid-Induced Respiratory Depression Through Implementation of an Enhanced Monitoring Program

BACKGROUND

Opioid-induced respiratory depression (OIRD) is a serious complication that can lead to negative outcomes. There are known risk factors for OIRD; however, a lack of national guidelines for the prevention and early detection of OIRD exists.

METHODS

An evidence-based practice study was conducted to create an enhanced monitoring (EM) program. The EM program consisted of risk stratification of surgical spine patients, including the use of STOP-BANG screening for obstructive sleep apnea, capnography monitoring, use of home positive airway pressure therapy, capnography alarm optimization, hospitalist consultation, nursing education, and patient education.

RESULTS

Approximately 17% (N = 937/5,462) of surgical spine patients were enrolled in the EM program. Fifty-six percent of EM patients were monitored with capnography and had out of range end-tidal carbon dioxide levels 17% of the time. The rate of transfers to the intensive care unit (ICU) for OIRD decreased, though not statistically significant (p = .151).

CONCLUSIONS

The EM program with risk stratification was found to reduce transfers to the ICU for OIRD. Although not statistically significant, the decreased number of transfers was clinically significant. Engagement of the interprofessional team and capnography alarm parameter optimization helped to reduce nonactionable alarms.

Physiological dead space and alveolar ventilation in ventilated infants

BACKGROUND

Dead space is the volume not taking part in gas exchange and, if increased, could affect alveolar ventilation if there is too low a delivered volume. We determined if there were differences in dead space and alveolar ventilation in ventilated infants with pulmonary disease or no respiratory morbidity.

METHODS

A prospective study of mechanically ventilated infants was undertaken. Expiratory tidal volume and carbon dioxide levels were measured. Volumetric capnograms were constructed to calculate the dead space using the modified Bohr-Enghoff equation. Alveolar ventilation (VA) was also calculated.

RESULTS

Eighty-one infants with a median (range) gestational age of 28.7 (22.4-41.9) weeks were recruited. The dead space [median (IQR)] was higher in 35 infants with respiratory distress syndrome (RDS) [5.7 (5.1-7.0) ml/kg] and in 26 infants with bronchopulmonary dysplasia (BPD) [6.4 (5.1-7.5) ml/kg] than in 20 term controls with no respiratory disease [3.5 (2.8-4.2) ml/kg, p < 0.001]. Minute ventilation was higher in both infants with RDS or BPD compared to the controls. VA in infants with RDS or BPD was similar to that of the controls [p = 0.54].

CONCLUSION

Prematurely born infants with pulmonary disease have a higher dead space than term controls, which may influence the optimum level during volume-targeted ventilation.

IMPACT

Measurement of the dead space was feasible in ventilated newborn infants. The physiological dead space was a significant proportion of the delivered volume in ventilated infants. The dead space (per kilogram) was higher in ventilated infants with respiratory distress syndrome or evolving bronchopulmonary dysplasia compared to term controls without respiratory disease. The dead space volume should be considered when calculating the most appropriate volume during volume-targeted ventilation.

Changes in dead space components during pressure-controlled inverse ratio ventilation: A secondary analysis of a randomized trial

Background

We previously reported that there were no differences between the lung-protective actions of pressure-controlled inverse ratio ventilation and volume control ventilation based on the changes in serum cytokine levels. Dead space represents a ventilation-perfusion mismatch, and can enable us to understand the heterogeneity and elapsed time changes in ventilation-perfusion mismatch.

Methods

This study was a secondary analysis of a randomized controlled trial of patients who underwent robot-assisted laparoscopic radical prostatectomy. The inspiratory to expiratory ratio was adjusted individually by observing the expiratory flow-time wave in the pressure-controlled inverse ratio ventilation group (n = 14) and was set to 1:2 in the volume-control ventilation group (n = 13). Using volumetric capnography, the physiological dead space was divided into three dead space components: airway, alveolar, and shunt dead space. The influence of pressure-controlled inverse ratio ventilation and time factor on the changes in each dead space component rate was analyzed using the Mann-Whitney U test and Wilcoxon’s signed rank test.

Results

The physiological dead space and shunt dead space rate were decreased in the pressure-controlled inverse ratio ventilation group compared with those in the volume control ventilation group (p < 0.001 and p = 0.003, respectively), and both dead space rates increased with time in both groups. The airway dead space rate increased with time, but the difference between the groups was not significant. There were no significant changes in the alveolar dead space rate.

Conclusions

Pressure-controlled inverse ratio ventilation reduced the physiological dead space rate, suggesting an improvement in the total ventilation/perfusion mismatch due to improved inflation of the alveoli affected by heterogeneous expansion disorder without hyperinflation of the normal alveoli. However, the shunt dead space rate increased with time, suggesting that atelectasis developed with time in both groups.

Evaluation of the Integrated Pulmonary Index® during non-anesthesiologist sedation for percutaneous endoscopic gastrostomy

Standard monitoring of heart rate, blood pressure and arterial oxygen saturation during endoscopy is recommended by current guidelines on procedural sedation. A number of studies indicated a reduction of hypoxic (art. oxygenation < 90% for > 15 s) and severe hypoxic events (art. oxygenation < 85%) by additional use of capnography. Therefore, U.S. and the European guidelines comment that additional capnography monitoring can be considered in long or deep sedation. Integrated Pulmonary Index® (IPI) is an algorithm-based monitoring parameter that combines oxygenation measured by pulse oximetry (art. oxygenation, heart rate) and ventilation measured by capnography (respiratory rate, apnea > 10 s, partial pressure of end-tidal carbon dioxide [PetCO2]). The aim of this paper was to analyze the value of IPI as parameter to monitor the respiratory status in patients receiving propofol sedation during PEG-procedure. Patients reporting for PEG-placement under sedation were randomized 1:1 in either standard monitoring group (SM) or capnography monitoring group including IPI (IM). Heart rate, blood pressure and arterial oxygen saturation were monitored in SM. In IM additional monitoring was performed measuring PetCO2, respiratory rate and IPI. Capnography and IPI values were recorded for all patients but were only visible to the endoscopic team for the IM-group. IPI values range between 1 and 10 (10 = normal; 8-9 = within normal range; 7 = close to normal range, requires attention; 5-6 = requires attention and may require intervention; 3-4 = requires intervention; 1-2 requires immediate intervention). Results on capnography versus standard monitoring of the same study population was published previously. A total of 147 patients (74 in SM and 73 in IM) were included in the present study. Hypoxic events occurred in 62 patients (42%) and severe hypoxic events in 44 patients (29%), respectively. Baseline characteristics were equally distributed in both groups. IPI = 1, IPI < 7 as well as the parameters PetCO2 = 0 mmHg and apnea > 10 s had a high sensitivity for hypoxic and severe hypoxic events, respectively (IPI = 1: 81%/81% [hypoxic/severe hypoxic event], IPI < 7: 82%/88%, PetCO2: 69%/68%, apnea > 10 s: 84%/84%). All four parameters had a low specificity for both hypoxic and severe hypoxic events (IPI = 1: 13%/12%, IPI < 7: 7%/7%, PetCO2: 29%/27%, apnea > 10 s: 7%/7%). In multivariate analysis, only SM and PetCO2 = 0 mmHg were independent risk factors for hypoxia. IPI (IPI = 1 and IPI < 7) as well as the individual parameters PetCO2 = 0 mmHg and apnea > 10 s allow a fast and convenient conclusion on patients' respiratory status in a morbid patient population. Sensitivity is good for most parameters, but specificity is poor. In conclusion, IPI can be a useful metric to assess respiratory status during propofol-sedation in PEG-placement. However, IPI was not superior to PetCO2 and apnea > 10 s.

Continuous Capnography Reduces the Incidence of Opioid-Induced Respiratory Rescue by Hospital Rapid Resuscitation Team

OBJECTIVE

The aim of this study was to determine the impact of end tidal carbon dioxide or capnography monitoring in patients requiring patient-controlled analgesia (PCA) on the incidence of opioid-induced respiratory depression (OIRD) in the setting of rapid response.

METHODS

A retrospective analysis was conducted in an urban tertiary care facility on the incidence of OIRD in the setting of rapid response as defined by a positive response to naloxone from January 2012 to December 2015. In March 2013, continuous capnography monitoring was implemented for all patients using PCA.

RESULTS

The preintervention incidence of OIRD in the setting of rapid response was 0.4% of patients receiving opioids. After the implementation of capnography, the incidence of OIRD in the setting of rapid response was reduced to 0.2%, which was statistically significant (χ2 = 46.246; df, 1; P < 0.0001). The rate of transfers to a higher level of care associated with these events was also reduced by 79% (baseline, 7.6 transfers/month; postintervention, 1.6 transfers/month).

CONCLUSIONS

Continuous capnography monitoring in patients receiving PCA significantly reduces the incidence of OIRD in the setting of rapid response and unplanned transfers to a higher level of care.

Use of supraglottic airway devices under capnography monitoring during cardiopulmonary resuscitation: A systematic review

BACKGROUND

Bag-valve-mask ventilation is the most commonly applied method during cardiopulmonary resuscitation. Globally, advanced airway management with blind insertion devices such as supraglottic airway devices has been implemented for years by different emergency services. The efficiency of ventilation via such devices could be measured by capnography.

OBJECTIVE

The objective of this study was to determine whether capnography is useful in patients undergoing cardiopulmonary resuscitation and to assess the effectiveness of ventilation via supraglottic airway devices.

REVIEW METHODS USED

This is a systematic review written following the steps of Preferred Reporting Items for Systematic Review and Meta-analyses protocols.

DATA SOURCES

A bibliographic search was carried out from the following databases: EBSCOhost, Scopus, EMBASE, Virtual Health Library, PubMed, Cochrane Library, Spanish Medical Index, Spanish Bibliographic Index in Health Sciences, and Latin American and Caribbean Health Sciences Literature, from inception until September 2019.

REVIEW METHODS

Studies describing the use of capnography with supraglottic airway devices during cardiopulmonary resuscitation manoeuvres were selected and evaluated using the Critical Appraisal Skills Programme.

RESULTS

Twenty-four articles were identified by title and abstract: six were randomised clinical trials, 11 were nonrandomised clinical trials, six were descriptive prospective studies, and one was a descriptive retrospective study. Nine primary research articles were selected for synthesis. Only one provided objective values of capnography obtained with ventilation with these devices, correlating them with the results of resuscitation.

CONCLUSIONS

The evidence published so far is scarce, mostly from observational studies with high risk of bias in general. Although a degree of recommendation cannot be established, some results indicate that capnography has the potential to facilitate advanced clinical practice of ventilation with supraglottic airway devices during cardiopulmonary resuscitation.

Validity of Empirical Estimates of the Ratio of Dead Space to Tidal Volume in ARDS

BACKGROUND

The ratio of dead space to tidal volume (V_D/V_T) is a clinically relevant parameter in ARDS; it has been shown to predict mortality, and it determines the extent to which extracorporeal CO₂ removal reduces tidal volume (V_T) and driving pressure (ΔP). V_D/V_T can be estimated with volumetric capnography, but empirical formulas using demographic and physiological information have been proposed to estimate V_D/V_T without the need of additional equipment. It is unknown whether estimated and measured V_D/V_T produce similar estimates of the predicted effect of extracorporeal CO₂ removal on ΔP.

METHODS

We performed a secondary analysis of data from a previous clinical trial including subjects with ARDS in whom V_D/V_T and CO₂ production ([Formula: see text]) were measured with volumetric capnography. The estimated ratio of dead space to tidal volume (V_D,est/V_T) was calculated using standard empiric formulas. Agreement between measured and estimated values was evaluated with Bland-Altman analysis. Agreement between the predicted change in ΔP with extracorporeal CO₂ removal as computed using the measured ratio of alveolar dead space to tidal volume (V_Dalv/V_T) or estimated V_Dalv/V_T (V_Dalv,est/V_T) was also evaluated.

RESULTS

V_D,est/V_T was higher than measured V_D/V_T, and agreement between them was low (bias 0.05, limits of agreement -0.21 to 0.31). Differences between measured and estimated [Formula: see text] accounted for 57% of the error in V_D,est/V_T. The predicted reduction in ΔP with extracorporeal CO₂ removal computed using V_Dalv,est/V_T was in reasonable agreement with the expected reduction using V_Dalv/V_T (bias -0.7 cm H₂O, limits of agreement -1.87 to 0.47 cm H₂O). In multivariable regression, measured V_D/V_T was associated with mortality (odds ratio 1.9, 95% CI 1.2-3.1, P = .01), but V_D,est/V_T was not (odds ratio 1.2, 95% CI 0.8-1.8, P = .3).

CONCLUSIONS

V_D/V_T and V_D,est/V_T showed low levels of agreement and cannot be used interchangeably in clinical practice. Nevertheless, the predicted decrease in ΔP due to extracorporeal CO₂ removal was similar when computed from either estimated or measured V_Dalv/V_T.

Breath emulator for simulation and modelling of expired tidal breath carbon dioxide characteristics

BACKGROUND

In this work we describe a breath emulator system, used to simulate temporal characteristics of exhaled carbon dioxide (CO₂) concentration waveform versus time simulating how much CO2 is present at each phase of the human lung respiratory process. The system provides a method for testing capnometers incorporating fast response non-dispersive infrared (NDIR) CO₂ gas sensing devices - in a clinical setting, capnography devices assess ventilation which is the CO₂ movement in and out of the lungs. A mathematical model describing the waveform of the expired CO₂ characteristic and influence of CO₂ gas sensor noise factors and speed of response is presented and compared with measured and emulated data.

OBJECTIVE

A range of emulated capnogram temporal waveforms indicative of normal and restricted respiratory function demonstrated. The system can provide controlled introduction of water vapour and/ or other gases, simulating the influence of water vapour in exhaled breath and presence of other gases in a clinical setting such as anaesthetic agents (eg N₂O). This enables influence of water vapour and/ or other gases to be assessed and modelled in the performance of CO₂ gas sensors incorporated into capnography systems. As such the breath emulator provides a means of controlled testing of capnometer CO₂ gas sensors in a non-clinical setting, allowing device optimisation before use in a medical environment.

METHODS

The breath emulator uses a unique combination of mass flow controllers, needle valves and a fast acting switchable pneumatic solenoid valve (FASV), used to controllably emulate exhaled CO₂ temporal waveforms for normal and restricted respiratory function. Output data from the described emulator is compared with a mathematical model using a range of input parameters such as time constants associated with inhalation/ exhalation for different parts of the respiratory cycle and CO₂ concentration levels. Sensor noise performance is modelled, taking into account input parameters such as sampling period, sensor temperature, sensing light throughput and pathlength.

RESULTS

The system described here produces realistic human capnographic waveforms and has the capability to emulate various waveforms associated with chronic respiratory diseases and early stage detection of exacerbations. The system has the capability of diagnosing medical conditions through analysis of CO₂ waveforms. Demonstrated in this work the emulator has been used to test NDIR gas sensor technology deployed in capnometer devices prior to formal clinical trialling.

The Association Between Ventilatory Ratio and Mortality in Children and Young Adults

BACKGROUND

The ventilatory ratio (VR) is a dead-space marker associated with mortality in mechanically ventilated adults with ARDS. The end-tidal alveolar dead space fraction (AVDSf) has been associated with mortality in children. However, AVDSf requires capnography measurements, whereas VR does not. We sought to examine the prognostic value of VR, in comparison to AVDSf, in children and young adults with acute hypoxemic respiratory failure.

METHODS

We conducted a retrospective study of prospectively collected data from 180 mechanically ventilated children and young adults with acute hypoxemic respiratory failure. VR was calculated as (minute ventilation × [Formula: see text])/(age-adjusted predicted minute ventilation × 37.5). AVDSf was calculated as [Formula: see text].

RESULTS

VR and AVDSf had a moderate correlation (rho 0.31, P < .001). VR was similar between survivors at 1.22 (interquartile range [IQR] 1.0-1.52) and nonsurvivors at 1.30 (IQR 0.96-1.95) (P = .2). AVDSf was lower in survivors at 0.12 (IQR 0.03-0.23) than nonsurvivors at 0.24 (IQR 0.13-0.33) (P < .001). In logistic regression and competing risk regression analyses, VR was not associated with mortality or rate of extubation at any given time (competing risk death; all P > .3). An AVDSf in the highest 2 quartiles, in comparison to the lowest quartile (AVDSf < 0.06), was associated with higher mortality after adjustment for oxygenation index and severity of illness (AVDSf ≥ 0.15-0.26: odds ratio 3.58, 95% CI 1.02-12.64, P = .047, and AVDSf ≥ 0.26: odds ratio 3.91 95% CI-1.03-14.83, P = .045). At any given time after intubation, a child with an AVDSf ≥ 0.26 was less likely to be extubated than a child with an AVDSf < 0.06, after adjustment for oxygenation index and severity of illness (AVDSf ≥ 0.26: subdistribution hazard ratio 0.55, 95% CI 0.33-0.94, P = .03).

CONCLUSIONS

VR should not be used for prognostic purposes in children and young adults. AVDSf added prognostic information to the severity of oxygenation defect and overall severity of illness in children and young adults, consistent with previous research.

Evaluation in Healthy Subjects of a Transcutaneous Carbon Dioxide Monitoring Wristband during Hypo and Hypercapnia Conditions

The development of wearable devices for healthcare monitoring is of primary interest, in particular for homecare applications. But it is challenging to develop an evaluation framework to test and optimize such a device by following a non-invasive protocol. As well established reference devices do exist for capnometry, we propose a protocol to evaluate and compare the performance of the transcutaneous carbon dioxide monitoring wristband that we develop. We present here this protocol, the signal processing pipeline and the data analysis based on signal alignment and intercorrelation study, and the first results on a cohort of 13 healthy subjects. This test allows demonstrating the influence of the device response time and of the carbon dioxide content in the ambient air.Clinical Relevance-The protocol described here allows to test and optimize the new device in clinical conditions simulating hypo and hypercapnia variations on a subject at rest, as it would be the case at home to monitor the health status of chronic respiratory patients, and to compare the performances with reference devices. A strong intercorrelation greater than 0.8 has been observed in 5 healthy subjects out of 13 and factors influencing the intercorrelation are suggested.

Covariance intersection to improve the robustness of the photoplethysmogram derived respiratory rate

Respiratory rate (RR) can be estimated from the photoplethysmogram (PPG) recorded by optical sensors in wearable devices. The fusion of estimates from different PPG features has lead to an increase in accuracy, but also reduced the numbers of available final estimates due to discarding of unreliable data. We propose a novel, tunable fusion algorithm using covariance intersection to estimate the RR from PPG (CIF). The algorithm is adaptive to the number of available feature estimates and takes each estimates' trustworthiness into account. In a benchmarking experiment using the CapnoBase dataset with reference RR from capnography, we compared the CIF against the state-of-the-art Smart Fusion (SF) algorithm. The median root mean square error was 1.4 breaths/min for the CIF and 1.8 breaths/min for the SF. The CIF significantly increased the retention rate distribution of all recordings from 0.46 to 0.90 (p < 0.001). The agreement with the reference RR was high with a Pearson's correlation coefficient of 0.94, a bias of 0.3 breaths/min, and limits of agreement of -4.6 and 5.2 breaths/min. In addition, the algorithm was computationally efficient. Therefore, CIF could contribute to a more robust RR estimation from wearable PPG recordings.

A Novel Nasal Cannula Type Mainstream Capnometer System Capable of Oxygen Administration

Capnometry is a method to measure carbon dioxide (CO₂) in exhaled gas and has been used to monitor patient's respiratory status. During moderate or deep sedation, monitoring for the presence of exhaled CO₂ is recommended for evaluating the adequacy of ventilation. Oxygen administration is usually given to patients with a nasal cannula to avoid hypoxia during sedation. However, the flow of oxygen administration can interfere with CO₂ measurement. We developed a nasal cannula type adapter called cap-ONE nasal adapter system based on the mainstream capnography which is designed to monitor CO₂ while supplying oxygen. In this study, we evaluated the basic performance of the system as compared with a conventional device using a spontaneous breathing model. The cap-ONE nasal adapter system could accurately measure PetCO₂ without being disturbed by oxygen flow and efficiently supply oxygen.

A Novel Mainstream Capnometer System for Non-invasive Positive Pressure Ventilation

Capnometry is a method to measure carbon dioxide (CO₂) in exhaled gas and it has been used to monitor patient respiratory status. CO₂ monitoring is also used for patients receiving non-invasive positive pressure ventilation (NPPV) therapy during mechanical ventilation. Ventilators actively dilute exhaled gas during non-invasive ventilation. In order to accurately measure end-tidal CO₂, an adequate amount of expired gas needs to be filled in a CO₂ measurement cell before expiratory positive airway pressure (EPAP) gas from the ventilator arrives to the cell. This is the reason why it is difficult to measure CO₂ stably during non-invasive ventilation using the conventional CO₂ measurement method. Therefore, we developed NPPV cap-ONE mask, which accurately measures CO₂ in exhaled gas during non-invasive ventilation. In this study, we evaluated the basic performance of the NPPV cap-ONE mask system. The NPPV cap-ONE mask system could accurately measure CO₂ in exhaled gas comparing to the conventional device in this study.

Unanticipated Respiratory Compromise and Unplanned Intubations on General Medical and Surgical Floors

BACKGROUND

Unanticipated respiratory compromise that lead to unplanned intubations is a known phenomenon in hospitalized patients. Most events occur in patients at high risk in well-monitored units; less is known about the incidence, risk factors, and trajectory of patients thought at low risk on lightly monitored general care wards. The aims of our study were to quantify demographic and clinical characteristics associated with unplanned intubations on general care floors and to analyze the medications administered, monitoring strategies, and vital-sign trajectories before the event.

METHODS

We performed a multicenter retrospective cohort study of hospitalized subjects on the general floor who had unanticipated, unplanned intubations on general care floors from August 2014 to February 2018.

RESULTS

We identified 448 unplanned intubations. The incidence rate was 0.420 per 1,000 bed-days (95% CI 0.374-0.470) in the academic hospital and was 0.430 (95% CI 0.352-0.520) and 0.394 per 1,000 bed-days (95% CI 0.301-0.506) at our community hospitals. Extrapolating these rates to total hospital admissions in the United States, we estimate 64,000 events annually. The mortality rate was 49.1%. Within 12 h preceding the event, 35.3% of the subjects received opiates. All received vital-sign assessments. Most were monitored with pulse oximetry. In contrast, 2.5% were on cardiac telemetry, and only 4 subjects used capnography; 53.7% showed significant vital-sign changes in the 24 h before the event. However, 46.3% had no significant change in any vital signs.

CONCLUSIONS

Our study showed unanticipated respiratory compromise that required an unplanned intubation of subjects on the general care floor, although not common, carried a high mortality. Besides pulse oximetry and routine vital-sign assessments, very little monitoring was in use. A significant portion of the subjects had no vital-sign abnormalities leading up to the event. Further research is needed to determine the phenotype of the different etiologies of unexpected acute respiratory failure to identify better risk stratification and monitoring strategies.

The comparison of capnography and epigastric auscultation to assess the accuracy of nasogastric tube placement in intensive care unit patients

BACKGROUND

Placement of nasogastric (NG) tubes is a common procedure for patients especially in intensive care units (ICUs). Thus, it is important to determine the correct placement of the tube to prevent misplacement in the airways. Accordingly, the aim of this study was to compare the epigastric auscultation and capnography in assessing the accuracy of NG tube insertion in ICU patients.

METHODS

In this descriptive comparative study, 60 patients were selected trough convenience sampling. After insertion of the NG tube in a standard method, the accuracy of placement of the tube with both epigastric auscultation and capnography was investigated. The NG tube insertion accuracy was then confirmed via radiography. Data analysis was performed using statistical software SPSS version 23.

RESULTS

The result showed that capnography had a sensitivity, specificity, and accuracy of 100, 92.5, and 95% respectively, but epigastric auscultation had 90, 80, and 83.4% respectively. The Kappa agreement coefficient between two methods was - 0.759.

CONCLUSION

The results revealed that the use of the capnography is preferable over the epigastric auscultation to confirm the correct insertion of the NG tube. It is recommended that more than one method be applied to detect and confirm the correct insertion of the NG tube.