Diagnosis and Severity Assessment of COPD Using a Novel Fast-Response Capnometer and Interpretable Machine Learning.

INTRODUCTION: Spirometry is the gold standard for COPD diagnosis and severity determination, but is technique-dependent, nonspecific, and requires administration by a trained healthcare professional. There is a need for a fast, reliable, and precise alternative diagnostic test. This study's aim was to use interpretable machine learning to diagnose COPD and assess severity using 75-second carbon dioxide (CO2) breath records captured with TidalSense's N-TidalTM capnometer. METHOD: For COPD diagnosis, machine learning algorithms were trained and evaluated on 294 COPD (including GOLD stages 1-4) and 705 non-COPD participants. A logistic regression model was also trained to distinguish GOLD 1 from GOLD 4 COPD with the output probability used as an index of severity. RESULTS: The best diagnostic model achieved an AUROC of 0.890, sensitivity of 0.771, specificity of 0.850 and positive predictive value (PPV) of 0.834. Evaluating performance on all test capnograms that were confidently ruled in or out yielded PPV of 0.930 and NPV of 0.890. The severity determination model yielded an AUROC of 0.980, sensitivity of 0.958, specificity of 0.961 and PPV of 0.958 in distinguishing GOLD 1 from GOLD 4. Output probabilities from the severity determination model produced a correlation of 0.71 with percentage predicted FEV1. CONCLUSION: The N-TidalTM device could be used alongside interpretable machine learning as an accurate, point-of-care diagnostic test for COPD, particularly in primary care as a rapid rule-in or rule-out test. N-TidalTM also could be effective in monitoring disease progression, providing a possible alternative to spirometry for disease monitoring.

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.

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.

Assessment of neonatal respiratory rate variability.

Accurate measurement of respiratory rate (RR) in neonates is challenging due to high neonatal RR variability (RRV). There is growing evidence that RRV measurement could inform and guide neonatal care. We sought to quantify neonatal RRV during a clinical study in which we compared multiparameter continuous physiological monitoring (MCPM) devices. Measurements of capnography-recorded exhaled carbon dioxide across 60-s epochs were collected from neonates admitted to the neonatal unit at Aga Khan University-Nairobi hospital. Breaths were manually counted from capnograms and using an automated signal detection algorithm which also calculated mean and median RR for each epoch. Outcome measures were between- and within-neonate RRV, between- and within-epoch RRV, and 95% limits of agreement, bias, and root-mean-square deviation. Twenty-seven neonates were included, with 130 epochs analysed. Mean manual breath count (MBC) was 48 breaths per minute. Median RRV ranged from 11.5% (interquartile range (IQR) 6.8-18.9%) to 28.1% (IQR 23.5-36.7%). Bias and limits of agreement for MBC vs algorithm-derived breath count, MBC vs algorithm-derived median breath rate, MBC vs algorithm-derived mean breath rate were - 0.5 (- 2.7, 1.66), - 3.16 (- 12.12, 5.8), and - 3.99 (- 11.3, 3.32), respectively. The marked RRV highlights the challenge of performing accurate RR measurements in neonates. More research is required to optimize the use of RRV to improve care. When evaluating MCPM devices, accuracy thresholds should be less stringent in newborns due to increased RRV. Lastly, median RR, which discounts the impact of extreme outliers, may be more reflective of the underlying physiological control of breathing.

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.

Modeling the Cost Savings of Continuous Pulse Oximetry and Capnography Monitoring of United States General Care Floor Patients Receiving Opioids Based on the PRODIGY Trial.

INTRODUCTION: Despite the high incidence of respiratory depression on the general care floor and evidence that continuous monitoring improves patient outcomes, the cost-benefit of continuous pulse oximetry and capnography monitoring of general care floor patients remains unknown. This study modeled the cost and length of stay savings, investment break-even point, and likelihood of cost savings for continuous pulse oximetry and capnography monitoring of general care floor patients at risk for respiratory depression. METHODS: A decision tree model was created to compare intermittent pulse oximetry versus continuous pulse oximetry and capnography monitoring. The model utilized costs and outcomes from the PRediction of Opioid-induced respiratory Depression In patients monitored by capnoGraphY (PRODIGY) trial, and was applied to a modeled cohort of 2447 patients receiving opioids per median-sized United States general care floor annually. RESULTS: Continuous pulse oximetry and capnography monitoring of high-risk patients is projected to reduce annual hospital cost by $535,531 and cumulative patient length of stay by 103 days. A 1.5% reduction in respiratory depression would achieve a break-even investment point and justify the investment cost. The probability of cost saving is ≥ 80% if respiratory depression is decreased by ≥ 17%. Expansion of continuous monitoring to high- and intermediate-risk patients, or to all patients, is projected to reach a break-even point when respiratory depression is reduced by 2.5% and 3.5%, respectively, with a ≥ 80% probability of cost savings when respiratory depression decreases by ≥ 27% and ≥ 31%, respectively. CONCLUSION: Compared to intermittent pulse oximetry, continuous pulse oximetry and capnography monitoring of general care floor patients receiving opioids has a high chance of being cost-effective. TRIAL REGISTRATION: www.clinicaltrials.gov , Registration ID: NCT02811302.

Opioid-induced respiratory depression increases hospital costs and length of stay in patients recovering on the general care floor.

BACKGROUND: Opioid-induced respiratory depression is common on the general care floor. However, the clinical and economic burden of respiratory depression is not well-described. The PRediction of Opioid-induced respiratory Depression In patients monitored by capnoGraphY (PRODIGY) trial created a prediction tool to identify patients at risk of respiratory depression. The purpose of this retrospective sub-analysis was to examine healthcare utilization and hospital cost associated with respiratory depression. METHODS: One thousand three hundred thirty-five patients (N = 769 United States patients) enrolled in the PRODIGY trial received parenteral opioids and underwent continuous capnography and pulse oximetry monitoring. Cost data was retrospectively collected for 420 United States patients. Differences in healthcare utilization and costs between patients with and without ≥1 respiratory depression episode were determined. The impact of respiratory depression on hospital cost per patient was evaluated using a propensity weighted generalized linear model. RESULTS: Patients with ≥1 respiratory depression episode had a longer length of stay (6.4 ± 7.8 days vs 5.0 ± 4.3 days, p = 0.009) and higher hospital cost ($21,892 ± $11,540 vs $18,206 ± $10,864, p = 0.002) compared to patients without respiratory depression. Patients at high risk for respiratory depression, determined using the PRODIGY risk prediction tool, who had ≥1 respiratory depression episode had higher hospital costs compared to high risk patients without respiratory depression ($21,948 ± $9128 vs $18,474 ± $9767, p = 0.0495). Propensity weighted analysis identified 17% higher costs for patients with ≥1 respiratory depression episode (p = 0.007). Length of stay significantly increased total cost, with cost increasing exponentially for patients with ≥1 respiratory depression episode as length of stay increased. CONCLUSIONS: Respiratory depression on the general care floor is associated with a significantly longer length of stay and increased hospital costs. Early identification of patients at risk for respiratory depression, along with early proactive intervention, may reduce the incidence of respiratory depression and its associated clinical and economic burden. TRIAL REGISTRATION: ClinicalTrials.gov , NCT02811302 .

Assessment of sidestream end-tidal capnography in ventilated infants on the neonatal unit.

OBJECTIVES: Continuous monitoring of carbon dioxide (CO2 ) levels can be achieved by capnography. Our aims were to compare the performance of a sidestream capnograph with a low dead space and sampling rate to a mainstream device and evaluate whether its results correlated with arterial/capillary CO2 levels in infants with different respiratory disease severities. WORKING HYPOTHESES: End-tidal carbon dioxide (EtCO2 ) results by sidestream and mainstream capnography would correlate, but the divergence of EtCO2 and CO2 results would occur in more severe lung disease. STUDY DESIGN: Prospective cohort study. PATIENT-SUBJECT SELECTION: Fifty infants with a median (interquartile range) gestational age of 31.1 (27.1-37.4) weeks and birth weight of 1.37 (0.76-2.95) kg. METHODOLOGY: Concurrent measurements of EtCO2 in ventilated infants were made using a new Microstream sidestream device and a mainstream capnograph (gold standard). Results from both devices were compared with arterial or capillary CO2 levels. The ratio of dead space to tidal volume (Vd/Vt) was calculated to assess respiratory disease severity. RESULTS: The mean difference between the concurrent measurements of EtCO2 was -0.54 ± 0.67 kPa (95% agreement levels - 1.86 to 0.77 kPa), the correlation between the two was r = .85 (P < .001). Sidestream capnography results correlated better with partial pressure of CO2 (PCO2 ) levels in infants with less (Vd/Vt < 0.35; r2 = .66, P < .001) rather than more severe (Vd/Vt > 0.35; r2 = .33, P = .01) lung disease. CONCLUSIONS: The sidestream capnography performed similarly to the mainstream capnography. The poorer correlation of EtCO2 to PCO2 levels in infants with severe respiratory disease should highlight to clinicians increased ventilation-perfusion mismatch.

Clinical and experimental validation of a capnodynamic method for end-expiratory lung volume assessment.

INTRODUCTION: Lung protective ventilation can decrease post-operative pulmonary complications. The aim of this study was to evaluate a capnodynamic method estimating effective lung volume (ELV) as a proxy for end-expiratory lung volume in response to PEEP changes in patients, healthy subjects and a porcine model. METHODS: Agreement and trending ability for ELV in anaesthetized patients and agreement in awake subjects were evaluated using nitrogen multiple breath wash-out/in and plethysmography as a reference respectively. Agreement and trending ability were evaluated in pigs during PEEP elevations with inert gas wash-out as reference. RESULTS: In anaesthetized patients bias (95% limits of agreement [LoA]) and percentage error (PE) at PEEP 0 cm H2 O were 133 mL (-1049 to 1315) and 71%, at PEEP 5 cm H2 O 161 mL (-1291 to 1613 mL) and 66%. In healthy subjects: 21 mL (-755 to 796 mL) and 26%. In porcines, at PEEP 5-20 cm H2 O bias decreased from 223 mL to 136 mL LoA (34-412) to (-30 to 902) and PE 29%-49%. Trending abilities in anaesthetized patients and porcines were 100% concordant. CONCLUSION: The ELV-method showed low bias but high PE in anaesthetized patients. Agreement was good in awake subjects. In porcines, agreement was good at lower PEEP levels. Concordance related to PEEP changes reached 100% in all settings. This method may become a useful trending tool for monitoring lung function during mechanical ventilation, if findings are confirmed in other clinical contexts.

End-tidal CO2 Monitoring is Available in Most Community Hospitals in a Rural State: A Health System Survey.

INTRODUCTION: Procedural sedation and analgesia (PSA) provides safe and effective relief for pain, anxiety and discomfort during procedures performed in the emergency department (ED). Our objective was to identify hospital-level factors associated with routine PSA capnography use in the ED. METHODS: This study was a cross-sectional telephone survey of ED nurse managers and designees in a Midwestern state. Respondents identified information about hospital infrastructure, physician staffing, family practice (FP) physicians only, board-certified emergency physicians (EPs) only (or both), and critical intervention capabilities. Additional characteristics including ED volume and hospital designation (i.e., rural-urban classification) were obtained from the Centers for Medicare and Medicaid Services and the state hospital association database, respectively. The primary outcome was reported use of PSA capnography. We conducted univariate analyses (relative risks, 95% confidence interval [CI]) to identify associations between hospital-level characteristics and PSA capnography use. RESULTS: We had an overall response rate of 98% (n=118 participating hospitals). The majority of EDs were in rural settings (78%), with a median of 5,057 visits per year (interquartile range 2,823-14,322). Nearly half of the EDs were staffed by FP physicians only, while 16% had board-certified EPs only. Nearly all hospitals (n=114, 97%), reported using continuous capnography for ventilated patients, and 74% reported use of capnography during PSA. Urban hospitals were more likely to use PSA capnography than critical access hospitals (relative risk 1.45; 95% CI, 1.22-1.73), and PSA capnography use increased with each ED volume quartile. Facilities with only EPs were 1.46 (95% CI, 1.15-1.87) times more likely to use PSA capnography than facilities with FP physicians only. CONCLUSION: Continuous capnography was available in nearly all EDs, independent of size, location or patient volume. The implementation of capnography during PSA was less penetrant. Smaller, rural departments were less likely than their larger, urban counterparts to implement these national guidelines. Rurality and hospital size may be potential institutional barriers to capnography implementation.

Investigating Capnography Innovation for Better Patient Monitoring in the Resource Limited Surgical Setting.

BACKGROUND: Access to basic anesthetic monitoring in the developing world is lacking, which contributes to the 100 times greater anesthesia-related mortality in low- and middle-income countries. We hypothesize that an environmental sensor with a lower sampling rate could provide some clinical utility by providing CO2 levels, respiratory rate, and support in detection of clinical abnormalities. MATERIALS AND METHODS: A bench-top lung simulation was created to replicate CO2 waveforms, and an environmental sensor was compared with industry-available technology. Sensor response time and respiratory rates were compared between devices. Additionally, an in silico model was created to replicate capnography pathology as waveforms would appear using the environmental sensor. RESULTS AND CONCLUSION: Breath simulations using the bench-top lung simulation produced similar results to industry standards with a degree of variability. Respiratory rates did not differ between the environmental sensor and all other devices tested. Finally, pathological waveforms created in silico carried a certain level of detail regarding ventilatory pathology, which could provide some clinical insight to an anesthesiologist. We believe our prototype is the first step toward making low-cost and portable capnography available in the resource-limited setting, and future efforts should focus on bridging the gap to safer anesthesia and surgery globally.

Using continuous quantitative capnography for emergency department procedural sedation: a systematic review and cost-effectiveness analysis.

End-tidal CO2 has been advocated to improve safety of emergency department (ED) procedural sedation by decreasing hypoxia and catastrophic outcomes. This study aimed to estimate the cost-effectiveness of routine use of continuous waveform quantitative end-tidal CO2 monitoring for ED procedural sedation in prevention of catastrophic events. Markov modeling was used to perform cost-effectiveness analysis to estimate societal costs per prevented catastrophic event (death or hypoxic brain injury) during routine ED procedural sedation. Estimates for efficacy of capnography and safety of sedation were derived from the literature. This model was then applied to all procedural sedations performed in US EDs with assumptions selected to maximize efficacy and minimize cost of implementation. Assuming that capnography decreases the catastrophic adverse event rate by 40.7% (proportional to efficacy in preventing hypoxia), routine use of capnography would decrease the 5-year estimated catastrophic event rate in all US EDs from 15.5 events to 9.2 events (difference 6.3 prevented events per 5 years). Over a 5-year period, implementing routine end-tidal CO2 monitoring would cost an estimated $2,830,326 per prevented catastrophic event, which translates into $114,007 per quality-adjusted life-year. Sensitivity analyses suggest that reasonable assumptions continue to estimate high costs of prevented catastrophic events. Continuous waveform quantitative end-tidal CO2 monitoring is a very costly strategy to prevent catastrophic complications of procedural sedation when applied routinely in ED procedural sedations.

Assessment of Alteration in Capnometry Monitoring during Intravenous Sedation with Midazolam for Oral Surgical Procedures.

INTRODUCTION: Capnography is routinely used for monitoring of patients subjected to sedation for different surgical procedures. There is still paucity of data highlighting the capnographic assessment of patients on midazolam sedation undergoing oral surgical procedures. Hence, we planned the present study to assess the alterations occurring in the end-tidal carbon dioxide (ETCO2) values monitored during intravenous (IV) sedation with midazolam during various oral surgical procedures. MATERIALS AND METHODS: The present study included assessment of alteration in ETCO2 values occurring during oral surgical procedure. After meeting the inclusion and exclusion criteria, a total of 40 participants were included in the present study. Pulse oximeter with capnograph (EmcoMeditek Pvt., Ltd., India) device was used for assessment of respiratory rate (RR) and ETCO2 values. The mean of 12 readings over a period of 1 minute before the starting of first infusion was referred to as baseline time. By evaluating the first four readings at an interval of 15 seconds during the 1st minute of infusion, we obtained the 1 minute average reading. All the data were compiled and recorded and assessed by the Statistical Package for the Social Sciences (SPSS) software. RESULTS: A total of 40 participants were included, out of which, 20 were males and 20 were females. At the baseline time, mean value of ETCO2 was 31 mm Hg, while mean value of oxygen saturation (SpO2) was 36%. Out of total 40 participants, 15 showed the presence of respiratory depression. Out of these 15 participants, ETCO2 changes from baseline were observed in 13 participants. CONCLUSION: No oxygen should be delivered, unless until required, to the healthy participants undergoing dental sedation procedures, for marinating the sensitivity of pulse oximetry during assessment of respiratory depression. CLINICAL SIGNIFICANCE: In patients undergoing sedation procedures, various monitoring techniques should be employed as respiratory depression is a commonly encountered risk factor.

Spirometry and volumetric capnography in lung function assessment of obese and normal-weight individuals without asthma / Espirometria e capnografia volumétrica na avaliação da função pulmonar de indivíduos obesos e eutróficos sem asma

Abstract Objective: To analyze and compare lung function of obese and healthy, normal-weight children and adolescents, without asthma, through spirometry and volumetric capnography. Methods: Cross-sectional study including 77 subjects (38 obese) aged 5-17 years. All subjects underwent spirometry and volumetric capnography. The evaluations were repeated in obese subjects after the use of a bronchodilator. Results: At the spirometry assessment, obese individuals, when compared with the control group, showed lower values of forced expiratory volume in the first second by forced vital capacity (FEV1/FVC) and expiratory flows at 75% and between 25 and 75% of the FVC (p < 0.05). Volumetric capnography showed that obese individuals had a higher volume of produced carbon dioxide and alveolar tidal volume (p < 0.05). Additionally, the associations between dead space volume and tidal volume, as well as phase-3 slope normalized by tidal volume, were lower in healthy subjects (p < 0.05). These data suggest that obesity does not alter ventilation homogeneity, but flow homogeneity. After subdividing the groups by age, a greater difference in lung function was observed in obese and healthy individuals aged >11 years (p < 0.05). Conclusion: Even without the diagnosis of asthma by clinical criteria and without response to bronchodilator use, obese individuals showed lower FEV1/FVC values and forced expiratory flow, indicating the presence of an obstructive process. Volumetric capnography showed that obese individuals had higher alveolar tidal volume, with no alterations in ventilation homogeneity, suggesting flow alterations, without affecting lung volumes.

Resumo Objetivo: Analisar e comparar a função pulmonar de crianças e adolescentes obesos e eutróficos saudáveis, sem asma, pela espirometria e capnografia volumétrica. Métodos: Estudo transversal com 77 indivíduos (38 obesos) entre cinco e 17 anos. Todos fizeram espirometria e capnografia volumétrica. Os obesos repetiram as avaliações após o uso de broncodilatador. Resultados: Na avaliação da espirometria, os indivíduos obesos, quando comparados com o grupo controle, apresentaram menores valores no volume expiratório forçado no primeiro segundo pela capacidade vital forçada (VEF1/CVF) e nos fluxos expiratórios a 75% da CVF e entre 25-75% da mesma (p < 0,05). A capnografia volumétrica demonstrou que os obesos apresentam maior volume produzido de dióxido de carbono e volume corrente alveolar (p < 0,05). Além disso, a relação entre o volume espaço morto e volume corrente, bem como o slope da fase 3 normalizado pelo volume corrente, foi menor nos indivíduos saudáveis (p < 0,05). Esses dados sugerem que a obesidade não altera a homogeneidade da ventilação, mas sim dos fluxos. Ao subdividir os grupos por idade, foi observada maior diferença na função pulmonar entre indivíduos obesos e saudáveis na faixa acima de 11 anos (p < 0,05). Conclusão: Mesmo sem o diagnóstico de asma por critérios clínicos e sem resposta ao uso de broncodilatador, os indivíduos obesos apresentaram menores valores no VEF1/CVF e nos fluxos expiratórios forçados, o que indica a presença de processo obstrutivo. A capnografia volumétrica indicou nos indivíduos obesos maior volume corrente alveolar, sem alterações na homogeneidade da ventilação, o que sugere alteração nos fluxos, sem comprometimento dos volumes pulmonares.

Spirometry and volumetric capnography in lung function assessment of obese and normal-weight individuals without asthma.

OBJECTIVE: To analyze and compare lung function of obese and healthy, normal-weight children and adolescents, without asthma, through spirometry and volumetric capnography. METHODS: Cross-sectional study including 77 subjects (38 obese) aged 5-17 years. All subjects underwent spirometry and volumetric capnography. The evaluations were repeated in obese subjects after the use of a bronchodilator. RESULTS: At the spirometry assessment, obese individuals, when compared with the control group, showed lower values of forced expiratory volume in the first second by forced vital capacity (FEV1/FVC) and expiratory flows at 75% and between 25 and 75% of the FVC (p<0.05). Volumetric capnography showed that obese individuals had a higher volume of produced carbon dioxide and alveolar tidal volume (p<0.05). Additionally, the associations between dead space volume and tidal volume, as well as phase-3 slope normalized by tidal volume, were lower in healthy subjects (p<0.05). These data suggest that obesity does not alter ventilation homogeneity, but flow homogeneity. After subdividing the groups by age, a greater difference in lung function was observed in obese and healthy individuals aged >11 years (p<0.05). CONCLUSION: Even without the diagnosis of asthma by clinical criteria and without response to bronchodilator use, obese individuals showed lower FEV1/FVC values and forced expiratory flow, indicating the presence of an obstructive process. Volumetric capnography showed that obese individuals had higher alveolar tidal volume, with no alterations in ventilation homogeneity, suggesting flow alterations, without affecting lung volumes.

Assessment of Bohr and Enghoff Dead Space Equations in Mechanically Ventilated Children.

BACKGROUND: Recent findings suggest that using alveolar PCO2 (PACO2 ) estimated by volumetric capnography in the Bohr equation instead of PaCO2 (Enghoff modification) could be appropriate for the calculation of physiological dead space to tidal volume ratio (VD/VT Bohr and VD/VT Enghoff, respectively). We aimed to describe the relationship between these 2 measurements in mechanically ventilated children and their significance in cases of ARDS. METHODS: From June 2013 to December 2013, mechanically ventilated children with various respiratory conditions were included in this study. Demographic data, medical history, and ventilatory parameters were recorded. Volumetric capnography indices (NM3 monitor) were obtained over a period of 5 min preceding a blood sample. Bohr's and Enghoff's dead space, S2 and S3 slopes, and the S2/S3 ratio were calculated breath-by-breath using dedicated software (FlowTool). This study was approved by Ste-Justine research ethics review board. RESULTS: Thirty-four subjects were analyzed. Mean VD/VT Bohr was 0.39 ± 0.12, and VD/VT Enghoff was 0.47 ± 0.13 (P = .02). The difference between VD/VT Bohr and VD/VT Enghoff was correlated with PaO2 /FIO2 and with S2/S3. In subjects without lung disease (PaO2 /FIO2 ≥ 300), mean VD/VT Bohr was 0.36 ± 0.11, and VD/VT Enghoff was 0.39 ± 0.11 (P = .056). Two children with status asthmaticus had a major difference between VD/VT Bohr and VD/VT Enghoff in the absence of a low PaO2 /FIO2 . CONCLUSIONS: This study suggests that VD/VT Bohr and VD/VT Enghoff are not different when there is no hypoxemia (PaO2 /FIO2 > 300) except in the case of status asthmaticus. In subjects with a low PaO2 /FIO2 , the method to measure VD/VT must be reported, and results cannot be easily compared if the measurement methods are not the same.

Assessment of fluid responsiveness with end-tidal carbon dioxide using a simplified passive leg raising maneuver: a prospective observational study.

BACKGROUND: Assessing fluid responsiveness is important in the management of patients with hemodynamic instability. Passive leg raising (PLR) is a validated dynamic method to induce a transient increase in cardiac preload and predict fluid responsiveness. Variations in end-tidal carbon dioxide (ETCO2) obtained by capnography correlate closely with variations in cardiac output when alveolar ventilation and carbon dioxide production are kept constant. In this prospective observational study, we tested the hypothesis that variations in ETCO2 induced by a simplified PLR maneuver can track changes in the cardiac index (CI) and thus predict fluid responsiveness. METHOD: A five-minute standardized PLR maneuver was performed in 90 paralyzed hemodynamically stable cardiac surgical patients receiving mechanical ventilation. Cardiac index was measured by thermodilution before and one minute after PLR. End-tidal CO2 measurements using capnography were obtained during the entire PLR maneuver. Fluid responsiveness was defined as a 15% increase in the CI. The Chi square test and Student's t test were used to compare responders and non-responders. Logistic regression analyses were then performed to determine factors of responsiveness. RESULTS: There were no differences between responders and non-responders in demographic and baseline hemodynamic variables. Fluid responsiveness was associated with an ETCO2 variation (ΔETCO2) of ≥ 2 mmHg during PLR [odds ratio (OR), 7.3; 95% confidence interval (CI), 2.7 to 20.2; P < 0.01; sensitivity 75%]. A low positive predictive value (54%) and a high negative predictive value (NPV) (86%) were observed. No other clinical or hemodynamic predictors were associated with fluid responsiveness. A logistic regression model established that a combination of ΔETCO2 ≥ 2 mmHg and a change in systolic blood pressure ≥ 10 mmHg induced by passive leg raising was predictive of fluid responsiveness (OR, 8.9; 95% CI, 2.5 to 32.2; P = 0.005). CONCLUSION: Use of a passive leg raising maneuver to induce variation in ETCO2 is a noninvasive and useful method to assess fluid responsiveness in paralyzed cardiac surgery patients receiving mechanical ventilation. Given its high NPV, fluid responsiveness is unlikely if a passive leg raising maneuver induces ΔETCO2 of < 2 mmHg.

Assessment of dead-space ventilation in patients with acute respiratory distress syndrome: a prospective observational study.

BACKGROUND: Physiological dead space (VD/VT) represents the fraction of ventilation not participating in gas exchange. In patients with acute respiratory distress syndrome (ARDS), VD/VT has prognostic value and can be used to guide ventilator settings. However, VD/VT is rarely calculated in clinical practice, because its measurement is perceived as challenging. Recently, a novel technique to calculate partial pressure of carbon dioxide in alveolar air (PACO2) using volumetric capnography (VCap) was validated. The purpose of the present study was to evaluate how VCap and other available techniques to measure PACO2 and partial pressure of carbon dioxide in mixed expired air (PeCO2) affect calculated VD/VT. METHODS: In a prospective, observational study, 15 post-cardiac surgery patients and 15 patients with ARDS were included. PACO2 was measured using VCap to calculate Bohr dead space or substituted with partial pressure of carbon dioxide in arterial blood (PaCO2) to calculate the Enghoff modification. PeCO2 was measured in expired air using three techniques: Douglas bag (DBag), indirect calorimetry (InCal), and VCap. Subsequently, VD/VT was calculated using four methods: Enghoff-DBag, Enghoff-InCal, Enghoff-VCap, and Bohr-VCap. RESULTS: PaCO2 was higher than PACO2, particularly in patients with ARDS (post-cardiac surgery PACO2 = 4.3 ± 0.6 kPa vs. PaCO2 = 5.2 ± 0.5 kPa, P < 0.05; ARDS PACO2 = 3.9 ± 0.8 kPa vs. PaCO2 = 6.9 ± 1.7 kPa, P < 0.05). There was good agreement in PeCO2 calculated with DBag vs. VCap (post-cardiac surgery bias = 0.04 ± 0.19 kPa; ARDS bias = 0.03 ± 0.27 kPa) and relatively low agreement with DBag vs. InCal (post-cardiac surgery bias = -1.17 ± 0.50 kPa; ARDS mean bias = -0.15 ± 0.53 kPa). These differences strongly affected calculated VD/VT. For example, in patients with ARDS, VD/VTcalculated with Enghoff-InCal was much higher than Bohr-VCap (VD/VT Enghoff-InCal = 66 ± 10 % vs. VD/VT Bohr-VCap = 45 ± 7 %; P < 0.05). CONCLUSIONS: Different techniques to measure PACO2 and PeCO2 result in clinically relevant mean and individual differences in calculated VD/VT, particularly in patients with ARDS. Volumetric capnography is a promising technique to calculate true Bohr dead space. Our results demonstrate the challenges clinicians face in interpreting an apparently simple measurement such as VD/VT.