A novel application of capnography during controlled human exposure to air pollution.
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BACKGROUND: The objective was to determine the repeatability and stability of capnography interfaced with human exposure facility. METHODS: Capnographic wave signals were obtained from five healthy volunteers exposed to particle-free, filtered air during two consecutive 5 min intervals, 10 min apart, within the open and then the sealed and operational human exposure facility (HEF). Using a customized setup comprised of the Oridion Microcap portable capnograph, DA converter and AD card, the signal was acquired and saved as an ASCII file for subsequent processing. The minute ventilation (VE), respiratory rate (RR) and expiratory tidal volume (VTE) were recorded before and after capnographic recording and then averaged. Each capnographic tracing was analyzed for acceptable waves. From each recorded interval, 8 to 19 acceptable waves were selected and measured. The following wave parameters were obtained: total length and length of phase II and III, slope of phase II and III, area under the curve and area under phase III. In addition, we recorded signal measures including the mean, standard deviation, mode, minimum, maximum--which equals end-tidal CO2 (EtCO2), zero-corrected maximum and true RMS. RESULTS: Statistical analysis using a paired t-test for means showed no statistically significant changes of any wave parameters and wave signal measures, corrected for RR and VTE, comparing the measures when the HEF was open vs. sealed and operational. The coefficients of variation of the zero-corrected and uncorrected EtCO2, phase II absolute difference, signal mean, standard deviation and RMS were less than 10% despite a sub-atmospheric barometric pressure, and slightly higher temperature and relative humidity within the HEF when operational. CONCLUSION: We showed that a customized setup for the acquisition and processing of the capnographic wave signal, interfaced with HEF was stable and repeatable. Thus, we expect that analysis of capnographic waves in controlled human air pollution exposure studies is a feasible tool for characterization of cardio-pulmonary effects of such exposures. (+info)
Respiratory therapies in the critical care setting. Should every mechanically ventilated patient be monitored with capnography from intubation to extubation?
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One of the most important aspects of caring for a critically ill patient is monitoring. Few would disagree that the most essential aspect of monitoring is frequent physical assessments. Complementing the physical examination is continuous monitoring of heart rate, respiratory rate, and blood oxygen saturation measured via pulse-oximetry, which have become the standard of care in intensive care units. Over the past decade one of the most controversial aspects of monitoring critically ill patients has been capnography. Although most clinicians use capnography to confirm endotracheal intubation, few clinicians use continuous capnography in the intensive care unit. This article reviews the medical literature on whether every mechanically ventilated patient should be monitored with capnography from intubation to extubation. There are numerous articles on capnography, but no definitive, randomized study has even attempted to address this specific question. Based on the available literature, it seems reasonable to use continuous capnography, for at least a subset of critically ill patients, to ensure integrity of the endotracheal tube and other ventilatory apparatus. However, at this point definitive data are not yet available to clearly support continuous capnography for optimizing mechanical ventilatory support. We hope that as new data become available, the answer to this capnography question will become clear. (+info)
Systematic errors and susceptibility to noise of four methods for calculating anatomical dead space from the CO2 expirogram.
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BACKGROUND: Anatomical dead space is usually measured using the Fowler equal area method. Alternative methods include the Hatch, Cumming, and Bowes methods, in which first, second, and third order polynomials, respectively, fitted to an expired CO2 volume vs expired volume curve, intercept the x-axis at the anatomical dead space. This study assessed systematic errors and susceptibility to noise of the Fowler, Hatch, Cumming, and Bowes dead spaces calculated over 40-80% of the CO2 expirogram. METHODS: Simulated CO2 expirograms with 220 ml anatomical dead space and varying alveolar plateau slopes were generated digitally and zero-mean Gaussian noise added. CO2 expirograms were recorded in 10 anaesthetized human subjects. Anatomical dead space was calculated by the Fowler, Hatch, Cumming, and Bowes methods. RESULTS: The Fowler, Hatch, Cumming, and Bowes methods displayed systematic biases of -1.8%, 13.2%, 2.4%, and -1.3%, respectively, at a normalized simulated alveolar plateau slope of 1.6 litre(-1). At a noise level of 0.0066 vol/vol, the standard deviations of recovered simulated dead spaces were 70.6, 1.8, 2.4, and 3.7 ml, respectively. The Hatch, Cumming, and Bowes methods applied to human expirograms differed significantly from that of Fowler by 13, -4, and -11 ml, respectively. In the human study, the Hatch and Cumming methods yielded the lowest intra-individual dead space variability. CONCLUSIONS: The Fowler method shows greatest susceptibility to measurement noise and the Hatch method exhibits the largest systematic error. The Cumming method, which exhibits both low bias and low noise susceptibility, is preferred for estimating anatomical dead space from CO2 expirograms. (+info)
Respiratory controversies in the critical care setting. Conference summary.
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Definitive evidence to settle the important clinical controversies we debated in this Journal Conference are not yet available. More randomized controlled trials are clearly needed for all of the topics presented. Additionally, neonatal and pediatric data are clearly lacking on most of these questions. The key points in many of the conversations on these controversial topics focused on the balance between efficacy and safety. When safety data exist without efficacy data, the uncontrolled variables often become the knowledge, experience, and support available in an individual intensive care unit. "New" therapies have the potential to help many patients but also have the potential to do great harm if clinicians do not follow standard guidelines and/or do not have the knowledge to use the therapy appropriately. It is clear that some current standards of care will be overthrown by future data while others will be finally substantiated. This Journal Conference queried the status quo to better enable clinicians to make informed decisions in the care of their critically ill patients. (+info)
Capnometry in the prehospital setting: are we using its potential?
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Capnometry is a non-invasive monitoring technique which allows fast and reliable insight into ventilation, circulation, and metabolism. In the prehospital setting it is mainly used to confirm correct tracheal tube placement. In addition it is a useful indicator of efficient ongoing cardiopulmonary resuscitation due to its correlation with cardiac output, and successful resuscitation. It helps to confirm the diagnosis of pulmonary thromboembolism and to sustain adequate ventilation in mechanically ventilated patients. In patients with haemorrhage, capnometry provides improved continuous haemodynamic monitoring, insight into adequacy of tissue perfusion, optimisation within current hypotensive fluid resuscitation strategy, and prevention of shock progression through controlled fluid administration. (+info)
Capnometry and air insufflation for assessing initial placement of gastric tubes.
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BACKGROUND: Nurses are often responsible for placement of large-bore gastric tubes. Tube misplacement into the lungs is a potential complication with serious sequelae. The reliability of common bedside methods for differentiating between pulmonary and gastric placement has not been acceptable. OBJECTIVE: To compare the accuracy of capnometry (colorimetric indicator of end-tidal carbon dioxide) and air insufflation/auscultation with the accuracy of radiography in detecting the location of gastric tubes. METHODS: A prospective convenience sample of insertions of Salem sump gastric tubes was studied. Tubes were inserted by nurses according to the unit's standard procedure, and air insufflation/auscultation, capnometry, and radiography were used to detect the position of the tubes. Results obtained with each of the methods were compared. RESULTS: A total of 91 tube placements were studied in 69 patients. No radiographically documented instances of lung placement occurred. Capnometry incorrectly indicated 15 of 91 gastric placements (16%) as placements in the lung. Air insufflation/auscultation incorrectly indicated 5 of 91 gastric placements (5%) as placements in the lung. CONCLUSIONS: Neither air insufflation nor capnometry is a fail-safe method for determining placement of gastric tubes. Radiography remains the preferred method. (+info)
Volumetric capnography and chronic obstructive pulmonary disease staging.
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Spirometry is difficult for some COPD patient to perform. Volumetric capnography could be a second choice test to evaluate the severity of functional disturbances. The aim of this work is to test this hypothesis. A total number of 98 subjects were classified either as normal ex-smokers (N=14) or COPD patients. The latter were staged following GOLD recommendations. Spirometry and volumetric capnography recordings were obtained from each patient. Spirometry parameters, Bohr Dead Space (V(D)Bohr), Airways Dead Space from the pre-interface expirate corrected curve (V(D)aw), Phase III slope (Sl(III)) and Volume of alveolar ejection (V(AE)) were measured. Index of Ventilatory Efficiency (IVE), and Index of Airways Heterogeneity (IAH) were calculated as: IVE = V(AE)/(V(T) - V(D)aw) and IAH = 1-[(V(T)-V(D)Bohr)/(V(T) - V(D)aw)]. In ANOCOVA analysis IAH showed the greatest association with stage (F >40), with no significant covariant dependence on V(T). A receiver operating characteristics curve analysis showed values of the area under the curve greater than 0.9 for IAH and IVE at all stage levels, with a sensitivity = specificity value greater than 80%. We conclude that IAH and IVE can be used when spirometry cannot be reliably performed, as an alternative test to evaluate the degree of functional involvement in COPD patients. (+info)
Mainstream end-tidal carbon dioxide monitoring in ventilated neonates.
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INTRODUCTION: Continuous noninvasive monitoring of the partial pressure of arterial carbon dioxide (PaCO2) in ventilated neonates would help clinicians to reduce arterial blood sampling. Our objective was to determine the correlation and agreement between end-tidal carbon dioxide (EtCO2) and PaCO2 in newborns ventilated for various clinical situations. METHODS: This prospective study was undertaken over 15 months in a teaching hospital. Simultaneous end-tidal and arterial CO2 pairs were obtained from ventilated neonates who were monitored by mainstream capnography and had indwelling arterial catheter. The correlation coefficient and degree of bias between EtCO2 and PaCO2 were assessed for various clinical situations. RESULTS: A total of 133 end-tidal and arterial CO2 pairs were analysed from 32 ventilated newborns. The mean gestational age was 34.6 +/- 3.8 weeks and birth weight was 2,200 +/- 780 g. The overall coefficient of correlation (r) was 0.73 (p-value is less than 0.001). The EtCO2 value was lower than the corresponding PaCO2 value in 86.5 percent pairs, with a mean bias of -6.65 +/- 7.54 mmHg (95 percent CI, - 7.9 to - 5.35). The r-value was more than or equal to 0.92 in neonates ventilated for sepsis, asphyxia and apnoea of prematurity, 0.67 in hyaline membrane disease (HMD) and 0.69 in meconium-aspiration syndrome. In HMD, neonates who received surfactant had a better r-value than those who did not (0.76 vs. 0.6). CONCLUSION: The correlation between mainstream EtCO2 and PaCO2 is good. Neonates with pulmonary disease will have a lower correlation. Surfactant therapy improves the correlation. EtCO2 monitoring is helpful in trending or screening for abnormal PaCO2 values. (+info)