Determinants of distortions in CO2 catheter sampling systems: A mathematical model

Epstein, Robert; Reznik, A. M.; Epstein, Miles L.

doi:10.1016/0034-5687(80)90028-6

Cited by 20 publications

(3 citation statements)

References 11 publications

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“…The nature of COz plug mixing in these patients is unclear. In a mathematical model of catheter sampling systems, Epstein and colleagues calculated that molecular axial diffusion could be neglected when Schmidt's number (a dimensionless number relating viscosity and density as an index of the diffusibility of gases) is greater than 0.43 (6). The Schmidt's number of C02 in air is 1.2, suggesting that molecular axial diffusion does not occur (6).…”

Section: Discussionmentioning

confidence: 97%

“…Flow was laminar in our sampling system (Reynolds number is 256, calculated for a 50-m catheter with a flow of 240 mL/min, a transit time of 20 s, a velocity of 251 cm/s, a radius of 0.07 cm, the density of air as 0.0012 g/mL, and the viscosity of air as 0.000165 poise). Parabolic distortion is different from molecular axial diffusion, which would not have occurred in our system (6).…”

Section: Capnogram Baseline Increase In Infantsmentioning

confidence: 92%

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Respiratory Frequency and Artifact Affect the Capnographic Baseline in Infants

Se²,

Je³

1993

Anesthesia & Analgesia

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We sought to determine the effect of rebreathing on the capnographic waveform baseline. In anesthetized infants, we studied the effect of respiratory frequency (f) and breathing circuit type (Bain, n = 6, and pediatric circle, n = 4) on capnography of respiratory gas aspirated from the circuit for mass spectrometry (PCO2asp) and flowing through an infrared analyzer (PCO2f-t). As f increased, measured values of PiCO2asp and PiCO2f-t increased in both Bain and circle groups, with the exception of PiCO2f-t values that remained zero in the circle group. PETCO2 decreased as f increased in the circle groups, but remained constant in the Bain groups. These data suggest that artifact, most likely due to parabolic distortion of CO2 plugs traversing long sampling catheters, makes up a significant percentage (8%-36%) of the aspiration capnographic baseline elevation depending on f and breathing circuit type. Despite increases in PiCO2 as f increased, PETCO2 does not increase in Bain circuits due primarily to an increase in minute ventilation (Ve) that offsets the increase in the PiCO2 to provide balance in the CO2 mass relationship (PETCO2 approximately VCO2/Ve+PiCO2). These findings are useful in the correct interpretation of elevated capnographic baseline in infants.

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Section: Discussionmentioning

confidence: 97%

Section: Capnogram Baseline Increase In Infantsmentioning

confidence: 92%

Respiratory Frequency and Artifact Affect the Capnographic Baseline in Infants

Se²,

Je³

1993

Anesthesia & Analgesia

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“…Este resultado pode também ter relação com a ausência de vedação perfeita do traqueotubo à traqueia e pelo alto fluxo de gases que foi empregado no sistema. Segundo Epstein, Reznik eEpstein (1980), no mecanismo de funcionamento do sistema sidestream, o gás expirado pode ser diluído com ar ambiente arrastado sempre que a vazão do gás cair abaixo do volume aspirado de forma constante pelo capnógrafo. O design do tubo de amostragem e seu posicionamento no circuito respiratório ou nas narinas (se for usado um cateter nasal) podem afetar a quantidade de ar circundante que é arrastado junto com o gás expirado.…”

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>b<Determinação da concentração expirada de isofluorano frente a estímulo nociceptivo supramáximo em mico-leão-da-cara-dourada (>i<Leontopithecus chrysomelas>/i<)>/b<

Rassy¹

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À minha amada esposa, Bruna Yolanda Bons, pelo amor, parceria, dedicação e incentivo, que se traduz no total apoio e ajuda que obtive durante esta fase e que foi abrilhantada com a chegada da nossa querida filha. À minha linda filha, Mariah Bons Rassy, que nestes poucos meses já me ensina, a cada dia, quais são as coisas mais importantes da vida. À Profª. Drª. Silvia Renata Gaido Cortopassi por ter aceitado esta jornada, confiando e me ajudando com toda sua a experiência profissional e simpatia que tanto admiro e respeito. Muito Obrigado! À minha mãe Ana Lídia Braga Rassy, pelo eterno apoio em minhas decisões e torcida.Ao meu irmão Fábio Braga Rassy por sempre me lembrar que eu deveria ter estudado. Kkk.Ao Dr. Paulo Magalhães Bressan e ao Dr. João Batista da Cruz, por acreditarem e possibilitarem a realização deste trabalho. À Fundação Parque Zoológico de São Paulo, em nome de todos seus trabalhadores, que se dedicam a esta instituição de forma incondicional. Todos foram muito importantes para a execução deste trabalho, sem exceção. Muito obrigado! Aos meus colegas Mario Ferraro, Andressa Kotleski, Luciano Cacciari e Paula Finkensieper que me ajudaram demais durante a execução deste projeto.A todos da Divisão de Veterinária (DV) que me ajudaram dividindo as responsabilidades em alguns momentos durante esta fase e que tornam viável o atendimento da grande rotina que temos diariamente. Obrigado! À Faculdade de Medicina Veterária e Zootecnia (FMVZ-USP) pela oportunidade de engrandecimento profissional.

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Accuracy of end-tidal carbon dioxide tension analyzers

Raemer

Calalang

1991

J Clin Monitor Comput

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Substantial mean differences between arterial carbon dioxide tension (PaCO2) and end-tidal carbon dioxide tension (PETCO2) in anesthesia and intensive care settings have been demonstrated by a number of investigators. We have explored the technical causes of error in the measurement of PETCO2 that could contribute to the observed differences. In a clinical setting, the measurement of PETCO2 is accomplished with one of three types of instruments, infrared analyzers, mass spectrometers, and Raman spectrometers, whose specified accuracies are typically +/- 2, +/- 1.5, and +/- 0.5 mm Hg, respectively. We examined potential errors in PETCO2 measurement with respect to the analyzer, sampling system, environment, and instrument. Various analyzer error sources were measured, including stability, warm-up time, interference from nitrous oxide and oxygen, pressure, noise, and response time. Other error sources, including calibration, resistance in the sample catheter, pressure changes, water vapor, liquid water, and end-tidal detection algorithms, were considered and are discussed. On the basis of our measurements and analysis, we estimate the magnitude of the major potential errors for an uncompensated infrared analyzer as: inaccuracy, 2 mm Hg; resolution, 0.5 mm Hg; noise, 2 mm Hg; instability (12 hours), 3 mm Hg; miscalibration, 1 mm Hg; selectivity (70% nitrous oxide), 6.5 mm Hg; selectivity (100% oxygen), -2.5 mm Hg; atmospheric pressure change, less than 1 mm Hg; airway pressure at 30 cm H2O, 2 mm Hg; positive end-expiratory pressure or continuous positive airway pressure at 20 cm H2O, 1.5 mm Hg; sampling system resistance, less than 1 mm Hg; and water vapor, 2.5 mm Hg. In addition to these errors, other systematic mistakes such as an inaccurate end-tidal detection algorithm, poor calibration technique, or liquid water contamination can lead to gross inaccuracies. In a clinical setting, unless the user is confident that all of the technical error sources have been eliminated and the physiologic factors are known, depending on PETCO2 to determine PaCO2 is not advised.

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Determinants of distortions in CO2 catheter sampling systems: A mathematical model

Cited by 20 publications

References 11 publications

Respiratory Frequency and Artifact Affect the Capnographic Baseline in Infants

Respiratory Frequency and Artifact Affect the Capnographic Baseline in Infants

>b<Determinação da concentração expirada de isofluorano frente a estímulo nociceptivo supramáximo em mico-leão-da-cara-dourada (>i<Leontopithecus chrysomelas>/i<)>/b<

Accuracy of end-tidal carbon dioxide tension analyzers

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