A model to describe the rate of oxyhaemoglobin desaturation during apnoea

Farmery, Andrew D.; Roe, Philip L.

doi:10.1093/bja/76.2.284

Cited by 183 publications

(95 citation statements)

References 13 publications

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“…10 Measurements of arterial oxygen tension, 6,7 ETN 2 , 11 ETO 2 12,13 concentrations reflect the efficacy of preoxygenation, whereas the slowing of the rate of arterial oxyhemoglobin desaturation during apnea 10,14 is indicative of its efficiency. Since there are many factors that affect the decrease of arterial oxyhemoglobin saturation during apnea, such as capacity of oxygen loading and total oxygen consumption, 10,15,16 it is of utmost importance to maximally preoxygenate the patient to fill the alveolar and arterial compartments with oxygen, especially when difficult ventilation and/ or intubation are anticipated.…”

Section: Discussionmentioning

confidence: 99%

Efficacy of preoxygenation using tidal volume and deep breathing techniques with and without prior maximal exhalation

Nimmagadda

Salem

Joseph

et al. 2007

Can J Anesth/J Can Anesth

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Purpose:We evaluated the influence of prior maximal exhalation on preoxygenation in 15 adult volunteers using tidal volume breathing (TVB) for five minutes and deep breathing (DB) for two minutes with and without prior maximal exhalation.Methods: Inspired and end-tidal oxygen, nitrogen and carbon dioxide were monitored continuously and recorded during room air breathing and at 30-sec intervals during 100% oxygen TVB or DB (rate of 8 breaths·min -1 ).Results: Tidal volume breathing with prior maximal exhalation resulted in an end-tidal oxygen concentration (ETO 2 ) slightly higher (P = 0.028) at 0.5 and 1.0 min as compared with TVB without prior maximal exhalation at the same time periods. Regardless of whether TVB was preceded by maximal exhalation or not, 2.5 min was required to reach a mean ETO 2 value of 90% or higher. With DB, there were no differences in ETO 2 values at any time period and 1.5 min was required to reach an ETO 2 of 90% or greater, with or without prior maximal exhalation. Conclusions:Maximal exhalation prior to TVB slightly steepens the initial rise in ETO 2 during the first minute, but confers no real benefit if maximal preoxygenation is the goal. Maximal exhalation prior to DB has no added value in enhancing preoxygenation.

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Section: Discussionmentioning

confidence: 99%

Efficacy of preoxygenation using tidal volume and deep breathing techniques with and without prior maximal exhalation

Nimmagadda

Salem

Joseph

et al. 2007

Can J Anesth/J Can Anesth

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“…According to Sands et al [4], the first theoretical analysis of the factors influencing apnoeic desaturation was that of Farmery and Roe [3]. This analysis was constructed from first principles using discrete equations, solved symbolically, and so this now seems rather quaint compared with more contemporary analyses that invariably use computational numerical techniques or simulation tools, such as Simulink The basis of all these analyses lies in a physical model with stated assumptions.…”

Section: Modelling Obstructed Apnoeamentioning

confidence: 99%

“…During obstructed apnoea, there is no influx from the trachea, yet oxygen continues to be removed from the alveolar compartment by the pulmonary blood, and so the alveolar PO 2 (P A O 2 ) and arterial PO 2 (P a O 2 ) begin to fall. Some models assume that alveolar volume remains constant during apnoea [3], whereas, in fact, the lung volume will diminish somewhat, because in early apnoea, oxygen uptake from the lung is greater than CO 2 delivery to it. This property is incorporated into other models [2], although the differences in model behaviours are not great.…”

Section: Modelling Obstructed Apnoeamentioning

confidence: 99%

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Simulating hypoxia and modelling the airway

Farmery

2011

Anaesthesia

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SummaryApnoea due to airway obstruction is an ever present concern in anaesthesia and critical care practice and results in rapid development of hypoxaemia that is not always remediable by manual bag‐mask ventilation. As it is often difficult or impossible to study experimentally (although some historical animal data exist), it is useful to model the kinetics of hypoxaemia following airway obstruction. Despite being a complex event, the consequences of airway obstruction can be predicted with reasonable fidelity using mathematical and computer modelling. Over the last 15 years, a number of high fidelity mathematical and computer models have been developed, that have thrown light on this important event.

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“…[2][3][4][5][6][7][8] Several barriers exist for widespread implementation of P ETCO 2 monitoring during sedation in clinical practice. They include: (1) lack of face mask options to accurately measure P ETCO 2 , (2) patients' inability to tolerate nasal cannula, and (3) perceived uncertainty in accuracy of the data.…”

Section: Introductionmentioning

confidence: 99%

Redesign of an Open-System Oxygen Face Mask With Mainstream Capnometer for Children

Napolitano

Nishisaki²,

Buffman

et al. 2016

Respir Care

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BACKGROUND: Partial pressure of end-tidal carbon dioxide (P ETCO 2 ) monitoring in children is important to detect apnea or hypopnea early to intervene before hypoxemia develops. Monitoring P ETCO 2 in children without a tracheal tube is challenging. To improve P ETCO 2 measurement accuracy in a commercially available mask with a mainstream CO 2 detector, we implemented design changes with deform-and-hold shaping technology and anterior-posterior adjustment of the expiratory gas flow cup. METHODS: Two sizes of redesigned face masks (small for 7-20 kg, medium for 10 -40 kg) were evaluated. Initial bench testing used a simulator modeling a spontaneously breathing infant and child with a natural airway. An infant/child manikin head was connected to the breathing lung simulator. A mass flow controller provided expiratory CO 2 . Mask fit was then evaluated on healthy human subjects to identify anatomical features associated with good fit, defined as square shape capnography waveform during expiration. A 3-dimensional digital scan was used to quantify anatomical features. The gaps between face mask rims and facial surface were manually measured. RESULTS: Bench testing revealed a P ETCO 2 difference of 3.4 ؎ 1.5 mm Hg between a measured P ETCO 2 by the redesigned mask and CO 2 concentration at trachea, as compared with 6.7 ؎ 6.2 mm Hg between P ETCO 2 measured by nasal cannula and trachea (P < .001). In the human mask fit study, 35 children (13 ؎ 4 kg) with the small mask and 38 (24 ؎ 8 kg) with the medium mask were evaluated. Capnography tracing was successfully obtained in 86% of the small and 100% of the medium masks. In children with small-size masks, the gap between the face mask rim and the child's face was not statistically different among those with good mask fit and without (1.0 ؎ 1.5 mm vs 1.4 ؎ 1.9 mm, P ‫؍‬ .73). CONCLUSIONS: P ETCO 2 measurement by a redesigned open-system face mask with a mainstream CO 2 detector was accurate in the bench setting. The redesigned face mask can attain good mask fit and accurate capnography tracings in the majority of infants and children.

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A model to describe the rate of oxyhaemoglobin desaturation during apnoea

Cited by 183 publications

References 13 publications

Efficacy of preoxygenation using tidal volume and deep breathing techniques with and without prior maximal exhalation

Efficacy of preoxygenation using tidal volume and deep breathing techniques with and without prior maximal exhalation

Simulating hypoxia and modelling the airway

Redesign of an Open-System Oxygen Face Mask With Mainstream Capnometer for Children

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