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Airway Management
Published in Ian Greaves, Keith Porter, Jeff Garner, Trauma Care Manual, 2021
Ian Greaves, Keith Porter, Jeff Garner
Capnography is mandatory for intubation; however, it is not infallible, and in particular it may show a CO2 trace from a tube sited in the oesophagus if the patient has recently consumed carbonated drinks. However, in this setting the capnograph should detect CO2 for only a few breaths before giving a true reading. If the cardiac output is very low or absent, for example in patients with cardiac arrest, the capnograph will not give a trace as CO2 will not be transported from the tissues to the lungs. This may suggest that the tube is incorrectly positioned when it is in fact in the trachea. Clinical examination and invasive blood pressure tracings should give clues to this.
Critical Care and Anaesthesia
Published in Tjun Tang, Elizabeth O'Riordan, Stewart Walsh, Cracking the Intercollegiate General Surgery FRCS Viva, 2020
Rajkumar Rajendram, Alex Joseph, John Davidson, Avinash Gobindram, Prit Anand Singh, Animesh JK Patel
How do you interpret a pulse oximeter SaO2 or ABG PaO2 reading?SaO2 and PaO2 are meaningless without knowledge of the FiO2 (concentration of inspired oxygen).A normal PaO2 in room air (FiO2 21%) is 12 kPa.The ratio of PaO2 to FiO2 should be around 0.6.A PaO2 of 12 in a patient with a FiO2 of 40% is clearly hypoxic (12/40 = 0.3). His PaO2 should be 24.The PaO2 has a non-linear relationship to SaO2, although the two are often confused.SaO2 can be normal despite a low PaO2 in acute pulmonary embolus, reinforcing the need for ABGs in acute respiratory failure.It must be remembered that pulse oximetry does not assess ventilation.End-tidal CO2 and capnography must also be measured.
Chronic respiratory failure – pathophysiology
Published in Claudio F. Donner, Nicolino Ambrosino, Roger S. Goldstein, Pulmonary Rehabilitation, 2020
Mafalda Vanzeller, Marta Drummond, João Carlos Winck
Capnography refers to the noninvasive measurement of the partial pressure of carbon dioxide (PCO2) in exhaled breath expressed as the CO2 concentration during time (11). The relationship of CO2 concentration to time is graphically represented by the CO2 waveform, or capnogram. Changes in its shape are diagnostic of disease conditions, while changes in end-tidal CO2 (EtCO2 − the maximum CO2 concentration at the end of each tidal breath) can be used to assess disease severity and treatment response (11). EtCO2 measurement is accomplished by placement of an infrared sensor in the arm or ear of the patient. A beam of infrared light is passed across the gas sample to fall on a sensor. The presence of CO2 in the gas leads to a reduction in the amount of light falling on the sensor, which changes the voltage in a circuit. The analysis is rapid and accurate and is the result of the human breath infrared absorptive power. Capnography became a routine part of anaesthesia, and EtCO2 is now being routinely used to titrate pressures in noninvasive ventilation laboratories and to monitor treatment efficacy. Capnography or EtCO2 provides instantaneous information about ventilation, perfusion and metabolism (how CO2 is eliminated, transported and produced) and complements the information given by pulse oximetry (11).
Optimizing Physiology During Prehospital Airway Management: An NAEMSP Position Statement and Resource Document
Published in Prehospital Emergency Care, 2022
Daniel P. Davis, Nichole Bosson, Francis X. Guyette, Allen Wolfe, Bentley J. Bobrow, David Olvera, Robert G. Walker, Michael Levy
In addition to confirming initial advanced airway placement, capnography is the best method for ongoing monitoring of airway position. EMS clinicians should use continuous capnography during transport and movement of patients in order to monitor the position of the advanced airway and to rapidly detect dislodgement. While colorimetric devices can initially detect exhaled carbon dioxide, their effectiveness declines with exposure to air and liquids. Thus, these devices are not reliable for ongoing monitoring of advanced airway placement to detect dislodgement and cannot guide ventilation. Pulse oximetry is routinely used by EMS to monitor oxygenation status but is an unreliable strategy to confirm initial advanced airway placement and provides only delayed detection of airway dislodgement (49–51). Revisualization by direct or video laryngoscopy may be used for confirming ETT placement but cannot be used for continuous monitoring of advanced airway position. While some EMS systems allow SGA insertion by basic life support clinicians, the lack of capnography at this level must be recognized as a limitation; in which case colorimetric end-tidal CO2 detectors along with clinical signs of proper ventilation (chest rise, auscultation of lungs sounds) are the best alternative to confirm SGA placement. In these cases, waveform capnography should be placed as soon as practicable by advanced life support or hospital personnel.
Emerging approaches in pediatric mechanical ventilation
Published in Expert Review of Respiratory Medicine, 2019
Duane C Williams, Ira M Cheifetz
Volumetric capnography is the measure of carbon dioxide elimination (VCO2) as a function of the volume of gas exhaled (ml/min) rather than a partial pressure (torr). VCO2 relates to the patient’s degree of metabolism (i.e. carbon dioxide production), minute ventilation, and pulmonary capillary perfusion. Together ETCO2 and VCO2 can provide an understanding into the efficiency of ventilation by providing a direct measurement of the lung’s current capability for gas exchange, the degree of lung collapse, and dynamic changes in lung recruitment [63,66,67]. Additionally, the use of VCO2 allows providers to calculate physiologic dead space (VD/VT) by subtracting the mixed-expired partial pressure of carbon dioxide (PĒCO2) from the PaCO2, then dividing by the PaCO2.
Breathing pattern recordings using respiratory inductive plethysmography, before and after a physiotherapy breathing retraining program for asthma: A case report
Published in Physiotherapy Theory and Practice, 2018
Rokhsaneh Tehrany, Ruth DeVos, Anne Bruton
Previous trials of asthma BR have not reported any significant changes in Nijmegen scores (Holloway and West, 2007; Thomas et al., 2009), but in these studies baseline mean group scores were below the threshold for hyperventilation, leaving little room for improvement. The patient’s subjective hyperventilation score started high (39) and reduced to well below the threshold for hyperventilation syndrome after the program. In contrast, one of the objective physiological parameters that might be associated with hyperventilation (ETCO2) was largely unchanged and remained within normal ranges. However, one of the limitations associated with using capnography to record carbon dioxide levels in awake individuals is the need for nasal cannulae, which will not capture the outgoing breaths in a habitual mouth breather. The patient’s controlled breath hold time increased (doubled) which suggests she had gained better control over her breathing, and may indicate an improved tolerance to carbon dioxide, but this is speculation.