Time Capnography Research Articles

Association of dead space fraction to mortality in patients with COVID-19-related ARDS: A historical cohort observational study

ObjectiveTo assess the correlation of dead space fraction (VD/VT) measured through time capnography, corrected minute volume (CMV) and ventilation ratio (VR) with clinical outcomes in COVID-19 patients requiring invasive mechanical ventilation. DesignObservational study of a historical cohort. SettingUniversity hospital in Medellin, Colombia. ParticipantsPatients aged 15 and above with a confirmed COVID-19 diagnosis admitted to the ICU and requiring mechanical ventilation. InterventionsMeasurement of VD/VT, CMV, and VR in COVID-19 patients. Main variables of interestVD/VT, CMV, VR, demographic data, oxygenation indices and ventilatory parameters. ResultsDuring the study period, 1047 COVID-19 patients on mechanical ventilation were analyzed, of whom 446 (42%) died. Deceased patients exhibited a higher prevalence of advanced age and obesity, elevated Charlson index, higher APACHE II and SOFA scores, as well as an increase in VD/VT ratio (0.27 in survivors and 0.31 in deceased) and minute ventilation volume on the first day of mechanical ventilation. The multivariate analysis revealed independent associations to in-hospital mortality, higher VD/VT (HR 1.24; 95%CI 1.003–1.525; p = 0.046), age (HR 1.024; 95%CI 1.014–1.034; p < 0.001), and SOFA score at onset (HR: 1.036; 95%CI: 1.001–1.07; p = 0.017). ConclusionsVD/VT demonstrated an association with mortality in COVID-19 patients with ARDS on mechanical ventilation. These findings suggest that VD/VT measurement may serve as a severity marker for the disease.

Comparison of real-time ultrasonography with waveform capnography in verifying endotracheal tube location- An observational study

Immediate post-intubation confirmation of endotracheal tube requires direct observational or secondary gadgets-dependent measures having variable sensitivity and specificity. In this study, dynamic real-time ultrasonography is used for the evaluation of endotracheal tube. The correlation between the gold standard test(Capnography) and the unconventional test(Ultrasonography) is also evaluated.One hundred ASA PS 1, and ASA PS 2 patients were evaluated for endotracheal intubation using real-time ultrasonography. The desired endotracheal intubation was further confirmed by using time capnography. Victorious tracheal intubation was identified using some radiological signs, only one air-mucosa interface with a comet-tail artefact and enhanced posterior acoustic shadowing indicative of endotracheal intubation. Two air-mucosa interfaces with comet-tail artefacts with posterior shadowing were indicative of oesophageal intubation.The mean (SD) ages of the studied patients were 41.25±7.76 Yrs. A total of 87% of patients had endotracheal intubation and 13% had oesophageal intubation based on ultrasonography scan findings. Capnography finding was 91% endotracheal intubations, 9% were true oesophageal. The true positive and true negative rate, positive predictive value and negative predictive values of real-time ultrasonography were 95%, (95% confidence interval (CI) 88% to 98%) 100% (95% CI 62% to 100%), 100% (95% CI 94% to 100%), 69% (95% CI 38% to 89%) respectively. Kappa (k) value was 0.8. Ultrasonography is a portable sensitive screening equipment for ETT position confirmation. There is a strong association between USG findings with time capnography results.

Asociación de fracción de espacio muerto con la mortalidad en pacientes con síndrome de dificultad respiratoria aguda por COVID-19: Un estudio observacional de una cohorte histórica

ObjectiveTo assess the association between dead space fraction (VD/VT) measured through time capnography, corrected minute volume (CMV), and ventilation ratio (VR) with clinical outcomes in COVID-19 patients requiring invasive mechanical ventilation. DesignObservational study of a historical cohort in an university hospital in Medellin, Colombia. ParticipantsPatients aged 15 and above with confirmed COVID-19 diagnosis admitted to the ICU requiring mechanical ventilation; interventions: measurement of VD/VT, CMV, and VR in COVID-19 patients. Main variables of interestVD/VT, CMV, VR, demographic data, oxygenation index, and ventilatory parameters. ResultsDuring the study period, 1,047 COVID-19 patients on mechanical ventilation were analyzed, of whom 446 (42%) died. Deceased patients exhibited a higher prevalence of advanced age and obesity, elevated Charlson index, higher APACHE II and SOFA scores, as well as an increase in VD/VT ratio (0.27 in survivors and 0.31 in deceased) and minute ventilation volume on the first day of mechanical ventilation. Multivariate analysis revealed independent associations with in-hospital mortality, higher VD/VT (HR: 1.24; 95% CI: 1.003-1.525; P=0.046), age (HR: 1.024; 95% CI: 1.014-1.034; P<0.001), and SOFA score at onset (HR: 1.036; 95% CI: 1.001-1.07; P=0.017). ConclusionsVD/VT demonstrated an association with mortality in COVID-19 ARDS patients on mechanical ventilation. These findings suggest that VD/VT measurement may serve as a severity marker for the disease.

Volumetric but Not Time Capnography Detects Ventilation/Perfusion Mismatch in Injured Rabbit Lung.

Whereas time capnography (Tcap) is routinely displayed during mechanical ventilation, the volumetric representation (Vcap) is seldom used. We compared the diagnostic value of indices derived from Tcap and Vcap following ventilation to perfusion ratio () mismatch subsequent to experimentally induced acute respiratory distress syndrome (ARDS), and alveolar recruitment by elevating the positive end-expiratory pressure (PEEP). Lung injury was induced by iv lipopolysaccharide, whole lung lavage and injurious ventilation in anesthetized, mechanically ventilated rabbits (n = 26). Mainstream Tcap and Vcap were performed to assess normalized phase 2 (Sn2T, Sn2V) and phase 3 slopes (Sn3T, Sn3V) in the time and volumetric domains. Vcap was also used to estimate Enghoff’s physiological dead space (VDE). Lung oxygenation index (PaO2/FiO2) and intrapulmonary shunt (Qs/Qt) were derived from arterial and central venous blood gas samples. All measurements were made under baseline conditions, and, following lung injury, under moderate (6 cmH2O) and high PEEP levels (9 cmH2O). Lung injury deteriorated the PaO2/FiO2 (baseline vs. injured 466 ± 10.2 [95% confidence interval] vs. 77.3 ± 17.1 mmHg, p < 0.05) and compromised all mechanical parameters significantly, whereas Tcap parameters exhibited contradictory or inconsistent changes. Conversely, Vcap indices exhibited consistent changes and provided excellent diagnostic value in detecting lung-function deterioration subsequent to lung injury [area under the receiver operating characteristic (ROC) curve of 1.0 ± 0.0, 0.87 ± 0.22 and 0.86 ± 0.22 for VDE, Sn3V and Sn3V/Sn2V, respectively]. Elevated PEEP increased PaO2/FiO2 and decreased Qs/Qt, which was reflected only in the Vcap slope ratio (Sn3V/Sn2V, p < 0.05). Our findings demonstrate the limited value of Tcap to detect ventilation to perfusion ratio () mismatch, following severe lung injury. Conversely, indices derived from Vcap proved to be sensitive for detecting lung volume loss and alveolar recruitment. Therefore, promotion of Vcap is of paramount importance as a real-time, non-invasive, bedside monitoring modality to detect the development of and to follow-up the progression of lung injury in a model of ARDS.

Capnogram slope and ventilation dead space parameters: comparison of mainstream and sidestream techniques

BackgroundCapnography may provide useful non-invasive bedside information concerning heterogeneity in lung ventilation, ventilation–perfusion mismatching and metabolic status. Although the capnogram may be recorded by mainstream and sidestream techniques, the capnogram indices furnished by these approaches have not previously been compared systematically. MethodsSimultaneous mainstream and sidestream time and volumetric capnography was performed in anaesthetized, mechanically ventilated patients undergoing elective heart surgery. Time capnography was used to assess the phase II (SII,T) and III slopes (SIII,T). The volumetric method was applied to estimate phase II (SII,V) and III slopes (SIII,V), together with the dead space values according to the Fowler (VDF), Bohr (VDB), and Enghoff (VDE) methods and the volume of CO2 eliminated per breath ( VCO2). The partial pressure of end-tidal CO2 ( PETCO2) was registered. ResultsExcellent correlation and good agreement were observed in SIII,T measured by the mainstream and sidestream techniques [ratio=1.05 (sem 0.16), R2=0.92, P<0.0001]. Although the sidestream technique significantly underestimated VCO2 and overestimated SIII,V [1.32 (0.28), R2=0.93, P<0.0001], VDF, VDB, and VDE, the agreement between the mainstream and sidestream techniques in the difference between VDE and VDB, reflecting the intrapulmonary shunt, was excellent [0.97 (0.004), R2=0.92, P<0.0001]. The PETCO2 exhibited good correlation and mild differences between the mainstream and sidestream approaches [0.025 (0.005) kPa]. ConclusionsSidestream capnography provides adequate quantitative bedside information about uneven alveolar emptying and ventilation–perfusion mismatching, because it allows reliable assessments of the phase III slope, PETCO2 and intrapulmonary shunt. Reliable measurement of volumetric parameters (phase II slope, dead spaces, and eliminated CO2 volumes) requires the application of a mainstream device.

Capnography as an aid in localizing the phrenic nerve in brachial plexus surgery. Technical note.

BackgroundTo determine whether monitoring end- tidal Carbon Dioxide (capnography) can be used to reliably identify the phrenic nerve during the supraclavicular exploration for brachial plexus injury.MethodsThree consecutive patients with traction pan-brachial plexus injuries scheduled for neurotization were evaluated under an anesthetic protocol to allow intraoperative electrophysiology. Muscle relaxants were avoided, anaesthesia was induced with propofol and fentanyl and the airway was secured with an appropriate sized laryngeal mask airway. Routine monitoring included heart rate, noninvasive blood pressure, pulse oximetry and time capnography. The phrenic nerve was identified after blind bipolar electrical stimulation using a handheld bipolar nerve stimulator set at 2–4 mA. The capnographic wave form was observed by the neuroanesthetist and simultaneous diaphragmatic contraction was assessed by the surgical assistant. Both observers were blinded as to when the bipolar stimulating electrode was actually in use.ResultsIn all patients, the capnographic wave form revealed a notch at a stimulating amplitude of about 2–4 mA. This became progressively jagged with increasing current till diaphragmatic contraction could be palpated by the blinded surgical assistant at about 6–7 mA.ConclusionCapnography is a sensitive intraoperative test for localizing the phrenic nerve during the supraclavicular approach to the brachial plexus.

Abstract 84: Hyperventilation Alert During Out-of-Hospital Cardiopulmonary Resuscitation Using an Automated Capnogram Analysis Algorithm

Background Hyperventilation during cardiopulmonary resuscitation (CPR) inhibits venous blood return, decreases coronary perfusion pressure, and is associated with decreased survival rates. Accurate computation of ventilation rate during CPR by defibrillator-based algorithms is difficult due to artifact induced on impedance waveforms. Real time capnography may help detect inadvertent hyperventilation during resuscitation. Objective To evaluate an automated defibrillator-based capnogram (CO2) analysis method to alert for excessive ventilation rate in the presence of low end-tidal CO2 (EtCO2). Methods Recordings from 270 OHCA patients with capnogram waveforms were collected between 2008 and 2010 from two EMS agencies based in Oregon and Texas. The hyperventilation detection algorithm was added to a previously reported EtCO2 analysis program. The hyperventilation algorithm employs exponentially-weighted moving-average filtering (alpha=0.25) to compute respiration rate (RR) and EtCO2 trends from individual breath-breath intervals and breath EtCO2 measurements. A combination of RR and EtCO2 is used in the decision tree. The algorithm was tested using a threshold of RR &gt; 12 bpm and EtCO2 &lt; 20 mmHg. The added requirement of a low EtCO2 avoids false detection on post-resuscitation spontaneous respirations which are unlikely to have low EtCO2. Hyperventilation alerts generated by algorithm were manually validated by two reviewers who had access to CO2, ECG, compression, and impedance-based respiration waveforms. Results The automated program generated 414 hyperventilation alerts in 148 (55%) patients. A total of 24 alerts were identified as false positive due to artifacts in the capnogram waveform. No false negative alert was identified. This yields an algorithm sensitivity of 100% and positive-predictive value 94%. During validated hyperventilation, the average maximum ventilation rate was 25 ±11 bpm, with an average minimum EtCO2 of 6 ±4 mmHg. Conclusion Hyperventilation is common in OHCA resuscitation. An automated capnogram analysis method can accurately detect episodes of hyperventilation and has the potential to alert EMS personal to excessive ventilation rates during OHCA resuscitation.

18: A Comparison of Capnographic Waveform Indices and Peak Flow Meter in the Monitoring of Asthmatic Patients in Emergency Departments

“Time capnography” is the continuous plot of levels of expired carbon dioxide over time producing a capnographic waveform. It is the analysis of such waveforms that forms the basis of this study. The normal capnogram has an almost square-wave pattern which consists of: 1) a latency phase (Phase I), corresponding to the expiration of the anatomical dead space; 2) slope phase (Phase II) corresponding to expiration of mixed air; and 3) plateau phase (Phase III), reflecting the elimination of alveolar air.

Capnography

Capnography URL: http://www.capnography.com/ , Institution: Harvard Medical School, Brigham and Women’s Hospital, Department of Anesthesia, Boston, Massachusetts , Author/Webmaster: Bhavani-Shankar Kodali, M.D. , Jeffrey M. Cusick, M.D. , Director of Anesthesiology , 56th Medical Group , Luke Air Force Base, Arizona , Preceptor of Anesthesiology , Midwestern University , Arizona College of Osteopathic Medicine, Glendale, Arizona , jeff@cusick.comDr. Bhavani-Shankar Kodali, a well-published expert on the subject of capnography, has created the Capnography Web site without sponsorship from any equipment or pharmaceutical company. His purpose is to fulfill his “long-standing goal of developing an easily accessible educational and interactive site on capnography, that cannot only address the basic principles but also be a forum for active discussion and learning on issues related to capnography in all medical fields.”Unlike a textbook, a Web site can contain interactive media to assist in the understanding of concepts. The Capnography Web site makes use of animated graphics known as animated .gif files. They provide a dynamic visual presentation, which facilitates easy learning. Capnographic tracings move across the screen as they do in a real capnograph. In addition, areas of interest are sometimes highlighted and labeled over time. The process then loops back to the beginning to be repeated.The Web site is well-organized and easy to use. It presents a scrolling frame on the left with labeled buttons to access the various areas of interest. The section entitled ASA Guidelines discusses the changes in standards pertaining to expired carbon dioxide monitoring. 1The basic knowledge area, called Why Capnography?, includes sections about physics, physiology, terminology, definitions, and clinical uses. The Capno-Encyclopedia contains an atlas of capnograms. Capno-Tips contains pointers for making the best use of capnography. The Capno-Quiz section can test your knowledge about capnography. The Capno-Magic Screen section pops up as a separate window and shows capnography tracings for more than 30 different clinical situations when the cursor is placed over the text of a subject. The Capno-Pitfalls section outlines major limitations of time capnography. The following separate sections are also included: Capnography in Pediatrics, Laparoscopy, Thoracic Surgery, and Intensive Care. A list of frequently asked questions is included, and the site has a guest book to leave comments.The Web site was written by the author with assistance from two contributors for technical consultation and creation of animations. The author has considerable experience related to capnography at a major academic center and has published many articles in established journals. There is some overlap and repetition of information throughout the various sections, which could benefit from minor reorganization. The sections are well-referenced, with many cited articles written by the author himself. The site offers excellent educational material, including a quiz area to test knowledge.The layout, formatting, and compatibility of the site could be improved. Odd highlighting of text with overuse of many different background colors detracts from the site’s readability. The Web site requires Internet Explorer Web browser (Microsoft, Redmond, WA) with a Microsoft Windows operating system to function properly. Unfortunately, the home page is a blank white screen when viewed with the latest Internet Explorer 5 with Macintosh operating systems 9.1 and X (Apple, Cupertino, CA). In Netscape Navigator 4.7 (Netscape Communications, Mountain View, CA), the Capno-Magic Screen is inoperable because of JAVA incompatibilities. In other browsers where JAVA is functional, highlighted text is invisible. Fortunately, the animated graphics are compatible with most Web browsers.Dr. Kodali has put forth great effort to produce the equivalent of a capnography textbook and made it freely available on the Internet. The site provides a complete review of end-tidal carbon dioxide monitoring during anesthesia and intensive care. In addition, his Web site provides animated graphics that are not possible to produce in a textbook and can greatly facilitate learning. The site could benefit from decreased use of distracting colors and improved compatibility, but these deficiencies can easily be overcome. Capnography.com is truly an “all-in-one” for the subject of capnography and a great teaching contribution.

Terminology and the current limitations of time capnography: a brief review.

The carbon dioxide (CO2) trace versus time (time capnography) is convenient and adequate for clinical use. This is the method most commonly utilized in capnography. However, the current terminology in time capnography has not yet been standardized and is, therefore, a potential source of confusion. Standard terminology that is based on convention and logic to represent the various phases of a time capnogram is essential. The time capnogram should be considered as two segments: an inspiratory segment and an expiratory segment. The inspiratory segment is termed as phase ); the expiratory segment is divided into phases I, II, III, and, occasionally, IV. Phase I represents the CO2-free gas from the airways (anatomical dead space); phase II consists of a rapid S-shaped upswing on the tracing due to mixing of dead space gas with alveolar gas; and phase III, the alveolar plateau, represents CO2-rich gas from the alveoli. The physiologic basis of phase IV, the terminal upswing at the end of phase III, which is observed in capnograms recorded under certain circumstances (such as in pregnant subjects and obese subjects) is discussed in detail. The clinical implications of the alpha angle, which is the angle between phases II and III, and the beta angle, which is the angle between phases III and the descending limb of phase 0, are outlined. The subtle but important limitations of time capnography are reviewed; its current status as well as its future potential are explored.