BET 1: Everything in graduation: arterial/end-tidal CO2 gradient and the diagnosis of pulmonary embolism.

A short cut review was carried out to establish the diagnostic characteristics of alveolar dead space fraction (AVDSf) in the diagnosis of pulmonary embolism (PE). This is calculated from the arterial and end-tidal CO2 Three papers were selected to answer the clinical question. The author, study type, relevant outcomes, results and weaknesses are tabulated. It is concluded that there is good evidence to support the use of AVDSf within a clinical prediction model to exclude a PE in patients when there is a low pretest probability. However, the specificity is not sufficient to support it as a 'rule in' test.

Evaluation of Capnography Sampling Line Compatibility and Accuracy when Used with a Portable Capnography Monitor.

Capnography is commonly used to monitor patient's ventilatory status. While sidestream capnography has been shown to provide a reliable assessment of end-tidal CO2 (ETCO2), its accuracy is commonly validated using commercial kits composed of a capnography monitor and its matching disposable nasal cannula sampling lines. The purpose of this study was to assess the compatibility and accuracy of cross-paired capnography sampling lines with a single portable bedside capnography monitor. A series of 4 bench tests were performed to evaluate the tensile strength, rise time, ETCO2 accuracy as a function of respiratory rate, and ETCO2 accuracy in the presence of supplemental O2. Each bench test was performed using specialized, validated equipment to allow for a full evaluation of sampling line performance. The 4 bench tests successfully differentiated between sampling lines from different commercial sources and suggested that due to increased rise time and decreased ETCO2 accuracy, not all nasal cannula sampling lines provide reliable clinical data when cross-paired with a commercial capnography monitor. Care should be taken to ensure that any cross-pairing of capnography monitors and disposable sampling lines is fully validated for use across respiratory rates and supplemental O2 flow rates commonly encountered in clinical settings.

Comparison of mainstream (Capnostat 5) and two low-flow sidestream capnometers (VM-2500-S and Capnostream) in spontaneously breathing rabbits anesthetized with a Bain coaxial breathing system.

OBJECTIVE: To evaluate agreement with PaCO2 of two low sampling rate sidestream capnometers and a mainstream capnometer in rabbits and the effect of using high fresh gas flow from a Bain coaxial breathing system. STUDY DESIGN: Prospective, crossover study. ANIMALS: A total of 10 New Zealand White rabbits weighing 3.4 ± 0.3 kg [mean ± standard deviation (SD)]. METHODS: Two sidestream analyzers (Viamed VM-2500-S and Capnostream 35) with a sampling rate of 50 mL minute-1 and a mainstream capnometer (Capnostat 5) were tested. All capnometers used infrared spectroscopy and advanced microprocessor technology. Rabbits were anesthetized and intubated with noncuffed endotracheal tubes of 3 mm internal diameter and adequate seal. A sidestream sampling adapter or the mainstream capnometer was attached to the endotracheal tube and connected to a Bain coaxial breathing system. Oxygen (1.5 L minute-1) delivered sevoflurane to maintain anesthesia. An auricular artery catheter allowed blood sampling for PaCO2 analysis corrected to rectal temperature. Inspired and end-tidal carbon dioxide (Pe'CO2) measurements were recorded during blood sample withdrawal. From each rabbit, 10 paired PaCO2/Pe'CO2 measurements were obtained. Each rabbit was recovered from anesthesia and was anesthetized again with an alternate capnometer after 1 week. Data were analyzed using Bland-Altman and two-way anova for repeated measures. RESULTS: Analysis included 100 paired samples. Negative bias reflects underestimation of PaCO2. Bland-Altman mean (±1.95 SD) was -16.7 (-35.2 to 1.8) mmHg for Capnostat 5, -27.9 (-48.6 to -7.2) mmHg for Viamed, and -18.1 (-34.3 to -1.9) mmHg for Capnostream. Viamed PaCO2-Pe'CO2 gradient was greater than other two capnometers. CONCLUSIONS: All three capnometers underestimated PaCO2. Capnostat 5 and Capnostream performed similarly. CLINICAL RELEVANCE: These capnometers underestimated PaCO2 in spontaneously breathing rabbits anesthetized using a Bain coaxial breathing system with high fresh gas flows.

Usefulness of Measurement of End-tidal CO2 Using a Portable Capnometer in Patients with Chronic Respiratory Failure Receiving Long-term Oxygen Therapy.

Objective Patients with chronic respiratory failure requiring long-term oxygen therapy (LTOT) are at a risk of CO2 retention because of excessive oxygen administration. The CapnoEye™ is a novel portable capnometer that can measure end-tidal CO2 (EtCO2) noninvasively. This retrospective study evaluated the usefulness of this device. Methods EtCO2 was measured using the CapnoEye™. The EtCO2 and partial pressure of venous carbon dioxide (PvCO2) were analyzed, and other clinical data were assessed. Patients Sixty-one consecutive patients with chronic respiratory failure receiving LTOT in the outpatient department at the Japanese Red Cross Medical Center between July 2017 and March 2018 were retrospectively reviewed. Results There was a significant correlation between EtCO2 and PvCO2 (r=0.63) in the total study population as well as in the COPD group (r=0.65) and ILD group (r=0.67). The PvCO2 and EtCO2 gradient was correlated with only the body mass index in a multivariate analysis (p=0.0235). The EtCO2 levels on the day of admission were significantly higher than those in the same patients when they were in a stable condition (p=0.0049). There was a significant correlation between ΔEtCO2 and ΔPvCO2 (r=0.4). A receiver-operating characteristic curve analysis revealed the optimal cut-off EtCO2 value for identifying hypercapnia to be 34 mmHg (p=0.0005). Conclusion The evaluation of EtCO2 by the CapnoEye™ was useful for predicting PvCO2. The body mass index was identified as a possible predictor of the PvCO2 and EtCO2 gradient. An increase in EtCO2 may indicate deterioration of the respiratory status in patients with chronic respiratory failure receiving LTOT.

Capnography-sample line leak and incremental positive end expiratory pressure (PEEP); an interesting interplay.

The capnography is an important monitor to assess the patient's respiratory status. Importance of education for clinicians in interpretation of alarms and various capnography waveforms in different clinical scenarios and equipment malfunction is an understatement. Capnography waveforms due to sample line tube leak is described well in literature. This report describes an interesting effect of incremental positive end expiratory pressure (PEEP) on capnography waveforms linked to sample line leak.

Implementation Science: Incorporating Obstructive Sleep Apnea Screening and Capnography Into Everyday Practice.

PURPOSE: This article describes the implementation and maintenance of obstructive sleep apnea (OSA) screening and capnography monitoring. DESIGN: A quality improvement project. METHODS: A multidisciplinary team provided staff education to three perianesthesia care units. Using the STOP-Bang screening tool, five or more positive responses indicated high risk for OSA. A postanesthesia care unit audit tool tracked STOP-Bang scores, capnography use, hypoventilation events, nursing interventions, and respiratory complications. FINDINGS: Among 314 patients with OSA, 36% were identified as high risk. Nurses used capnography on 76% of OSA patients and were able to readily identify hypoventilation and intervene. Respiratory complications occurred in 10.8% (n = 34) requiring a higher level of care. Postimplementation, all six postanesthesia care units employ this best practice. CONCLUSIONS: Perianesthesia nurses found OSA screening and capnography easy to incorporate into nursing practice. This process can reduce respiratory complications in the surgical patient with OSA. An Evidence-Based Practice Fellowship Program facilitated this practice change.

Use of Capnography and Cardiopulmonary Resuscitation Feedback Devices Among Prehospital Advanced Life Support Providers.

BACKGROUND: Capnography and cardiopulmonary resuscitation (CPR) feedback devices have been shown to improve resuscitation outcomes, with the American Heart Association recommending their use during advanced life support (ALS). Little is known about the availability of these devices, their protocoled use, and the attitudes toward them in the prehospital setting. OBJECTIVES: The objectives of this study were to assess the availability of capnography and CPR feedback devices among prehospital ALS agencies in New York State (NYS), to describe the protocoled use of these devices, and to evaluate the attitudes of providers toward the use of these devices. METHODS: Prehospital agencies that provide ALS services in NYS were identified using an online registry. Managers in these agencies were contacted by electronic mail and asked to complete a questionnaire regarding their agency's experience with capnography and CPR feedback devices. The questionnaire included questions on the availability of capnography and CPR feedback devices, the existence of clinical protocols for using capnography, and provider opinion on the utility of capnography and CPR feedback devices for improving pediatric resuscitation. RESULTS: Of 710 ALS agencies, 238 (33.5%) completed the survey. Ninety-five percent and 24% of agencies reported having capnography and CPR feedback devices available aboard ambulances, respectively. Ninety-seven percent of agencies reported having capnography clinical protocols for endotracheal intubation, 63% for return of spontaneous circulation, and 54% for guiding CPR. Forty-seven percent agreed that capnography improves outcomes in the resuscitation of pediatric patients, whereas 51% of providers were neutral and 2% disagreed. CONCLUSIONS: Capnography is available in most NYS ALS agencies surveyed. Cardiopulmonary resuscitation feedback devices are less common. Protocols for the use of capnography mainly focused on endotracheal intubation and less for the recognition of return of spontaneous circulation and for guiding CPR. Half of the providers surveyed were neutral on whether capnography improves outcomes in the resuscitation of pediatric patients.

An abnormal capnography trace due to air embolism in the lateral position.

Venous air embolism occurs when air is entrained into the venous system and travels to the right heart and pulmonary circulation, and commonly occurs as a complication in laparoscopic, neurosurgical and cardiac surgeries. We present a case of abnormal end-tidal carbon dioxide capnography tracing in the lateral position in a laparoscopic major liver procedure and discuss the potential novel use of this as a red flag in aiding the medical practitioner to diagnose air embolism.

Not All Oxygrams Are Mirror Image of Capnograms: A Case Report.

Generally the oxygram and the capnogram are mirror images of each other. We report a situation where a leak in the sample line produced a typical tails-up capnogram that was not accompanied by a mirror image oxygram. Air entrainment through the breach led to dilution of the gases on their way to the analyzer. The result was an oxygram resembling a series of mountain peaks.

Dislocation rates of postoperative airway exchange catheters - a prospective case series of 200 patients.

BACKGROUND: The dislocation rate of oral versus nasal airway exchange catheters (AEC) in the postoperative care unit (PACU) are unknown. Our aim was to establish dislocation rates and to assess the usefulness of waveform capnography to detect dislocation. METHODS: In this non-randomized, prospective observational trial at the University Hospital Bern, Switzerland, we included 200 patients admitted to PACU after extubation via AEC, having provided written informed consent. The study was approved by the local ethical committee. AEC position was assessed by nasal fiberoptic endoscopy at beginning of PACU stay and before removal of the AEC. Capnography was continuously recorded via the AEC. Additional measurements included retching and coughing of the patient, and re-intubation, if necessary. RESULTS: Data from 182 patients could be evaluated regarding dislocation. Overall dislocation rate was not different between oral and nasal catheters (7.2% vs. 2.7%, p = 0.16). Retching was more often noted in oral catheters (26% vs. 8%, p < 0.01). Waveform capnography was unreliable in predicting dislocation (negative predictive value 17%). Re-intubation was successful in all five of the nine re-intubations where an AEC was still in situ. In four patients, the AEC was already removed when re-intubation became necessary, and re-intubation failed once, with a front of neck access as a rescue maneuver. CONCLUSIONS: We found no difference in dislocation rate between nasal and oral position of an airway exchange catheter. However, nasal catheters seemed to be tolerated better. In the future, catheters like the staged extubation catheter may further increase tolerance. TRIAL REGISTRATION: The study was registered in a clinical study registry ( ISRCTN 96726807 ) on 10/06/2010.

Evaluation and application of a method for estimating nasal end-tidal O2 fraction while administering supplemental O2.

This paper describes a method for estimating the oxygen enhanced end-tidal fraction of oxygen (FetOe), the end-tidal fraction of oxygen (FetO2) that is raised by administering supplemental oxygen. The paper has two purposes: the first is to evaluate the method's accuracy on the bench and in volunteers; the second purpose is to demonstrate how to apply the method to compare two techniques of oxygen administration. The method estimates FetOe by analyzing expired oxygen as oxygen washes out of the lung. The method for estimating FetOe was first validated using a bench simulation in which tracheal oxygen was measured directly. Then it was evaluated in 30 healthy volunteers and compared to the bench simulation. Bland-Altman analysis compared calculated and observed FetOe/FetO2 measurements. After the method was evaluated, it was implemented to compare the FetOe obtained when administering oxygen using two different techniques (pulsed and continuous flow). A total of eighteen breath washout conditions were evaluated on the bench. FetOe estimates and tracheal FetO2 had a mean difference of - 0.016 FO2 with 95% limits of agreement from - 0.048 to 0.016 FO2. Thirteen breath washouts per volunteer were analyzed. Extrapolated and observed FetO2 had a mean difference of - 0.001 FO2 with 95% limits of agreement from - 0.006 to 0.004 FO2. Pulsed flow oxygen (PFO) achieved the same FetOe values as continuous flow oxygen (CFO) using 32.1% ± 2.27% (mean ± SD) of the CFO rate. This paper has demonstrated that the method estimates FetO2 enhanced by administering supplemental oxygen with clinically insignificant differences. This paper has also shown that PFO can obtain FetO2 similar to CFO using approximately one-third of the oxygen volume. After evaluating this method, we conclude that the method provides useful estimates of nasal FetO2 enhanced by supplemental oxygen administration.

Investigating Capnography Innovation for Better Patient Monitoring in the Resource Limited Surgical Setting.

BACKGROUND: Access to basic anesthetic monitoring in the developing world is lacking, which contributes to the 100 times greater anesthesia-related mortality in low- and middle-income countries. We hypothesize that an environmental sensor with a lower sampling rate could provide some clinical utility by providing CO2 levels, respiratory rate, and support in detection of clinical abnormalities. MATERIALS AND METHODS: A bench-top lung simulation was created to replicate CO2 waveforms, and an environmental sensor was compared with industry-available technology. Sensor response time and respiratory rates were compared between devices. Additionally, an in silico model was created to replicate capnography pathology as waveforms would appear using the environmental sensor. RESULTS AND CONCLUSION: Breath simulations using the bench-top lung simulation produced similar results to industry standards with a degree of variability. Respiratory rates did not differ between the environmental sensor and all other devices tested. Finally, pathological waveforms created in silico carried a certain level of detail regarding ventilatory pathology, which could provide some clinical insight to an anesthesiologist. We believe our prototype is the first step toward making low-cost and portable capnography available in the resource-limited setting, and future efforts should focus on bridging the gap to safer anesthesia and surgery globally.

Performance of a second generation pulmonary capnotracking system for continuous monitoring of cardiac output.

Technologies for minimally-invasive cardiac output measurement in patients during surgery remain little used in routine practice. We tested a redeveloped system based on CO2 elimination (VCO2) by the lungs for use in ventilated patients, which can be seamlessly integrated into a modern anesthesia/monitoring platform, and provides automated, continuous breath-by-breath cardiac output monitoring. A prototype measurement system was constructed to measure VCO2 and end-tidal CO2 concentration with each breath. A baseline measurement of non-shunt cardiac output was made during a brief oscillating change in ventilator rate, according to the differential CO2 Fick approach and repeated at 5-10 min intervals. Continuous breath-by-breath monitoring of cardiac output was performed between these intervals from measurement of VCO2, using a derivation of the Fick equation applied to pulmonary CO2 elimination and cardiac output displayed in real time. Measurements were compared with simultaneous measurements by thermodilution in 50 patients undergoing cardiac surgery or liver transplantation. Overall mean bias [sd] for agreement in cardiac output measurement was - 0.3 [1.1] L/min, percentage error ± 38.7%, intraclass correlation coefficient = 0.91. Concordance in measurement of changes of at least 15% in cardiac output was 81.4%, with a mean angular bias of - 1.7°, and radial limits of agreement of ± 76.2° on polar plot analysis. The accuracy and precision compared favourably to other clinical techniques. The method is relatively seamless and automated and has potential for continuous, cardiac output monitoring in ventilated patients during anesthesia and critical care.

Camera-based measurement of respiratory rates is reliable.

OBJECTIVES: Respiratory rate (RR) is one of the most important vital signs used to detect whether a patient is in critical condition. It is part of many risk scores and its measurement is essential for triage of patients in emergency departments. It is often not recorded as measurement is cumbersome and time-consuming. We intended to evaluate the accuracy of camera-based measurements as an alternative measurement to the current practice of manual counting. MATERIALS AND METHODS: We monitored the RR of healthy male volunteers with a camera-based prototype application and simultaneously by manual counting and by capnography, which was considered the gold standard. The four assessors were mutually blinded. We simulated normoventilation, hypoventilation and hyperventilation as well as deep, normal and superficial breathing depths to assess potential clinical settings. The volunteers were assessed while being undressed, wearing a T-shirt or a winter coat. RESULTS: In total, 20 volunteers were included. The results of camera-based measurements of RRs and capnography were in close agreement throughout all clothing styles and respiratory patterns (Pearson's correlation coefficient, r=0.90-1.00, except for one scenario, in which the volunteer breathed slowly dressed in a winter coat r=0.84). In the winter-coat scenarios, the camera-based prototype application was superior to human counters. CONCLUSION: In our pilot study, we found that camera-based measurements delivered accurate and reliable results. Future studies need to show that camera-based measurements are a secure alternative for measuring RRs in clinical settings as well.

Linshom thermodynamic sensor is a reliable alternative to capnography for monitoring respiratory rate.

Monitoring ventilation accurately is a technically challenging, yet indispensable aspect of patient care in the intra- and post-procedural settings. A new prototypical device known as the Linshom Respiratory Monitoring Device (LRMD) has been recently designed to non-invasively, inexpensively, and portably measure respiratory rate. The purpose of this study was to measure the accuracy and variability of LRMD measurements of respiratory rate relative to the measurement of capnography. In this prospective study, participants were enrolled and individually fitted with a face mask monitored by the LRMD and capnography. With a baseline oxygen flow rate and digital metronome to pace their respiratory rate, the participants were instructed to breathe at 10 breaths per minute (bpm) for 3 min, 20 bpm for 3 min, 30 bpm for 3 min, 0 bpm for 30 s, and resume regular breathing for 30 s. Both sensors were connected to a computer for continuous temperature and carbon dioxide waveform recordings. The data were then retrospectively analyzed. Twenty-six healthy volunteers, mean (range) age 27.8 (23-37) and mean (range) BMI 23.1 (18.8-29.2) kg/m2 were recruited. There were 15 males (57.7%) and 11 females (42.3%). After excluding 3 subjects for technical reasons, 13,800 s of breathing and 4,140 expiratory breaths were recorded. Throughout the protocol, the average standard deviation (SD) for the LRMD and capnography was 1.11 and 1.81 bpm, respectively. The overall mean bias (±2SD) between LRMD and capnography was -0.33 (±0.1.56) bpm. At the lowest and intermediate breathing rates reflective of hypoventilation and normal ventilation, the LRMD variance was 0.55 and 1.23 respectively, compared to capnography with 5.54 and 7.47, respectively. At higher breathing rates indicative of hyperventilation, the variance of the test device was 4.52, still less than that of capnography at 5.73. This study demonstrated a promising correlation between the LRMD and capnography for use as a respiratory rate monitor. The LRMD technology may be a significant addition to monitoring vital signs because it offers a minimally intrusive opportunity to detect respiratory rate and apnea, without expensive or complex anesthetic equipment, before the need for life-saving resuscitation arises.

Capnography as a tool to detect metabolic changes in patients cared for in the emergency setting.

OBJECTIVE:: to evaluate the usefulness of capnography for the detection of metabolic changes in spontaneous breathing patients, in the emergency and intensive care settings. METHODS:: in-depth and structured bibliographical search in the databases EBSCOhost, Virtual Health Library, PubMed, Cochrane Library, among others, identifying studies that assessed the relationship between capnography values and the variables involved in blood acid-base balance. RESULTS:: 19 studies were found, two were reviews and 17 were observational studies. In nine studies, capnography values were correlated with carbon dioxide (CO2), eight with bicarbonate (HCO3), three with lactate, and four with blood pH. CONCLUSIONS:: most studies have found a good correlation between capnography values and blood biomarkers, suggesting the usefulness of this parameter to detect patients at risk of severe metabolic change, in a fast, economical and accurate way. OBJETIVO:: avaliar a utilidade da capnografia para a detecção de alterações metabólicas em pacientes com respiração espontânea, no contexto das emergências e dos cuidados intensivos. MÉTODO:: pesquisa bibliográfica estruturada aprofundada, nas bases de dados EBSCOhost, Biblioteca Virtual em Saúde, PubMed, Cochrane Library, entre outras, identificando estudos que avaliavam a relação entre os valores da capnografia e as variáveis envolvidas no equilíbrio ácido-base sanguíneo. RESULTADOS:: foram levantados 19 estudos, dois eram revisões e 17 eram estudos observacionais. Em nove estudos, os valores capnográficos foram correlacionados com o dióxido de carbono (CO2), em oito com o bicarbonato (HCO3), em três com o lactato, e em quatro com o pH sanguíneo. CONCLUSÕES:: na maioria dos estudos foi observada uma correlação adequada entre os valores capnográficos e os biomarcadores sanguíneos, sugerindo a utilidade deste parâmetro para a identificação de pacientes com risco de sofrer uma alteração metabólica grave, de uma forma rápida, econômica e precisa. OBJETIVO:: explorar la utilidad de la capnografía para la detección de alteraciones metabólicas ante pacientes en respiración espontánea, en el ámbito de las emergencias y los cuidados críticos. MÉTODO:: búsqueda bibliográfica estructurada en profundidad, en bases de datos EBSCOhost, Biblioteca Virtual de la Salud, PubMed, Cochrane Library, entre otras, identificando estudios que evaluaban la relación entre valores de la capnografía y variables implicadas en el equilibrio ácido-base sanguíneo. RESULTADOS:: se recopilaron 19 estudios, dos eran revisiones y 17 observacionales. En nueve estudios, se correlacionaron los valores capnográficos junto al dióxido de carbono (CO2), en ocho con el bicarbonato (HCO3), tres con el lactato, y cuatro con el pH sanguíneo. CONCLUSIONES:: la mayoría de estudios han obtenido una correlación adecuada entre los valores capnográficos y biomarcadores sanguíneos, sugiriendo la utilidad de este parámetro para la detección de pacientes en riesgo de padecer una alteración metabólica grave, de forma rápida, económica y precisa.

Continuous Capnography in Pediatric Intensive Care.

Capnography or end-tidal carbon dioxide (Etco2) monitoring has a variety of uses in the pediatric intensive care setting. The ability to continuously measure exhaled carbon dioxide can provide vital information about airway, breathing, and circulation in critically ill pediatric patients. Capnography has diagnosis-specific applications for pediatric patients with congenital heart disease, reactive airway disease, neurologic emergencies, and metabolic derangement. This modality allows for noninvasive monitoring and has become the standard of care. This article reviews the basic principles and clinical applications of Etco2 monitoring in the pediatric intensive care unit.