Carbon dioxide monitoring and evidence-based practice - now you see it, now you don't.
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Carbon dioxide has been monitored in the body using a variety of technologies with a multitude of applications. The monitoring of this common physiologic variable in medicine is an illustrative example of the different levels of evidence that are required before any new health technology should establish itself in clinical practice. End-tidal capnography and sublingual capnometry are two examples of carbon dioxide monitoring that require very different levels of evidence before being disseminated widely. The former deserves its status as a basic standard based on observational data. The latter should be considered investigational until prospective controlled data supporting its use become available. Other applications of carbon dioxide monitoring are also discussed. (+info)
End tidal carbon dioxide as a predictor of the arterial PCO2 in the emergency department setting.
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OBJECTIVES: Patients arriving in the emergency department (ED) need rapid and reliable evaluation of their respiratory status. Mainstream end tidal carbon dioxide (ETCO(2)) is one of the methods used for this purpose during general anaesthesia of intubated patients in the operating theatre. Sidestream ETCO(2) (SSETCO(2)) might be a non-invasive, rapid, and reliable predictor of arterial Pco(2) in non-intubated patients in respiratory distress. The aim of this study was to verify whether SSETCO(2) can accurately predict the arterial Pco(2) and to detect variables that may affect this correlation. METHODS: A prospective semi-blind study. The participants were 73 patients (47 men, 26 women) referred to the ED for respiratory distress. Arterial blood gas pressures and SSETCO(2) measurements were performed and recorded for all patients. Other parameters recorded were: age; body temperature; respiratory rate; blood pressure; pulse rate; and medical diagnosis. RESULTS: A significant correlation was found between SSETCO(2) and arterial Pco(2) (r = 0.792). Compared with the correlation curve of the whole group, age under 50 years deflected the correlation curve to the left, while temperature above 37.6 degrees C deflected it to the right. The rest of the parameters had no clear influence on the SSETCO(2)/Pco(2) correlation curve. CONCLUSIONS: There is a good correlation between SSETCO(2) and arterial Pco(2) in the ED setting. Young age may increase the arterial Pco(2)/SSETCO(2) gradient while raised temperature may decrease this gradient. Further studies are needed to confirm these findings in the normal healthy population. (+info)
Cardiovascular stability during arteriovenous extracorporeal therapy: a randomized controlled study in lambs with acute lung injury.
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INTRODUCTION: Clinical application of arteriovenous (AV) extracorporeal membrane oxygenation (ECMO) requires assessment of cardiovascular ability to respond adequately to the presence of an AV shunt in the face of acute lung injury (ALI). This ability may be age dependent and vary with the experimental model. We studied cardiovascular stability in a lamb model of severe ALI, comparing conventional mechanical ventilation (CMV) with AV-ECMO therapy. METHODS: Seventeen lambs were anesthetized, tracheotomized, paralyzed, and ventilated to maintain normocapnia. Femoral and jugular veins, and femoral and carotid arteries were instrumented for the AV-ECMO circuit, systemic and pulmonary artery blood pressure monitoring, gas exchange, and cardiac output determination (thermodilution technique). A severe ALI (arterial oxygen tension/inspired fractional oxygen <200) was induced by lung lavage (repeated three times, each with 5 ml/kg saline) followed by tracheal instillation of 2.5 ml/kg of 0.1 N HCl. Lambs were consecutively assigned to CMV treatment (n = 8) or CMV plus AV-ECMO therapy using up to 15% of the cardiac output for the AV shunt flow during a 6-hour study period (n = 9). The outcome measures were the degree of inotropic and ventilator support needed to maintain hemodynamic stability and normocapnia, respectively. RESULTS: Five of the nine lambs subjected to AV-ECMO therapy (56%) died before completion of the 6-hour study period, as compared with two out of eight lambs (25%) in the CMV group (P > 0.05; Fisher's exact test). Surviving and nonsurviving lambs in the AV-ECMO group, unlike the CMV group, required continuous volume expansion and inotropic support (P < 0.001; Fisher's exact test). Lambs in the AV-ECMO group were able to maintain normocapnia with a maximum of 30% reduction in the minute ventilation, as compared with the CMV group (P < 0.05). CONCLUSION: AV-ECMO therapy in lambs subjected to severe ALI requires continuous hemodynamic support to maintain cardiovascular stability and normocapnia, as compared with lambs receiving CMV support. (+info)
Capnographic waveforms in the mechanically ventilated patient.
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A focus on patient safety has heightened the awareness of patient monitoring. The importance of clinical applications of capnography continues to grow, as reflected by the increasing number of medical societies recommending its use. Recognition of changes in the capnogram assists in clinical decision making and treatment and can increase patient safety by alerting the clinician to important situations and changes. This article describes the interpretation of capnograms and how capnogram interpretation influences airway management. (+info)
Accuracy of physiologic dead space measurements in patients with acute respiratory distress syndrome using volumetric capnography: comparison with the metabolic monitor method.
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BACKGROUND: Volumetric capnography is an alternative method of measuring expired carbon dioxide partial pressure (P(eCO2)) and physiologic dead-space-to-tidal-volume ratio (V(D)/V(T)) during mechanical ventilation. In this method, P(eCO2) is measured at the Y-adapter of the ventilator circuit, thus eliminating the effects of compression volume contamination and the need to apply a correction factor. We investigated the accuracy of volumetric capnography in measuring V(D)/V(T), compared to both uncorrected and corrected measurements, using a metabolic monitor in patients with acute respiratory distress syndrome (ARDS). METHODS: There were 90 measurements of V(D)/V(T) made in 23 patients with ARDS. The P(eCO2) was measured during a 5-min expired-gas collection period with a Delta-trac metabolic monitor, and was corrected for compression volume contamination using a standard formula. Simultaneous measurements of P(eCO2) and V(D)/V(T) were obtained using volumetric capnography. RESULTS: V(D)/V(T) measured by volumetric capnography was strongly correlated with both the uncorrected (r2 = 0.93, p < 0.0001) and corrected (r2 = 0.89, p < 0.0001) measurements of V(D)/V(T) made using the metabolic monitor technique. Measurements of V(D)/V(T) made with volumetric capnography had a bias of 0.02 and a precision of 0.05 when compared to the V(D)/V(T) corrected for estimated compression volume contamination. CONCLUSION: Volumetric capnography measurements of V(D)/V(T) in mechanically-ventilated patients with ARDS are as accurate as those obtained by metabolic monitor technique. . (+info)
Monitoring of end tidal carbon dioxide and transcutaneous carbon dioxide during neonatal transport.
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OBJECTIVE: To assess the accuracy of measurements of end tidal carbon dioxide (CO2) during neonatal transport compared with arterial and transcutaneous measurements. DESIGN: Paired end tidal and transcutaneous CO2 recordings were taken frequently during road transport of 21 ventilated neonates. The first paired CO2 values were compared with an arterial blood gas. The differences between arterial CO2 (Paco2), transcutaneous CO2 (TcPco2), and end tidal CO2 (Petco2) were analysed. The Bland-Altman method was used to assess bias and repeatability. RESULTS: Petco2 correlated strongly with Paco2 and TcPco2. However, Petco2 underestimated Paco2 at a clinically unacceptable level (mean (SD) 1.1 (0.70) kPa) and did not trend reliably over time within individual subjects. The Petco2 bias was independent of Paco2 and severity of lung disease. CONCLUSIONS: Petco2 had an unacceptable under-recording bias. TcPco2 should currently be considered the preferred method of non-invasive CO2 monitoring for neonatal transport. (+info)
Continuous end-tidal carbon dioxide monitoring for confirmation of endotracheal tube placement is neither widely available nor consistently applied by emergency physicians.
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OBJECTIVES: To determine the availability of end-tidal CO2 measurement in confirmation of endotracheal tube placement in the non-arrest patient, and to assess its use in academic and non-academic emergency departments. METHODS: Emergency physicians in the USA were surveyed by mail in the beginning of the year 2000 regarding availability at their institution of both colorimetric/qualitative and quantitative end-tidal CO2 capnography, frequency of use in their own practice, and descriptor of their hospital (academic, community teaching, and community non-teaching). Additionally, data were obtained from the National Emergency Airway Registry 97 series (NEAR) about how many intubations used this method of confirmation. NEAR site coordinators were surveyed as well. RESULTS: Of 1000 surveys, 550 were returned (55%). Colorimetric technology existed in 77% of respondents' hospitals (n = 421); 25% of respondents (n = 138) had continuous monitoring capability. Physicians practising at academic hospitals were more likely to have continuous monitoring (36%; n = 196) than community teaching institutions (32%; n = 173) and non-teaching centres (18%; n = 100) (p<0.001). Among physicians who had this technology available, only 14% (n = 19) "always" used it in non-arrest intubations; 57% "rarely" or "never" employed it (n = 75). Among NEAR centres (institutions committed to monitoring current airway practices) only 12% of 6009 (n = 716) intubations used continuous end-tidal CO2 measurement. Of these practitioners, only 40% "always" used it (n = 6/15) (83% response rate (n = 29/35)). CONCLUSIONS: Despite recommendations from national organisations that endorse continuous monitoring of end-tidal CO2 for confirming endotracheal tube placement, it is neither widely available nor consistently applied. (+info)
Intubating laryngeal mask for airway management in lateral decubitus state: comparative study of right and left lateral positions.
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BACKGROUND: The intubating laryngeal mask has been used for the emergency management of the airway in patients placed in the lateral decubitus position. We have conducted this prospective study to compare the feasibility of placement of an intubating laryngeal mask and blind tracheal intubation guided by the intubating laryngeal mask in patients placed in the right and the left lateral positions. METHODS: A total of 82 adults of both sexes with normal airways, scheduled for cholecystectomy, were allocated randomly to be placed in either the right (n=41) or left (n=41) lateral position for the insertion of an intubating laryngeal mask and blind tracheal intubation guided by the intubating laryngeal mask under balanced general anaesthesia. A sequence of standard manoeuvres was performed after each failed attempt at intubating laryngeal mask placement and intubation. RESULTS: The intubating laryngeal mask was placed in all patients at the first attempt. Ventilation of the lungs through the intubating laryngeal mask was possible in 40 patients (97.5%) from each group after the first attempt at insertion (P=1). Following adjustments, adequate ventilation could be achieved in all patients. The first attempt success rates of blind tracheal intubation were 85.3% (35/41) and 87.8% (36/41) in the right and left lateral groups, respectively (P=1). The remaining patients from both groups (except for one patient in the left lateral group who had a failed intubation) were intubated at the second attempt. CONCLUSION: Insertion of the intubating laryngeal mask and blind tracheal intubation through it in the lateral position is feasible in patients with normal airways. These procedures have a high and comparable success rate when patients are placed in the right and left lateral positions. (+info)