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PubMed2004

Volumetric capnography as a screening test for pulmonary embolism in the emergency department.

STUDY OBJECTIVE: To compare the diagnostic performance of volumetric capnography (VCap), which is the plot of the expired CO(2) partial pressure against the expired volume during a single breath, with the PaCO(2) to end-tidal CO(2) (EtCO(2)) gradient, in the case of suspected pulmonary embolism (PE). DESIGN: Single-center, prospective study. SETTING: Emergency department of a teaching hospital. PATIENTS: A total of 45 outpatients with positive enzyme-linked immunosorbent assay d-dimer levels of > 500 ng/mL. The diagnosis of PE was confirmed in 18 outpatients according to a validated procedure based on the ventilation-perfusion lung scan and/or spiral CT scanning. INTERVENTIONS: Curves of VCap were obtained from a compact monitor connected to a computer. A sequence of four to six stable breaths allowed the calculation of the following several variables: alveolar dead space fraction; the ratio of alveolar dead space (VDalv) to airway dead space (VDaw); the VDalv to physiologic dead space (VDphys) fraction; the slope of phase 3; and the late dead space fraction (Fdlate) corresponding to the extrapolation of the capnographic curve to a volume of 15% of the predicted total lung capacity. RESULTS: The mean (+/- SD) PaCO(2)-EtCO(2) gradient was 5.3 +/- 0.7 mm Hg in the PE-positive group and 2.8 +/- 0.7 mm Hg in the PE-negative group (p = 0.019). Four variables of the VCap exhibited a statistical difference between both groups, as follows: the VDalv/VDaw fraction(;) the slope of phase 3; the VDalv/VDphys fraction; and the Fdlate, which was 8.2 +/- 3.3% vs -7.7 +/- 2.8%, respectively (p = 0.000011). The diagnostic performance expressed as the mean area under a receiver operating characteristic curve comparison was 75.9 +/- 7.4% for the PaCO(2)-EtCO(2) gradient and 87.6 +/- 4.9% for the Fdlate (p = 0.02). CONCLUSION: Fdlate, a variable of VCap, had a statistically better diagnostic performance in suspected PE than the PaCO(2)-EtCO(2) gradient. VCap is a promising computer-assisted bedside application of pulmonary pathophysiology. Future research should define the place of this technique in the diagnostic workup of PE, especially in the presence of positive d-dimers.

Breath Tests↗
PubMed1998

The role of the capnography head-up tilt test in the diagnosis of syncope in children and adolescents.

OBJECTIVES: To evaluate the role of the capnography head-up tilt test (CHUTT) in the diagnosis of syncope in pediatric patients. METHODS: The CHUTT is a head-up tilt test with concomitant capnometry. Hyperventilation on CHUTT was diagnosed when the patient's end-tidal carbon dioxide pressure (ETPCO2) was </=25 mm Hg. Hyperventilation syncope was diagnosed when three criteria were met: loss of consciousness, ETPCO2 </=25 mm Hg, and no significant drop in blood pressure. The cohort included 65 consecutive children and adolescents (mean age, 14.2 years) who were assessed for syncope by routine investigations and CHUTT. RESULTS: The cause of the syncope was established in 67% of cases: cardioinhibitory reaction in 17%, vasodepressor in 20%, psychogenic in 22%, and mixed neurally mediated-psychogenic in 8% of the patients. The history indicated a cause of syncope in 40%, the CHUTT in 49%, and a combination of the history and positive CHUTT in 66% of patients. Neither the patients' clinical data nor values of the blood pressure, heart rate, respiratory rate, and ETPCO2 measured during recumbency predicted which patients would manifest hyperventilation or hyperventilation syncope on tilt. CONCLUSIONS: The CHUTT contributes substantially to the diagnosis of syncope in pediatric patients. The CHUTT advances the understanding of the pathophysiological mechanisms of syncope and enables the physician to reassure the patient regarding the essentially benign nature of the condition. Because it is not possible to predict which patients would develop a hyperventilation syncope on the standard tilt test, the modification of this procedure by measuring the ETPCO2 for the assessment of children with syncope should be considered.

Adolescent↗
PubMedDate not supplied

Monitoring pediatric dental patients with nasal mask capnography.

PURPOSE: The purpose of this study was to evaluate the potential of using capnography to analyze respiratory samples taken from a scavenging nitrous oxide nasal hood during routine pediatric dental procedures. METHODS: Twenty-two subjects, aged 60-116 months, were administered alternately either 40% nitrous oxide/60% oxygen or 100% oxygen during two sequential restorative appointments. All subjects were monitored continuously for end-tidal carbon dioxide and respiratory rate using a capnograph whose sampling line was attached directly to the nitrous oxide nasal hood. The subject's breath sound, displayed behavior, type of dental procedure being performed, and presence of rubber dam isolation were recorded every minute throughout the two appointments. RESULTS: Values for end-tidal carbon dioxide and respiratory rate were displayed on the capnograph when administering either oxygen or a combination of nitrous oxide/oxygen inhalation through the nasal hood. These respiratory values were lowered significantly when comparing 40% nitrous oxygen-60% oxygen to 100% oxygen inhalation. They were not significantly altered by the type of breath sound, patient behavior, dental procedure, or presence of rubber dam isolation, with the exception of some dental procedures which significantly lowered end-tidal carbon dioxide. The apnea alarm on the capnograph occurred during 5% of the total treatment time, but its occurrence represented a 97% false positive rate. The occurrence of the apnea alarm was significantly associated with the type for breath sound, patient behavior, and dental procedure. When used in this manner, the capnograph was effective in alerting the practitioner to potential apneic events, but likely has limited value in monitoring valid end-tidal carbon dioxide levels due to limitations in the sampling technique. CONCLUSIONS: This study demonstrated the potential of the capnograph as a respiratory monitor for pediatric dental patients when the sampling line was attached to a scavenging nitrous oxide nasal hood.

Anesthesia, Dental↗
PubMed2003

Membrane oxygenator exhaust capnography for continuously estimating arterial carbon dioxide tension during cardiopulmonary bypass.

Typically, the standard practice for measuring the arterial blood carbon dioxide tension (PaCO2) during cardiopulmonary bypass (CPB) is to take intermittent blood samples for analysis by a bench blood gas analyzer. Continuous inline blood gas monitors are available but are expensive. A potential solution is the capnograph, which was evaluated by determining how accurately the carbon dioxide tension in the oxygenator exhaust gases (PECO2) predicts PaCO2. A standard capnograph monitoring line was attached to the exhaust port of the membrane oxygenator. During CPB, the capnograph reading and arterial blood temperature were recorded at the same time as routine arterial blood gases were taken. One hundred fifty-seven blood samples were collected from 78 patients. A good correlation was found between the PECO2 and the temperature corrected PaCO2 (r2 = 0.833, P < .001). There was also a reasonable degree of agreement between the PECO2 and the temperature corrected PaCO2 during all phases of CPB: accuracy (bias or mean difference between PaCO2 and PECO2) of -1.2 mmHg; precision (95% limits of agreement) of +/- 4.7 mmHg. These results suggest that oxygenator exhaust capnography may be a simple and inexpensive adjunct to the bench blood gas analyzer in continuously estimating PaCO2 of a clinically useful degree of accuracy during CPB.

Adult↗
PubMed2005

Capnography in sedation and pain management.

Monitoring respiratory rate, effort and efficacy of ventilation during pain management and sedation can be difficult in the field. Capnography is an ideal monitor for use during the administration of narcotics and benzodiazepines. The addition of EtCO2 monitoring enables earlier identification of respiratory depression in this group of patients. Standard vital signs, oxygen saturation and EtCO2 must also be monitored continuously. End-tidal carbon dioxide monitoring, although not required on all patients, provides an earlier indication of respiratory depression than pulse oximetry and respiratory rate alone.

Capnography↗
PubMed2005

Oxygenator exhaust capnography for prediction of arterial carbon dioxide tension during hypothermic cardiopulmonary bypass.

Continuous monitoring and control of arterial carbon dioxide tension (P(a)CO2) during cardiopulmonary bypass (CPB) is essential. A reliable, accurate, and inexpensive system is not currently available. This study was undertaken to assess whether the continuous monitoring of oxygenator exhaust carbon dioxide tension (PexCO2) can be used to reflect P(a)CO2 during CPB. A total of 33 patients undergoing CPB for cardiac surgery were included in the study. During normothermia (37 degrees C) and stable hypothermia (31 degrees C), the values of PexCO2 from the oxygenator exhaust outlet were monitored and compared simultaneously with the P(a)CO2 values. Regression and agreement analysis were performed between PexCO2 and temperature corrected-P(a)CO2 and temperature uncorrected-P(a)CO2. At normothermia, a significant correlation was obtained between PexCO2 and P(a)CO2 (r = 0.79; p < 0.05); there was also a strong agreement between PexCO2 and P(a)CO2 with a gradient of 3.4 +/- 1.9 mmHg. During stable hypothermia, a significant correlation was obtained between PexCO2 and the temperature corrected-P(a)CO2 (r = 0.78; p < 0.05); also, there was a strong agreement between PexCO2 and temperature corrected-P(a)CO2 with a gradient of 2.8 +/- 2.0 mmHg. During stable hypothermia, a significant correlation was obtained between PexCO2 and the temperature uncorrected-P(a)CO2 (r = 0.61; p < 0.05); however, there was a poor agreement between PexCO2 and the temperature uncorrected-P(a)CO2 with a gradient of 13.2 +/- 3.8 mmHg. Oxygenator exhaust capnography could be used as a mean for continuously monitoring P(a)CO2 during normothermic phase of cardiopulmonary bypass as well as the temperature-corrected P(a)CO2 during the stable hypothermic phase of CPB.

Aged↗
PubMed1997

[The value of capnography and exhaled CO2 in neonatal intensive care units].

OBJECTIVE: The objective of this study was to investigate the reliability of end-tidal CO2 (PetCO2) as a non-invasive guide of PaCO2 in the newborn and to analyze the influence of the relationship between ventilation-perfusion in the correlation between both determinations. PATIENTS AND METHODS: End-tidal CO2 (PetCO2) was monitored by capnography in 9 ventilated newborns: 146 arterial blood gas samples were drawn and the results were compared with the PetCO2 values obtained. The gradient or difference between PaCO2 and PetCO2 was calculated to determine the correlation. The ratio a/AO2 was used as an indirect indicator of the ventilation/perfusion relationship (V/Q ratio). RESULTS: The mean gestational age was 30.9 +/- 2.8 weeks and birth weight 1,648 +/- 596 g. The age at the beginning of the study was 2 +/- 1.5 days. The diagnoses corresponded to 5 cases of RDS (56%), 2 cases of wet lung syndrome (22%), 1 case of pneumonia (11%) and 1 pneumothorax (11%). The results of this monitoring were classified in function of the a/AO2 ratio obtained: Group A, a/AO2 < 0.2 and PaCO2-PetCO2 gradient = 13.3 +/- 5; Group B, a/AO2 = 0.2-0.29 and PaCO2-PetCO2 gradient = 8 +/- 2.7; and Group C, a/AO2 > 0.29 and PaCO2-PetCO2 gradient = 2 +/- 1.7. The results show a very good correlation from a a/AO2 ratio > or = 0.3 onwards. The a/AO2 ratio is the major determinant of PaCO2-PetCO2 differences and respiratory frequency has less influence. CONCLUSIONS: 1) Monitoring of end-tidal CO2 does not maintain a good correlation with PaCO2 in serious lung illness. 2) End-tidal CO2 measurement is an effective and accurate technique for the monitoring of newborns when the a/AO2 ratio > or = 0.3 and it can be useful for weaning of mechanical ventilation. 3) PaCO2-PetCO2 differences accurately show the changes in the ventilation-perfusion relationship.

Blood Gas Analysis↗
PubMed1992

Capnography does not reliably detect double-lumen endotracheal tube malplacement.

Two patients are described in whom double-lumen endotracheal tube malplacement and its ventilatory consequences were not detected by infrared capnography. Problems were suspected on auscultation, and the malplacement was diagnosed by means of bronchospirometry. We conclude that bronchospirometry helps detect problems with endotracheal intubation.

Carbon Dioxide↗
PubMed1985

Factors influencing capnography in the Bain circuit.

The Bain circuit provides continuous fresh gas flow near the airway. The potential mixing of this fresh gas with expired gas may prevent reliable analysis of expired gas. We therefore investigated the interaction of sampling site, fresh gas flow rate, expiratory flow rate, and sampling flow rate on expiratory capnography. Sampling near the fresh gas outlet yielded inaccurate results under several of these conditions. The magnitude of the error was related to the fresh gas and expiratory flow rates. A reliable sampling region near the endotracheal tube was identified.

Anesthesiology↗
PubMed1991

Pulse oximetry and capnography in anaesthetic practice: an epidemiological appraisal.

In the evaluation of any medical technology the efficacy, effectiveness, and efficiency must each be considered before routine deployment is recommended. Since the widespread practice of patient monitoring by pulse oximetry and capnography has occurred before the performance of rigorously controlled trials, definitive proof of worth is lacking. The purpose of this review is to appraise critically the effectiveness of this technology. The assessment was performed using concepts developed in epidemiology and community medicine to establish a given factor to be causative to a given outcome. The current literature pertaining to anaesthetic adverse outcomes was reviewed, and the use of monitors evaluated against the criteria of a causal relationship. While the conclusions are based more on the absence of positive data (owing to low frequency of adverse anaesthetic occurrences) rather than negative results, it must be concluded that the effectiveness of such monitoring has yet to be demonstrated. Such a conclusion should not detract from their use, for the role of an individual factor in the complex chain of accident evolution will seldom be demonstrable. Rather, such an appraisal should encourage a clear perspective of the depth of our clinical science, and encourage more rigorous critical evaluation in the future.

Anesthesia↗
PubMed1992

Inspiratory valve malfunction in a circle system: pitfalls in capnography.

Capnography is a useful technique in monitoring the integrity of anaesthetic equipment such as the malfunctioning of unidirectional valves in circle system. However, the lack of a precise mechanism in existing capnographs to identify the start of inspiration and the beginning of expiration in the capnograms, makes the analysis of the carbon dioxide waveforms during inspiration difficult and thus results in inaccurate assessment of rebreathing. We report a case where, during the malfunction of the inspiratory unidirectional valve in the circle system, the capnograph failed to detect the presence of substantial rebreathing. Critical analysis of the capnogram recorded during the malfunction revealed that there was substantial rebreathing which was underestimated by the capnograph as it reports only the lowest CO2 concentration rebreathed during inspiration in such abnormal situations.

Anesthesia, Closed-Circuit↗
PubMed1987

Use of capnography and transcutaneous oxygen monitoring during outpatient general anesthesia for oral surgery.

The combination of the capnograph (respired CO2 monitor) and the transcutaneous oxygen monitor was evaluated as a non-invasive system for monitoring of respiratory function in 10 ASA class I patients undergoing ultralight general anesthesia for removal of third molars. Capnography proved to be a sensitive and accurate method for detecting apnea and airway obstruction using the continuous display of the CO2 waveform. All episodes of apnea or obstruction were immediately detected as the respired CO2 level fell to zero baseline. The end-tidal CO2 (PetCO2) obtained via nasal prong sampling was not significantly different from the PaCO2. PetCO2 values served as useful indicators of hypoventilation. During steady-state conditions of respiration, transcutaneous oxygen tensions (PtcO2) correlated well with simultaneously measured PaO2 (r = 0.93). However, during any period when oxygenation was rapidly changing (step increase in FIO2, step decrease in FIO2, or apnea) the PtcO2 lagged behind changes in PaO2 even after a five-minute equilibration period, thereby not accurately reflecting the true state of oxygenation. Consequently, the transcutaneous oxygen monitor does not appear to be optimal as a respiratory monitor in the setting of ultralight general anesthesia where rapid, critical changes in oxygenation must be detected without delay.

Adolescent↗
PubMed1990

Early detection of "rebreathing" in afferent and efferent reservoir breathing systems using capnography.

Capnography was used to determine the onset of rebreathing in afferent (AR) and efferent (ER) reservoir breathing systems in a spontaneous ventilation lung model. In the case of the Lack and enclosed AR systems, the best sampling site was found to be in the exhaust limb of the systems, 5 cm from the Y connector. For the Magill system, fitted with a hooded scavenging valve, the best site was deep inside the hooded valve. In contrast, the best sampling site in an ER system (e.g. Bain system) was in the tracheal tube. For AR systems, the loss of a fresh gas elimination pattern (carbon dioxide trace failing to reach zero) was shown to occur at the onset of rebreathing. As the sampling site was moved distally into the exhaust limb, the same pattern was seen at greater flow rates--that is, before rebreathing was actually occurring. When sampling was within the tracheal tube, using ER systems, a typical "rebreathing wave" occurred at the onset of established rebreathing.

Anesthesia, Inhalation↗
PubMed1997

The capnography-tilt test for the diagnosis of hyperventilation syncope.

We describe the capnography tilt test (CTT) for the diagnosis of hyperventilation syncope. The CTT is a 10-min supine, 30-min head-up tilt test with simultaneous monitoring of end-tidal PCO2 (ETPCO2). Hyperventilation (HV) was defined as ETPCO2 < or = 25 mmHg. Hyperventilation syncope (HV syncope) was defined as loss of consciousness with ETPCO2 < or = 25 mmHg and no significant drop in blood pressure. Four groups of patients had the CTT: group I (n = 14), patients presenting with syncope who during a prior tilt test had lost consciousness without concomitant fall in blood pressure; group II (n = 50), syncope, primary evaluation, no prior tilt test done; group III (n = 20), generalized anxiety disorder, no syncope; group IV (n = 80), arterial hypertension, no syncope. Hyperventilation was found in 11/14 patients in group I, 5/50 in group II, 7/20 in group III, and none in group IV; HV syncope was diagnosed in seven patients, all in group I. None of the parameters measured in the evaluation, including ETPCO2, predicted HV syncope on tilting. The mechanisms of resting HV and HV during tilt are not well understood. We confirm the existence of HV syncope. The tilt test should probably be used to screen patients presenting with syncope, with the CTT reserved for patients who lose consciousness during the tilt test without an associated fall in blood pressure, as HV is not always clinically obvious.

Adolescent↗
PubMed1995

Intraoperative end-tidal carbon dioxide values and derived calculations correlated with outcome: prognosis and capnography.

OBJECTIVE: To determine how much information concerning resuscitation and outcome is provided by the end-tidal CO2 and derived variables obtained during surgery. DESIGN: Retrospective chart review. SETTING: Emergency hospital operating room. PATIENTS: One hundred critically ill or injured patients requiring major surgery and having a mortality rate of 41%. INTERVENTIONS: Standard intraoperative monitoring, including continuous capnography, plus arterial blood gas analyses every 1 to 1.5 hrs during surgery. MEASUREMENTS AND MAIN RESULTS: There was only a fair correlation between the PaCO2 and end-tidal CO2 (r2 = .14). The mortality rates in these patients were highest in those patients who had the lowest end-tidal CO2 values, the highest arterial to end-tidal CO2 differences, and the highest estimated alveolar deadspace fraction. A persistent end-tidal CO2 of < or = 28 torr (< or = 3.8 kPa) was associated with a mortality rate of 55% (vs. 17% in those patients with a higher end-tidal CO2). The mortality rate was also increased in patients with a persistent arterial to end-tidal CO2 difference of > or = 8 torr (> or = 1.1 kPa) (58% vs. 23%). CONCLUSIONS: End-tidal CO2 and derived values should be monitored closely in critically ill or injured patients. Efforts should be made--by increasing cardiac output and core temperature and by adjusting ventilation as needed--to maintain the end-tidal CO2 at > or = 29 torr (> or = 3.9 kPa) and the arterial to end-tidal CO2 difference at < or = 7 torr (< or = 1.0 kPa).

Adult↗
PubMed1996

Capnography facilitates tight control of ventilation during transport.

OBJECTIVE: We tested the hypothesis that Paco2 would be more tightly controlled if end-tidal CO2 monitoring was used during hand ventilation for transport of intubated patients. DESIGN: Randomized, prospective analysis of the no-monitor and monitor-blind groups (the monitor was on the bed during transport but only the investigator was aware of the end-tidal CO2 values). Nonrandomized, prospective analysis of the monitor group (ventilation controlled using end-tidal CO2 value from monitor). SETTING: University hospital operating room and intensive care unit (ICU). PATIENTS: Fifty intubated patients who were transported from the operating room to the ICU or from the ICU to the neuroradiology suite were assigned randomly to one of two groups: a) no-monitor group (n = 25); and b) monitor-blind group (n = 25). An additional group (monitor group, n = 10) was subsequently added to the study. INTERVENTIONS: Capnography was instituted in all patients in a blocked fashion. MEASUREMENTS AND MAIN RESULTS: Arterial blood gases and end-tidal CO2 values were measured before and after transport. When comparing overall group data, pre- and post-Paco2 values were similar: monitor 39 +/- 2 vs. 41 +/- 2 torr (5.2 +/- 0.3 vs. 5.5 +/- 0.3 no-monitor 39 +/- 1 vs. 37 +/- torr (5.2 +/- 0.1 vs. 5.0 +/- 0.1 kPa). However, when comparing Paco2 values for individual patients, we found that there was significantly greater variability for Paco2 after transport when end-tidal CO2 was not used for control of ventilation during transport. CONCLUSIONS: These data do not support routine monitoring of end-tidal CO2 during short transport times in adult patients requiring mechanical ventilation. However, the monitor may prevent morbidity in patients requiring tight control of Paco2.

Adolescent↗
PubMed1992

Evaluation of capnography to predict arterial PCO 2 in neurosurgical patients.

This study was designed to see if capnography could be used to predict PaCO 2 so as to adjust ventilation to maintain PaCO 2 within the desired range in head-injured patients undergoing prolonged mechanical ventilation. It was further designed to see if P ETCO 2 could accurately predict PaCO 2 based on only one arterial blood gas (ABG) measurement or if more frequent, i.e., daily, ABG measurements were required.

Adolescent↗