Noninvasive carbon dioxide monitoring during neurosurgical procedures in adults: end-tidal versus transcutaneous techniques

BACKGROUND: We prospectively compared transcutaneous (TC) versus end-tidal (ET) carbon dioxide monitoring during neurosurgical procedures in adults. METHODS: After calibration and an equilibration time for the TC-CO2 monitor, arterial blood gas (ABG) values were obtained as clinically indicated. The PaCO2 values were compared with the values recorded by the noninvasive monitors (TC and ET). RESULTS: The ET-CO2 to PaCO2 difference was 6.1 +/- 5.6 mm Hg, and the TC-CO2 to PaCO2 difference was 3.7 +/- 2.9 mm Hg. The difference between the PaCO2 and ET-CO2 was 3 mm Hg or less in 17 of 57 values, while the difference between the PaCO2 and TC-CO2 was 3 mm Hg or less in 35 of 57 values. Linear regression analysis of ET-CO2 versus PaCO2 revealed a slope of 0.381 +/- 0.007. Linear regression analysis of TC-CO2 versus PaCO2 revealed a slope of 1.17 +/- 0.008. CONCLUSION: Transcutaneous CO2 monitoring provides a more accurate estimate of PaCO2 than ET-CO2 monitoring during neurosurgical procedures.     

Monitoring end-tidal carbon dioxide

Learn how a simple colorimetric device helps verify correct endotracheal tube placement.     

Noninvasive monitoring of carbon dioxide: A comparison of the partial pressure of transcutaneous and end-tidal carbon dioxide with the partial pressure of arterial carbon dioxide

This study compares two noninvasive techniques for monitoring the partial pressure of carbon dioxide (Pco2) in 24 anesthetized adult patients. End-tidal PCO₂ (PETCO₂) and transcutaneous Pco₂ (PtcCO₂) were simultaneously monitored and compared with arterial Pco₂ (PaCO₂) determined by intermittent analysis of arterial blood samples. PETCO₂ and PtcCO₂ values were compared with PaCO₂ values corrected to patient body temperature (PaC0_2T) and PaCO₂ values determined at a temperature of 37°C (PaCO₂). Linear regression was performed along with calculations of the correlation coefficient (r), bias, and precision of the four paired variables:PETCO₂ versus PaCO₂ and PaCO_2T (n = 211), and PtcCO₂ versus PaCO₂ and PaCO_2T (n = 233). Bias is defined as the mean difference between paired values, whereas precision is the standard deviation of the difference. The following values were found forr, bias, and ± precision, respectively.PetCO₂ versus PaCO₂: 0.67, ?7.8 mm Hg, ±6.1 mm Hg;PETCO₂ versus PaCO_2T: 0.73, ?5.8 mm Hg, ±5.9 mm Hg;PETCO₂ versus PaCO₂: 0.87, ?1.6 mm Hg, ±4.3 mm Hg; PtcCO₂ versus PaC0_2T: 0.84, +0.7 mm Hg, ±4.8 mm Hg. Although each of thesePCO ₂ variables is physiologically different, there is a significant correlation (P < 0.001) between the noninvasively monitored values and the blood gas values. Temperature correction of the arterial values (PaCO_2T) slightly improved the correlation, with respect toPETCO₂, but it had the opposite effect for PtcCO₂. In this study, the chief distinction between these two noninvasive monitors was thatPETCO₂ had a large negative bias, whereas PtcCO₂ had a small bias. We conclude from these data that PtcCO₂ may be used to estimate PaCO₂ with an accuracy similar to that ofPetCO₂ in anesthetized patients.     

Cardiac output and end-tidal carbon dioxide

Previous studies demonstrated selective increases in mixed venous carbon dioxide tension (PvCO2) during CPR in a porcine model of cardiac arrest. This was associated with a decrease in end-tidal carbon dioxide concentration (ETCO2), possibly due to a critical reduction in cardiac output and therefore pulmonary blood flow during CPR. We investigated the relationship between ETco2 and cardiac output before cardiac arrest and during CPR. Observations in 19 minipigs confirmed a high linear correlation between ETco2 and cardiac output. We conclude that the increase in Pvco2 and the concurrent decrease in ETco2 reflect a critical reduction in cardiac output, which reduces alveolar blood flow to the extent that carbon dioxide clearance by the lung fails to keep pace with systemic CO2 production.     

Colorimetric end-tidal carbon dioxide monitoring during transfer of intubated children

We report the use of a cheap, pocket-sized colorimeter to assess the end-tidal carbon dioxide concentration during transfer of intubated children. The device provided breath by breath confirmation of tracheal tube placement and identified one episcde of reduced pulmonary perfusion. We would advocate the use of this detector to provide early warning of tracheal tube displacement during the transfer of children weighing more than 15 kg.     

Measurement of end-tidal carbon dioxide concentration during cardiopulmonary resuscitation.

End-tidal carbon dioxide concentrations were measured prospectively in 12 cardiac arrest patients undergoing cardiopulmonary resuscitation (CPR) in an accident and emergency department. The end-tidal carbon dioxide (CO2) concentration decreased from a mean (+/- SD) of 4.55 +/- 0.88% 1 min after chest compression and ventilation was established, to values ranging from 2.29 +/- 0.84% at 2 min to 1.56 +/- 0.66% following 8 min of CPR. Spontaneous circulation was restored in five patients. This was accompanied by a rapid rise in end-tidal CO2 which peaked at 2 min (3.7 +/- 1.08%). Changes in end-tidal CO2 values were often the first indication of return of spontaneous cardiac output. There was a significant difference in the end-tidal CO2 in patients undergoing CPR before return of spontaneous circulation (2.63 +/- 0.32%) and patients who failed to develop spontaneous output (1.64 +/- 0.89%) (p < 0.001). We conclude that measurement of end-tidal CO2 concentration provides a simple and non-invasive method of measuring blood flow during CPR and can indicate return of spontaneous circulation.     

Discrepancies between transcutaneous and end-tidal carbon dioxide monitoring in the critically ill neonate with respiratory distress syndrome

PaCO2, transcutaneous PCO2 (PtcCO2), and end-tidal PCO2 (PetCO2) measurements were studied in 12 critically ill neonates. PtcCO2 was measured using a combination CO2/O2 sensor during the routine care of these patients. End-tidal sidestream sampling was performed during blood gas measurement as dictated by the patient's clinical condition. There was a linear correlation between PtcCO2 and PaCO2 (n = 51, r = .71, slope = 0.90). PetCO2 and PaCO2 did not correlate as well (n = 51, r = .52, slope = 0.42). Acidosis negatively affected the correlation between PtcCO2 and PaCO2. When pH was greater than 7.30, r = .75 and slope = 1.28 (n = 38), whereas when pH was less than 7.30, r = .62 and slope = 0.73 (n = 13). The presence or absence of a metabolic acidosis did not have a significant effect on the slopes obtained. PtcCO2 monitoring using combined sensors is a useful and practical means of monitoring in the neonatal ICU, although acidosis affects the ability to correlate transcutaneous and arterial values. End-tidal sidestream measurements are not as clinically useful because they vary due to different ventilation/perfusion relationships in the sick neonate.     

Noninvasive monitoring of carbon dioxide in infants and children with congenital heart disease: end-tidal versus transcutaneous techniques

End-tidal CO2 (ET(CO2)) monitoring and transcutaneous (TC) CO2 monitoring were prospectively compared in 53 patients, 1 month to 16 years of age, with congenital heart disease (CHD). There were 32 patients with cyanotic CHD and 21 with acyanotic CHD. The TC-Pa(CO2) difference was 2 +/- 1 mm Hg and the ET-Pa(CO2) difference was 5 +/- 3 mm Hg (P < .0001). The TC-Pa(CO2) difference was < or = 2 mm Hg in 30 of 53 patients and < or = 5 mm Hg in 53 of 53 patients. The ET-Pa(CO2) difference was < or = 2 mm Hg in 9 of 53 patients and < or = 5 mm Hg in 30 of 53 patients (P < .001). No variation in the TC-Pa(CO2) difference was noted based on the type of CHD (acyanotic vs cyanotic) or age. The ET-Pa(CO2) difference was greater in patients with cyanotic versus acyanotic CHD (7 +/- 3 mm Hg vs 4 +/- 2 mm Hg, P < .0001) and in patients < or = 1 year of age versus patients > or = 1 year of age (6 +/- 3 mm Hg vs 4 +/- 2, P = .008). In infants and children with CHD, TC monitoring provides a more accurate estimation of Pa(CO2) than ET monitoring.     

Accuracy of end-tidal carbon dioxide tension analyzers

Substantial mean differences between arterial carbon dioxide tension (PaCO₂) and end-tidal carbon dioxide tension (PetCO₂) in anesthesia and intensive care settings have been demonstrated by a number of investigators. We have explored the technical causes of error in the measurement ofPetCO₂ that could contribute to the observed differences. In a clinical setting, the measurement ofPetCO₂ is accomplished with one of three types of instruments, infrared analyzers, mass spectrometers, and Raman spectrometers, whose specified accuracies are typically ±2, ±1.5, and ±0.5 mm Hg, respectively. We examined potential errors inPetCO₂ measurement with respect to the analyzer, sampling system, environment, and instrument. Various analyzer error sources were measured, including stability, warm-up time, interference from nitrous oxide and oxygen, pressure, noise, and response time. Other error sources, including calibration, resistance in the sample catheter, pressure changes, water vapor, liquid water, and end-tidal detection algorithms, were considered and are discussed. On the basis of our measurements and analysis, we estimate the magnitude of the major potential errors for an uncompensated infrared analyzer as: inaccuracy, 2 mm Hg; resolution, 0.5 mm Hg; noise, 2 mm Hg; instability (12 hours), 3 mm Hg; miscalibration, 1 mm Hg; selectivity (70% nitrous oxide), 6.5 mm Hg; selectivity (100% oxygen), −2.5 mm Hg; atmospheric pressure change, <1 mm Hg; airway pressure at 30 cm H₂O, 2 mm Hg; positive end-expiratory pressure or continuous positive airway pressure at 20 cm H₂O, 1.5 mm Hg; sampling system resistance, <1 mm Hg; and water vapor, 2.5 mm Hg. In addition to these errors, other systematic mistakes such as an inaccurate end-tidal detection algorithm, poor calibration technique, or liquid water contamination can lead to gross inaccuracies. In a clinical setting, unless the user is confident that all of the technical error sources have been eliminated and the physiologic factors are known, depending onPetCO₂ to determine PaCO₂ is not advised. An erratum to this article is available at .     

Accuracy of end-tidal carbon dioxide tension analyzers

Substantial mean differences between arterial carbon dioxide tension (PaCO₂) and end-tidal carbon dioxide tension (PetCO₂) in anesthesia and intensive care settings have been demonstrated by a number of investigators. We have explored the technical causes of error in the measurement ofPetCO₂ that could contribute to the observed differences. In a clinical setting, the measurement ofPetCO₂ is accomplished with one of three types of instruments, infrared analyzers, mass spectrometers, and Raman spectrometers, whose specified accuracies are typically ±2, ±1.5, and ±0.5 mm Hg, respectively. We examined potential errors inPetCO₂ measurement with respect to the analyzer, sampling system, environment, and instrument. Various analyzer error sources were measured, including stability, warm-up time, interference from nitrous oxide and oxygen, pressure, noise, and response time. Other error sources, including calibration, resistance in the sample catheter, pressure changes, water vapor, liquid water, and end-tidal detection algorithms, were considered and are discussed. On the basis of our measurements and analysis, we estimate the magnitude of the major potential errors for an uncompensated infrared analyzer as: inaccuracy, 2 mm Hg; resolution, 0.5 mm Hg; noise, 2 mm Hg; instability (12 hours), 3 mm Hg; miscalibration, 1 mm Hg; selectivity (70% nitrous oxide), 6.5 mm Hg; selectivity (100% oxygen), –2.5 mm Hg; atmospheric pressure change, <1 mm Hg; airway pressure at 30 cm H₂O, 2 mm Hg; positive end-expiratory pressure or continuous positive airway pressure at 20 cm H₂O, 1.5 mm Hg; sampling system resistance, <1 mm Hg; and water vapor, 2.5 mm Hg. In addition to these errors, other systematic mistakes such as an inaccurate end-tidal detection algorithm, poor calibration technique, or liquid water contamination can lead to gross inaccuracies. In a clinical setting, unless the user is confident that all of the technical error sources have been eliminated and the physiologic factors are known, depending onPetCO₂ to determine PaCO₂ is not advised.     

Accuracy of end-tidal carbon dioxide tension analyzers

The online version of the original article can be found at     

Simple and accurate monitoring of end-tidal carbon dioxide tensions during high-frequency jet ventilation

To determine whether end-tidal carbon dioxide tension (PETCO2) accurately reflects PaCO2 during high-frequency jet ventilation (HFJV), 43 studies were performed on eight mongrel dogs with normal lungs. During HFJV, minute volume was modified to obtain a range of PaCO2 values from 15.5 to 74.5 torr. When PETCO2 was measured with an infrared gas analyzer, there was a poor correlation between PaCO2 and PETCO2 values. However, when the high-frequency ventilator was adjusted to deliver large tidal-volume (sigh) breaths, PETCO2 values were significantly (r = 0.94, p less than .001) correlated with PaCO2. Our data suggest that the PETCO2 of alveolar gas is an accurate indicator of the PaCO2 during HFJV in nondiseased lungs.     

潮气末二氧化碳分压在机械通气中的应用价值

在机械通气过程中,测定动脉血二氧化碳分压(PaCO2)对于调整呼吸机参数具有重要意义。潮气末二氧化碳分压(PETCO2)监测具有无创、连续监测等特点,并可在不同程度上反映PaCO2变化趋势,但由于影响PETCO2测量结果的因素较多,所以它的临床价值一直受到争议。为此,我们通过分析急诊重     

Accurate determination of end-tidal carbon dioxide during administration of oxygen by nasal cannulae

Measurement of end-tidal carbon dioxide tension (PetCO₂) by mass spectrometry or infrared capnometry provides a clinically useful approximation of arterial carbon dioxide tension (PaCO₂) in intubated patients. Although several devices have been proposed to samplePetCO₂ during spontaneous breathing (i.e., unintubated patients receiving supplemental oxygen), thus far no reports have documented their efficacy. This article reports the use of an easily constructed modification of simple nasal cannulae that permits accurate sampling ofPetCO₂ during oxygen administration to unintubated patients. After amputation of the closed tip, a cap from a syringe was inserted via a slit made at the base into one prong of a pair of nasal cannulae. A capnometer was connected to the syringe cap, andPetCO₂ and PaCO₂ were determined simultaneously during the administration of 3 L/min oxygen via nasal cannulae to 21 normocapnic patients. The PaCO₂ —PetCO₂ gradients were calculated and compared with values obtained in the same patients after intubation and mechanical ventilation. No significant difference was found between the calculated gradients with nasal cannulae (2.09±2.18 mm Hg) versus intubation (2.87±2.82 mm Hg). Simultaneous oxygen administration and accurate sampling ofPetCO₂ may be achieved in unintubated patients by using this easily constructed modification of nasal cannulae.Supported in part by PPG Biomedical Systems, Lenexa, KS.The apparatus and method described herein are covered by U.S. Patent Application S.N. 181,814: Method and Apparatus for Inhalation of Treating Gas for Quantitative Analysis. Filed April 15, 1988—in the name of Edwin A. Bowe, et al.     

Stroke volumes and end-tidal carbon dioxide generated by precordial compression during ventricular fibrillation

OBJECTIVE: The objective of this study was to measure stroke volumes produced by precordial compression during cardiopulmonary resuscitation and to quantitate relationships of stroke volume to measurements of end-tidal carbon dioxide. DESIGN: A prospective, observational animal study. SETTING: Medical research laboratory in a university-affiliated research and educational foundation. SUBJECTS: Domestic pigs. INTERVENTIONS: Eighteen anesthetized male, domestic pigs weighing between 40 and 45 kg were investigated. Ventricular fibrillation was electrically induced and continued for intervals ranging from 4 to 10 mins. Precordial compression was maintained at 80 per minute together with mechanical ventilation after endotracheal intubation. MEASUREMENTS AND MAIN RESULTS: Stroke volumes were measured with the aid of transesophageal echocardiographic imaging. End-tidal carbon dioxide was quantitated with conventional capnography. Baseline values of thermodilution cardiac output were highly correlated with echocardiographic measurements (r =.92). The stroke volume index produced by precordial compression averaged 0.45 mL/kg or approximately 37% of the average prearrest value of 1.22 mL/kg. The end-tidal carbon dioxide was highly predictive of stroke volume index (r =.88, p <.001) with a mean bias of 0.003 mL/kg. CONCLUSIONS: We confirmed that precordial compression produces approximately one third of prearrest stroke volumes during cardiopulmonary resuscitation and demonstrated that end-tidal carbon dioxide was quantitatively predictive of stroke volume index estimated by transesophageal echocardiographic imaging.     

潮气末二氧化碳分压对心肺复苏结果的指导和预测作用

目的 探讨潮气末二氧碳(PetCO2)监测在心肺复苏(CPR)期间的临床意义并寻求定值以指导临床抢救.方法 采用回顾性研究方法,选择2003年5月至2009年3月解放军第四五一医院急诊科院内外非外伤性心搏骤停已明确原因的患者124例,监测心搏骤停患者在CPR过程中PetCO2的变化.结果 ①恢复自主循环(ROSC)的71例与未恢复的53例气管插管后性别、年龄、抢救时间比较P值分别为＜0.05,＜0.05,＜0.01,差异具有统计学意义,说明上述因素与复苏成功正相关,但性别和年龄与最终存活率无相关性.②最终存活者PetCO2水平高于未复苏成功者和虽复苏成功但最终院内死亡者,并与施救时间相关.③经过20 min的高级生命支持没有恢复自主循环者PetCO2平均水平在(6.7±1.2) mmHg(1mmHg =0.133 kPa),恢复自主循环者在(33.9±7.8) mmHg (P＜0.01),以20 min高级生命支持后PetCO2水平高于14.4 mmHg作为参考值预期死亡,阳性率和阴性率均为100％.结论 CPR过程中PetCO2的监测对复苏有指导和预测作用.     

Sensitivity of a disposable end-tidal carbon dioxide detector

A small disposable carbon dioxide detector that can be used to provide evidence of correct endotracheal tube placement is now commercially available (FEF). The device contains an indicator that changes color when exposed to carbon dioxide. This study measured the lowest concentration of carbon dioxide causing a perceivable color change in the device. Ten volunteers were blinded to the concentrations of carbon dioxide in an airway circuit/lung model, and the minimal concentration of carbon dioxide that caused a perceivable color change was recorded. The mean minimum concentration required for detection of a color change was 0.54% (4.1 mm Hg) and ranged from 0.25 to 0.60% (1.9 to 4.6 mm Hg). We conclude that this device should produce a detectable color change even in patients with low end-tidal carbon dioxide, as might be observed during cardiopulmonary resuscitation.Presented in part at the annual meeting of the American Society of Anesthesiologists, New Orleans, October 1989.     

妇科腹腔镜手术动脉与呼末CO2差值的变化及两者相关性研究

目的 研究丙泊酚或异氟醚麻醉下头低位CO2气腹期间PaCO2、PETCO2变化及二者相关关系.方法 24例ASA Ⅰ、Ⅱ级妇科腹腔镜手术患者,以丙泊酚或异氟醚、维库溴铵及芬太尼行全麻诱导及维持,机械通气VT=7 mL/kg,f=14次/min;建立气腹后立即取头低位,分别于气腹前、气腹后10、20和60 min时采集桡动脉血行血气分析,同步记录PETCO2并计算二者的差值pa-ETCO2.结果 与气腹前比较,气腹后PaCO2及PETCO2均显著增加（均P＜0.01）,气腹后10、60 min时Pa-ETCO2显著增加（P＜0.05及P＜0.01）.气腹后20min时PaCO2与PETCO2相关关系不显著.结论 妇科腹腔镜手术期间PaCO2及PETCO2均显著增加,应适当增加通气量,PETCO2不能准确反映PaCO2.