Measurement Of Carbon Dioxide Tension Research Articles

Transcutaneous Measurement of Carbon Dioxide Tension During Extended Monitoring: Evaluation of Accuracy and Stability, and an Algorithm for Correcting Calibration Drift

When polysomnography is indicated in a patient with a presumed sleep disorder, continuous monitoring of arterial carbon dioxide tension (P(aCO(2))) is desirable, especially if nocturnal hypoventilation is suspected. Transcutaneous CO(2) monitors (P(tcCO(2))) provide a noninvasive correlate of P(aCO(2)), but their accuracy and stability over extended monitoring have been considered inadequate for the diagnosis of hypoventilation. We examined the stability and accuracy of P(tcCO(2)) measurements and the performance of a previously described linear interpolation technique designed to correct for calibration drift. We compared the P(tcCO(2)) values from 2 TINA TCM-3 monitors to P(aCO(2)) values from arterial blood samples obtained at the beginning, every 15 min of the first hour, and then hourly over 8 hours of monitoring in 6 hemodynamically stable, male, intensive care patients (mean age 46 ± 17 y). Time had a significant (P = .002) linear effect on the P(tcCO(2))-P(aCO(2)) difference, suggesting calibration drift over the monitoring period. We found no differences between monitor type or interaction between time and monitor type. For the 2 monitors the uncorrected bias was 3.6 mm Hg and the limits of agreement were -5.1 to 12.3 mm Hg. Our linear interpolation algorithm improved the bias and limits of agreement to 0.4 and -5.5 to 6.4 mm Hg, respectively. Following stabilization and correction for both offset and drift, P(tcCO(2)) tracks P(aCO(2)) with minimal residual bias over 8 hours of monitoring. Should future research confirm these findings, then interpolated P(tcCO(2)) may have an increased role in detecting sleep hypoventilation and assessing the efficacy of treatment.

Accuracy of Transcutaneous Carbon Dioxide Tension Measurements during Cardiopulmonary Exercise Testing

Background: Measurements of transcutaneous carbon dioxide tension (PtcCO₂) with current devices are proven to provide clinically acceptable agreement with measurements of partial arterial carbon dioxide tension (PaCO₂) in several settings but not during cardiopulmonary exercise testing (CPET). Objectives: The primary objective of this study was to investigate the agreement between PaCO₂ and PtcCO₂ measurements (using a Tosca 500 with a Tosca sensor 92) during CPET. A secondary objective was to investigate the agreement between arterial and transcutaneous oxygen saturation (SaO₂, SpO₂) as measured with this sensor during CPET. Methods: In patients with various pulmonary diseases, PtcCO₂ and SpO₂ were continuously measured and compared with arterial blood gas samples during CPET. A maximum bias of 0.5 kPa and 95% limits of agreement (LOA) of 1 kPa between carbon dioxide pressure (PCO₂) measurements were determined as clinically acceptable. Results: In total 101 ‘paired’ arterial and transcutaneous measurements were obtained from 21 patients. Bias between PaCO₂ and PtcCO₂ was –0.03 kPa with LOA from –0.78 to 0.71 kPa. Bias between SaO₂ and SpO₂ was –1.0% with LOA from –2.83 to 0.83%. Conclusions: Transcutaneous estimations of PCO₂ and SpO₂ are accurate and can be used in CPET, circumvening the need for arterial cannulation.

Marcos F. Vidal Melo, M.D., Ph.D., Recipient of the 2007 Presidential Scholar Award

Marcos F. Vidal Melo, M.D., Ph.D., Recipient of the 2007 Presidential Scholar Award

Combined Pulse Oximetry/Cutaneous Carbon Dioxide Tension Monitoring during Colonoscopies: Pilot Study with a Smart Ear Clip

Background: We compared the accuracy and practicability of a new combined ear sensor device measuring pulse oximetry and transcutaneous carbon dioxide tension. Methods: Validation studies were done by comparing the results of the combined sensor with arterial blood gas measurements. In an observational part, monitoring data were obtained from 25 patients undergoing colonoscopy, sedated with midazolam and alfentanil and from 8 patients without sedation. Results: There was an excellent correlation between the oxygen saturation and carbon dioxide tension measurements comparing the combined sensor with arterial blood gas analysis (R 0.96 and 0.93, respectively). A mean rise in transcutaneous carbon dioxide tension of 7.6 mm Hg was detectable during sedation with midazolam/alfentanil and of 2.3 mm Hg without sedation. Conclusion: Combined POX/PcCO₂ monitoring at the ear lobe is a novel approach to improve patient safety during sedation and may be helpful in preventing an unintentional slide into a state of deep sedation with impairment of ventilation.

Does Early Administration of Epidural Analgesia Affect Obstetric Outcome in Nulliparous Women Who Are in Spontaneous Labor?

Background Some studies suggest that epidural analgesia prolongs labor and increases the incidence of cesarean section, especially if it is administered before 5 cm cervical dilation. The purpose of the current study was to determine whether early administration of epidural analgesia affects obstetric outcome in nulliparous women who are in spontaneous labor. Methods Informed consent was obtained from 344 healthy nulliparous women with a singleton fetus in a vertex presentation, who requested epidural analgesia during spontaneous labor at at least 36 weeks' gestation. Each patient was randomized to receive either early or late epidural analgesia. Randomization occurred only after the following conditions were met: (1) the patient requested pain relief at that moment, (2) a lumbar epidural catheter had been placed, and (3) the cervix was at least 3 cm but less than 5 cm dilated. Patients in the early group immediately received epidural bupivacaine analgesia. Patients in the late group received 10 mg nalbuphine intravenously. Late-group patients did not receive epidural analgesia until they achieved a cervical dilation of at least 5 cm or until at least 1 h had elapsed after a second dose of nalbuphine. Ten of the 344 patients were excluded because of a protocol violation or voluntary withdrawal from the study. Results Early administration of epidural analgesia did not increase the incidence of oxytocin augmentation, prolong the interval between randomization and the diagnosis of complete cervical dilation, or increase the incidence of malposition of the vertex at delivery. Also, early administration of epidural analgesia did not result in an increased incidence of cesarean section or instrumental vaginal delivery. Seventeen (10%) of 172 women in the early group and 13 (8%) of 162 women in the late group underwent cesarean section (relative risk for the early group 1.22; 95% confidence interval 0.62-2.40). Patients in the early group had lower pain scores between 30 and 150 min after randomization. Infants in the late group had lower umbilical arterial and venous blood pH and higher umbilical venous blood carbon dioxide tension measurements at delivery. Conclusions Early administration of epidural analgesia did not prolong labor, increase the incidence of oxytocin augmentation, or increase the incidence of operative delivery, when compared with intravenous nalbuphine followed by late administration of epidural analgesia, in nulliparous women who were in spontaneous labor at term.

Does Early Administration of Epidural Analgesia Affect Obstetric Outcome in Nulliparous Women Who Are in Spontaneous Labor?

Some studies suggest that epidural analgesia prolongs labor and increases the incidence of cesarean section, especially if it is administered before 5 cm cervical dilation. The purpose of the current study was to determine whether early administration of epidural analgesia affects obstetric outcome in nulliparous women who are in spontaneous labor. Informed consent was obtained from 344 healthy nulliparous women with a singleton fetus in a vertex presentation, who requested epidural analgesia during spontaneous labor at at least 36 weeks' gestation. Each patient was randomized to receive either early or late epidural analgesia. Randomization occurred only after the following conditions were met: (1) the patient requested pain relief at that moment, (2) a lumbar epidural catheter had been placed, and (3) the cervix was at least 3 cm but less than 5 cm dilated. Patients in the early group immediately received epidural bupivacaine analgesia. Patients in the late group received 10 mg nalbuphine intravenously. Late-group patients did not receive epidural analgesia until they achieved a cervical dilation of at least 5 cm or until at least 1 h had elapsed after a second dose of nalbuphine. Ten of the 344 patients were excluded because of a protocol violation or voluntary withdrawal from the study. Early administration of epidural analgesia did not increase the incidence of oxytocin augmentation, prolong the interval between randomization and the diagnosis of complete cervical dilation, or increase the incidence of malposition of the vertex at delivery. Also, early administration of epidural analgesia did not result in an increased incidence of cesarean section or instrumental vaginal delivery. Seventeen (10%) of 172 women in the early group and 13 (8%) of 162 women in the late group underwent cesarean section (relative risk for the early group 1.22; 95% confidence interval 0.62-2.40). Patients in the early group had lower pain scores between 30 and 150 min after randomization. Infants in the late group had lower umbilical arterial and venous blood pH and higher umbilical venous blood carbon dioxide tension measurements at delivery. Early administration of epidural analgesia did not prolong labor, increase the incidence of oxytocin augmentation, or increase the incidence of operative delivery, when compared with intravenous nalbuphine followed by late administration of epidural analgesia, in nulliparous women who were in spontaneous labor at term.

Comparison of Noninvasive Measurements of Carbon Dioxide Tension During Withdrawal from Mechanical Ventilation

Pulmonary and Critical Care Division, Department of Medicine, University of Rochester at Rochester General Hospital, Rochester, New York

History of blood gas analysis. III. Carbon dioxide tension.

The measurement of carbon dioxide tension (Pco2) owes its development to the 1952 polio epidemics in Copenhagen and the United States, during which artificial ventilation was first widely and effectively used and it was necessary to assess its effectiveness. Pco2 had been determined by various "bubble methods" in which carbon dioxide (CO2) was measured in gas equilibrated with blood at body temperature, or by one of two methods using the manometric apparatus of Van Slyke: interpolation on a plot of CO2 content versus equilibration gas Pco2 or use of the Henderson-Hasselbalch equation to calculate Pco2 from pH and plasma CO2 content. In 1954 Richard Stow described a CO2 electrode--a new concept--using a rubber membrane permeable to CO2 to separate a wet pH and reference electrode from the blood sample. This was the first membrane electrode, a device now used in hundreds of different ways. Severinghaus developed Stow's electrode, stabilizing it with a bicarbonate-salt solution and a spacer. The CO2 electrode concept had occurred to Gesell in 1925, but for measurement of gas only, and to Gertz and Loeschcke, who were unaware of the Stow-Severinghaus electrode, in 1958. The development of the CO2 electrode terminated the use of bubble methods, the Van Slyke methods, and the Astrup technique and at the same time reinforced the Astrup-Siggaard-Andersen acid-base analytic theory.

Laser Doppler flowmetry and transcutaneously measured carbon dioxide tension for observing changes of skin blood flow in fingers.

Laser Doppler flowmetry (LDF) and transcutaneous carbon dioxide tension measurements (PtcCO2) were performed on fingers of healthy volunteers subjected to a sequence of hydrostatic and thermal stimuli. LDF response using an unheated probe agreed well with measurements made with Xenon133 clearance and strain gauge plethysmography in a previous work. The PtcCO2 results, however, were found not in any way to reflect changes in skin blood flow.

Transcutaneous Measurement of Carbon Dioxide Tension: Effect of Sleep State in Term Infants

Transcutaneous measurement of carbon dioxide tension (tcPO2) was used to assess the effect of sleep state on arterial carbon dioxide tension (PaCO2) in infants. Initially, tcPCO2 was correlated with PaCO2 in 50 sick preterm and term neonates with indwelling arterial lines. At a skin electrode temperature of 42 degrees C, the correlation coefficient between tcPCO2 and PaCO2 was .95. In eight healthy term infants there was a small but significant decrease in tcPCO2 of 2 +/- 1 mm Hg (P less than .001) during active as compared to quiet sleep. This decrease in tcPCO2 was accompanied by a significant decrease in transcutaneous oxygen tension (tcPO2) of 5 +/- 4 mm Hg (P less than .02) as has been previously described. The simultaneous decrease of both tcPCO2 and tcPO2 appears to indicate ventilation/perfusion inequalities in these infants during active sleep. These findings illustrate that tcPCO2 can accurately predict PaCO2 in infants and that this is a useful technique for studying neonatal respiratory control during various stages of sleep.

Quality control of measurements of pH, carbon dioxide tension, and total carbon dioxide in plasma.

We have measured total carbon dioxide in plasma with a new carbon dioxide analyzer, and compared the results with total carbon dioxide data derived from measurements of carbon dioxide tension and pH. The results agree sufficiently well to demonstrate that the new instrument provides a simple, efficient procedure for monitoring the precision and accuracy of pH, carbon dioxide tension, or total carbon dioxide in plasma.

In vivo measurement of carbon dioxide tension with a miniature electrode.

A commercially available catheter type electrode with which PCO2 can be continuously measured in vivo and in vitro gave progressively less accurate results the longer the measuring period was extended. This proved to be due to temperature effects and a change in sensitivity with time. A correction procedure for these effects was developed which was based on two observations. 1. The relationship between temperature and the logarithm of the sensitivity of the electrode-amplifier combination was linear and virtually identical for 9 electrodes: 8% change in sensitivity for a deviation of 1 degree C from the temperature during calibration. 2. The change in sensitivity due to drift of the electrode output is approximately a logarithmic function of time: 1 h after calibration all electrodes exhibited a decreased sensitivity, varying between 0.3 and 16.7%. The drift effect can be dealt with by repeated calibrations, preferably at 1 1/2 h intervals. The adequacy of the correction procedure was assessed in in vivo measurements in cats and dogs. The mean PCO2 difference between the in vivo measurement, corrected for temperature and drift, and samples analyzed with a conventional electrode, was 0.005 kPa (0.04 mm Hg) with a standard deviation of 0.187 kPa (1.39 mm Hg).

Measurement of alveolar carbon dioxide tension at maximal expiration as an estimate of arterial carbon dioxide tension in patients with airway obstruction.

Arterial and alveolar carbon dioxide tension at end-tidal and maximal expiration were measured simultaneously in 104 patients with chronic obstructive respiratory disease. Regardless of the degree of abnormality of distribution of ventilation, there was a consistent relationship between arterial and maximal expiratory carbon dioxide tension. Therefore, close approximation of arterial carbon dioxide tension was obtained from the measurement of carbon dioxide tension at maximal expiration by rapid infrared carbon dioxide analysis. An infrared carbon dioxide analyzer might be used at the bedside or in the laboratory for frequent monitoring of arterial carbon dioxide tension without repeated arterial punctures.

Measurement of carbon dioxide tension in poorly buffered solutions with thepCO2 electrode

An improved electrode system is described for measuring thepCO2 in poorly buffered solutions, such as cerebrospinal fluid. The drift and the CO2 loss from the cuvette are considerably reduced compared with the Severinghaus electrode. The “memory effect” was found to be caused by two factors: Both factors are reproducible and corrections can be made for this effect. The calibration and measuring procedure described are suitable for routine measurements. The standard deviation of a single reading is 0.4 mm Hg.

Oscillations in blood pressure associated with phrenic nerve activity.

WE have observed periodic oscillations in systemic blood pressure synchronous with bursts of phrenic nerve activity in dogs during apnoea. The phrenic nerve was isolated in the neck, and nerve impulses detected with bipolar platinum electrodes. The nervous activity was amplified and rectified, and the impulses integrated by a method described previously1. Catheters were placed in both femoral arteries to record the arterial blood pressure continuously as well as to sample arterial blood so as to measure the arterial carbon dioxide tension every minute. Spontaneous breathing was arrested by the intravenous administration of succinyl choline, and the dogs were ventilated artificially with 100 per cent oxygen for twenty minutes using a Harvard pump. Initial measurements of carbon dioxide tension and phrenic nerve activity were made at the end of this control period. Artificial ventilation was then stopped and the dog connected by its endotracheal tube to a spirometer containing 100 per cent oxygen. By this means arterial oxygen was maintained at normal tension during the ensuing period of apnoea, when carbon dioxide tension increased at the rate of 6.0 mm of mercury/min.

EFFECT OF GASEOUS ANESTHESIA ON BLOOD CARBON DIOXIDE MEASUREMENTS.

The present study of the effect of two common anaesthetic gases on blood acid-base parameters shows that the micro-Astrup measurement of carbon dioxide tension is not invalidated by the presence of nitrous oxide. This result was anticipated from the theoretical aspect of this technique. The mean error involved in estimating plasma carbon dioxide content in the presence of nitrous oxide using the volumetric Van Slyke apparatus without absorption of carbon dioxide by sodium hydroxide can be of the order of 25%. No such effect was measurable in estimating carbon dioxide contents in the presence of halothane. The degree of respiratory alkalosis during anaesthesia reported in earlier papers (Walker, Morgan, Breckenridge, Watt, Ogilvie, and Douglas, 1963; Morgan, Ogilvie, and Walker, 1963) was greater than had been originally appreciated.A ;false' increase in carbon dioxide content will also falsely increase buffer base or ;base excess' as calculated from standard nomograms (Singer and Hastings, 1948; Davenport, 1958; Siggaard-Andersen, 1963).