Transcutaneous Pco2 monitoring in critically ill adults: Clinical evaluation of a new sensor*

Concordance between transcutaneous and arterial measurements of carbon dioxide in an ED

BACKGROUND

Transcutaneous carbon dioxide pressure (PtcCO(2)) has been suggested as a noninvasive surrogate of arterial carbon dioxide pressure (PaCO(2)). Our study evaluates the reliability of this method in spontaneously breathing patients in an emergency department.

PATIENTS AND METHODS

A prospective, observational study was performed in nonintubated dyspneic patients who required measurement of arterial blood gases. Simultaneously and blindly to the physicians in charge, PtcCO(2) was measured using a TOSCA 500 monitor (Radiometer, Villeurbanne, France). Agreement between PaCO(2) and PtcCO(2) was assessed using the Bland-Altman method.

RESULTS

Forty-eight patients (mean age, 65 years) were included, and 50 measurements were done. Eleven (23%) had acute heart failure; 10 (21%), pneumonia; 7 (15%), acute asthma; and 7 (15%), exacerbation of chronic obstructive pulmonary disease. Median PaCO(2) was 42 mm Hg (range, 17-109). Mean difference between PaCO(2) and PtcCO(2) was 1 mm Hg with 95% limits of agreement of -3.4 to +5.6 mm Hg. All measurement differences were within 5 mm Hg, and 32 (64%) were within 2 mm Hg.

CONCLUSION

Transcutaneous carbon dioxide pressure accurately predicts PaCO(2) in spontaneously breathing patients.

Transcutaneous monitor approximates PaCO(2) but not PaO(2) in anesthetized rabbits

OBJECTIVE

To compare the accuracy of transcutaneous (tc) to arterial partial pressure of carbon dioxide (PaCO(2) ) and partial pressure of oxygen (PaO(2) ) in anesthetized rabbits.

STUDY DESIGN

Prospective, randomized, experimental study.

ANIMALS

Eight healthy adult female New Zealand white rabbits weighing 4.05± 0.30 kg.

METHODS

Isoflurane anesthetized rabbits received six treatments in random order; PaCO(2) <35, 35-45, and >45 mmHg and PaO(2)  < 80, 100-200, >200 mmHg. Arterial and transcutaneous measurements were taken after 15 minutes of stabilization at each condition. Linear regression, correlation and Bland-Altman analysis were performed to compare PtcCO(2) to PaCO(2) and PtcO(2) to PaO(2) .

RESULTS

Over a range of measured PaCO(2) values from 21 to 67 mmHg (n=24) mean bias for PtcCO(2) was -1 mmHg and the 95% limits of agreement were -7 to 5 mmHg. The correlation between PtcCO(2) and PaCO(2) was strong with R(2) value of 0.9454. Over the entire range of measured PaO(2) values (46-508 mmHg) mean bias for PtcO(2) was -61 mmHg and the 95% limits of agreement were -226 to 104 mmHg. Correlation was poor with R(2) =0.5969. Comparing PtcO(2) to PaO(2) over a narrower range [PaO(2) < 150 mmHg (n=13)] improved the correlation, with an R(2) value of 0.8518, mean bias of -7 mmHg and 95% limits of agreement from -33 to 19 mmHg.

CONCLUSIONS AND CLINICAL RELEVANCE

In healthy anesthetized rabbits, PtcCO(2) closely approximated PaCO(2) . In contrast PtcO(2) underestimated PaO(2) , particularly at high values. The PtcCO(2) sensor may be a useful noninvasive way to assess adequacy of ventilation in anesthetized rabbits.

Noninvasive monitoring of PaCO(2) during one-lung ventilation and minimal access surgery in adults: End-tidal versus transcutaneous techniques

Background:

Previous studies have suggested that end-tidal CO₂ (ET-CO₂) may be inaccurate during one-lung ventilation (OLV). This study was performed to compare the accuracy of the noninvasive monitoring of PCO₂ using transcutaneous CO₂ (TC-CO₂) with ET-CO₂ in patients undergoing video-assisted thoracoscopic surgery (VATS) during OLV.

Materials and Methods:

In adult patients undergoing thoracoscopic surgical procedures, PCO₂ was simultaneously measured with TC-CO₂ and ET-CO₂ devices and compared with PaCO₂.

Results:

The cohort for the study included 15 patients ranging in age from 19 to 71 years and in weight from 76 to 126 kg. During TLV, the difference between the TC-CO₂ and the PaCO₂ was 3.0 ± 1.8 mmHg and the difference between the ET-CO₂ and PaCO₂ was 6.2 ± 4.7 mmHg (P=0.02). Linear regression analysis of TC-CO2 vs. PaCO₂ resulted in an r² = 0.6280 and a slope = 0.7650 ± 0.1428, while linear regression analysis of ET-CO₂vs. PaCO₂ resulted in an r² = 0.05528 and a slope = 0.1986 ± 0.1883. During OLV, the difference between the TC-CO₂ and PaCO₂ was 3.5 ± 1.7 mmHg and the ET-CO₂ to PaCO₂ difference was 9.6 ± 3.6 mmHg (P=0.03 vs. ET-CO₂ to PaCO₂ difference during TLV; and P<0.0001 vs. TC-CO₂ to PaCO₂ difference during OLV). In 13 of the 15 patients, the TC-CO₂ value was closer to the actual PaCO₂ than the ET-CO₂ value (P =0.0001). Linear regression analysis of TC-CO₂vs. PaCO₂ resulted in an r² = 0.7827 and a slope = 0.8142 ± 0.0.07965, while linear regression analysis of ET-CO₂vs. PaCO₂ resulted in an r² = 0.2989 and a slope = 0.3026 ± 0.08605.

Conclusions:

During OLV, TC-CO₂ monitoring provides a better estimate of PaCO₂ than ET-CO2 in patients undergoing VATS.

Validation of a transcutaneous CO(2) monitor in adult patients with chronic respiratory failure

BACKGROUND

Home mechanical ventilation is usually started in hospital as arterial blood gas sampling is deemed necessary to monitor CO(2) and O(2) adequately during institution of ventilatory support. A non-invasive device to reliably measure CO(2) transcutaneously would alleviate the need for high care settings for measurement and open the possibility for home registration.

OBJECTIVES

In this study we investigated whether the TOSCA® transcutaneous CO(2) (PtcCO(2)) measurements, performed continuously during the night, reliably reflect arterial CO(2) (PaCO(2)) measurements in adults with chronic respiratory failure.

METHODS

Paired measurements were taken in 15 patients hospitalised to evaluate their blood gas exchange. Outcomes were compared 30 min, 2, 4, 6 and 8 h after attaching the sensor to the earlobe. A maximum difference of 1.0 kPa and 95% limits of agreement (LOA) of 1 kPa between CO(2) pressure measurements, following the analysis by Bland and Altman, were determined as acceptable.

RESULTS

Mean PtcCO(2) was 0.4 kPa higher (LOA -0.48 to 1.27 kPa) than mean PaCO(2) after 30 min. These figures were 0.6 kPa higher (LOA -0.60 to 1.80 kPa) after 4 h, with a maximum of 0.72 kPa (LOA 0.35 to 1.79 kPa) after 8 h. The corresponding values for changes in PtcCO(2) versus PaCO(2) were not significant (ANOVA).

CONCLUSIONS

PtcCO(2) measurement, using TOSCA, is a valid method showing an acceptable agreement with PaCO(2) during 8 h of continuous measurement. Therefore, this device can be used to monitor CO(2) adequately during chronic ventilatory support.

Accuracy of a transcutaneous carbon dioxide pressure monitoring device in emergency room patients with acute respiratory failure

PURPOSE

Transcutaneous CO(2) monitors are widely used in neonatal ICUs. Until recently, these devices performed poorly in adults. Recent technical modifications have produced transcutaneous CO(2) monitors that have performed well in adults with chronic illnesses. We evaluated the accuracy of one of these devices, the TOSCA(®) 500, in adults admitted to an emergency department for acute respiratory failure.

METHODS

We prospectively collected 29 pairs of simultaneous transcutaneous arterial CO(2) (PtcCO(2)) and arterial CO(2) (PaCO(2)) values in 21 consecutive adults with acute respiratory failure (acute heart failure, n = 6; COPD exacerbation, n = 8; acute pneumonia, n = 6; and pulmonary embolism, n = 1). Agreement between PaCO(2) and PtcCO(2) was evaluated using the Bland-Altman method.

RESULTS

Mean arterial oxygen saturation was 90%, arterial oxygen tension ranged from 32 to 215 mmHg, and PaCO(2) ranged from 23 to 84 mmHg. The mean difference between PaCO(2) and PtcCO(2) was 0.1 mmHg, and the Bland-Altman limits of agreement (bias ± 1.96 SD) ranged from -6 to 6.2 mmHg. None of the patients experienced adverse effects from heating of the device clipped to the earlobe.

CONCLUSION

PtcCO(2) showed good agreement with PaCO(2) in adults with acute respiratory failure.

Transcutaneous monitoring as a replacement for arterial PCO(2) monitoring during nocturnal non-invasive ventilation

BACKGROUND

Continuous, non-invasive assessment of alveolar ventilation achieved by transcutaneous PCO(2) (PtcCO(2)) monitoring is clearly superior to intermittent, invasive blood gas analyses in patients receiving nocturnal non-invasive positive pressure ventilation (NPPV), but the reliability and accuracy of PtcCO(2)-monitoring is still disputed. The present study was aimed at investigating the capability of modern PtcCO(2)-monitoring to reliably assess alveolar ventilation during nocturnal NPPV.

METHODS

Capillary blood gas measurements (11pm, 2am, 5am and 7am) and 8 h of continuous PtcCO(2)-monitoring using three of the latest generation devices (SenTec Digital Monitor, Radiometer TCM4-TINA and Radiometer TOSCA500) were performed during polysomnography-proven sleep studies in 24 patients receiving NPPV (15 with COPD, 9 with restrictive disorders).

RESULTS

The technical calibration drift for SenTec DM, TCM4-TINA and TOSCA500 was 0.1, -0.4 and -0.5 mmHg/h, respectively. Bland-Altman method comparison of PaCO(2)/drift-uncorrected PtcCO(2) revealed a mean bias (limits of agreement) of 1.0 (-4.7 to 6.7), -1.5 (-15.6 to 12.5) and 0.8 (-6.8 to 8.3) mmHg, respectively. Continuous overnight PtcCO(2)-monitoring detected variations in alveolar ventilation, with median ranges of 12.3 (10.7-14.5) mmHg for SenTec DM, 14.5 (12.5-17.0) mmHg for TCM4-TINA and 11.5 (11.0-13.0) mmHg for TOSCA500 (RM-ANOVA, p < 0.001). The four capillary PaCO(2) values ranged by a median of 6.3 (4.7-9.7) mmHg.

CONCLUSIONS

Modern PtcCO(2)-monitoring is reliable, accurate and robust. Since PtcCO(2)-monitoring is also non-invasive, does not disrupt sleep quality and provides a more complete picture of alveolar ventilation than intermittent capillary PaCO(2), PtcCO(2)-monitoring should become the preferred technique for assessing alveolar ventilation during nocturnal NPPV.

TRIAL REGISTRATION

DRKS00000433 at http://apps.who.int/trialsearch/default.aspx.

Accuracy of three transcutaneous carbon dioxide monitors in critically ill children

OBJECTIVES

To study the accuracy of three devices for measuring transcutaneous CO(2) tension in critically ill children.

METHODS

A prospective study comparing the values from three transcutaneous CO(2) monitors (SenTec, TOSCA 500, and TINA TCM3) with simultaneous arterial CO(2) (PaCO(2)) and end-tidal CO(2) (EtCO(2)) values. Clinical data were collected from the patients. Influence of core-skin temperature gradient and doses of inotropic drugs was evaluated.

RESULTS

There were 62 samples from 41 critically ill children with ages between 2 and 192 months (median, 18.5 months) and weights between 3.1 and 72 kg (median, 9 kg). The median PaCO(2) was 42.5 mmHg (range, 28-85 mmHg). Transcutaneous CO(2) (PtcCO(2)) values correlated better with PaCO(2) than with EtCO(2). The correlation coefficient between PaCO(2) and PtCO(2) was 0.833 with the TINA TCM3 monitor, 0.931 with the SenTec monitor, and 0.765 with the TOSCA 500 monitor. The mean (SD) differences between the PaCO(2) and PtcCO(2) were 4.5 (3.7) mmHg, 4.3 (3.8) mmHg, and 5.6 (5.1) mmHg, respectively, with the three monitors, and the differences between the PaCO(2) and PtcCO(2) were less than 7.5 mmHg in 77.7%, 81.2%, and 67.7% of the samples. Bland-Altman analysis showed a precision of +/-11.5 mmHg for TINA TCM3 monitor, +/-10.6 mmHg for SenTec monitor, and +/-14.8 mmHg for TOSCA monitor. No influence of core-skin temperature gradient and inotropic index on the differences between PaCO(2) and PtcCO(2) was observed.

CONCLUSIONS

The three transcutaneous CO(2) monitors have an acceptable correlation with arterial CO(2) tension and can be useful in critically ill children.

Assessing PaCO2 in acute respiratory disease: accuracy of a transcutaneous carbon dioxide device

BACKGROUND

Pulse oximetry non-invasively assesses the arterial oxygen saturation of patients with acute respiratory disease; however, measurement of the arterial partial pressure of carbon dioxide (PaCO(2)) requires an arterial blood gas. The transcutaneous partial pressure of carbon dioxide (PtCO(2) ) has been used in other settings with variable accuracy. We investigated the accuracy of a PtCO(2) device in the assessment of PaCO(2) in patients with asthma and suspected pneumonia attending the emergency department.

METHODS

Patients with severe asthma (FEV(1) < 50% predicted) or suspected pneumonia (fever, cough and respiratory rate >18/min) were enrolled. Subjects were excluded if they had a history of chronic obstructive pulmonary disease or other conditions associated with respiratory failure. Arterial blood gases were taken at the discretion of the investigator according to clinical need, and paired with a simultaneous reading from the PtCO(2) probe.

RESULTS

Twenty-five patients were studied with one set of data excluded because of poor PtCO(2) signal quality. The remaining 24 paired samples comprised 12 asthma and 12 pneumonia patients. The range of PaCO(2) was 19-64 mmHg with a median of 36.5 mmHg. Bland-Altman analysis showed a mean (SD) PaCO(2) - PtCO(2) difference of -0.13 (1.9) mmHg with limits of agreement of plus or minus 3.8 mmHg (-3.9 to +3.7).

CONCLUSION

A PtCO(2) device was accurate in the assessment of PaCO(2) in patients with acute severe asthma and suspected pneumonia when compared with an arterial blood gas. These bedside monitors have the potential to improve patient care by non-invasively monitoring patients with acute respiratory disease at risk of hypercapnia.

Weaning mechanical ventilation after off-pump coronary artery bypass graft procedures directed by noninvasive gas measurements

OBJECTIVE(S)

Partial pressure of carbon dioxide and oxygen were transcutaneously measured in adults after off-pump coronary artery bypass (OPCAB) surgery. The clinical use of such measurements and interchangeability with arterial blood gas measurements for weaning patients from postoperative mechanical ventilation were assessed.

DESIGN

This was a prospective observational study.

SETTING

Tertiary referral heart hospital.

PARTICIPANTS

Postoperative OPCAB surgical patients.

INTERVENTIONS

Transcutaneous oxygen and carbon dioxide measurements.

MEASUREMENTS AND MAIN RESULTS

In this prospective observational study, 32 consecutive adult patients in a tertiary care medical center underwent OPCAB surgery. Noninvasive measurement of respiratory gases was performed during the postoperative period and compared with arterial blood gases. The investigator was blinded to the reports of arterial blood gas studies and weaned patients using a "weaning protocol" based on transcutaneous gas measurement. The number of patients successfully weaned based on transcutaneous measurements and the number of times the weaning process was held up were noted. A total of 212 samples (pairs of arterial and transcutaneous values of oxygen and carbon dioxide) were obtained from 32 patients. Bland-Altman plots and mountain plots were used to analyze the interchangeability of the data. Twenty-five (79%) of the patients were weaned from the ventilator based on transcutaneous gas measurements alone. Transcutaneous carbon dioxide measurements were found to be interchangeable with arterial carbon dioxide during 96% of measurements, versus 79% for oxygen measurements.

CONCLUSION

More than three fourths of the patients were weaned from mechanical ventilation and extubated based on transcutaneous gas values alone after OPCAB surgery. The noninvasive transcutaneous carbon dioxide measurement can be used as a surrogate for arterial carbon dioxide measurement to manage postoperative OPCAB patients.

Transcutaneous PCO2 monitors are more accurate than end-tidal PCO2 monitors

PURPOSE

The accuracy of monitors for measuring transcutaneous PCO2 (TcPCO2), end-tidal PCO2 (EtPCO2), and nasal EtPCO2 was evaluated.

METHODS

The measuring devices included a TcPCO2 monitor (TCM3; Radiometer Trading), an EtPCO2 monitor (Ultima; Datex-Ohmeda), and a nasal EtPCO2 monitor (TG-920P; Nihon Kohden). The sensor electrode of the TCM3 TcPCO2 monitor was applied to the skin of the subject's upper arm. A sampling tube attached to the proximal end of the tracheal tube was connected to the Ultima EtPCO2 monitor. The miniature sensor of the TG-920P nasal EtPCO2 monitor was attached to the nostril. The values obtained were compared with direct measurements of arterial PCO2 (PaCO2) obtained by means of an ABL700 blood gas analyzer (Radiometer Trading) in surgically treated patients. The means +/- 2 SD of the differences between variables were calculated.

RESULTS

The TcPCO2 monitor (0.19 +/- 4.8 mmHg, mean +/- 2-SD) was more accurate than the EtPCO2 monitor (-4.4 +/- 6.5 mmHg, mean +/- 2-SD) in patients receiving artificial ventilation via an endotracheal tube and the TcPCO2 monitor was also more accurate than the nasal EtPCO2 monitor (-6.3 +/- 9.8 mmHg, bias +/- 2-SD) in patients breathing spontaneously.

CONCLUSION

We found that the TcPCO2 monitor was more accurate than the EtPCO2 or nasal EtPCO2 monitor in surgically treated patients.

Longtime performance and reliability of two different PtcCO2 and SpO2 sensors in neonates

OBJECTIVES

Blood gas monitoring is necessary in treatment of critically ill neonates. Whereas SaO2 can be estimated by pulse oximetry, PaCO2 is still most often assessed from blood samples.

AIM

To compare long time performance of an ear sensor for combined assessment of transcutaneous carbon dioxide (PtcCO2) and oxygen saturation (SpO2) (TOSCA Monitor; Radiometer, Switzerland) with a conventional PtcCO2 monitor (MicroGas 7650-500 rapid, Radiometer, Switzerland) in critically ill neonates.

METHODS

Prospective, observational study. Twenty critically ill neonates were monitored for PtcCO2 and SpO2 using the Tosca and the MicroGas monitor for 24 h. TOSCA ear sensor was changed to the other ear lobe after 12 h and the MicroGas sensor four hourly on the trunk. Values obtained were compared with SaO2 and PaCO2 from arterial blood gas analysis using Bland-Altman analysis. Data are presented as median (range).

RESULTS

Eighty-two paired measurements were obtained. Median age of the 20 patients was 4.5 days (1-26 days) and weight was 3.05 kg (0.98-3.95 kg). Bias and precision between PaCO2 and PtcCO2 were 0.14 and 1.45 kPa for the Tosca monitor and -0.08 and 1.2 kPa for the MicroGas monitor, respectively. The two biases were significantly different (P = 0.0036). SpO2 assessment by TOSCA was comparable to SaO2 values (bias 0.26% and precision 4.14%).

CONCLUSION

The TOSCA monitor allows safe estimation of PtcCO2 and SaO2 in neonates. Measurements of PtcCO2 were less reliable with TOSCA compared with conventional monitoring but still allow assessing a trend of ventilation status in newborn patients.

The effects of different analgesic regimens on transcutaneous CO2 after major surgery

Ventilatory impairment may be detected by a rise in transcutaneous carbon dioxide levels (PtcCO(2)). This observational study assessed the clinical utility of PtcCO(2) monitoring in the postoperative period, and quantified the effect of different peri-operative analgesic regimens on postoperative respiratory function. Following pre-operative baseline PtcCO(2) recording, continuous PtcCO(2) monitoring was performed in 30 patients after major colorectal surgery for up to 24 h. Mean postoperative values of PtcCO(2) were 1.3 kPa (95% CI 1.0-1.5) higher than pre-operative values (p < 0.001). Patients receiving intravenous opioid patient controlled analgesia had a significantly higher elevation in postoperative PtcCO(2) compared to patients receiving epidural infusion analgesia, 1.8 kPa (CI 1.5-2.1) vs 0.7 kPa (CI 0.5-0.9) respectively (p < 0.001). The mean rise in PtcCO(2) following a single intravenous bolus of morphine delivered via PCA was 0.05 kPa (SEm 0.01), peaking at 12 min post-dose. The transcutaneous capnometer successfully recorded data for 98% of the total time it was applied to patients.

Transcutaneous PCO2 monitoring during initiation of noninvasive ventilation

BACKGROUND

To assess the efficacy of transcutaneous Pco2 (Ptcco2) measurements for monitoring alveolar ventilation in patients requiring noninvasive positive-pressure ventilation (NPPV).

METHODS

In a prospective study on method agreement pairs of Paco2 and Ptcco2 (SenTec Digital Monitor; SenTec AG; Therwil, Switzerland), measurements were performed every 10 min during the establishment of NPPV over a 4-h period in 10 patients (8 patients with COPD) presenting with acute-on-chronic hypercapnic respiratory failure, thus providing 250 pairs of measurement.

RESULTS

Mean (+/- SD) Paco2 decreased from 67.2 +/- 11.9 mm Hg (Ptcco2, 65.5 +/- 13.9 mm Hg) to 54.6 +/- 8.8 mm Hg (Ptcco2, 47.8 +/- 8.8 mm Hg), and mean pH increased from 7.36 +/- 0.03 to 7.44 +/- 0.04. Following Ptcco2 assessment, Ptcco2 in the ensuing 2-min period was the strongest predictor for Paco2 compared to Ptcco2 in the ensuing 5-min period and to real-time measurements. Ptcco2 was highly correlated with Paco2 (r = 0.916; p < 0.001), as determined by linear regression analysis. The mean difference between Paco2 and Ptcco2 was 4.6 mm Hg, and the limits of agreement (bias +/- 1.96 SDs) ranged from -3.9 to 13.2 mm Hg, following the Bland and Altman analysis. Retrospective drift correction produced an even higher correlation (r = 0.956; p < 0.001) with lower limits of agreement (-1.7 to 7.5 mm Hg).

CONCLUSIONS

Ptcco2 measurements provide a sensitive, continuous, and noninvasive method for monitoring alveolar ventilation in patients who are receiving short-term NPPV therapy. Drift correction of Ptcco2 measurements improves the accuracy of Ptcco2 monitoring compared to the "gold standard" Paco2 assessment. A lag time of approximately 2 min is present for reliable Ptcco2 values compared to Paco2 values. However, individual variance between Paco2 and Ptcco2 cannot be excluded.

TRIAL REGISTRATION

www.uniklinik-freiburg.de/zks/live/uklregister/Oeffentlich.html Identifier:UKF001271.

Determination of reference ranges for transcutaneous oxygen and carbon dioxide tension and the oxygen challenge test in healthy and morbidly obese subjects

BACKGROUND

Transcutaneous monitoring of oxygen and carbon dioxide tension emerged decades ago as reliable, indirect measurements of arterial pressure of oxygen and carbon dioxide in neonates. Investigators have since found other valuable roles for this modality, particularly in critically ill adults. This investigation was undertaken to further characterize these measurements in normal and in obese adults, who are contributing to a rising proportion of intensive care unit admissions.

MATERIALS AND METHODS

Transcutaneous sensors were adjusted for barometric pressure and calibrated to reference gases. The following were measured: equilibration time; oxygen saturation; transcutaneous oxygen tension; and transcutaneous carbon dioxide tension on room air and after administering fraction of inspired oxygen of 1.0 for 5 min (Oxygen Challenge Test).

RESULTS

One hundred three healthy and 47 obese subjects were enrolled. Oxygen Challenge Test values were 131.5 +/- 57.4 and 171.6 +/- 65.9 mm Hg for obese and healthy subjects, respectively (P value <0.001). Smoking status, respiratory rate, and transcutaneous oxygen tension on room air best predicted the Oxygen Challenge Test response. A negative correlation was found between transcutaneous oxygen on room air and the Oxygen Challenge Test versus body mass index (P < 0.001).

CONCLUSIONS

Reference ranges were determined for transcutaneous oxygen and carbon dioxide tension and the Oxygen Challenge Test in obese and in normal, healthy subjects. Increasing body mass index was associated with a lower baseline transcutaneous oxygen tension, but it was not an independent predictor of the Oxygen Challenge Test response in multivariate analysis.

The design, use, and results of transcutaneous carbon dioxide analysis: current and future directions

Transcutaneous carbon dioxide (CO2) analysis was introduced in the early 1980s using locally heated electrochemical sensors that were applied to the skin surface. This methodology provides a continuous noninvasive estimation of the arterial CO2 value and can be used for assessing adequacy of ventilation. The technique is now established and used routinely in clinical practice. Transcutaneous partial pressure of CO2 (tcPco2) sensors are available as a single Pco2 sensor, as a combined Pco2/Po2 sensor, and more recently, as a combined Pco2/Spo2 sensor. CO2 is still measured potentiometrically by determining the pH of an electrolyte layer. The methodology has been continuously developed during the last 20 yr, making the tcPco2 systems easier and more reliable for use in clinical practice: smaller sensor size (diameter 15 mm, height 8 mm), less frequent sensor re-membraning (every 2 wk) and calibration (twice a day), sensor ready to use when connected to the monitor, lower sensor temperature (42 degrees C), shorter arterialization time (3 min), and increased measurement reliability through protection of the membrane. The present tcPco2 sensors still need to be regularly re-membraned and calibrated. One way to overcome these procedures is to use optical-only detection means. Two techniques have been developed using optical absorption in the near-infrared light, in the evanescent wave of a waveguide integrated in the sensor surface, or in a micro-optics sampling cell. Preliminary in vitro and in vivo CO2 measurements have been performed. The sensor is not affected by drift over several days, and its response time is <1 min.

The accuracy of non-invasive carbon dioxide monitoring: a clinical evaluation of two transcutaneous systems

We determined the accuracy of two transcutaneous carbon dioxide monitoring systems (SenTec Digital Monitor with V-Sign Sensor and TOSCA 500 with TOSCA Sensor 92) for the measurement of single values and trends in the arterial partial pressure of carbon dioxide in 122 adult patients during major surgery and in 50 adult patients in the intensive care unit. One or several paired measurements were performed in each patient. The first measurement was used to determine the accuracy of a single value of transcutaneous carbon dioxide; the difference between the first and the last measurements was used to analyse the accuracy and to track trends. We defined a 95% limit of agreement of <or=1 kPa as being clinically useful. There was insufficient agreement between transcutaneous carbon dioxide partial pressure values derived from the two systems and arterial carbon dioxide values for both single values and trends as defined by our suggested limit of agreement. We conclude that these systems cannot replace conventional blood gas analysis in the clinical setting studied.

Systemic hypotension is a late marker of shock after trauma: a validation study of Advanced Trauma Life Support principles in a large national sample

BACKGROUND

Systolic blood pressure is used extensively to triage trauma patients as stable or unstable, contrary to Advanced Trauma Life Support recommendations. We hypothesized that systemic hypotension is a late marker of shock.

METHODS

The National Trauma Data Bank was queried (n = 115,830). Base deficit was used as a measure of circulatory shock. Systolic blood pressure was correlated with the presence and the severity of base-deficit derangement.

RESULTS

Systolic blood pressure correlated poorly with base deficit (r = .28). There was wide variation in systolic blood pressure within each base-deficit group. The mean and median systolic blood pressure did not decrease to less than 90 mm Hg until the base deficit was worse than -20, with mortality reaching 65%.

CONCLUSIONS

We validated the Advanced Trauma Life Support principle that systemic hypotension is a late marker of shock. A normal blood pressure should not deter aggressive evaluation and resuscitation of trauma patients.