Comparison of end-tidal and transcutaneous measures of carbon dioxide during general anaesthesia in severely obese adults

Transcutaneous carbon dioxide measurements in anesthetized apneic patients with BMI > 35 kg/m2

Transcutaneous carbon dioxide measurement (TcCO2) offers the ability to continuously and non-invasively monitor carbon dioxide (CO2) tensions when end-tidal monitoring is not possible. The accuracy of TcCO2 has not been established in anesthetized apneic patients with obesity. In this secondary publication, we present a methods comparison analysis of TcCO2 with the gold standard arterial PCO2, in adult patients with body mass index (BMI) > 35kg/m2 who were randomized to receive high flow or low flow nasal oxygenation during post-induction apnea. Agreement between PaCO2 and TcCO2 at baseline, the start of apnea and the end of apnea were assessed using a non-parametric difference plot. Forty-two participants had a median (IQR) BMI of 52 (40-58.5) kg/m2. The mean (SD) PaCO2 was 33.9 (4.0) mmHg at baseline and 51.4 (7.5) mmHg at the end of apnea. The bias was the greatest at the end of apnea median (95% CI, 95% limits of agreement) 1.90 mmHg (-2.64 to 6.44, -7.10 to 22.90). Findings did not suggest significant systematic differences between the PaCO2 and TcCO2 measures. For a short period of apnea, TcCO2 showed inadequate agreement with PaCO2 in patients with BMI > 35 kg/m2. These techniques require comparison in a larger population, with more frequent sampling and over a longer timeframe, before TcCO2 can be confidently recommended in this setting.

Transcutaneous carbon dioxide monitoring during prolonged apnoea with high-flow nasal oxygen

BACKGROUND

The duration of apnoeic oxygenation with high-flow nasal oxygen is limited by hypercapnia and acidosis and monitoring of arterial carbon dioxide level is therefore essential. We have performed a study in patients undergoing prolonged apnoeic oxygenation where we monitored the progressive hypercapnia with transcutaneous carbon dioxide. In this paper, we compared the transcutaneous carbon dioxide level with arterial carbon dioxide tension.

METHODS

This is a secondary publication based on data from a study exploring the limits of apnoeic oxygenation. We compared transcutaneous carbon dioxide monitoring with arterial carbon dioxide tension using Bland-Altman analyses in anaesthetised and paralysed patients undergoing prolonged apnoeic oxygenation until a predefined limit of pH 7.15 or PCO₂ of 12 kPa was reached.

RESULTS

We included 35 patients with a median apnoea duration of 25 min. Mean pH was 7.14 and mean arterial carbon dioxide tension was 11.2 kPa at the termination of apnoeic oxygenation. Transcutaneous carbon dioxide monitoring initially slightly underestimated the arterial tension but at carbon dioxide levels above 10 kPa it overestimated the value. Bias ranged from -0.55 to 0.81 kPa with limits of agreement between -1.25 and 2.11 kPa.

CONCLUSION

Transcutaneous carbon dioxide monitoring provided a clinically acceptable substitute for arterial blood gases but as hypercapnia developed to considerable levels, we observed overestimation at high carbon dioxide tensions in patients undergoing apnoeic oxygenation with high-flow nasal oxygen.

Strategy to Reduce Hypercapnia in Robot-Assisted Radical Prostatectomy Using Transcutaneous Carbon Dioxide Monitoring: A Prospective Observational Study

Purpose

Monitoring end-tidal carbon dioxide partial pressure (P_ETCO₂) is a noninvasive, continuous method, but its accuracy is reduced by prolonged capnoperitoneum and the steep Trendelenburg position in robot-assisted radical prostatectomy (RARP). Transcutaneous carbon dioxide partial pressure (P_TCCO₂) monitoring, which is not affected by ventilator–perfusion mismatch, has been suggested as a suitable alternative. We compared the agreement of noninvasive measurements with the arterial carbon dioxide partial pressure (PaCO₂) over a long period of capnoperitoneum, and investigated its sensitivity and predictive power for detecting hypercapnia.

Patients and Methods

The patients who underwent RARP were enrolled in this study prospectively. Intraoperative measurements of P_ETCO₂, P_TCCO₂, and PaCO₂ were analyzed. The primary outcome was the agreement of noninvasive monitoring with PaCO₂ during prolonged capnoperitoneum. Bias and precision between noninvasive measurements and PaCO₂ were assessed using Bland–Altman analysis. The bias and mean absolute difference were compared using a two-tailed Wilcoxon signed-rank test for pairs. The secondary outcome was the sensitivity and predictive power for detecting hypercapnia. To assess this, the Yates corrected chi-square test and the area under the receiver operating characteristic curve were used.

Results

The study analyzed 219 datasets from 46 patients. Compared with P_ETCO₂, P_TCCO₂ had lower bias, greater precision, and better agreement with PaCO₂ throughout the RARP. The mean absolute difference in P_ETCO₂ and PaCO₂ was larger than that of P_TCCO₂ and PaCO_2, and continued to exceed the clinically acceptable range of 5 mmHg after 1 hour of capnoperitoneum. The sensitivity during capnoperitoneum and overall predictive power of P_TCCO₂ for detecting hypercapnia were significantly higher than those of P_ETCO₂, suggesting a greater contribution to ventilator adjustment, to treat hypercapnia.

Conclusion

P_TCCO₂ monitoring measured PaCO₂ more accurately than P_ETCO₂ monitoring during RARP requiring prolonged capnoperitoneum and a steep Trendelenburg position. P_TCCO₂ monitoring also provides more sensitive measurements for ventilator adjustment and detects hypercapnia more effectively than P_ETCO₂ monitoring.

Intraoperative Monitoring of the Obese Patient Undergoing Surgery: A Narrative Review

With the increasing prevalence of obesity in the population, anaesthetists must confidently manage both the pathophysiological and technical challenges presented in bariatric and non-bariatric surgery. The intraoperative period represents an important opportunity to optimise and mitigate risk. However, there is little formal guidance on what intraoperative monitoring techniques should be used in this population. This narrative review collates the existing evidence for intraoperative monitoring devices in the obese patients. Although a number of non-invasive blood pressure monitors have been tested, an invasive arterial line remains the most reliable monitor if accurate, continuous monitoring is required. Goal-directed fluid therapy is recommended by clinical practice guidelines, but the methods tested to assess this had guarded applicability to the obese population. Transcutaneous carbon dioxide (CO₂) monitoring may offer additional benefit to standard capnography in this population. Individually titrated positive end expiratory pressure (PEEP) and recruitment manoeuvres improved intraoperative mechanics but yielded no benefit in the immediate postoperative period. Depth of anaesthesia monitoring appears to be beneficial in the perioperative period regarding recovery times and complications. Objective confirmation of reversal of neuromuscular blockade continues to be a central tenet of anaesthesia practice, particularly relevant to this group who have been characterised as an "at risk" extubation group. Where deep neuromuscular blockade is used, continuous neuromuscular blockade is suggested. Both obesity and the intraoperative context represent somewhat unstable search terms, as the clinical implications of the obesity phenotype are not uniform, and the type and urgency of surgery have significant impact on the intraoperative setting. This renders the generation of summary conclusions around what intraoperative monitoring techniques are suitable in this population highly challenging.

Non-invasive carbon dioxide monitoring in patients with cystic fibrosis during general anesthesia: end-tidal versus transcutaneous techniques

INTRODUCTION

The gold standard for measuring the partial pressure of carbon dioxide remains arterial blood gas (ABG) analysis. For patients with cystic fibrosis undergoing general anesthesia or polysomnography studies, continuous non-invasive carbon dioxide monitoring may be required. The current study compares end-tidal (ETCO₂), transcutaneous (TCCO₂), and capillary blood gas carbon dioxide (Cap-CO₂) monitoring with the partial pressure of carbon dioxide (PaCO₂) from an ABG in patients with cystic fibrosis.

METHODS

Intraoperatively, a single CO₂ value was simultaneously obtained using ABG (PaCO₂), capillary (Cap-CO₂), TCCO₂, and ETCO₂ techniques. Tests for correlation (Pearson's coefficient) and agreement (Bland-Altman analysis) were performed. Data were further stratified into two subgroups based on body mass index (BMI) and percent predicted forced expiratory volume in 1 s (FEV₁%). Additionally, the absolute difference in the TCCO₂, ETCO₂, and Cap-CO₂ values versus PaCO₂ was calculated. The mean ± SD differences were compared using a paired t test while the number of times the values were ≤ 3 mmHg and ≤ 5 mmHg from the PaCO₂ were compared using a Fishers' exact test.

RESULTS

The study cohort included 47 patients (22 males, 47%) with a mean age of 13.4 ± 7.8 years, median (IQR) BMI of 18.7 kg/m² (16.7, 21.4), and mean FEV₁% of 87.3 ± 18.3%. Bias (SD) was 4.8 (5.7) mmHg with Cap-CO₂ monitoring, 7.3 (9.7) mmHg with TCCO₂ monitoring, and 9.7 (7.7) mmHg with ETCO₂ monitoring. Although there was no difference between the degree of bias in the population as a whole, when divided based on FEV₁% and BMI, there was greater bias with ETCO₂ in patients with a lower FEV₁% and a higher BMI. The Cap-CO₂ vs. PaCO₂ difference was 5.2 ± 5.3 mmHg (SD), with 16 (48%) ≤ 3 mmHg and 20 (61%) ≤ 5 mmHg from the ABG value. The TCCO₂-PaCO₂ difference was 9.1 ± 7.2 mmHg (SD), with 11 (27%) ≤ 3 mmHg and 15 (37%) ≤ 5 mmHg from the ABG value. The ETCO₂-PaCO₂ mean difference was 11.2 ± 7.9 mmHg (SD), with 5 (12%) ≤ 3 mmHg and 11 (26%) ≤ 5 mmHg from the ABG value.

CONCLUSIONS

While Cap-CO₂ most accurately reflects PaCO₂ as measured on ABG, of the non-invasive continuous monitors, TCCO₂ was a more accurate and reliable measure of PaCO₂ than ETCO₂, especially in patients with worsening pulmonary function (FEV₁% ≤ 81%) and/or a higher BMI (≥ 18.7 kg/m²).

The effect of a forced-air warming blanket on patients' end-tidal and transcutaneous carbon dioxide partial pressures during eye surgery under local anaesthesia: a single-blind, randomised controlled trial

Surgical drapes used during eye surgery are impermeable to air and hence risk trapping air underneath them. We investigated the effect of a forced-air warming blanket on carbon dioxide accumulation under the drapes in patients undergoing eye surgery under local anaesthesia without sedation. Forty patients of ASA physical status 1 and 2 were randomly assigned to either the forced-air warmer (n = 20) or a control heated overblanket (n = 20). All patients were given 1 l.min(-1) oxygen. We measured transcutaneous and end-tidal carbon dioxide partial pressures, heart rate, arterial pressure, respiratory rate, temperature and oxygen saturation before and after draping, then every 5 min thereafter for 30 min. The mean (SD) transcutaneous carbon dioxide partial pressure in the forced-air warming group stayed constant after draping at 5.7 (0.2) kPa but rose to a maximum of 6.4 (0.4) kPa in the heated overblanket group (p = 0.0001 for the difference at time points 15 min and later). We conclude that forced-air warming reduces carbon dioxide accumulation under the drapes in patients undergoing eye surgery under local anaesthesia.

Evaluation of transcutaneous and end-tidal carbon dioxide levels during inhalation sedation in volunteers

Measurement of end-tidal carbon dioxide (PETCO2) is useful because of its noninvasiveness, continuity, and response time when sudden changes in ventilation occur during inhalation sedation. We compared the accuracy of PETCO2 using a nasal mask and nasal cannula with the accuracy of transcutaneous carbon dioxide (TC-CO2) and determined which method is more useful during inhalation sedation in volunteers. We used a modified nasal mask (MNM) and modified nasal cannula (MNC) for measurement of PETCO2. The capnometer measured PETCO2 in the gas expired from the nasal cavity by means of two devices. The volunteers received supplemental O2 by means of each device at a flow rate of 6 L/min. After the volunteers lay quietly for 5 min with a supply of 100 % O2, they received supplemental N2O by means of each device at concentrations of 10, 20, and 25 % for 5 min and 30 % for 25 min. The correlation coefficient was poorer in the MNM than in the MNC, and the mean difference between TC-CO2 and PETCO2 in the MNM was greater than that in the MNC. The difference between the TC-CO2 and PETCO2 ranged from 3 to 6 mmHg in the MNM and from 2 to 5 mmHg in the MNC. The difference between two variables against the TC-CO2 and the CO2 waveforms obtained by means of the two devices were within the clinically acceptable range. Our two devices can provide continuous monitoring of PETCO2 with a supply of N2O/O2 in patients undergoing inhalation sedation.

Carbon dioxide monitoring during laparoscopic-assisted bariatric surgery in severely obese patients: transcutaneous versus end-tidal techniques

Various factors including severe obesity or increases in intra-abdominal pressure during laparoscopy can lead to inaccuracies in end-tidal carbon dioxide (PETCO2) monitoring. The current study prospectively compares ET and transcutaneous (TC) CO2 monitoring in severely obese adolescents and young adults during laparoscopic-assisted bariatric surgery. Carbon dioxide was measured with both ET and TC devices during insufflation and laparoscopic bariatric surgery. The differences between each measure (PETCO2 and TC-CO2) and the PaCO2 were compared using a non-paired t test, Fisher's exact test, and a Bland-Altman analysis. The study cohort included 25 adolescents with a mean body mass index of 50.2 kg/m2 undergoing laparoscopic bariatric surgery. There was no difference in the absolute difference between the TC-CO2 and PaCO2 (3.2±3.0 mmHg) and the absolute difference between the PETCO2 and PaCO2 (3.7±2.5 mmHg). The bias and precision were 0.3 and 4.3 mmHg for TC monitoring versus PaCO2 and 3.2 and 3.2 mmHg for ET monitoring versus PaCO2. In the young severely obese population both TC and PETCO2 monitoring can be used to effectively estimate PaCO2. The correlation of PaCO2 to TC-CO2 is good, and similar to the correlation of PaCO2 to PETCO2. In this population, both of these non-invasive measures of PaCO2 can be used to monitor ventilation and minimize arterial blood gas sampling.

The application of transcutaneous CO2 pressure monitoring in the anesthesia of obese patients undergoing laparoscopic bariatric surgery

To investigate the correlation and accuracy of transcutaneous carbon dioxide partial pressure (PTCCO2) with regard to arterial carbon dioxide partial pressure (PaCO2) in severe obese patients undergoing laparoscopic bariatric surgery. Twenty-one patients with BMI>35 kg/m(2) were enrolled in our study. Their PaCO2, end-tidal carbon dioxide partial pressure (PetCO2), as well as PTCCO2 values were measured at before pneumoperitoneum and 30 min, 60 min, 120 min after pneumoperitoneum respectively. Then the differences between each pair of values (PetCO2-PaCO2) and. (PTCCO2-PaCO2) were calculated. Bland-Altman method, correlation and regression analysis, as well as exact probability method and two way contingency table were employed for the data analysis. 21 adults (aged 19-54 yr, mean 29, SD 9 yr; weight 86-160 kg, mean 119.3, SD 22.1 kg; BMI 35.3-51.1 kg/m(2), mean 42.1,SD 5.4 kg/m(2)) were finally included in this study. One patient was eliminated due to the use of vaso-excitor material phenylephrine during anesthesia induction. Eighty-four sample sets were obtained. The average PaCO2-PTCCO2 difference was 0.9 ± 1.3 mmHg (mean ± SD). And the average PaCO2-PetCO2 difference was 10.3 ± 2.3 mmHg (mean ± SD). The linear regression equation of PaCO2-PetCO2 is PetCO2 = 11.58+0.57 × PaCO2 (r(2) = 0.64, P<0.01), whereas the one of PaCO2-PTCCO2 is PTCCO2 = 0.60 + 0.97 × PaCO2 (r(2) = 0.89). The LOA (limits of agreement) of 95% average PaCO2-PetCO2 difference is 10.3 ± 4.6 mmHg (mean ± 1.96 SD), while the LOA of 95% average PaCO2-PTCCO2 difference is 0.9 ± 2.6 mmHg (mean ± 1.96 SD). In conclusion, transcutaneous carbon dioxide monitoring provides a better estimate of PaCO2 than PetCO2 in severe obese patients undergoing laparoscopic bariatric surgery.

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.

Comparison of combined oximetry and cutaneous capnography using a digital sensor with arterial blood gas analysis

BACKGROUND

Cutaneous carbon dioxide tension (PcCO(2)) is a promising non-invasive surrogate measure of arterial partial pressure of carbon dioxide (PaCO(2)).

OBJECTIVES

To compare values of PcCO(2) and oxygen saturation (SpO(2)) with arterial blood gas (ABG) analysis.

METHODS

SpO(2) and PcCO(2) were measured with a v-Sign-sensor (Sentec AG, Therwil, Switzerland) and the values compared with simultaneously obtained SaO(2) and PaCO(2) obtained from ABG analysis (ABL 725, Radiometer, Copenhagen, Denmark) in 275 adult patients referred to the lung function laboratory.

RESULTS

Median of the PcCO(2) was 4.7 kPa (interquartile range [IQR] 0.9 kPa). Median of the SpO(2) was 97% (IQR 3%). Bland-Altman analysis for comparison of PcCO(2) with PaCO(2) showed a bias of -0.1 kPa with a precision of +/- 0.9 kPa with 3.7% outlying values. Bland-Altman analysis for the comparison of SpO(2) and SaO(2) showed a bias of 20.1 % with a precision of +/- 3.5%. There were no complications.

CONCLUSION

There is a good agreement between combined cutaneous capnography and oximetry values with ABG analysis. Due to the excellent safety profile and the short time to get a continuous measurement, this technique should be examined in settings where it can complement repeated ABG analysis when ventilatory disturbances are suspected or non-invasive monitoring of ventilation is needed.

Transcutaneous carbon dioxide monitoring in infants and children

OBJECTIVE

To review the technology required for and the applications of transcutaneous carbon dioxide (TC-CO2) monitoring in infants and children.

DATA SOURCE

A computerized, bibliographic search regarding the applications of transcutaneous carbon dioxide (TC-CO2) monitoring in infants and children.

RESULTS

Although the direct measurement of P(a)CO2 remains the gold standard, it provides only a single measurement of what is often a rapidly changing and evolving clinical picture. Given these concerns, there remains a clinical need for a means to continuously monitor P(a)CO2 without the need for repeated blood gas analysis. Although initially introduced into the neonatal intensive care unit; with improvements in the technology, TC-CO2 monitoring can now be used in infants, children and even adults. When compared with end-tidal carbon dioxide (ET-CO2) monitoring techniques, TC-CO2 monitoring has been shown to be equally as accurate in patients with normal respiratory function and more accurate in patients with shunt or ventilation-perfusion inequalities. TC-CO2 monitoring can be applied in situations that generally preclude ET-CO2 monitoring such as high frequency ventilation, apnea testing, and noninvasive ventilation. TC-CO2 monitoring has also been used in spontaneously breathing children with airway and respiratory issues such as croup and status asthmaticus as well as to monitor metabolic status during treatment of acidosis related to diabetic ketoacidosis.

CONCLUSIONS

Transcutaneous carbon dioxide monitoring may be a useful adjunct in various clinical scenarios in infants and children. It should be viewed as a complimentary technology and may be used in combination with ET-CO2 monitoring.

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.

Anesthetic complications of gross obesity

PURPOSE OF REVIEW

The number of obese patients undergoing anesthesia and surgery is increasing. This article aims to present recent achievements in the management of gross and morbidly obese patients in order to improve safety.

RECENT FINDINGS

Current investigations have demonstrated that the type of anesthesia (total intravenous anesthesia or volatile) and the anesthetics used have an important influence on the perioperative period, especially on postanesthesia recovery and respiratory failure during the postoperative period. These findings were compared with previous publications. Practical advice is also presented for performing successful intubation and mechanical ventilation in the morbidly obese patient, as well as describing drug dosage and administration.

SUMMARY

The progress in anesthesia techniques and modern drugs allows for safe management of obese patients, with mortality decreasing in this group of patients.

Transcutaneous monitoring of partial pressure of carbon dioxide in the elderly patient: a prospective, clinical comparison with end-tidal monitoring

STUDY OBJECTIVE

To evaluate the accuracy and precision of estimation of partial pressure of carbon dioxide (Pa(CO2)) using end-tidal or transcutaneous CO2 (TcP(CO2)) measurements during mechanical ventilation in the elderly patient.

DESIGN

A prospective, observational study was conducted.

SETTINGS

The study was done in the anesthesia department of a university hospital.

PATIENTS

Seventeen anesthetized, mechanically ventilated patients older than 60 years were studied.

INTERVENTIONS AND MEASUREMENTS

During standard sevoflurane anesthesia, and after proper calibration and an equilibration time of 30 minutes with stable hemodynamic and respiratory variables, arterial (Pa(CO2)), end-tidal (Pet(CO2)), and transcutaneous (TcP(CO2)) CO2 partial pressures were determined. In each patient, 1 to 5 sample sets (Pa(CO2), Pet(CO2), and TcP(CO2)) were obtained.

MAIN RESULTS

A total of 45 sample sets were obtained from the patients studied. The Pa(CO2) values ranged between 21 and 58 mm Hg. The Pa(CO2) - Pet(CO2) tension gradient was 6 +/- 5 mmHg (95% confidence interval, -3 to 16 mmHg), whereas the Pa(CO2) - TcP(CO2) tension gradient was 2 +/- 4 mmHg (95% confidence interval, -6 to 9 mmHg) (P = 0.0005). The absolute value of the difference between Pa(CO2) and Pet(CO2) was 3 mm Hg or less in 7 of 45 sample sets (15%), whereas the absolute value of the difference between Pa(CO2) and TcP(CO2) was 3 mm Hg or less in 21 of 45 sample sets (46%) (P = 0.003). Linear regression analysis for TcP(CO2) versus Pa(CO2) showed a slope of 0.84 (r(2) = 0.73), whereas the linear regression analysis for Pet(CO2) versus Pa(CO2) showed a slope of 0.54 (r(2) = 0.50).

CONCLUSION

Transcutaneous monitoring of CO(2) partial pressure gives a more accurate estimation of arterial CO(2) partial pressure than does Pet(CO2) monitoring.

Transcutaneous carbon dioxide monitoring

Technologies now exist that measure carbon dioxide levels transcutaneously. Rapid assessment of patients who have depressed ventilation or suspected sepsis can improve treatment decisions including the need for admission to the ICU and pulmonary artery catheterization.

Anesthesia for Pediatric Obesity

This article discusses the unique anesthetic implications of obesity, with an emphasis on children and adolescents. It also touches on the issues surrounding bariatric surgery in the morbidly obese adolescent population. Adolescent bariatric surgery is moving to the forefront as a treatment modality because weight-loss programs alone are not keeping pace with the growth of the problem. Bariatric surgery offers the potential to achieve the weight reductions necessary to reverse the debilitating and costly comorbidities of obesity.

Limitations of Transcutaneous Carbon Dioxide Measurements for Assessing Long-term Mechanical Ventilation

STUDY OBJECTIVES

Transcutaneous CO(2) pressure (Ptcco(2)) and transcutaneous O(2) pressure (Ptco(2)) measurements are routinely used in pediatric ICUs in order to avoid serial arterial punctures. The aim of this study was to determine the value of Ptcco(2) assessment during the evaluation of home ventilation in 12 adult patients with COPD or restrictive respiratory failure in the stable state (mean [+/- SD] basal Paco(2), 48.8 +/- 8.3 mm Hg) who were treated by mask or tracheotomy-mediated ventilation.

METHODS

After radial catheter insertion, patients were instructed to breathe spontaneously for 40 min and then to receive ventilation for 40 min according to their individual home ventilation modalities. An in vivo calibration was performed in the initial stage of the study in order to optimize the arterial Pco(2) and Ptcco(2) values. Every 5 min, transcutaneous measurements were performed and simultaneously compared with arterial values.

MEASUREMENTS AND RESULTS

Ptcco(2) and Ptco(2) were correlated with arterial values (p < 0.0001) except for Paco(2) values of > 56 mm Hg and Pao(2) values of > 115 mm Hg. During ventilation, Paco(2) decreased >or= 4 mm Hg in seven patients. Ptcco(2) variations recorded during consecutive 5-min periods while the patient received mechanical ventilation were well correlated with the arterial variations (p = 0.0033), with a delay of < 5 min.

CONCLUSION

Ptcco(2) values and variations accurately reflected Paco(2) values and variations during mechanical ventilation. However, the accuracy of these data seems to be restricted to patients with Paco(2) values of < 56 mm Hg.

Cutaneous carbon dioxide monitoring in adults

PURPOSE OF REVIEW

Arterial blood gas analysis is the 'gold standard' method to measure the arterial partial pressure of carbon dioxide (PaCO2). However, arterial sampling including arterial catheterization is invasive and expensive. Cutaneous carbon dioxide tension (PcCO2) measurement is used as a noninvasive surrogate measure of PaCO2, which is used to either estimate PaCO2 or determine trend changes in the measurement. There has been considerable progress in the technical aspects of PcCO2 monitoring in the last few years. In this article, we evaluate recent developments and the renewed interest in the subject of PcCO2 monitoring in adults and discuss the technical aspects, clinical applications and the future outlook for this technique in the clinical setting.

RECENT FINDINGS

With evolution in technology, PcCO2 monitoring is now less cumbersome than before. Combined PcCO2 measurement and pulse oximetry is now possible with a single earlobe sensor.

SUMMARY

The clinical settings in which PcCO2 monitoring can be applied include patient monitoring during and after anaesthesia, patients receiving noninvasive ventilation, post extubation, endoscopy under sedation, the sleep laboratory and the lung function laboratory. Although there is an overlap of the clinical indications when both PcCO2 and end-tidal carbon dioxide monitoring may be used, it is our opinion that both these methods have independent indications and are sometimes also complementary to each other in patient care.