A comparison of transcutaneous end-tidal and arterial measurements of carbon dioxide during general anaesthesia

Tube or tubeless: an anesthetic strategy for upper airway surgery

Since the patient's airway is shared between an anesthesiologist and a surgeon, airway management during upper airway surgery can be challenging. Beyond the conventional method of general anesthesia, high-flow nasal oxygenation (HFNO) has recently been used as a key technique for tubeless anesthesia. HFNO provides humidified, heated oxygen up to 70 L/min, which promises improved oxygenation and ventilation, allowing for prolonged apneic oxygenation. In previous physiological and clinical studies, HFNO has been demonstrated that tubeless anesthesia safely provide an uninterrupted surgical field during laryngeal surgeries. Although tubeless anesthesia remains uncommon, it can be a good alternative to conventional anesthesia if an anesthesiologist and a surgeon select appropriate patients together with sufficient experience. A safe strategy for tubeless anesthesia, along with appropriate backup plans, including endotracheal intubation and high-frequency jet ventilation, should be considered for upper airway surgery.

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.

Response time of indirectly accessed gas exchange depends on measurement method

Noninvasive techniques are routinely used for assessment of tissue effects of lung ventilation. However, comprehensive studies of the response time of the methods are scarce. The aim of this study was to compare the response time of noninvasive methods for monitoring of gas exchange to sudden changes in the composition of the inspired gas. A prospective experimental study with 16 healthy volunteers was conducted. A ventilation circuit was designed that enabled a fast change in the composition of the inspiratory gas mixture while allowing spontaneous breathing. The volunteers inhaled a hypoxic mixture, then a hypercapnic mixture, a hyperoxic mixture and finally a 0.3% CO mixture. The parameters with the fastest response to the sudden change of O2 in inhaled gas were peripheral capillary oxygen saturation (SpO2) and regional tissue oxygenation (rSO2). Transcutaneous oxygen partial pressure (tcpO2) had almost the same time of reaction, but its time of relaxation was 2-3 times longer. End-tidal carbon dioxide (EtCO2) response time to change of CO2 concentration in inhaled gas was less than half in comparison with transcutaneous carbon dioxide partial pressure (tcpCO2). All the examined parameters and devices reacted adequately to changes in gas concentration in the inspiratory gas mixture.

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.

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.

Recent advance in patient monitoring

Recent advance in technology has developed a lot of new aspects of clinical monitoring. We can monitor sedation levels during anesthesia using various electroencephalographic (EEG) indices, while it is still not useful for anesthesia depth monitoring. Some attempts are made to monitor the changes in sympathetic nerve activity as one of the indicators of stress, pain/analgesia, or anesthesia. To know the balance of sympathetic and parasympathetic activity, heart rate or blood pressure variability is investigated. For trend of cardiac output, low invasive monitors have been investigated. Improvement of ultrasound enables us to see cardiac structure and function continuously and clearer, increases success rate and decreases complication of central venous puncture and various kinds of nerve blocks. Without inserting an arterial catheter, trends of arterial oxygen tension or carbon dioxide tension can be monitored. Indirect visualization of the airway decreases difficult intubation and makes it easier to teach tracheal intubation. The changes in blood volume can be speculated non-invasively. Cerebral perfusion and metabolism are not ordinary monitored yet, but some studies show their usefulness in management of critically ill. This review introduces recent advances in various monitors used in anesthesia and critical care including some studies of the author, especially focused on EEG and cardiac output. However, the most important is that these new monitors are not almighty but should be used adequately in a limited situation where their meaning is confirmed.

Transcutaneous carbon dioxide monitoring accurately predicts arterial carbon dioxide partial pressure in patients undergoing prolonged laparoscopic surgery

BACKGROUND

There may be large differences between measurements of end-tidal carbon dioxide partial pressure (Petco(2)) and arterial carbon dioxide partial pressure (Paco(2)) during laparoscopic surgeries. Transcutaneous carbon dioxide (Ptcco(2)) monitoring can be used to noninvasively and continuously estimate Paco(2). In the present study we evaluated the accuracy of Ptcco(2) monitoring in predicting the Paco(2) during laparoscopic surgeries with prolonged pneumoperitoneum.

METHODS

Sixteen patients who underwent laparoscopic radical gastrectomy or radical proctectomy under general anesthesia were included in the study. Their Paco(2), Petco(2), and Ptcco(2) values were measured at 3 time points before and after pneumoperitoneum. Agreement among measures was assessed by the Bland-Altman method.

RESULTS

Forty-eight sample sets were obtained. The average Paco(2)- Ptcco(2) difference was -0.9 + or - 6.4 mm Hg (mean + or - 2 SD). The average Paco(2) - Petco(2) difference was 7.5 + or - 7.0 mm Hg (mean + or - 2 SD). Paco(2) - Ptcco(2) was less than or equal to + or -5 mm Hg for 88% of the samples. Paco(2) - Petco(2) was less than or equal to + or -5 mm Hg for 17% of the samples (P < 0.05).

CONCLUSIONS

While undergoing long-term pneumoperitoneum laparoscopic surgery, Ptcco(2) monitoring is more accurate than is PETCO(2) monitoring in predicting the patients' Paco(2).

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.

Evaluation of a combined transcutaneous carbon dioxide pressure and pulse oximetry sensor in adult sheep and dogs

OBJECTIVE

To evaluate a combined transcutaneous carbon dioxide pressure (tcPCO(2)) and pulse oximetry sensor in sheep and dogs.

ANIMALS

13 adult sheep and 11 adult dogs.

PROCEDURES

During inhalation anesthesia, for the first 10 minutes following sensor placement, arterial blood gas was analyzed and tcPCO(2) was recorded every 2 minutes. Subsequently, the animals were hyper-, normo-, and hypoventilated. The simultaneously obtained tcPCO(2) and PaCO(2) values were analyzed by use of Bland-Altman statistical analysis.

RESULTS

Mean +/- SD overall difference between tcPCO(2) and PaCO(2) 10 minutes after sensor application was 13.3 +/- 8.4 mm Hg in sheep and 8.9 +/- 12 mm Hg in dogs. During hyper-, normo-, and hypoventilation, mean difference (bias) and precision (limits of agreement [bias +/- 2 SD]) between tcPCO(2) and PaCO(2) values were 13.2 +/- 10.4 mm Hg (limits of agreement, -7.1 and 33.5 mm Hg) in sheep and 10.6 +/- 10.5 mm Hg (limits of agreement, -9.9 and 31.2 mm Hg) in dogs, respectively. Changes in PaCO(2) induced by different ventilation settings were detected by the tcPCO(2) sensor with a lag (response) time of 4.9 +/- 3.5 minutes for sheep and 6.2 +/- 3.6 minutes for dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

The tcPCO(2) sensor overestimated PaCO(2) in sheep and dogs and followed changes in PaCO(2) with a considerable lag time. The tcPCO(2) sensor might be useful for noninvasive monitoring of changes but cannot be used as a surrogate measure for PaCO(2).

Comparison of the transcutaneous oxygen and carbon dioxide tension in different electrode locations during general anaesthesia

BACKGROUND AND OBJECTIVE

The best place for the electrode of transcutaneous measurement of oxygen tension (tcPO2) and carbon dioxide tension (tcPCO2) during general anaesthesia was investigated in three different locations.

METHODS

Fifteen patients for major abdominal surgery in the supine position were studied. The electrode of the TCM4 (Radiometer, Copenhagen, Denmark) was put on the chest, upper arm or forearm. TcPO2, tcPCO2, end-tidal carbon dioxide tension (etCO2), percutaneous oxygen saturation (SaO2), arterial oxygen tension (PaO2 ) and arterial carbon dioxide tension (PaCO2) were simultaneously measured at four different etCO2 concentrations and inhaled oxygen percentages and the location of the electrode was changed to other places to repeat the same measurement. In total, 12 measurements for each patient and 60 measurements for each place were performed.

RESULTS

TcPO2 correlated better than SaO2 (R2 = 0.58) with PaO2 (R2 = 0.76), and tcPCO2 correlated well with PaCO2 (R2 = 0.76) and etCO2 (R2 = 0.74) when the electrode was put on the chest, while not on the upper arm or forearm (R2 < 0.5). However, limits of agreement were too big to use tcPO2 (bias, -67.9; limits of agreement, 16.5, -152.3) and tcPCO2 (bias, -0.47; limits of agreement, 8.7, -9.64) as surrogate measures of PaO2 and PaCO2, respectively even when the electrode was put on the chest.

CONCLUSIONS

When the electrode was put on the chest, tcPO2 and tcPCO2 might be available as non-invasive monitors of oxygenation and CO2 status during general anaesthesia, while the absolute values were not interchangeable with PaO2 and PaCO2, respectively.

Agreement of carbon dioxide levels measured by arterial, transcutaneous and end tidal methods in preterm infants < or = 28 weeks gestation

OBJECTIVE

To assess the agreement of transcutaneous carbon dioxide (TcPCO(2)) and end tidal carbon dioxide (PetCO(2)) with arterial carbon dioxide (PaCO(2)) values in infants < 28 weeks gestational age.

STUDY DESIGN

In all, 27 ventilated preterm infants were prospectively studied. PaCO(2) was compared with TcPCO(2) and PetCO(2) measured at three similar time points within first 24 hours after birth.

RESULTS

The Intraclass correlation coefficients for TcPCO(2) and PaCO(2) were 0.45, 0.73 and 0.53; and for PetCO(2) and PaCO(2) were 0.61, 0.56 and 0.57 at 4, 12 and 24 hours after birth, respectively.

CONCLUSION

A moderate agreement with a wide variation in individual values was observed between noninvasive methods and PaCO(2) in preterm infants in the first 24 hours. Noninvasive monitoring methods cannot be substituted for PaCO(2) analyses in preterm infants during this critical period.

Extended/advanced monitoring techniques in gastrointestinal endoscopy

The practice of sedation and analgesia is under increasing scrutiny by numerous regulatory agencies, with the aim of making these procedures safer and reducing the incidence of cardiopulmonary complications during GI endoscopy. As we move toward more evidence-based medicine, new technologies will have to be assessed in a manner that demonstrates their efficacy and utility in clinical practice. Although there have been no controlled studies examining whether more intensive monitoring during endoscopy improves outcomes, extended monitoring with capnography seems to offer an advantage over conventional monitoring in that, by providing a real-time indication of any change in adequate ventilation before oxygen desaturation occurs, it can detect early phases of respiratory depression, which can allow a more precise and safer titration of medications. There is a close agreement among experts that capnography may reduce the risk of adverse outcomes during deep sedation; therefore, its use should be required for patients undergoing advanced endoscopic procedures with the potential for deep sedation. Extended monitoring with capnography should also be endorsed whenever propofol is considered as an alternative to standard sedation with a benzodiazepine or narcotic. Our understanding of the clinical application of techniques for monitoring of depth of sedation is in its infancy, and its full contribution to the practice of endoscopy has yet to be determined. Their potential role in improving sedation practice during endoscopy needs to be confirmed by controlled trials. If we consider the lack of proven efficacy of these emerging monitoring techniques in reducing the adverse outcomes associated with sedation and analgesia, the importance of appropriate monitoring cannot be overemphasized. However, it is vital for the endoscopist to be thoroughly familiar with the type of sedation chosen, to be able to recognize the various levels of sedation, and, above all, to rescue patients should they unintentionally progress to a deeper level of sedation than intended.

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

BACKGROUND

Patients with severe obesity (body mass index (BMI) greater than 35 kg x m(-2)) present difficulties for end-tidal carbon dioxide (FE'(CO(2))) monitoring. Previous studies suggest that transcutaneous (TC) carbon dioxide measurements could be valuable, so we compared FE' and TC measures with Pa(CO(2)) in severely obese patients during anaesthesia.

METHODS

We studied patients with severe obesity (BMI >or=40 kg x m(-2)) undergoing gastric bypass surgery. Carbon dioxide was measured with both FE' and TC devices. The difference between each measure (FE'(CO(2)) and TC-CO(2)) and the Pa(CO(2)) was averaged for each patient to provide one value, and data compared with a non-paired, two-way t-test, Fisher's exact test.

RESULTS

We studied 30 adults (aged 18-54 yr, mean 41, SD 8.0 yr; weight: 115-267 kg, mean 162, SD 35 kg). The absolute difference between the TC-CO(2) and Pa(CO(2)) was 0.2 (0.2) (mean, SD) kPa while the absolute difference between the FE'(CO(2)) and Pa(CO(2)) was 0.7 (0.4) kPa (P<0.0001). The bias and precision were +0.1 (0.3) kPa for TC vs arterial carbon dioxide and -0.7 (0.4) kPa for FE' vs arterial carbon dioxide.

CONCLUSIONS

Transcutaneous carbon dioxide monitoring provides a better estimate of Pa(CO(2)) than FE'(CO(2)) in patients with severe obesity.

A comparative evaluation of transcutaneous and end-tidal measurements of CO2 in thoracic anesthesia

We performed this study to assess the accuracy of transcutaneous CO(2) (PTCCO(2)) monitoring compared with end-tidal CO(2) (PETCO(2)) in thoracic anesthesia. Twenty-six patients undergoing pneumonectomy with thoracotomy for which a long period of one-lung ventilation (OLV) was required were studied. The lungs were mechanically ventilated in the lateral decubitus position. PTCCO(2), PETCO(2), and arterial CO(2) (PaCO(2)) were simultaneously measured during two-lung ventilation (TLV) and during OLV at intervals of 15 min. All patients completed the study protocol. Bland-Altman analysis revealed a bias of -0.4 mm Hg with a precision of +/-2.5 mm Hg during OLV and 1.4 mm Hg with +/-4.3 mm Hg during TLV when PTCCO(2) and PaCO(2) were compared and revealed a bias of -5.8 mm Hg with a precision of +/-4.1 mm Hg during OLV and -7.1 mm Hg with +/-4.6 mm Hg during TLV when PETCO(2) and PaCO(2) were compared. We conclude that PTCCO(2) monitoring is accurate for evaluating CO(2) levels during thoracic anesthesia.

Noninvasive carbon dioxide monitoring during one-lung ventilation: end-tidal versus transcutaneous techniques

OBJECTIVE

To compare transcutaneous CO(2) (TCCO(2)) and end-tidal CO(2) (ETCO(2)) monitoring during one-lung ventilation (OLV).

DESIGN

Prospective study.

SETTING

Operating room of a University Hospital.

PARTICIPANTS

Fifteen patients undergoing thoracic surgical procedures in whom one-lung ventilation was deemed necessary.

INTERVENTION

TC and ETCO(2) monitors were used simultaneously in the patients and compared with arterial blood gases (ABGs) during 2-lung ventilation and OLV.

MEASUREMENTS AND MAIN RESULTS

During 2-lung ventilation (TLV), the ET to PaCO(2) difference was 3.9 +/- 1.6 mmHg, whereas the TC to PaCO(2) difference was 2.5 +/- 0.8 mmHg (p = 0.0049). During OLV, the ET to PaCO(2) difference increased to 5.8 +/- 2.3 mmHg, whereas the TC to PaCO(2) difference was 2.7 +/- 1.4 mmHg (p = 0.0049 for ET to PaCO(2) difference during OLV v TLV and p = 0.0004 for ET to PaCO(2) gradient v TC to PaCO(2) gradient during OLV). During TLV, the difference between the ET and PaCO(2) was < or = 5 mmHg in 13 of 15 patients, whereas the difference between the TC and PaCO(2) was < or = 5 mmHg in 15 of 15 patients (p = not significant). During OLV, the difference between the ET and the PaCO(2) was < or = 5 mmHg in 6 of 15 patients, whereas the difference between the TC and PaCO(2) was < or = 5 mmHg in 14 of 15 patients (p = 0.0052, odds ratio 21.0 for ET v TC techniques and p = 0.02, odds ratio 9.75 for ET to PaCO(2) during TLV v OLV).

CONCLUSIONS

During OLV, TCCO(2) monitoring provides a more accurate estimate of PaCO(2) than ET techniques.

Carbon dioxide absorption during extraperitoneal and transperitoneal endoscopic hernioplasty

Transabdominal preperitoneal (TAPP) or total extraperitoneal (TEP) hernioplasty are probably associated with differing degrees of CO(2) absorption which can influence anesthetic management and perioperative morbidity. We studied 20 patients with either TAPP or TEP for perioperative CO(2) absorption (calculated from CO(2) elimination and metabolic CO(2) production) and ventilatory changes required to maintain normocapnia (blood gas analyses). CO(2) absorption reached plateau values in the TAPP group, but increased over time in the TEP group. Median CO(2) absorption during insufflation was 61 mL/min (range 43-78) for TAPP and 114 mL/min (range 75-178) for TEP, with a maximum of 114 mL/min (range 75-178) for TAPP and 258 mL/min (range 112-585) for TEP. Median minute ventilation (V(E)) required for maintaining normocapnia was 9. 5 L/min (range 7.7-11.5) for TAPP and 12.9 L/min (range 9.0-22.6) for TEP (P: < 0.01). Seven patients in the TEP group required over 18 L/min V(E), although no patient in the TAPP group required more than 14 L/min V(E). All patients in the TEP group had significant subcutaneous emphysema resulting in one case of delayed tracheal extubation. We conclude that CO(2) absorption is consistently less with TAPP.

IMPLICATIONS

The greater magnitude of carbon dioxide absorption during total extraperitoneal hernioplasty puts an additional load on the lungs and could pose a risk for patients with chronic lung disease who might be unable to eliminate excess carbon dioxide.

Carbon dioxide absorption during extraperitoneal and transperitoneal endoscopic hernioplasty

Transabdominal preperitoneal (TAPP) or total extraperitoneal (TEP) hernioplasty are probably associated with differing degrees of CO(2) absorption which can influence anesthetic management and perioperative morbidity. We studied 20 patients with either TAPP or TEP for perioperative CO(2) absorption (calculated from CO(2) elimination and metabolic CO(2) production) and ventilatory changes required to maintain normocapnia (blood gas analyses). CO(2) absorption reached plateau values in the TAPP group, but increased over time in the TEP group. Median CO(2) absorption during insufflation was 61 mL/min (range 43-78) for TAPP and 114 mL/min (range 75-178) for TEP, with a maximum of 114 mL/min (range 75-178) for TAPP and 258 mL/min (range 112-585) for TEP. Median minute ventilation (V(E)) required for maintaining normocapnia was 9. 5 L/min (range 7.7-11.5) for TAPP and 12.9 L/min (range 9.0-22.6) for TEP (P: < 0.01). Seven patients in the TEP group required over 18 L/min V(E), although no patient in the TAPP group required more than 14 L/min V(E). All patients in the TEP group had significant subcutaneous emphysema resulting in one case of delayed tracheal extubation. We conclude that CO(2) absorption is consistently less with TAPP.

IMPLICATIONS

The greater magnitude of carbon dioxide absorption during total extraperitoneal hernioplasty puts an additional load on the lungs and could pose a risk for patients with chronic lung disease who might be unable to eliminate excess carbon dioxide.

A randomized, controlled trial of transcutaneous carbon dioxide monitoring during ERCP

BACKGROUND

Pulse oximetry, used to monitor oxygen saturation during endoscopy, does not directly measure hypoventilation. Study goals were to determine whether transcutaneous carbon dioxide (PtcCO(2)) monitoring during endoscopic retrograde cholangiopancreatography (ERCP) prevents severe hypoventilation and to assess the accuracy of clinical observation and pulse oximetry in detecting hypoventilation.

METHODS

All patients received intensive clinical and electronic monitoring including pulse oximetry. Supplemental oxygen was administered for pulse oximetry < 90%. Patients were randomized to a treatment arm (group 1) where PtcCO(2) monitoring guided sedation or a control arm (group 2) where PtcCO(2) was recorded but unavailable for guiding sedation.

RESULTS

Group 1 had significantly fewer episodes of severe carbon dioxide retention (rise in PtcCO(2) >/=40 mm Hg above baseline) than group 2 (0 of 199 versus 5 of 196, respectively, p = 0.03), as well a shorter mean duration of procedure discomfort (8.3% of procedure duration rated as "uncomfortable" versus 11.5%, p = 0.04). Correlations between clinical observation and objective measures of ventilation were poor: level of sedation versus PtcCO(2) (R = 0.3) or pulse oximetry (R = 0.06); slowest respiratory rate versus PtcCO(2) (R = 0.4) or pulse oximetry (R = -0.4). PtcCO(2) rises of greater than 20 mm Hg occurred without oxygen desaturation in 10.7% of patients receiving supplemental oxygen.

CONCLUSIONS

Carbon dioxide retention during ERCP is not reliably detected by clinical observation or by pulse oximetry in patients receiving supplemental oxygen. The addition of PtcCO(2) monitoring prevents severe carbon dioxide retention more effectively than intensive clinical monitoring and pulse oximetry alone. The clinical relevancy of this observation needs to be determined in an appropriately designed outcome study.

Transcutaneous CO2/O2 and CO2/air suction in patients undergoing cataract surgery with retrobulbar anaesthesia

We investigated transcutaneous partial CO2 and O2 pressures and respiratory rate in unpremedicated elderly patients of ASA physical status 1 to 3 who underwent cataract surgery under retrobulbar anaesthesia. In group A no air suction was used. In group B suction was applied under the sterile drapes to avoid rebreathing of CO2. In group A transcutaneous partial CO2 pressure and respiratory rate significantly increased compared with baseline, whereas in group B they remained constant. In both groups transcutaneous partial O2 pressure and oxygen saturation as measured by pulse oximetry significantly rose after insufflating oxygen 31.min-1. Heart rate and mean arterial blood pressure remained constant. Our results demonstrate that the application of suction near the patient's head prevents CO2 rebreathing and subsequent hypercapnia associated with an elevated respiratory rate. The use of suction makes it unnecessary to raise oxygen administration. Suction combined with monitoring of partial CO2 pressure using transcutaneous sensors should be used in all ophthalmological operations under retrobulbar anaesthesia.

Transcutaneous PCO2 monitoring during laparoscopic cholecystectomy in pregnancy

PURPOSE

Respiratory acidosis during carbon dioxide (CO2) insufflation has been suggested as a cause of spontaneous abortion and preterm labour following laparoscopic cholecystectomy during pregnancy. Capnography may not be adequate as a guide to adjust pulmonary ventilation during laparoscopic surgery and hence arterial carbon dioxide (PaCO2) monitoring has been recommended. We report the feasibility and benefits of transcutaneous carbon dioxide monitoring (PtcCO2) as an approach to optimise ventilation during laparoscopic surgery in pregnancy.

METHOD

A healthy parturient received general anaesthesia for laparoscopic cholecystectomy. Pulmonary ventilation was adjusted to maintain end-tidal carbon dioxide (conventional PETCO2) at 32 mmHg during CO2 insufflation. A PtcCO2 monitor was used to trend PaCO2 throughout the procedure. Mechanical ventilation was interrupted every five minutes to obtain an end-tidal PCO2 value at large tidal volume (squeeze PETCO2).

RESULTS

The PtcCO2 increased from 39 mmHg before induction to 45 mmHg after CO2 insufflation. This corresponds to an estimated maximum PaCO2 of 39-40 mmHg during insufflation. The PtcCO2 gradually returned to pre-induction baseline values one hour after the termination of CO2 insufflation. Squeeze PETCO2 values approximated PtcCO2 more closely than did conventional PETCO2 values (P < 0.01).

CONCLUSION

Continuous PtcCO2 measurements as well as squeeze PETCO2 may be of clinical value in trending and preventing hypercarbia during laparoscopic surgery.

Application of transcutaneous blood carbon dioxide monitoring to the magnetic resonance imaging of rat

A transcutaneous blood gas monitor is a non-invasive tool that is used clinically. Magnetic resonance imaging (MRI) of the rat has been performed for basic research of pathology and brain science. Non-invasive monitoring of blood gas is expected for such small animal experiments because of the need to minimize blood loss. We applied a commercially available transcutaneous blood gas monitor to rat experiments with MRI. The monitoring responses to rat arterial tension of carbon dioxide (paCO2) appeared to change exponentially with the time constant 1820 +/- 40 s, which was five times slower than that of man. The jump in paCO2, however, can be translated only by a differential slope of values monitored by transcutaneous measurement of carbon dioxide (tcpCO2) at the timing of paCO2 change without waiting for the saturated value of tcpCO2. The magnetic field of MRI did not affect blood gas monitoring and magnetic material in the blood gas sensor did not jeopardize the magnetic homogeneity of imaging. The transcutaneous blood gas monitor can be applied to MRI measurements with paCO2 jumps.

Anaesthesia for adenotonsillectomy: a comparison between tracheal intubation and the armoured laryngeal mask airway

A prototype armoured laryngeal mask airway (LMA) was compared with tracheal intubation (ETT) for anaesthesia for adenotonsillectomy. Fifty-five children were randomised into the LMA group and 54 into the ETT group. During insertion of the LMA, peripheral oxyhaemoglobin desaturation (SpO2) < 94% occurred in ten patients (18.2%) and in seven patients (13%) during tracheal intubation (NS). After opening the Boyle-Davis gag, airway obstruction occurred in ten patients (18.2%) in the LMA group and in three patients (6%) in the ETT group (P = 0.07). In five patients (9%) the LMA was abandoned in favour of tracheal intubation. In all others (91%), when the need for adequate depth of anaesthesia was realized, a satisfactory airway was achieved more rapidly than with tracheal intubation (P < 0.001), and maintained throughout surgery. Manually assisted ventilation was required in all patients in the ETT group, mean duration 373 +/- 385 sec, and in 26 patients (52%) in the LMA group, mean duration 134 +/- 110 sec, P < 0.001. Mean end-tidal CO2 (PetCO2) was 45.5 +/- 6.21 mmHg in the ETT group and 46.6 +/- 6.09 in the LMA group (NS). The LMA did not limit surgical access. Heart rate, MAP and blood loss in the LMA group were 110 +/- 21, 74 +/- 9 mmHg and 1.92 +/- 1.22 ml.kg-1 respectively, compared with 143 +/- 13 (P < 0.001), 85 +/- 12 mmHg (P < 0.001) and 2.62 +/- 1.36 ml.kg-1 (P < 0.05) with tracheal intubation. Fibreoptic laryngoscopy at the end of surgery in 19 patients in the LMA group revealed no blood in the larynx.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbon dioxide retention and oxygen desaturation during gastrointestinal endoscopy

BACKGROUND

Pulse oximetry measures arterial oxygen saturation (SpO2), not hypoventilation, which is directly reflected by increases in carbon dioxide tension.

METHODS

In the present study, transcutaneous carbon dioxide tension (PtcCO2) and SpO2 were measured during 101 endoscopic procedures selected for long duration or comorbid illnesses, and relationships between hypercapnia and hypoxemia were evaluated. Nasal oxygen was administered only for sustained desaturation (SpO2 < 90%).

RESULTS

Mean peak increase in PtcCO2 was significantly higher in patients requiring oxygen for sustained desaturation (16.3 mm Hg; range, 4-52) than in patients breathing room air who had transient or no desaturation (10.2 mm Hg [range, 3-19] and 5.1 mm Hg [range, 0-15]). If nasal oxygen corrected desaturation, even transient recurrence of desaturation indicated worsening CO2 retention, which preceded respiratory arrest in one patient. Independent predictors of hypercapnia were fentanyl and midazolam doses, oxygen requirement, and dementia.

CONCLUSIONS

Severe hypoventilation may occur during endoscopy, undetected by clinical observation or pulse oximetry, but only in sedated patients who require supplemental oxygen to maintain SpO2 above 90%. After oxygen supplementation corrects desaturation, recurrence of desaturation implies severe hypoventilation and warrants limitation of further sedation.

What's new in monitoring the coronary surgery patient?

Monitoring has been extensively reviewed in most textbooks of cardiothoracic surgery and anaesthesia, particularly in the recent textbooks on monitoring edited by Carol L Lake 1 and Casey D Blitt 2 and in the Journal of Clinical Monitoring. Although monitoring properly includes both pre- and postoperative periods, this review will concentrate exclusively on the operative period. I will also concentrate on new approaches or information which relate to more traditional approaches to monitoring. The emphasis in this review will not be on what we can monitor, but rather on what we should monitor. In this regard, I will analyse accuracy and identify sources of error and try to answer the following questions. Does the device or parameter measure (monitor) what we want to know? Does it improve patient outcome and safety? Is it cost-effective? Unfortunately, data are not always available to answer all these questions at present, but hopefully the discussions will make us aware of what we do and do not know, and what we should look for in the near future.

Increase in cerebrospinal fluid pressure in normocapnic volunteers in response to nalbuphine

We have carried out a double-blind randomized study of the effect of nalbuphine (0.2 mg.kg-1 i.v.) or placebo on mean lumbar cerebrospinal fluid (CSF) pressure, mean cerebral perfusion pressure (CPP), transcutaneous PCO2 (tcPCO2), mean arterial blood pressure (MAP), and heart rate (HR) in 10 spontaneously breathing volunteers using invasive CSF pressure measurement. Nalbuphine increased CSF pressure from 9.2 mmHg to 16.4 mmHg and decreased CPP from 83.6 mmHg to 74.4 mmHg without significantly changing tcPCO2, MAP, or heart rate. In the placebo group there were no significant changes in CSF pressure, CPP, tcPCO2, MAP, or heart rate. These findings suggest that nalbuphine should be used with caution in patients at risk of intracranial hypertension.