J Clin Monit Comput DOI 10.1007/s10877-014-9587-1
ORIGINAL RESEARCH
Carbon dioxide monitoring during laparoscopic-assisted bariatric surgery in severely obese patients: transcutaneous versus end-tidal techniques Joanna M. Dion • Chris McKee • Joseph D. Tobias Daniel Herz • Paul Sohner • Steven Teich • Marc Michalsky
•
Received: 25 February 2014 / Accepted: 31 May 2014 Ó Springer Science+Business Media New York 2014
Abstract 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 J. M. Dion (&) C. McKee J. D. Tobias P. Sohner Department of Anesthesiology and Pain Medicine, Nationwide Children’s Hospital, Ohio State University, 700 Children’s Drive, Columbus, OH 43205, USA e-mail: [email protected] J. D. Tobias S. Teich M. Michalsky Department of Surgery, Nationwide Children’s Hospital, Ohio State University, Columbus, OH, USA D. Herz Department of Urology, Nationwide Children’s Hospital, Ohio State University, Columbus, OH, USA
of PaCO2 to PETCO2. In this population, both of these noninvasive measures of PaCO2 can be used to monitor ventilation and minimize arterial blood gas sampling. Keywords Adolescent Physiologic monitoring: transcutaneous CO2 monitoring Obesity Laparoscopy Bariatric surgery
1 Introduction The standard for assessing the efficacy of mechanical ventilation remains the measurement of the partial pressure of carbon dioxide in arterial blood (PaCO2). Although the absolute measure remains direct intermittent arterial sampling and arterial blood gas (ABG) analysis, the technique is invasive. Furthermore, ABG analysis provides only a single instantaneous measurement of what may be a constantly changing baseline. To overcome such problems, non-invasive techniques such as end-tidal carbon dioxide (PETCO2) monitoring remain a standard of care during general anesthesia. However, various factors which disrupt normal matching of ventilation and perfusion may interfere with the accuracy of PETCO2 monitoring [1–5]. Such problems may be encountered in patients with severe obesity (body mass index or BMI [35 kg/m2) related to a decrease in functional residual capacity and alterations in the matching of ventilation and perfusion [4, 6]. Laparoscopy and the insufflation can also result in physiological alterations that may diminish the accuracy of PETCO2 monitoring [7]. Transcutaneous (TC) devices can also be used for the continuous and non-invasive monitoring of PaCO2. Although used most commonly in the neonatal population, these techniques may be used successfully in various
123
J Clin Monit Comput
clinical scenarios in older pediatric patients, adolescents, and adults [8–22]. The accuracy of these monitors has been questioned in obese adult patients and at extremes of PaCO2 [18, 23, 24]. However, other studies have demonstrated that TC-CO2 monitoring may provide a more accurate assessment of PaCO2 than PETCO2 monitoring [23]. The current study prospectively compares TC and PETCO2 monitoring during robotic, laparoscopic-assisted bariatric surgery in severely obese adolescents and young adults.
2 Methods Approval for this study was granted by the Institutional Review Board of Nationwide Children’s Hospital (Columbus, Ohio). The need for written, informed consent was waived. The study included adolescent and young adults with a BMI C40 kg/m2 presenting for laparoscopicassisted bariatric surgery (vertical sleeve gastrectomy). The anesthetic technique included premedication with intravenous midazolam followed by anesthetic induction with propofol and fentanyl. Endotracheal intubation was facilitated by the administration of either rocuronium or succinylcholine. Maintenance anesthesia included desflurane titrated to maintain the bispectral index at 40–60, a dexmedetomidine infusion at 0.2–0.25 lg/kg/h, and remifentanil to maintain hemodynamic stability. After intubation of the trachea, ventilation was controlled using a tidal volume of 6–8 ml/kg, an inspiratory to expiratory (I:E) ratio of 1:2–3, positive end-expiratory pressure (PEEP) of 5 cm H2O, and an FIO2 of 0.5. The respiratory rate was adjusted to maintain normocarbia. PETCO2 was measured using an infrared analyzer with side-stream sampling at a flow rate of 150 ml/min (DatexOhmeda Avance CO2 infrared sensor, GE Healthcare, Madison, WI, USA). The digital readout of the PETCO2 is based on an algorithm that evaluates two successive waveforms and the valley between them with the PETCO2 being the maximum value from the first waveform. TCCO2 was measured using the Sentec Digital Monitoring System (SenTec AG, Therwil, Switzerland). One of the authors calibrated, placed, and maintained the monitor. Before placement, the electrode was cleaned, a new membrane applied, and calibration performed according to the manufacturer’s recommendations using a calibration gas supply. The working temperature of the electrode was set at 42 °C and the electrode was placed on the palmar surface of the forearm or the infraclavicular area. The algorithm used by the TC-CO2 monitor corrects the temperature as well as the increased CO2 production generated by the difference in temperature from 37 °C. The area where the electrode was placed was
123
swabbed with alcohol before placement to facilitate adhesion of the disk to the skin. Samples were taken for ABG analysis as clinically indicated throughout the surgical procedure. The ABG samples were measured and reported at 37 °C. When an arterial blood sample was obtained for PaCO2 analysis, simultaneous PETCO2 and TC-CO2 values were recorded on the data sheet. The absolute difference between the PETCO2 and the PaCO2 was compared with the absolute difference between the TC-CO2 and the PaCO2 using a non-paired, two-way t test. A Fisher’s exact test and a two-way contingency table were used to compare the number of PETCO2 and TC-CO2 values whose absolute difference deviated B3 mmHg from the actual PaCO2 value. A Bland–Altman analysis was also used to compare the ET and TC values to the actual PaCO2. All data are expressed as the mean ± SD with P \ 0.05 considered significant.
3 Results The study cohort included 26 adolescents. One patient and their data were eliminated from subsequent analysis due to recording errors on the data sheets. The demographic data from the 25 included patients is listed in Table 1. The mean surgical time from skin incision to skin suture was 150 ± 63 min, and the mean pneumoperitoneum pressure during the laparoscopic portion of the procedure was 16 ± 3 cm H2O. The absolute difference between the TC-CO2 and the PaCO2 was 3.2 ± 3.0 mmHg while the absolute difference between the PETCO2 and the PaCO2 was 3.7 ± 2.5 mmHg (P = NS). Thirty-nine of 63 of the TC-CO2 values were B3 mmHg from the actual PaCO2 while 32 of 73 PETCO2 values were B3 mmHg different from the PaCO2 (P = 0.04). Figures 1 and 2 display the Bland–Altman analyses of PaCO2 versus TC-CO2 and PaCO2 versus PETCO2, respectively. The bias and precision were 0.3 and 4.3 mmHg for TC-CO2 versus PaCO2 and 3.2 and 3.2 mmHg for PETCO2 versus PaCO2. The 95 % LOA was -8.2 to ?8.8 mmHg for TC-CO2 versus PaCO2 and -3.1 to ?9.4 mmHg for PETCO2 versus PaCO2.
Table 1 Demographic data of the study cohort (n = 25) (The data are listed as the mean ± SD) Age (years)
17.2 ± 2.1
Weight (kg)
133.1 ± 31.1
Body mass index (kg/m2)
50.2 ± 11.0
Gender (male–female)
4–21
J Clin Monit Comput
Fig. 1 Bland–Altman analysis of TC-CO2 versus PaCO2. The difference of the two values (mmHg) is listed on the y axis and the average of the two values is listed on the x axis (mmHg)
Fig. 2 Bland–Altman analysis of PETCO2 versus PaCO2. The difference of the two values (mmHg) is listed on the y axis and the average of the two values is listed on the x axis (mmHg)
4 Discussion Both ET and TC-CO2 showed a clinically acceptable accuracy as a surrogate for continuous PaCO2 monitoring during robotic, laparoscopic bariatric surgery in adolescents and young adults. PETCO2 is generally relied upon by anesthesiologists to estimate ventilation, although its usefulness has been questioned during laparoscopy and in obese patients [18, 23, 24]. Our study agrees with that by Griffin and colleagues which found that TC-CO2 was at least an equivalent and possibly superior measure of PaCO2 in obese adults when compared to PETCO2 monitoring [23]. Data from our study shows that TC-CO2 monitoring demonstrated a closer accuracy to PaCO2 than PETCO2 with more values that were B3 mmHg from the actual PaCO2 value. However, the Bland–Altman analysis demonstrated less precision with TC-CO2 monitoring (4.3 vs. 3.2 mmHg with PETCO2). Of note, one of the TC-CO2 data points was a significant outlier (-17.5 mmHg) and may have led to the lower precision for TC-CO2 monitoring. There was no apparent cause of this value as the other TCCO2 readings on the same subject were very congruent to
PaCO2. Although the bias was much lower with TC-CO2 monitoring, this is a result of the fact that in general TCCO2 values are distributed evenly above and below the actual PaCO2 value while PETCO2 values are lower than the PaCO2. In this study, comparisons of PaCO2 from arterial blood were made with simultaneous PETCO2 and TC-CO2 readings during conditions of steady state ventilation (ventilation parameters were not adjusted for at least 20 minutes before data was collected at any given time point). This would allow the physiologic relationships between PaCO2, PETCO2 and TC-CO2 to be established given physiologic delays and different time constants in the body. The overall improved accuracy of PETCO2 in adolescent and young adult patients when compared to their older adult counterparts is likely due to their overall better pulmonary function. Aging results in loss of the elastic properties of the lungs leading to increased closing capacity resulting in ventilation–perfusion inequalities during tidal breathing. These changes are hastened by tobacco use and other co-morbid disease processes. The ‘healthy’ lungs of the patients in the current study allowed for adequate gas exchange thereby making PETCO2 an effective monitor even during a laparoscopic procedure. Although TC-CO2 will never replace the indispensable utilities of PETCO2, it may offer another avenue for continuous PaCO2 monitoring especially during clinical scenarios which may interfere with the accuracy of PETCO2 monitoring. Furthermore given the ever present risk of respiratory depression during the postoperative period especially when opioids are administered to patients with co-morbid conditions, it may be that TC-CO2 monitoring will provide an early warning of respiratory depression in patients without an artificial airway in whom PETCO2 monitoring may be impractical.
Ethical standards This study complies with the current ethical laws in the United States. Conflict of interest of interest.
The authors declare that they have no conflict
References 1. Bhavani-Shankar K, Moseley H, Kumar AY, et al. Capnometry and anaesthesia. Can J Anaesth. 1992;39:617–32. 2. Pansard JL, Cholley B, Devilliers C, et al. Variation in arterial to end-tidal CO2 tension differences during anesthesia in the ‘kidney rest’ lateral decubitus position. Anesth Analg. 1992;75: 506–10. 3. Grenier B, Verchere E, Meslie A, et al. Capnography monitoring during neurosurgery: reliability in relation to various intraoperative positions. Anesth Analg. 1999;88:43–8.
123
J Clin Monit Comput 4. Sivarajan VB, Bohn D. Monitoring of standard hemodynamic parameters: heart rate, systemic blood pressure, atrial pressure, pulse oximetry, and end-tidal CO2. Pediatr Crit Care Med. 2011;12(Suppl):S2–11. 5. Raemer D, Francis D, Philip JH. Variations in PCO2 between arterial and peak expired gas during anaesthesia. Anesth Analg. 1982;62:1065–9. 6. Oberg B, Poulsen TD. Obesity: an anaesthetic challenge. Acta Anaesthesiol Scand. 1996;40:191–200. 7. Nguyen NT, Anderson JT, Budd M, et al. Effects of pneumoperitoneum on intraoperative pulmonary mechanics and gas exchange during laparoscopic gastric bypass. Surg Endosc. 2004; 18:64–71. 8. Tobias JD, Meyer DJ. Noninvasive monitoring of carbon dioxide during respiratory failure in toddlers and infants: end-tidal versus transcutaneous carbon dioxide. Anesth Analg. 1997;85:55–8. 9. Nosovitch MA, Johnson JO, Tobias JD. Noninvasive intraoperative monitoring of carbon dioxide in children: endtidal versus transcutaneous techniques. Paediatr Anaesth. 2002;12:48–52. 10. McBride DS, Johnson JO, Tobias JD. Noninvasive carbon dioxide monitoring during neurosurgical procedures in adults: endtidal versus transcutaneous techniques. South Med J. 2002;95: 870–4. 11. Rithalia SVS, Ng YN, Tinker J. Measurement of transcutaneous PCO2 in critically ill patients. Resuscitation. 1982;10:13–8. 12. Rithalia SVS, Clutton-Brock TH, Tinker J. Characteristics of transcutaneous carbon dioxide tension monitors in normal adults and critically ill patients. Intensive Care Med. 1984;10:149–53. 13. Bhavani-Shankar K, Steinbrook RA, Mushlin PS, et al. Transcutaneous PCO2 monitoring during laparoscopic cholecystectomy in pregnancy. Can J Anaesth. 1998;45:164–9. 14. Janssens JP, Howarth-Frey C, Chevrolet JC, et al. Transcutaneous PCO2 to monitor noninvasive mechanical ventilation in adults. Chest. 1998;113:768–73.
123
15. Sanders MH, Kern NE, Costantino JP, et al. Accuracy of endtidal and transcutaneous PCO2 monitoring during sleep. Chest. 1994;106:472–83. 16. Evans EN, Ganeshalingam K, Ebden P. Changes in oxygen saturation and transcutaneous carbon dioxide and oxygen levels in patients undergoing fiberoptic bronchoscopy. Respir Med. 1998;92:739–42. 17. Phan CQ, Tremper KK, Lee SE, et al. Noninvasive monitoring of carbon dioxide: a comparison of the partial pressure of transcutaneous and end-tidal carbon dioxide with the partial pressure of arterial carbon dioxide. J Clin Monit. 1987;3:149–54. 18. Miller DR, Hull KA, Baines J, et al. A comparison of transcutaneous, end-tidal and arterial measurements of carbon dioxide during general anaesthesia. Can J Anaesth. 1992;39:31–6. 19. Bendjelid K, Schutz N, Stotz M, et al. Transcutaneous PCO2 monitoring in critically ill adults: clinical evaluation of a new sensor. Crit Care Med. 2005;33:2203–6. 20. Parker SM, Gibson GJ. Evaluation of a transcutaneous carbon dioxide monitor (‘‘TOSCA’’) in adult patients in routine respiratory practice. Respir Med. 2007;101:261–4. 21. McEvedy BA, McLeod ME, Mulera M, et al. End-tidal, transcutaneous and arterial PCO2 measurements in critically ill neonates: a comparative study. Anesthesiology. 1988;69:112–6. 22. Bernet-Buettiker V, Ugarte MJ, Frey B, et al. Evaluation of a new combined transcutaneous measurement of PCO2/pulse oximetry oxygen saturation ear sensor in newborn patients. Pediatrics. 2005;115:64–8. 23. Griffin J, Terry BE, Burton RK, et al. Comparison of end-tidal and transcutaneous measures of carbon dioxide during general anaesthesia in severely obese adults. Br J Anaesth. 2003;91: 498–501. 24. Maniscalco M, Zedda A, Faraone S, et al. Evaluation of a transcutaneous carbon dioxide monitor in severe obesity. Intensive Care Med. 2008;34:1340–4.
ORIGINAL RESEARCH
Carbon dioxide monitoring during laparoscopic-assisted bariatric surgery in severely obese patients: transcutaneous versus end-tidal techniques Joanna M. Dion • Chris McKee • Joseph D. Tobias Daniel Herz • Paul Sohner • Steven Teich • Marc Michalsky
•
Received: 25 February 2014 / Accepted: 31 May 2014 Ó Springer Science+Business Media New York 2014
Abstract 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 J. M. Dion (&) C. McKee J. D. Tobias P. Sohner Department of Anesthesiology and Pain Medicine, Nationwide Children’s Hospital, Ohio State University, 700 Children’s Drive, Columbus, OH 43205, USA e-mail: [email protected] J. D. Tobias S. Teich M. Michalsky Department of Surgery, Nationwide Children’s Hospital, Ohio State University, Columbus, OH, USA D. Herz Department of Urology, Nationwide Children’s Hospital, Ohio State University, Columbus, OH, USA
of PaCO2 to PETCO2. In this population, both of these noninvasive measures of PaCO2 can be used to monitor ventilation and minimize arterial blood gas sampling. Keywords Adolescent Physiologic monitoring: transcutaneous CO2 monitoring Obesity Laparoscopy Bariatric surgery
1 Introduction The standard for assessing the efficacy of mechanical ventilation remains the measurement of the partial pressure of carbon dioxide in arterial blood (PaCO2). Although the absolute measure remains direct intermittent arterial sampling and arterial blood gas (ABG) analysis, the technique is invasive. Furthermore, ABG analysis provides only a single instantaneous measurement of what may be a constantly changing baseline. To overcome such problems, non-invasive techniques such as end-tidal carbon dioxide (PETCO2) monitoring remain a standard of care during general anesthesia. However, various factors which disrupt normal matching of ventilation and perfusion may interfere with the accuracy of PETCO2 monitoring [1–5]. Such problems may be encountered in patients with severe obesity (body mass index or BMI [35 kg/m2) related to a decrease in functional residual capacity and alterations in the matching of ventilation and perfusion [4, 6]. Laparoscopy and the insufflation can also result in physiological alterations that may diminish the accuracy of PETCO2 monitoring [7]. Transcutaneous (TC) devices can also be used for the continuous and non-invasive monitoring of PaCO2. Although used most commonly in the neonatal population, these techniques may be used successfully in various
123
J Clin Monit Comput
clinical scenarios in older pediatric patients, adolescents, and adults [8–22]. The accuracy of these monitors has been questioned in obese adult patients and at extremes of PaCO2 [18, 23, 24]. However, other studies have demonstrated that TC-CO2 monitoring may provide a more accurate assessment of PaCO2 than PETCO2 monitoring [23]. The current study prospectively compares TC and PETCO2 monitoring during robotic, laparoscopic-assisted bariatric surgery in severely obese adolescents and young adults.
2 Methods Approval for this study was granted by the Institutional Review Board of Nationwide Children’s Hospital (Columbus, Ohio). The need for written, informed consent was waived. The study included adolescent and young adults with a BMI C40 kg/m2 presenting for laparoscopicassisted bariatric surgery (vertical sleeve gastrectomy). The anesthetic technique included premedication with intravenous midazolam followed by anesthetic induction with propofol and fentanyl. Endotracheal intubation was facilitated by the administration of either rocuronium or succinylcholine. Maintenance anesthesia included desflurane titrated to maintain the bispectral index at 40–60, a dexmedetomidine infusion at 0.2–0.25 lg/kg/h, and remifentanil to maintain hemodynamic stability. After intubation of the trachea, ventilation was controlled using a tidal volume of 6–8 ml/kg, an inspiratory to expiratory (I:E) ratio of 1:2–3, positive end-expiratory pressure (PEEP) of 5 cm H2O, and an FIO2 of 0.5. The respiratory rate was adjusted to maintain normocarbia. PETCO2 was measured using an infrared analyzer with side-stream sampling at a flow rate of 150 ml/min (DatexOhmeda Avance CO2 infrared sensor, GE Healthcare, Madison, WI, USA). The digital readout of the PETCO2 is based on an algorithm that evaluates two successive waveforms and the valley between them with the PETCO2 being the maximum value from the first waveform. TCCO2 was measured using the Sentec Digital Monitoring System (SenTec AG, Therwil, Switzerland). One of the authors calibrated, placed, and maintained the monitor. Before placement, the electrode was cleaned, a new membrane applied, and calibration performed according to the manufacturer’s recommendations using a calibration gas supply. The working temperature of the electrode was set at 42 °C and the electrode was placed on the palmar surface of the forearm or the infraclavicular area. The algorithm used by the TC-CO2 monitor corrects the temperature as well as the increased CO2 production generated by the difference in temperature from 37 °C. The area where the electrode was placed was
123
swabbed with alcohol before placement to facilitate adhesion of the disk to the skin. Samples were taken for ABG analysis as clinically indicated throughout the surgical procedure. The ABG samples were measured and reported at 37 °C. When an arterial blood sample was obtained for PaCO2 analysis, simultaneous PETCO2 and TC-CO2 values were recorded on the data sheet. The absolute difference between the PETCO2 and the PaCO2 was compared with the absolute difference between the TC-CO2 and the PaCO2 using a non-paired, two-way t test. A Fisher’s exact test and a two-way contingency table were used to compare the number of PETCO2 and TC-CO2 values whose absolute difference deviated B3 mmHg from the actual PaCO2 value. A Bland–Altman analysis was also used to compare the ET and TC values to the actual PaCO2. All data are expressed as the mean ± SD with P \ 0.05 considered significant.
3 Results The study cohort included 26 adolescents. One patient and their data were eliminated from subsequent analysis due to recording errors on the data sheets. The demographic data from the 25 included patients is listed in Table 1. The mean surgical time from skin incision to skin suture was 150 ± 63 min, and the mean pneumoperitoneum pressure during the laparoscopic portion of the procedure was 16 ± 3 cm H2O. The absolute difference between the TC-CO2 and the PaCO2 was 3.2 ± 3.0 mmHg while the absolute difference between the PETCO2 and the PaCO2 was 3.7 ± 2.5 mmHg (P = NS). Thirty-nine of 63 of the TC-CO2 values were B3 mmHg from the actual PaCO2 while 32 of 73 PETCO2 values were B3 mmHg different from the PaCO2 (P = 0.04). Figures 1 and 2 display the Bland–Altman analyses of PaCO2 versus TC-CO2 and PaCO2 versus PETCO2, respectively. The bias and precision were 0.3 and 4.3 mmHg for TC-CO2 versus PaCO2 and 3.2 and 3.2 mmHg for PETCO2 versus PaCO2. The 95 % LOA was -8.2 to ?8.8 mmHg for TC-CO2 versus PaCO2 and -3.1 to ?9.4 mmHg for PETCO2 versus PaCO2.
Table 1 Demographic data of the study cohort (n = 25) (The data are listed as the mean ± SD) Age (years)
17.2 ± 2.1
Weight (kg)
133.1 ± 31.1
Body mass index (kg/m2)
50.2 ± 11.0
Gender (male–female)
4–21
J Clin Monit Comput
Fig. 1 Bland–Altman analysis of TC-CO2 versus PaCO2. The difference of the two values (mmHg) is listed on the y axis and the average of the two values is listed on the x axis (mmHg)
Fig. 2 Bland–Altman analysis of PETCO2 versus PaCO2. The difference of the two values (mmHg) is listed on the y axis and the average of the two values is listed on the x axis (mmHg)
4 Discussion Both ET and TC-CO2 showed a clinically acceptable accuracy as a surrogate for continuous PaCO2 monitoring during robotic, laparoscopic bariatric surgery in adolescents and young adults. PETCO2 is generally relied upon by anesthesiologists to estimate ventilation, although its usefulness has been questioned during laparoscopy and in obese patients [18, 23, 24]. Our study agrees with that by Griffin and colleagues which found that TC-CO2 was at least an equivalent and possibly superior measure of PaCO2 in obese adults when compared to PETCO2 monitoring [23]. Data from our study shows that TC-CO2 monitoring demonstrated a closer accuracy to PaCO2 than PETCO2 with more values that were B3 mmHg from the actual PaCO2 value. However, the Bland–Altman analysis demonstrated less precision with TC-CO2 monitoring (4.3 vs. 3.2 mmHg with PETCO2). Of note, one of the TC-CO2 data points was a significant outlier (-17.5 mmHg) and may have led to the lower precision for TC-CO2 monitoring. There was no apparent cause of this value as the other TCCO2 readings on the same subject were very congruent to
PaCO2. Although the bias was much lower with TC-CO2 monitoring, this is a result of the fact that in general TCCO2 values are distributed evenly above and below the actual PaCO2 value while PETCO2 values are lower than the PaCO2. In this study, comparisons of PaCO2 from arterial blood were made with simultaneous PETCO2 and TC-CO2 readings during conditions of steady state ventilation (ventilation parameters were not adjusted for at least 20 minutes before data was collected at any given time point). This would allow the physiologic relationships between PaCO2, PETCO2 and TC-CO2 to be established given physiologic delays and different time constants in the body. The overall improved accuracy of PETCO2 in adolescent and young adult patients when compared to their older adult counterparts is likely due to their overall better pulmonary function. Aging results in loss of the elastic properties of the lungs leading to increased closing capacity resulting in ventilation–perfusion inequalities during tidal breathing. These changes are hastened by tobacco use and other co-morbid disease processes. The ‘healthy’ lungs of the patients in the current study allowed for adequate gas exchange thereby making PETCO2 an effective monitor even during a laparoscopic procedure. Although TC-CO2 will never replace the indispensable utilities of PETCO2, it may offer another avenue for continuous PaCO2 monitoring especially during clinical scenarios which may interfere with the accuracy of PETCO2 monitoring. Furthermore given the ever present risk of respiratory depression during the postoperative period especially when opioids are administered to patients with co-morbid conditions, it may be that TC-CO2 monitoring will provide an early warning of respiratory depression in patients without an artificial airway in whom PETCO2 monitoring may be impractical.
Ethical standards This study complies with the current ethical laws in the United States. Conflict of interest of interest.
The authors declare that they have no conflict
References 1. Bhavani-Shankar K, Moseley H, Kumar AY, et al. Capnometry and anaesthesia. Can J Anaesth. 1992;39:617–32. 2. Pansard JL, Cholley B, Devilliers C, et al. Variation in arterial to end-tidal CO2 tension differences during anesthesia in the ‘kidney rest’ lateral decubitus position. Anesth Analg. 1992;75: 506–10. 3. Grenier B, Verchere E, Meslie A, et al. Capnography monitoring during neurosurgery: reliability in relation to various intraoperative positions. Anesth Analg. 1999;88:43–8.
123
J Clin Monit Comput 4. Sivarajan VB, Bohn D. Monitoring of standard hemodynamic parameters: heart rate, systemic blood pressure, atrial pressure, pulse oximetry, and end-tidal CO2. Pediatr Crit Care Med. 2011;12(Suppl):S2–11. 5. Raemer D, Francis D, Philip JH. Variations in PCO2 between arterial and peak expired gas during anaesthesia. Anesth Analg. 1982;62:1065–9. 6. Oberg B, Poulsen TD. Obesity: an anaesthetic challenge. Acta Anaesthesiol Scand. 1996;40:191–200. 7. Nguyen NT, Anderson JT, Budd M, et al. Effects of pneumoperitoneum on intraoperative pulmonary mechanics and gas exchange during laparoscopic gastric bypass. Surg Endosc. 2004; 18:64–71. 8. Tobias JD, Meyer DJ. Noninvasive monitoring of carbon dioxide during respiratory failure in toddlers and infants: end-tidal versus transcutaneous carbon dioxide. Anesth Analg. 1997;85:55–8. 9. Nosovitch MA, Johnson JO, Tobias JD. Noninvasive intraoperative monitoring of carbon dioxide in children: endtidal versus transcutaneous techniques. Paediatr Anaesth. 2002;12:48–52. 10. McBride DS, Johnson JO, Tobias JD. Noninvasive carbon dioxide monitoring during neurosurgical procedures in adults: endtidal versus transcutaneous techniques. South Med J. 2002;95: 870–4. 11. Rithalia SVS, Ng YN, Tinker J. Measurement of transcutaneous PCO2 in critically ill patients. Resuscitation. 1982;10:13–8. 12. Rithalia SVS, Clutton-Brock TH, Tinker J. Characteristics of transcutaneous carbon dioxide tension monitors in normal adults and critically ill patients. Intensive Care Med. 1984;10:149–53. 13. Bhavani-Shankar K, Steinbrook RA, Mushlin PS, et al. Transcutaneous PCO2 monitoring during laparoscopic cholecystectomy in pregnancy. Can J Anaesth. 1998;45:164–9. 14. Janssens JP, Howarth-Frey C, Chevrolet JC, et al. Transcutaneous PCO2 to monitor noninvasive mechanical ventilation in adults. Chest. 1998;113:768–73.
123
15. Sanders MH, Kern NE, Costantino JP, et al. Accuracy of endtidal and transcutaneous PCO2 monitoring during sleep. Chest. 1994;106:472–83. 16. Evans EN, Ganeshalingam K, Ebden P. Changes in oxygen saturation and transcutaneous carbon dioxide and oxygen levels in patients undergoing fiberoptic bronchoscopy. Respir Med. 1998;92:739–42. 17. Phan CQ, Tremper KK, Lee SE, et al. Noninvasive monitoring of carbon dioxide: a comparison of the partial pressure of transcutaneous and end-tidal carbon dioxide with the partial pressure of arterial carbon dioxide. J Clin Monit. 1987;3:149–54. 18. Miller DR, Hull KA, Baines J, et al. A comparison of transcutaneous, end-tidal and arterial measurements of carbon dioxide during general anaesthesia. Can J Anaesth. 1992;39:31–6. 19. Bendjelid K, Schutz N, Stotz M, et al. Transcutaneous PCO2 monitoring in critically ill adults: clinical evaluation of a new sensor. Crit Care Med. 2005;33:2203–6. 20. Parker SM, Gibson GJ. Evaluation of a transcutaneous carbon dioxide monitor (‘‘TOSCA’’) in adult patients in routine respiratory practice. Respir Med. 2007;101:261–4. 21. McEvedy BA, McLeod ME, Mulera M, et al. End-tidal, transcutaneous and arterial PCO2 measurements in critically ill neonates: a comparative study. Anesthesiology. 1988;69:112–6. 22. Bernet-Buettiker V, Ugarte MJ, Frey B, et al. Evaluation of a new combined transcutaneous measurement of PCO2/pulse oximetry oxygen saturation ear sensor in newborn patients. Pediatrics. 2005;115:64–8. 23. Griffin J, Terry BE, Burton RK, et al. Comparison of end-tidal and transcutaneous measures of carbon dioxide during general anaesthesia in severely obese adults. Br J Anaesth. 2003;91: 498–501. 24. Maniscalco M, Zedda A, Faraone S, et al. Evaluation of a transcutaneous carbon dioxide monitor in severe obesity. Intensive Care Med. 2008;34:1340–4.
