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Year : 2018  |  Volume : 62  |  Issue : 4  |  Page : 298-302  

Anaesthesia for laparoscopic nephrectomy: Does end-tidal carbon dioxide measurement correlate with arterial carbon dioxide measurement?

Department of Anaesthesia and Critical Care, VPS Lakeshore Hospital, Kochi, Kerala, India

Date of Web Publication11-Apr-2018

Correspondence Address:
Dr. Nithin Jayan
Department of Anaesthesiology and Critical Care, VPS Lakeshore Hospital, Nettoor, Maradu, Kochi - 682 040, Kerala
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ija.IJA_740_17

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Background and Aims: Not many studies have explored the correlation between arterial carbon dioxide tension (PaCO2) and end-tidal carbon dioxide tension (ETCO2) in surgeries requiring pneumoperitoneum of more than 1 hour duration with the patient in non-supine position. The aim of our study was to evaluate the correlation of ETCO2with PaCO2in patients undergoing laparoscopic nephrectomy under general anaesthesia. Methods: A descriptive study was performed in thirty patients undergoing laparoscopic nephrectomy from September 2014 to August 2015. The haemodynamic parameters, minute ventilation, PaCO2and ETCO2measured at three predetermined points during the procedure were analysed. Correlation was checked using Pearson's Correlation Coefficient Test. P <0.05 was considered statistically significant. Results: Statistical analysis of the values showed a positive correlation between ETCO2and PaCO2(P < 0.05). Following carbon dioxide insufflation, both ETCO2and PaCO2increased by 5.4 and 6.63 mmHg, respectively, at the end of the 1st hour. The PaCO2-ETCO2gradient was found to increase during the 1st hour following insufflation (4.07 ± 2.05 mmHg); it returned to the pre-insufflation values in another hour (2.93 ± 1.43 mmHg). Conclusion: Continuous ETCO2monitoring is a reliable indicator of the trend in arterial CO2fluctuations in the American Society of Anesthesiologists Grades 1 and 2 patients undergoing laparoscopic nephrectomy under general anaesthesia.

Keywords: Blood gas monitoring, capnography, carbon dioxide partial pressure determination, pneumoperitoneum

How to cite this article:
Jayan N, Jacob JS, Mathew M. Anaesthesia for laparoscopic nephrectomy: Does end-tidal carbon dioxide measurement correlate with arterial carbon dioxide measurement?. Indian J Anaesth 2018;62:298-302

How to cite this URL:
Jayan N, Jacob JS, Mathew M. Anaesthesia for laparoscopic nephrectomy: Does end-tidal carbon dioxide measurement correlate with arterial carbon dioxide measurement?. Indian J Anaesth [serial online] 2018 [cited 2021 Jul 26];62:298-302. Available from: https://www.ijaweb.org/text.asp?2018/62/4/298/229809

   Introduction Top

Arterial blood gas analysis is the gold standard for assessing the adequacy of ventilation. Peripheral arterial catheters are commonly used for this purpose but may be associated with complications ranging from temporary occlusion of the artery to distal ischaemia, pseudoaneurysm formation and sepsis.[1] Apart from the blood loss due to recurrent sampling, a further disadvantage of arterial blood analysis is that it only reflects homoeostasis at the time of sampling, which can change considerably within a short period of time. End-tidal carbon dioxide (ETCO2) measurements may be satisfactory surrogate measures of arterial carbon dioxide (PaCO2) in select patients obviating the need for serial arterial blood gas determination. Under normal circumstances, a gradient of approximately 4–5 mmHg exists between the two.[2] There can be wide variations in this gradient between PaCO2 and ETCO2 depending on the patient's condition, the position adopted for surgery and the surgery itself – this relationship does not remain constant over time.

Capnoperitoneum is associated with CO2 absorption and an increase in CO2 concentration in the bloodstream, leading to a rise in the ETCO2 and PaCO2. The rise in ETCO2 is initially sharp, followed by a plateau as equilibrium is achieved.[3]

Few studies have explored the correlation between ETCO2 and PaCO2 in surgeries requiring pneumoperitoneum for a long duration with the patient in non-supine position. Laparoscopic nephrectomy requires pneumoperitoneum of at least 120 min duration with the patient maintained in lateral decubitus position. Under anaesthesia, the lateral decubitus position is itself associated with ventilatory compromise.[4] Overinflation and underperfusion of non-dependent lung and gravity favoured perfusion of the dependent underventilated lung leads to ventilation-perfusion mismatch affecting both oxygenation and elimination of carbon dioxide. Hence, measuring PaCO2 in addition to ETCO2 might be a more accurate reflection of the adequacy of ventilation.

In our study, we aimed to determine if the ETCO2 values correlate with PaCO2 during anaesthesia for laparoscopic nephrectomy.

   Methods Top

After obtaining Institutional Ethics Committee approval, a prospective observational study was conducted in thirty individuals undergoing laparoscopic nephrectomy in the period between September 2014 and August 2015. The sample size was calculated to be 30 so as to have a power of 90%; this was based on the information obtained from the study by Hu et al. which found a correlation coefficient of 0.579 between ETCO2 and PaCO2.[5] Written informed consent was obtained from patients undergoing laparoscopic nephrectomy who satisfied the inclusion criteria of age group between 20 and 50 years and surgeries requiring a duration of pneumoperitoneum of >120 min.

The exclusion criteria included patients belonging to the American Society of Anaesthesiologists (ASA) grades ≥3, patients with significant cardiovascular disease (New York Heart Association classes III and IV) and established chronic obstructive pulmonary disease (COPD), a negative Allen's test during the preoperative evaluation, and patients with a body mass index >30 kg/m 2. We excluded data if the surgery was converted to open nephrectomy.

The patients underwent pre-operative anaesthetic evaluation on the day before surgery during which they were explained about the ongoing study and consent obtained. Modified Allen's test was done to ensure patency of collateral circulation of the hand. As per institutional practice, solid food was withheld for 6 hours while clear fluids were allowed up to 2 hours before surgery. All patients received premedication in the form of tablet lorazepam 2 mg and tablet ondansetron 8 mg, 2 hours before surgery.

On arrival in the operation theatre (OT), all patients were pre-oxygenated with 100% O2 for 3 minutes using a semi-closed breathing circuit. Anaesthesia was induced with 2 mcg/kg fentanyl and 2 mg/kg propofol. Intubation was performed 90 seconds after administration of 0.9 mg/kg rocuronium. Intermittent positive pressure ventilation mode was used with a tidal volume of 8 ml/kg and an initial respiratory rate of 12 breaths/min. The lungs were ventilated with air-oxygen mixture (FiO20.5) and sevoflurane (end tidal concentration: 1.5- 2.0%) using Dräger Fabius ® GS premium Anaesthesia workstation. A 20/22 G 4 cm long BD Insyte™ (BD, USA) -WTM cannula was inserted into the radial artery under aseptic precautions.

Pneumoperitoneum was created by insufflation with CO2 after positioning the anaesthetised patient in lateral position. Intra-abdominal pressure was monitored and maintained below 12 mmHg. Expired tidal volumes, airway pressure and minute ventilation were monitored continuously throughout the surgery on the anaesthesia workstation. ETCO2 was monitored using mainstream capnography (GE CAPNOSTAT™ CO2 module) and minute ventilation was adjusted to maintain the ETCO2 between 30 and 35 mmHg.

Maintenance of anaesthesia was with air-oxygen mixture (FiO20.5) and sevoflurane (end tidal concentration: 1.5- 2.0%). Muscle relaxation was ensured with bolus doses of short-acting neuromuscular blockers (atracurium) at the discretion of the anaesthesiologist; additional analgesics used included intravenous fentanyl or morphine, and paracetamol.

The patients were monitored with ECG, pulse oximetry, intermittent non-invasive blood pressure monitoring, nasopharyngeal temperature probe and mainstream capnography (GE Dash 4000™ monitor). In addition, the breathing circuit had an oxygen sensor in the inspiratory limb to determine the fraction of inspired oxygen concentration delivered to the patient. As per our department protocol for patients undergoing laparoscopic nephrectomy, arterial blood gas sampling was done at definite points (following lateral positioning, at 60 min of pneumoperitoneum and 120 min of pneumoperitoneum) during the surgery.

For the current study, the haemodynamic parameters, minute ventilation, PaCO2 and ETCO2 at the same three predetermined points during the surgery were analysed.

The time points analysed were: Baseline, T1: After induction and lateral positioning of the patient, while the surgical site was prepared and draped; 1 h after insufflation of pneumoperitoneum, T2; After 2 h of pneumoperitoneum, T3.

Data were entered in Excel sheet after coding. SPSS version 16.0 (trial version) was used for analysis of the data. Qualitative variables were summarised using proportion; quantitative variables were summarised using mean with standard deviation. Statistical analysis was done using Pearson correlation coefficient test and paired t-test. P < 0.05 was considered statistically significant.

   Results Top

The mean age of the patients was 42.87 ± 7.26 years. Twenty five male and five female patients participated in our study. Statistical analysis of the values showed a positive correlation between ETCO2 and PaCO2(P< 0.05). Following laparoscopic insufflation, both ETCO2 and PaCO2 increased by 5.4 and 6.63 mmHg, respectively, by the end of the 1st hour [Table 1] and [Table 2]. The PaCO2-ETCO2 gradient was found to increase during the 1st hour following insufflation (4.07 ± 2.05 mmHg); it returned to the pre-insufflation values in another hour (2.93 ± 1.43 mmHg) [Figure 1].
Table 1: Paired sample statistics

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Table 2: Correlation

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Figure 1: Change in the arterial carbon dioxide-end-tidal carbon dioxide difference over time

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   Discussion Top

From our study, we have been able to demonstrate a positive correlation between ETCO2 and PaCO2 in healthy patients undergoing laparoscopic nephrectomy.

The PaCO2-ETCO2 gradient varies with various patient positions adopted for surgery: it decreases slightly in prone position and increases significantly in the lateral decubitus position.[6] Our study revealed a mean PaCO2-ETCO2 gradient of 2.67 mmHg in patients in the lateral decubitus posture. The effect of lateral decubitus positioning on the gradient was not assessed since samples were not drawn before lateral positioning.

The samples drawn 1 hour post-insufflation showed that both arterial and ETCO2 values increased – the mean PaCO2-ETCO2 gradient increased to 4.07 ± 2.05 mmHg. This is consistent with the findings of other researchers such as Tanaka et al.[7] Seed et al. proposed that during laparoscopy absorption of CO2 occurs from the peritoneum.[8] The elimination of absorbed CO2 depends on cardiac output, ventilation: perfusion ratios and alveolar ventilation.[2] Over a short period of time, CO2 is buffered in the alveolar-arterial interface of the lung and in visceral stores and it is ultimately expired by the lung.[8] Absorption of CO2 from the peritoneal cavity may be poor and inconsistent because of a reduction of capillary blood flow caused by increased intra-abdominal pressure and general anaesthesia.[9] Analysis of the third arterial blood sample in our study seems to confirm this hypothesis – the PaCO2-ETCO2 gradient returned to the pre-insufflation values in the second hour (2.93 ± 1.43 mmHg) despite ongoing capnoperitoneum.

Capnographs measure CO2 concentration using mainstream or sidestream configurations. Mainstream end-tidal CO2 measurement, as used in our study, provides a more accurate estimation of arterial CO2 as compared to sidestream measurement. Fresh gas entrainment during sidestream sampling can dilute expired CO2 tension and contribute to the underestimation of PaCO2.[10]

Prolonged intra-abdominal insufflation with CO2 in anaesthetised and mechanically ventilated patients during abdominal laparoscopic surgery does not significantly affect the reliability of ETCO2 monitoring in predicting PaCO2 in healthy ASA grades 1 and 2 participants.[2],[9],[11] Our results confirmed the same. However, this may not be the case in patients with pre-existing pulmonary disease or moderate-to-severe cardiac compromise. An increasing number of patients requiring renal surgery are presenting with substantial comorbidities such as diabetes mellitus, COPD and cardiovascular disease. Most of the patients undergoing partial or radical nephrectomies for renal cell carcinoma are of advanced age and belong to ASA grade 3.[12] The changes produced during lateral positioning and CO2 pneumoperitoneum may be varied in this category of patients owing to the altered physiology. These patients may benefit from direct arterial PaCO2 monitoring in addition to continuous ETCO2 monitoring.

Since continuous ETCO2 monitoring serves as a reliable indicator of the trend in arterial CO2 fluctuations, this would facilitate timely adjustments in ventilatory parameters to maintain homoeostasis and avoid complications of hypercapnia. Capnography being a non-invasive and continuous monitoring modality is advantageous in that it obviates the need for multiple arterial punctures (in healthy patients). Arterial blood sampling, on the other hand, is invasive and reflects the CO2 values at the particular time when the sample is drawn. In our study, we found that ETCO2 monitoring correlates with PaCO2 in patients during anaesthesia for laparoscopic nephrectomy. Considering the adverse events and expenses associated with repeated arterial blood sampling, we recommend that observation of the trends in ETCO2 would suffice to monitor ventilation in patients belonging to ASA grades 1 and 2 undergoing laparoscopic nephrectomy. High-risk patients may require invasive arterial PaCO2 monitoring in addition.

Our study has a number of limitations: we included only healthy patients belonging to ASA grades 1 and 2, the effect of lateral positioning per se on the ETCO2-PaCO2 gradient was not assessed, specific time points for drawing blood samples were chosen. Hence we cannot authoritatively conclude that the same correlation exists at all times during the surgical period. Further studies involving diverse patient populations undergoing laparoscopic nephrectomies are required to conclusively establish the correlation.

   Conclusion Top

Continuous ETCO2 monitoring is a reliable indicator of the trend in arterial CO2 fluctuations in the American Society of Anaesthesiologists Grades 1 and 2 patients undergoing laparoscopic nephrectomy under general anaesthesia.


We would like to thank Dr. Jenyz M Mundodan, Assistant Professor, Department of Community Medicine, Amala Institute of Medical Sciences, Thrissur, Kerala, for helping us with the statistical analysis of our work.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Scheer B, Perel A, Pfeiffer UJ. Clinical review: Complications and risk factors of peripheral arterial catheters used for haemodynamic monitoring in anaesthesia and intensive care medicine. Crit Care 2002;6:199-204.  Back to cited text no. 1
Wahba RW, Mamazza J. Ventilatory requirements during laparoscopic cholecystectomy. Can J Anaesth 1993;40:206-10.  Back to cited text no. 2
Liem MS, Kallewaard JW, de Smet AM, van Vroonhoven TJ. Does hypercarbia develop faster during laparoscopic herniorrhaphy than during laparoscopic cholecystectomy? Assessment with continuous blood gas monitoring. Anesth Analg 1995;81:1243-9.  Back to cited text no. 3
Dunn PF. Physiology of the lateral decubitus position and one-lung ventilation. Int Anesthesiol Clin 2000;38:25-53.  Back to cited text no. 4
Hu D, Tang J, Xu T, Zhong Z, Liang Z, Liang J, et al. Correlation between pet-CO2 and PaCO2 in morbidly obese patients during anesthesia for laparoscopic gastric bypass surgery. Nan Fang Yi Ke Da Xue Xue Bao 2014;34:121-3.  Back to cited text no. 5
Joo J, Kim YH, Lee J, Choi JH. Difference in the value of arterial and end-tidal carbon dioxide tension according to different surgical positions: Does it reliably reflect ventilation-perfusion mismatch? Korean J Anesthesiol 2012;63:216-20.  Back to cited text no. 6
Tanaka T, Satoh K, Torii Y, Suzuki M, Furutani H, Harioka T, et al. Arterial to end-tidal carbon dioxide tension difference during laparoscopic colorectal surgery. Masui 2006;55:988-91.  Back to cited text no. 7
Seed RF, Shakespeare TF, Muldoon MJ. Carbon dioxide homeostasis during anaesthesia for laparoscopy. Anaesthesia 1970;25:223-31.  Back to cited text no. 8
Nyarwaya JB, Mazoit JX, Samii K. Are pulse oximetry and end-tidal carbon dioxide tension monitoring reliable during laparoscopic surgery? Anaesthesia 1994;49:775-8.  Back to cited text no. 9
Chan KL, Chan MT, Gin T. Mainstream vs. sidestream capnometry for prediction of arterial carbon dioxide tension during supine craniotomy. Anaesthesia 2003;58:149-55.  Back to cited text no. 10
Parikh BK, Shah VR, Modi PR, Butala BP, Parikh GP. Anaesthesia for laparoscopic kidney transplantation: Influence of trendelenburg position and CO2 pneumoperitoneum on cardiovascular, respiratory and renal function. Indian J Anaesth 2013;57:253-8.  Back to cited text no. 11
[PUBMED]  [Full text]  
Han KR, Kim HL, Pantuck AJ, Dorey FJ, Figlin RA, Belldegrun AS, et al. Use of American Society of Anesthesiologists physical status classification to assess perioperative risk in patients undergoing radical nephrectomy for renal cell carcinoma. Urology 2004;63:841-6.  Back to cited text no. 12


  [Figure 1]

  [Table 1], [Table 2]


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