Abstract
Background and study aims Peroral endoscopic myotomy (POEM) has become a recognized treatment for achalasia. The technique requires CO 2 insufflation. It is estimated that the partial pressure of CO 2 (PaCO 2 ) is 2 to 5 mm Hg higher than the end tidal CO 2 (etCO 2 ), and etCO 2 is used as a surrogate for PaCO 2 because PaCO 2 requires an arterial line. However, no study has compared invasive and noninvasive CO 2 monitoring during POEM.
Patients and methods Seventy-one patients who underwent POEM were included in a prospective comparative study. PaCO 2 plus etCO 2 was measured in 32 patients (invasive group) and etCO 2 only in 39 matched patients (noninvasive group). Pearson correlation coefficient (PCC) and Spearman’s Rho were used to calculate the correlation between PaCO 2 and ETCO 2 .
Results PaCO 2 and ETCO 2 were strongly correlated: PCC R value: 0.8787 P ≤ 0.00001, Spearman’s Rho R value: 0.8775, P ≤ 0.00001. Within the invasive group, the average difference between PaCO 2 and ETCO 2 was 3.39 mm Hg (median 3, standard deviation 3.5), within the 2- to 5-mm Hg range. The average procedure time (scope in to scope out) was increased 17.7 minutes ( P = 0.044) and anesthesia duration was 46.3 minutes. Adverse events (AEs) included three hematomas and one nerve injury in the invasive group and one pneumothorax in the noninvasive group. There were no differences in AE rates between the groups (13 % vs 3 % P = 0.24).
Conclusions Universal PaCO 2 monitoring contributes to increased procedure and anesthesia times without any decrease in AEs in patients undergoing POEM. CO 2 monitoring with an arterial line should only be performed in patients with major cardiovascular comorbidities; in all other patients, ETCO 2 is an appropriate tool.
Introduction
Achalasia is a motor disorder of the esophagus characterized by impaired relaxation of the lower esophageal sphincter, as a consequence of the loss of myenteric neurons. There are multiple options available for its treatment, including medications, pneumatic balloon dilation, and surgical myotomy 1 2 . POEM is an endoscopic technique that evolved from the concept of natural orifice transluminal endoscopic surgery. The procedure involves the creation of a submucosal tunnel and then myotomy of the muscular fibers of the distal esophagus, including the lower esophageal sphincter. First described in humans more than a decade ago, the reported safety and clinical efficacy of this treatment modality in all types of achalasia, as well as in other spastic disorders of the esophagus, has been well demonstrated 3 4 .
Carbon dioxide (CO 2 ) insufflation is a crucial component of third space endoscopy, and permits work in the submucosal space with less risk of barotrauma because it is reabsorbed faster than air 3 5 . Controlled or minimized CO 2 insufflation during the creation of the submucosal tunneling, as well as during the myotomy, can still be associated with complications 6 . The recognition and treatment of the physiological changes that occur as a consequence of CO 2 is of utmost importance to improve patient safety. End tidal CO 2 (ETCO 2 ) offers an acceptable estimate of alveolar CO 2 measured as arterial CO 2 (PaCO2) 7 , and is recommended as a surrogate for PaCO 2 in most patients, although its reliability can be compromised in patient with pulmonary diseases 7 8 .
PaCO 2 provides the most accurate evaluation of alveolar CO 2 but requires the presence of an arterial line. Interestingly, no study has evaluated whether there are any differences between invasive and noninvasive CO 2 monitoring during POEM. The aim of our study was to elucidate if the use of an arterial line with direct measurement of PaCO 2 was of any benefit, when compared to only ETCO 2 .
Patients and methods
Patient population
A prospective comparative study was performed in our institution. Information on all patients 18 years or older who underwent POEM for the treatment of achalasia and were able to provide consent was included in a prospectively collected database. Information on patients with known pulmonary disease or advanced cardiovascular disease was excluded. A total of 71 patients were included in the study. In the group in which PaCO 2 plus ETCO2 was measured, also known as invasive group, included 32 patients, an arterial line was placed prior to starting the POEM and the PaCO 2 was checked on average every 28 minutes. The group in which only ETCO 2 was measured, also known as the noninvasive group, included 39 matched patients. ETCO 2 was recorded every 12 minutes on average in both groups.
Periprocedure details
All the patients at our institution require a thorough evaluation before a diagnosis of achalasia is made, which includes a history and physical focusing on the Eckardt score, esophagogastroduodenoscopy, high-resolution manometry and endoluminal impedance measurement. Absolute contraindications for POEM are severe coagulopathy unable to be reversed as well as end-stage cirrhosis with sequelae of portal hypertension such as esophageal or gastric varices.
After the decision has been made for POEM, patients are placed on a full liquid diet for 2 days prior to the procedure, and then nil per os (NPO) for at least 8 hours. Preprocedurally patients are given a high-dose proton pump inhibitor (PPI), scopolamine patch and ondansetron to prevent nausea as well as prophylactic antibiotics, usually a quinolone.
The procedure is performed under general anesthesia with endotracheal intubation, paralytics are usually administered throughout the procedure, and pressure-controlled ventilation is favored over volume-controlled ventilation. In the pediatric population, the available evidence about the best anesthetic practices for POEM is scarce, and usually management is driven by the available data from adult patients 9 . The patient is placed in the supine position, and the endoscopist performs the procedure at the head of the bed, which allows for continuous visualization of the patient’s abdomen to monitor for the development of capnoperitoneum 10 . A high-definition gastroscope is required, with 4-mm transparent cap attached to the distal end. Several endoscopic knives and an electrosurgical generator are used for dissection; however, a hybrid knife (ERBE, Marietta, Georgia, United States) is preferred to allow simultaneous injection and dissection. A posterior approach is usually chosen for dissection and myotomy, and submucosal injection is performed using a solution consisting of normal saline and methylene blue. A coag gasper (Olympus, Center Valley, Pennsylvania, United States) is used to prevent or treat bleeding. CO 2 is used for insufflation with an insufflator with adjustable output flow rate ranging from ultralow to high (ERBE). Medium flow is used before tunneling and then is switched to low during submucosal dissection and myotomy; if there is persistent elevation of CO 2 on ETCO 2 , the flow is switched to ultralow. There is also continuous communication with the anesthesia team and the respiratory rate is also increased to decrease the CO 2 . When there is persistent CO 2 elevation along with elevated peak pressure despite the aforementioned measures, the neck, chest and abdomen are examined to look for signs of CO 2 extravasation at those sites. When there is significant abdominal distention, suctioning of the stomach is performed using the endoscope, and then percutaneous needle decompression of pneumoperitoneum is carried out with a 14G needle to decrease the level of CO 2 on ETCO 2 . If there is persistent elevation of CO 2 , the procedure is temporarily stopped until the CO 2 on ETCO 2 drops below 40 mm Hg. After the myotomy is performed, the tunnel can be lavaged with diluted gentamycin on a case-by-case basis. Finally, the tunnel is closed using endoscopic clips or endoscopic suturing.
Patients are extubated post procedure and recover in the postprocedure area of the endoscopy unit. Most of our patients are admitted to the hospital 1 night for observation and kept NPO until a gastrografin esophagram is performed the next day to rule out contrast extravasation. After a negative study, a clear liquid diet is started and if the diet is tolerated, patients are discharged home on antibiotics to complete 5 days of treatment. High-dose PPI and antiemetics are continued on discharge. Patients continue a clear liquid diet for 3 days, and then transition to a full liquid diet for another 3 days and then a soft diet, which is advanced as tolerated.
Statistical analysis
Data were captured in a registry (NCT05051358) deemed exempt by WCG IRB (February 17, 2021).
Information on demographics, procedural details, post-procedure outcomes, and adverse events (AEs) was collected and compared. Results are reported as mean ± standard deviation (SD) or median (range) for quantitative variables and percentages for categorical variables. The difference in procedure time, anesthesia time as well as AEs were reported in both groups. Significant associations were defined as P < 0.05.
We calculated Pearson correlation coefficient (PCC) and Spearman’s Rho to calculate the correlation between PaCO 2 and ETCO 2 . PaCO 2 plus ETCO 2 were measured in 32 patients (invasive group) and ETCO 2 only in 39 matched patients (noninvasive group).
Two-sided P < 0.05 were considered statistically significant. All descriptive and statistical analyses were conducted using MedCalc V18.9 (MedCalc Software, Ostend, Belgium).
Results
Both groups had similar demographics and there were no significant differences in age, length of myotomy, subtype of achalasia or severe tortuosity when comparing the groups ( Table 1 ). The average procedure time (scope in and out) was increased 17.7 minutes ( P = 0.04) in the invasive monitoring group ( Table 2 ). Anesthesia duration was increased 46.3 minutes in addition to endoscopy time in the invasive monitoring group ( P ≤ 0.00001). Within the PaCO 2 group, the average difference between PaCO 2 and ETCO 2 was 3.39 mm Hg (Median 3, SD 3.5), within the 2– to 5-mm Hg range ( Fig. 1 ). The Frequency of ETCO 2 monitoring in the two groups was not significantly different ( P = 0.74). PaCO 2 and ETCO 2 were strongly correlated in patients undergoing POEM, PCC R value: 0.8787 P ≤ 0.00001, Spearman’s Rho R value: 0.8775, P ≤ 0.00001.
Table 1. Demographics of both groups, PaCO 2 plus ETCO 2 and ETCO 2 only.
| Groups | PaCO 2 + ETCO 2 group | ETCO 2 only group | ||||
| Cases | N = 32 | N = 39 | ||||
| Males/females | 14/18 (44 %/56 %) | 15/24 (38 %/62 %) | ||||
| Age (standard deviation) | 54.41 mean (16.04) | 58.6 mean (19.44) | ||||
| Esophageal myotomy | 13 cm mean | 13 cm mean | ||||
| Gastric myotomy | 3 cm mean | 3 cm mean | ||||
| Achalasia subtypes | I n = 10 (31 %) | II n = 17 (53 %) | III n = 5 (16 %) | I n = 12 (31 %) | II n = 21 (54 %) | III n = 6 (15 %) |
| Severe tortuosity/sigmoid esophagus | 3 % | 5 % | ||||
PaCO 2 , partial pressure of CO 2 , ETCO 2 , end tidal CO 2 .
Table 2. Comparison between both groups, PaCO 2 plus ETCO 2 and ETCO 2 only.
| Groups | PaCO 2 + ETCO 2 group | ETCO 2 only group | P value | ||||
| Cases | N = 32 | N = 39 | |||||
| Males/females | 14/18 | 15/24 | |||||
| Average | Median (range) | SD | Average | Median (range) | SD | ||
| Procedure time in minutes (scope in and out) | 96.7 | 80 (50 to 291) | 50.7 | 79 | 70 (22–172) | 33.2 | 0.04 |
| Age | 54.41 | 58 (22–88) | 16.04 | 58.6 | 63 (18–94) | 19.44 | 0.33 |
| pH | 7.37 | 7.38 (7.22 to 7.5) | 0.064 | N/A | N/A | N/A | |
| PaCO 2 (mm Hg) | 41.23 | 41 (26 to 64) | 7.3 | N/A | N/A | N/A | |
| PaCO 2 frequency in minutes | Every 28 | Every 27 (14.5 to 56) | 7.8 | N/A | N/A | N/A | |
| ETCO 2 (mm Hg) | 37.8 | 38 (26 to 60) | 5.6 | 36.7 | 37 (27 to 48) | 4.21 | 0.27 |
| ETCO 2 frequency in minutes | Every 12.3 | Every 11.6 (4.9 to 29.2) | 4.9 | Every 11.9 | Every 12.8 (3 to 14.5) | 3.6 | 0.74 |
| Adverse event | 13 % (3 hand hematoma,1 nerve injury) | 3 % (1 pneumothorax 1 ) | 0.24 | ||||
PaCO 2 , partial pressure of CO 2 , ETCO 2 , end tidal CO 2 ; SD, standard deviation; N/A, not applicable.
Inadvertent use of air instead of CO 2 during the procedure.
Fig. 1.
Correlation between PaCO 2 and ETCO 2 .
There were no differences between the groups in AEs (13 % vs 3 % P = 0.24). AEs included three hematomas and one nerve injury related to arterial line placement in the invasive group and one pneumothorax due to inadvertent air insufflation in the noninvasive group. The episode of pneumothorax in the noninvasive group was caused by inadvertent use of air instead of CO 2 insufflation, and required stopping the procedure as well as chest tube placement. After the pneumothorax resolved the patient decided not to pursue another procedure.
The three hematomas in the invasive group were managed conservatively while the patient with nerve injury is undergoing ambulatory physiotherapy.
Discussion
Appropriate distention is required for good visibility during endoscopy. Initially air was being used for insufflation during endoscopy and in the 1970 s, it was discovered that use of electrosurgical instruments during air insufflation could lead to a fatal explosion in the bowels and barotrauma, 11 . CO 2 happens to be less expensive and more rapidly absorbed than regular air, because CO 2 is absorbed 160 times faster than nitrogen and 12 times faster than oxygen, the two main components of air. After being absorbed, the CO 2 is transported by the blood to the lungs and then exhaled 12 .
POEM involves the creation of a tunnel across the submucosal space with frequent exposure of the mediastinum. The most common AEs associated with POEM are related to excess insufflation, including pneumomediastinum, pneumothorax, pneumoperitoneum, and subcutaneous emphysema because endoscopically insufflated gas may be inadvertently absorbed into surrounding tissues, compromising cardiorespiratory function. According to prior studies, insufflation-related AEs are quite variable in incidence, ranging from 7.5 % to 55.5 % 13 14 15 16 17 .
Initial studies of POEM showed that use of CO 2 was associated with less risk of insufflation-related complications when compared to air, and although its use did not completely eliminate the risk, it was decreased substantially 18 19 . The use of general anesthesia also facilitates achievement of positive intrathoracic pressure and decreases risk of mediastinal emphysema 20 .
CO 2 plays various roles in the human body, including regulation of blood pH, respiratory drive, and affinity of hemoglobin for oxygen; therefore, CO 2 levels should be closely monitored to maintain them under 45 mm Hg 13 21 . It is estimated that partial pressure of CO 2 (PaCO 2 ) is 2 to 5 mm Hg higher than ETCO 2 22 23 , and the recommended level of ETCO 2 during POEM is approximately 40 mm Hg. Another parameter to consider is the peak inspiratory pressure or P max ; elevated peak pressure ( > 38 cm H 2 0 or 20 % above the baseline) along with abdominal distention could represent increased abdominal pressure, and the need for percutaneous needle decompression of pneumoperitoneum 21 24 .
Previous studies have demonstrated the adequacy of ETCO 2 to evaluate hypercapnia and monitor ventilation during anesthesia because it is continuous and noninvasive 7 8 22 25 26 .
This prospective comparative study confirmed that, among patients undergoing POEM, ETCO 2 correlates strongly with PaCO 2 with an average difference that is within the expected 2- to 5-mm Hg range as reported in studies in non-POEM patients 22 23 . The gradient between ETCO 2 and PaCO 2 is directly proportional to the degree of physiologic dead space 27 28 29 . Although the typical alveolar CO 2 concentration is slightly greater than PaCO 2 , ETCO 2 is normally 2 to 5 mm Hg lower than PaCO 2 due to mixing of CO 2 -containing alveolar gas with exhaled gas devoid of CO 2 from the anatomical dead space. As a result, ETCO 2 levels are maintained in a normal physiologic range (30–40 mm Hg), corresponding to a PaCO 2 range of 35 to 45 21 22 23 . Because the observed average difference in ETCO 2 and PaCO 2 in our study was within the 2– to 5-mm Hg range, ETCO 2 can be used as a noninvasive surrogate measure for PaCO 2 in patients undergoing POEM. In patients with concurrent lung disease, the reliability of ETCO 2 can be compromised because the 2- to 5-mm Hg gradient can increase with any increase in the dead space volume; indeed, the addition of alveolar dead space further dilutes ETCO 2 relative to PaCO 2 . In such patients, endoscopists should exercise caution because the same ETCO 2 values may reflect greater PaCO 2 values, and thus, increased risk of hypercapnia-related complications 7 8 .
Although it is recognized that POEM poses unique anesthesia-related challenges, standardized management has yet to be established and the necessity for arterial line placement has not previously been investigated. In our study, there was no significant difference in AEs between the invasive and noninvasive groups, suggesting that using ETCO 2 as a safe surrogate measure for PaCO 2 allows for prompt recognition and response to emergent hypercapnia-related complications. While there was an instance of pneumothorax in the noninvasive group due to use of air for insufflation instead of CO 2 , it was inadvertent and not due to using ETCO 2 as a surrogate measure for PaCO 2 . However, compared to POEM procedures performed in the invasive group, those performed in the noninvasive group had a significantly shorter mean procedure time and anesthesia duration. Longer procedure times and anesthesia durations among the invasive group due to the placement of an arterial line may increase the risk of complications. In our study, the widespread placement of arterial line was associated with an increased incidence of hematoma and nerve injuries.
A retrospective case series review by Loser et al demonstrated that insufflation-related cardiorespiratory responses are likely inevitable during POEM. The cardiorespiratory response tends to include an increased peak inspiratory pressure, ETCO 2 levels, mean arterial pressures, and heart rate 24 . The goal of periprocedural monitoring is to identify abnormalities at an early stage to prevent or mitigate harm to the patient 7 . Previous studies have reported the safety of ETCO 2 during POEM 13 21 24 . Our study has several strengths, including being the first to compare invasive versus noninvasive CO 2 monitoring in patients undergoing POEM, demonstrating that ETCO 2 correlates strongly with PaCO 2 and should be used as a surrogate of PaCO 2 in patients undergoing POEM, and universal PaCO 2 monitoring contributes to increased duration of anesthesia, as well as total procedure and turnover time.
Conclusions
In conclusion, POEM is a relatively new procedure, continuously evolving. It has unique perioperative aspects that need to be understood by the team performing the procedure, which includes the endoscopist, the anesthesiologist, anesthetist, perioperative nurses and endoscopy technician.
One of the limitations of our study is that it was not randomized. However, it demonstrates the viability of ETCO 2 as a surrogate measure for PaCO 2 , allowing recognition of CO 2 -related complications without the need for arterial line placement during the POEM procedure. Invasive CO 2 monitoring with an arterial line should be performed in patients with major cardiopulmonary comorbidities on a case-by-case basis.
Competing interests Dr. Tyberg is a consultant for Ninepoint Medical, Endogastric Solutions, and Obalon Therapeutics. Dr. Sarkar has done consulting work for US Endoscopy and Obalon Therapeutics. Dr. Shahid has done consulting work for US Endoscopy. Dr. Kahaleh has received grant support from Boston Scientific, Fujinon, W.L. Gore, Apollo Endosurgery, Cook Endoscopy, GI Dynamics, Merit Medical, Interscope Med, Olympus, ERBE, and MI Tech. He is a consultant for Boston Scientific and Laboratories Inc., AbbVie. None of that funding was related to this paper. Dr. Gaidhane is a consultant for 3 D Matrix.
Digestive Disease Week: This study was presented as an abstract during DDW 2022
References
- 1.Inoue H, Shiwaku H, Iwakiri K et al. Clinical practice guidelines for peroral endoscopic myotomy. Dig Endosc. 2018;30:563–579. doi: 10.1111/den.13239. [DOI] [PubMed] [Google Scholar]
- 2.Zaninotto G, Bennett C, Boeckxstaens G. The 2018 ISDE achalasia guidelines. Dis Esophagus. 2018;31 doi: 10.1093/dote/doy071. [DOI] [PubMed] [Google Scholar]
- 3.Inoue H, Minami H, Kobayashi Y et al. Peroral endoscopic myotomy (POEM) for esophageal achalasia. Endoscopy. 2010;42:265–271. doi: 10.1055/s-0029-1244080. [DOI] [PubMed] [Google Scholar]
- 4.Weusten B, Barret M, Bredenoord A J et al. Endoscopic management of gastrointestinal motility disorders – part 1: European Society of Gastrointestinal Endoscopy (ESGE) Guideline. Endoscopy. 2020;52:498–515. doi: 10.1055/a-1160-5549. [DOI] [PubMed] [Google Scholar]
- 5.Bapaye A, Korrapati S K, Dharamsi S et al. Third space endoscopy: lessons learnt from a decade of submucosal endoscopy. J Clin Gastroenterol. 2020;54:114–129. doi: 10.1097/MCG.0000000000001296. [DOI] [PubMed] [Google Scholar]
- 6.Yamashita-Ichimura M, Toyama E, Sasoh M et al. Bladder pressure monitoring and CO2 gas-related adverse events during per-oral endoscopic myotomy. J Clin Monit Comput. 2018;32:1111–1116. doi: 10.1007/s10877-018-0122-7. [DOI] [PubMed] [Google Scholar]
- 7.Rackley C R. Monitoring during mechanical ventilation. Respir Care. 2020;65:832–846. doi: 10.4187/respcare.07812. [DOI] [PubMed] [Google Scholar]
- 8.Ortega R, Connor C, Kim S et al. Monitoring ventilation with capnography. N Engl J Med. 2012;367:e27. doi: 10.1056/NEJMvcm1105237. [DOI] [PubMed] [Google Scholar]
- 9.Sbaraglia F, Familiari P, Maiellare F. Pediatric anesthesia and achalasia: 10 years’ experience in peroral endoscopy myotomy management. J Anesth Analg Crit Care. 2022 doi: 10.1186/s44158-022-00054-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Tanaka E, Murata H, Minami H et al. Anesthetic management of peroral endoscopic myotomy for esophageal achalasia: a retrospective case series. J Anesth. 2014;28:456–459. doi: 10.1007/s00540-013-1735-0. [DOI] [PubMed] [Google Scholar]
- 11.Williams C B. Who's for CO2? Gastrointest Endosc. 1986;32:365–367. doi: 10.1016/s0016-5107(86)71891-9. [DOI] [PubMed] [Google Scholar]
- 12.Bretthauer M, Kalager M, Adami H O et al. Who is for CO2? Slow adoption of carbon dioxide insufflation in colonoscopy. Ann Intern Med. 2016;165:145–146. doi: 10.7326/M16-0209. [DOI] [PubMed] [Google Scholar]
- 13.Darisetty S, Nabi Z, Ramchandani M et al. Anesthesia in per-oral endoscopic myotomy: A large tertiary care centre experience. Indian J Gastroenterol. 2017;36:305–312. doi: 10.1007/s12664-017-0782-0. [DOI] [PubMed] [Google Scholar]
- 14.Akintoye E, Kumar N, Obaitan I et al. Peroral endoscopic myotomy: a meta-analysis. Endoscopy. 2016;48:1059–1068. doi: 10.1055/s-0042-114426. [DOI] [PubMed] [Google Scholar]
- 15.Ren Z, Zhong Y, Zhou P et al. Perioperative management and treatment for complications during and after peroral endoscopic myotomy (POEM) for esophageal achalasia (EA) (data from 119 cases) Surg Endosc. 2012;26:3267–3272. doi: 10.1007/s00464-012-2336-y. [DOI] [PubMed] [Google Scholar]
- 16.Jayan N, Jacob J S, Mathew M et al. Anesthesia for peroral endoscopic myotomy: A retrospective case series. J Anaesthesiol Clin Pharmacol. 2016;32:379–381. doi: 10.4103/0970-9185.188829. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17.Talukdar R, Inoue H, Nageshwar Reddy D. Efficacy of peroral endoscopic myotomy (POEM) in the treatment of achalasia: a systematic review and meta-analysis. Surg Endosc. 2015;29:3030–3046. doi: 10.1007/s00464-014-4040-6. [DOI] [PubMed] [Google Scholar]
- 18.Cai M Y, Zhou P H, Yao L Q et al. Thoracic CT after peroral endoscopic myotomy for the treatment of achalasia. Gastrointest Endosc. 2014;80:1046–1055. doi: 10.1016/j.gie.2014.05.004. [DOI] [PubMed] [Google Scholar]
- 19.Zhang X C, Li Q L, Xu M D et al. Major perioperative adverse events of peroral endoscopic myotomy: a systematic 5-year analysis. Endoscopy. 2016;48:967–978. doi: 10.1055/s-0042-110397. [DOI] [PubMed] [Google Scholar]
- 20.Bang Y S, Park C. Anesthetic consideration for peroral endoscopic myotomy. Clin Endosc. 2019;52:549–555. doi: 10.5946/ce.2019.033. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Yang D, Pannu D, Zhang Q et al. Evaluation of anesthesia management, feasibility and efficacy of peroral endoscopic myotomy (POEM) for achalasia performed in the endoscopy unit. Endosc Int Open. 2015;3:E289–E295. doi: 10.1055/s-0034-1391965. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 22.Razi E, Moosavi G A, Omidi K et al. Correlation of end-tidal carbon dioxide with arterial carbon dioxide in mechanically ventilated patients. Arch Trauma Res. 2012;1:58–62. doi: 10.5812/atr.6444. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23.Sullivan K J, Kissoon N, Goodwin S R.End-tidal carbon dioxide monitoring in pediatric emergencies Pediatr Emerg Care 200521327–332.quiz 333–325 [DOI] [PubMed] [Google Scholar]
- 24.Loser B, Werner Y B, Punke M A et al. Anesthetic considerations for patients with esophageal achalasia undergoing peroral endoscopic myotomy: a retrospective case series review. Can J Anaesth. 2017;64:480–488. doi: 10.1007/s12630-017-0820-5. [DOI] [PubMed] [Google Scholar]
- 25.Fujimoto S, Suzuki M, Sakamoto K et al. Comparison of End-Tidal, Arterial, Venous, and Transcutaneous PCO2. Respir Care. 2019;64:1208–1214. doi: 10.4187/respcare.06094. [DOI] [PubMed] [Google Scholar]
- 26.Gaur P, Harde M, Gujjar P et al. A study of partial pressure of arterial carbon dioxide and end-tidal carbon dioxide correlation in intraoperative and postoperative period in neurosurgical patients. Asian J Neurosurg. 2017;12:475–482. doi: 10.4103/1793-5482.180959. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27.Yamanaka M K, Sue D Y. Comparison of arterial-end-tidal PCO2 difference and dead space/tidal volume ratio in respiratory failure. Chest. 1987;92:832–835. doi: 10.1378/chest.92.5.832. [DOI] [PubMed] [Google Scholar]
- 28.Fletcher R. The arterial-end-tidal CO2 difference during cardiothoracic surgery. J Cardiothorac Anesth. 1990;4:105–117. doi: 10.1016/0888-6296(90)90457-q. [DOI] [PubMed] [Google Scholar]
- 29.Burrows F A. Physiologic dead space, venous admixture, and the arterial to end-tidal carbon dioxide difference in infants and children undergoing cardiac surgery. Anesthesiology. 1989;70:219–225. doi: 10.1097/00000542-198902000-00007. [DOI] [PubMed] [Google Scholar]