Original Article

Safety of Microstream Capnography Monitoring in Patients Under Sedation for Colonoscopy


  • Sibel Oba
  • Hacer Şebnem Türk
  • Canan Tülay Işıl
  • Pınar Sayın
  • Leyla Kılınç

Received Date: 10.10.2018 Accepted Date: 03.12.2018 Med Bull Haseki 2019;57(3):232-239


The purpose of this study was to investigate the effectiveness of micro stream capnography in early recognition of adverse events during sedation for colonoscopy.


This prospective randomized study was performed implemented on 82 adults scheduled for elective colonoscopy. SpO2, ETCO2 and integrated pulmonary index (IPI) values were measured with the use of micro stream capnography and recorded. Arterial blood gas samples were taken at the beginning, 10th minute and end of the procedure and analyzed.


The correlation between mean values of IPI and mean values of ETCO2, SpO2 and PaCO2 was not statistically significant. There was a statistically significant correlation between IPI value at the beginning and PaCO2 value at the end of the procedure. Correlation of IPI value at the 10th minute with SpO2 at the 10th minute and SPO2 value at the end of the procedure was statistically significant.


Non-invasive ETCO2 monitoring with micro stream capnography is correlated with PaCO2 values in arterial blood gas analysis, which is useful for monitoring of sedation and hypoventilation during colonoscopy procedures. However, IPI monitoring is not of clinical benefit to early recognition of hypoventilation. Non-invasive ETCO2 monitoring with micro stream capnography should be a part of routine monitoring for safe anesthetic practice outside the operating room.

Keywords: Capnography, EndCO2, IPI, micro stream, PaCO2


Recently, sedation for colonoscopy has become a frequent anesthetic practice. Possible hypoxic episodes due to sedation are monitored with pulse-oxymeter saturation (SpO2) and respiratory depression or apnea is detected with SpO2 measurement. However, the quality of ventilation monitoring is not satisfactory in patients receiving sedation (1). Carbon dioxide (CO2) measurements, which can be analysed via arterial blood gas sampling correctly, are the best method to assess alveolar ventilation. However, it is difficult to take several arterial blood samples and biochemically analyse them during a short procedure such as colonoscopy. Therefore, the end-tidal carbon dioxide (ETCO2) monitoring has become the favorite method of carbon dioxide monitoring. It is a continuous and non-invasive method of measuring CO2. Capnographs are indispensable for expiratory carbon dioxide measurements in the operation theaters. However, these monitors can measure ETCO2 only in intubated patients. Thus, various devices have been developed for monitoring ETCO2 non-invasively in spontaneously breathing patients (2,3).

Micro stream capnograph is a medical device providing continuous monitoring of ETCO2 non-invasively through a nasal sampling line at the patient’s bedside (4,5). Micro stream monitor can also assess the Integrated Pulmonary Index (IPI) value which is a mathematically determined factor based on parameters of capnography (ETCO2, respiratory rate) and pulse oximetry (pulse rate and SpO2). Previously, reliability of this device was studied in critically ill patients with spontaneous breathing, and non-invasive ETCO2 was found to be correlated with arterial blood gas analyses (6,7).

Patients presenting for gastrointestinal endoscopy under sedation may have a high-risk profile and despite many studies to increase the safety of endoscopic procedures, mortality and morbidity associated with cardiopulmonary complications during endoscopic procedures remain a challenge.

In this study, we aimed to investigate the efficacy of micro stream capnography for early recognition of adverse events in patients under sedation for colonoscopy. We assessed the correlation between non-invasive ETCO2 measurement and arterial blood gas analyses and the correlation of IPI with ETCO2, SPO2 and PaCO2.


After obtaining approval from the Local Ethics Committee of Şisli Etfal Training and Research Hospital (03.03.2015/883) and verbal and written informed consent from all patients, this prospective randomized study was performed in the gastrointestinal endoscopy unit at our hospital between March and September 2015.

A total of 100 adults aged >18 years, graded as American Society of Anesthesiologists physical status (ASA) I-III, and scheduled for elective colonoscopy were included in the study. Those, who did not want to participate, children, pregnant women, patients with severe cardiac or respiratory insufficiency, neuropsychiatric disorders, alcohol or drug addiction, allergy to anesthetics, peripheral vascular diseases or airway deformities, were excluded from the study.

All patients were inserted an 18-gauge intravenous catheter. No premedication was used. In the procedure room, the patient was placed in the lateral decubitus position. Standard monitoring with electrocardiography, non-invasive systemic blood pressure and pulse oxymeter (SPO2) was done and heart rate (HR), mean arterial blood pressure (MABP) and SPO2 values at the baseline were recorded. A nasal sample line (Nasal FilterLine™, Covidien, Colorado, USA) was placed; ETCO2 and respiratory rate (RR) and IPI were measured and recorded with a microstream monitor (CapnoStream™, Covidien, Colorado, U.S.A.). Bispectral Index (BIS) monitoring (BIS monitor™, Covidien, Colorado, U.S.A.) was also performed and baseline value was recorded.

All patients received standard anesthetic induction with 1 µg.kg-1 fentanyl (Talinat® 0.5 mg/10 mL ampule, VEM, İstanbul, Turkey) and 1.0 mg.kg-1 propofol (Propofol® 1% 10 mL ampule, Fresenius, Uppsala, Sweden). During the procedure, all patients were given additional 0.5 mg.kg-1 dose of propofol, when necessary, to maintain the Ramsey Sedation Score (RSS) between 3 and 4.

Immediately after sedation a radial arterial cannula was inserted. Beginning arterial blood gas sample was taken and analysed at the beginning of the procedure. Two more samples were taken at the 10th minute and at the end of the procedure. pH, PaO2, PaCO2, SO2, HCO3 and base excess values were recorded. HR, MABP, SPO2, RSS, BIS, ETCO2, IPI and RR were recorded synchronously with arterial blood gas samplings. The correlation of IPI values with patient status are shown in Table 1.

Oxygen insufflation was done with oxygen flowing at 2 L/min via nasal prongs in patients with a SPO2<90% and these patients were recorded.

Anesthesia time was the time from anesthetic induction to recovery. Endoscopy time was defined as the time from endoscopy start to endoscopy completion. Recovery time was the time from the end of endoscopy until patient’s recovery to RSS 2.

Patients who achieved an Aldrete score of 9 were discharged.

The total propofol dose was calculated and recorded. Allergic reactions, which were observed during the procedure, bradycardia (HR<50 beats per min), tachycardia (20% increase in HR), hypotension (MABP <60 mmHg), hypertension (20% increase in MABP), respiratory depression, desaturation (SPO2<90%), hypoventilation (>20% reduction in ETCO2 compared with baseline value), nausea, vomiting, hemorrhage and perforation were recorded.


A total of 82 patients were included in this study. Fail arterial cannulation, clotted blood sample and discontinuation of colonoscopy due to inadequate colon cleansing were the reasons for exclusion of 18 patients.

The male-to-female ratio was 42/40; 34 patients were graded as ASA I, 36 patients - ASA II and 12 patients - ASA III. Demographic characteristics of the patients are shown in Table 2.

Variations in HR, SpO2, MABP and ETCO2 at three times analysis were statistically significant (p<0.001). ETCO2 measurements at the 10th minute and end of the procedure were statistically significantly higher compared to that at the beginning of the procedure (p=0.002) (p=0.005). There was no statistically significant difference between ETCO2 measurements at the 10th minute and end of the procedure (p=0.416). IPI values at the beginning, 10th minute and at the end of the procedure were not statistically different (p=0.152).

Bispectral index (BIS) value was statistically significantly decreased at the 10th minute and end of the procedure compared to that at the beginning of the procedure (p<0.001)
(Table 3).

RSS scores were statistically significantly different than the baseline values (p<0.001). There was no statistically significant difference between baseline and 10th minute RSS scores and between RSS scores at the10th minute and end of the procedure. There was a statistically significant difference between baseline RSS score and that at the end of the procedure (p=0.001).

Correlations in pH, PaO2, PaCO2, HCO3 and SpO2 were statistically significant (Table 4).

No statistically significant difference was determined in PaCO2 and ETCO2 between all measurements (Table 5).

The correlation between the mean IPI value and the mean ETCO2, SpO2 and PaCO2 values was not statistically significant (Table 6).

There was a statistically significant correlation between baseline IPI value and PaCO2 value at the end of the procedure; IPI value at the 10th minute and SpO2 value at the 10th minute; IPI value at the 10th minute and SPO2 value at the end of the procedure (Table 7).

Desaturation was observed in three patients and treated with oxygen supplement. Hypotension was observed in nine patients; five patients received fluid and ephedrine intravenously and four patients received fluid replacement. Bradycardia was observed in the presence of hypotension. ETCO2 measurement revealed hypoventilation in nine patients while IPI levels under 7 were recorded in four patients. Arterial blood gas PaCO2 showed hypoventilation in 13 patients. Complication associated with the procedure was not observed in any patient.

Statistical Analysis

For statistical analysis, NCSS (Number Cruncher Statistical System) 2007 (Kaysville, Utah, USA) program was used. Study data was evaluated with descriptive statistical methods (mean, standard deviation, median, frequency, percentage minimum, maximum). Quantitative data in normal distribution was compared with the repeated measures ANOVA. Correlation between the variables was evaluated with Pearson’s correlation coefficient. A p value of less than 0.01 or 0.05 was considered statistically significant.


Recently ETCO2 measuring has become a part of routine monitoring and capnographs are commonly used in operation theaters and intensive care units (7-9). Capnographic monitoring also prevents redundant blood gas analyses, thus reduces unnecessary costs (9).

Non-invasive devices have been developed to monitor ETCO2 values in spontaneously breathing patients. These are usually used in intensive care units to monitor ETCO2 in patients receiving non-invasive mechanical ventilation (10-12). One of them is micro stream capnography, which measures ETCO2 and IPI values through a nasal cannula (6).

Sedation is given in the endoscopy units for gastroscopy and colonoscopy procedures and patient’s recovery is usually monitored with SpO2 (8). ETCO2, which is the most important value in assessing ventilation, is not monitored routinely during sedation. Most recent guidelines do not recommend a routine use of capnography during endoscopic sedation (6). Anesthesia outside the operating room is difficult to practice. To make anesthetic procedures safer, some questions need to be answered: Should ETCO2 routinely be monitored? To what degree are the measurements correlated with arterial blood gas analyses? Is IPI value is predictive of hypoventilation? In this study, the answers to these questions were investigated on patients monitored with micro stream capnograph during colonoscopy.

Arterial blood gas analyses in endoscopic procedures with or without sedation to evaluate oxygenation and ventilation showed no variations in PaCO2 values in patients under sedation, but a decrease in PaO2 values. This decrease was of short duration and recovered to the baseline value. In the literature all studies were conducted in upper gastrointestinal system endoscopy and under benzodiazepine sedation (13-15). However, propofol is commonly used for sedation in colonoscopy procedures today. However, propofol has respiratory depressant effects (16).

Despite increasing efforts to increase the safety of endoscopic procedures, mortality and morbidity associated with cardiopulmonary complications during endoscopic procedures remain a challenge. In this study, we measured ETCO2  and IPI values with micro stream capnography, which has advanced technology and works even with very low tidal volumes such as 50 mL without trapping moisture and water. We aimed to investigate the safety of endoscopic procedures monitored by micro stream capnography.

There have been different studies examining the efficiency of micro stream capnography conducted in different age groups and intubated and extubated patients (10,17,18).

There are few studies in the literature investigating ETCO2 measurements with microstream during endoscopic procedures. These studies were mostly conducted on patients who underwent upper gastrointestinal endoscopy (4,5,11).

In their study including 163 children undergoing 174 elective gastroinstestinal procedures, Lightdale et al. (11) randomized the patients to micro stream capnography and control groups. Endoscopy staff, who were blinded to additional capnography monitoring, reported poor ventilation in 3% of all procedures and no apnea, whereas capnography indicated alveolar hypoventilation and apnea during 56% and 24% of the procedures, respectively. The researchers concluded that sedation for endoscopy was safer with capnograph monitoring.

Yarchi et al. (4) measured ETCO2 with the micro stream capnography in patients who received either general anesthesia or sedation for endoscopic procedures and underlined the importance of ETCO2 monitoring especially in upper gastrointestinal procedures under general anesthesia.

Qadeer et al. (5) monitored ETCO2 with the micro stream capnography in patients undergoing endoscopic retrograde cholangiopancreatograpy and endoscopic ultrasonography. They concluded that capnography monitoring improves patient safety during procedural sedation for endoscopy by reducing the frequency of respiratory depression.

Kugelman et al. (17) assessed correlation of capnographic ETCO2 measured with micro stream and arterial blood gas PaCO2 in premature infants ventilated with high frequency ventilation. The study results indicated correlation and feasibility of microstream capnography.

Casati et al. (10) conducted a similar study in adults, who underwent orthopedic or vascular surgery under general anesthesia, and compared ETCO2 and PaCO2 between intubated ventilated and spontaneously breathing non-intubated patients. The ETCO2 and PaCO2 values showed a perfect correlation in both groups as no significant difference was observed in ETCO2 and PaCO2 between intubated (7.3±4 mmHg) and non-intubated (6.5±4.8 mmHg) patients. Micro stream capnographical ETCO2 showed a closer correlation to PaCO2 in spontaneously breathing non-intubated patients. In our study this difference was 5.22±4.26 mmHg at the beginning, 5.25±4.98 mmHg at the 10th minute and 5.13±3.85 mmHg at the end of sedation in our spontaneously breathing non-intubated patients. These data were not statistically significantly different, which indicates safety of ETCO2 monitoring with micro stream capnography.

Singh et al. (19) reported microstream capnograph monitoring also to be easy to use during interhospital transport of intubated critically ill children, because the monitor had low weight, long battery life, audiovisual alarms, quantitative and graphic real-time detection of ETCO2 (20). Besides, micro stream capnography monitoring was also safe in confirming proper endotracheal tube positioning. Our study was realized outside the operating room. This is why easy transport of the monitor and also easy usage were very important.

A small number of studies reported that accurate ETCO2 measurements could not be done in non-intubated patients who received general anesthesia (21-22).

Cheng et al. (22) compared patients receiving general anesthesia with controlled ventilation and patients receiving total intravenous anesthesia with spontaneous breathing through the normal airway during gynecologic laparoscopic surgery and recorded ETCO2 and PaCO2 values at different time intervals and positions. ETCO2 was sampled through a suction catheter inserted into the nasopharynx. The results of this study showed that ETCO2 and PaCO2 values were correlated during the first 20 minutes after the change to the Trendelenburg position, but afterwards, PaCO2 monitoring was still necessary. This study indicated that patient’s position during capnographic monitoring may be important. In our study, we had relatively precise correlation between the measurements. This may be a result of a lateral decubitis position given to all patients. However, ETCO2 sampling and monitoring should also be considered. We used a nasal sampling line belonging to the microstream capnograph monitor, which may also be helpful to achieve precise measurements.

Bower et al. (23) evaluated sedation depth during endoscopic procedures by measuring BIS and Observer’s Assessment of Alertness/Sedation which were correlated to each other. A BIS level near 82 was sufficient for sedation. BIS monitoring can inform the anesthesiologist about the patient’s sedation status objectively. In our study, we evaluated the sedation depth using both the RSS and BIS. The mean RSS score was 4 and BIS was 60.7±6.44. Our sedation depth was quite sufficient for colonoscopical examination and the colonoscopist was satisfied.

IPI was presented as a factor combining the best of all monitoring techniques to based on parameters of capnography and pulse oximetry. The use of IPI in monitoring patients under sedation was questioned in recent studies. In their study, Berkenstandt et al. (24) observed only a limited agreement between respiratory physiological parameters and IPI. Riphaus et al. (6) evaluated clinical value of IPI during sedation for interventional upper GI-endoscopy and concluded that IPI monitoring does not add significant clinical benefit to standard monitoring. On the contrary, Garah et al. (25) in their study on 109 pediatric patients undergoing mainly upper endoscopy under sedation found that IPI had a high sensitivity in predicting apnea episodes and hypoxia events. In our study, IPI values were correlated with ETCO2, SpO2 and PaCO2 values.

In our study, desaturation was observed in three patients. These patients were treated with oxygen supplement. Micro stream capnography was useful in detection of hypoventilation in nine patients. We observed that an IPI of <7 in four of our patients correlated with 10th minute SpO2 values. We believe that desaturation was rarely observed in our patients in comparison with hypoventilation because of short duration of sedation. In case of long duration of anesthesia outside the operating room, hypoventilation may occur more frequently. In such patients, the use of micro stream capnography may play an important role in preventing and decreasing hypoxic events. In our study, IPI monitoring did not add a clinical benefit to early recognition of hypoventilation.


In conclusion, even if IPI monitoring does not add a clinical benefit to early recognition of hypoventilation, we believe that non-invasive ETCO2 monitoring with micro stream capnography is useful for monitoring sedation and hypoventilation during colonoscopy procedures and it was found to be well correlated with PaCO2 values in arterial blood gas sampling. This study shows that non-invasive ETCO2 monitoring with micro stream capnography should be a part of routine monitoring for safe anesthetic practice outside the operating room.


The authors thank all the members of the endoscopy unit team for their support.

Authorship Contributions

Surgical and Medical Practices: S.O., H.Ş.T., C.T.I., P.S., L.K. Concept: S.O., H.Ş.T., C.T.I., P.S., L.K. Design: S.O., H.Ş.T., C.T.I., P.S., L.K. Data Collection or Processing: S.O., H.Ş.T., C.T.I., P.S., L.K. Analysis or Interpretation: S.O., H.Ş.T., C.T.I., P.S., L.K. Literature Search: S.O., H.Ş.T., C.T.I., P.S., L.K. Writing: S.O., H.Ş.T., C.T.I., P.S., L.K.

Conflict of Interest: No conflict of interest was declared by the authors.

Financial Disclosure: The authors declared that this study received no financial support.

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