Validation of Novel Completely Sealed Nasal Positive Airway Pressure Device: SuperNO₂VA™ EtCO₂ Measurement and Pressure Test Performance

Michael J. Pedro¹, Steven H. Cataldo²

¹Vyaire Medical Inc., Mettawa, IL, USA.
²CareMount Medical, PC, Mount Kisco, New York, USA.

DOI: 10.4236/ojanes.2020.1010030                

Abstract

Background: SuperNO₂VA^™ Et Nasal Mask (Vyaire Medical, Inc., United States) is a new nasal mask with an integrated sampling hood to capture exhaled gases and enable accurate measurements of end tidal carbon dioxide (EtCO₂). The authors hypothesized that the SuperNO₂VA Et design would measure EtCO₂ more accurately than a predicate EtCO₂ sampling line, the Smart CapnoLine^® Plus, Adult/Intermediate CO₂ Oral-Nasal Set (Medtronic, United States). Methods: A simulated patient setup enabled comparison of the accuracy of CO₂ measurements within the SuperNO₂VA Et and a predicate device for eight condition combinations of input CO₂; breath rate and tidal volume (VT); and O₂ flow rates. These tests were repeated with simulating Nasal Breathing and Oral Breathing. Results: Testing demonstrated that measurements of 1% and 5% input CO₂ within the SuperNO₂VA Et were accurate for a range of respiratory rates, VT, O₂ flows, and CO₂ concentrations. CO₂ measurement errors were significantly larger for the Oral-Nasal Set compared to the SuperNO₂VA Et for both 1% Input CO₂ (-0.12%vol vs. -0.01%vol, p = 0.0005) and 5% Input CO₂ (-0.93%vol vs. -0.08%vol, p < 0.0001). At 5% Input CO₂, eight of the 12 trials for the Oral-Nasal Set failed to meet the ISO accuracy specification, while all SuperNO₂VA Et measurements met the specification. The accuracy of CO₂ measurement within the SuperNO₂VA were not different for Oral and Nasal Breathing trials for both CO₂ concentration (1%: p = 0.33, 5%: p = 0.064). With the Oral-Nasal Set, CO₂ measurements were lower during Oral compared to Nasal Breathing (1%: p = 0.0005, 5%: p = 0.0091). Conclusions: Based on performance outcomes, use of the SuperNO₂VA Et offers significantly more accurate measurement of EtCO₂ than the predicate EtCO₂ sampling line. Measurements of EtCO₂ within the SuperNO₂VA Et are accurate over a range of CO₂, breathing rates, tidal volumes, and O₂ flows, as well as for nasal and oral breathing.

Keywords

Capnography, Sedation, Hypoxemia, Hypoventilation, Ventilation

1. Introduction

Moderate and deep sedation have long been associated with high rates of respiratory complications such as hypoxemia and hypoventilation [1] [2] [3]. These complications arise from sedation medications and inadequate monitoring that contribute to or cause upper airway obstruction (UAO), central respiratory depression, or both [1] [2] [3]. Ventilation monitoring and supplemental oxygenation can mitigate respiratory complications in both sedation settings.

1.1. Monitoring

Traditionally, pulse oximetry had enabled limited and indirect respiratory monitoring. Because such devices measure only peripheral oxygen saturation, their use created the potential for delaying complication detection, with possible subsequent health risks for the patient. For example, pulse oximetry is unable to directly detect hypoventilation or apnea, especially in patients undergoing procedural sedation while receiving supplemental oxygen [4] [5].

A superior monitoring approach involves the breath-to-breath measurement of the concentration of carbon dioxide (CO₂) in exhaled respiratory gas, which has gained ready acceptance, particularly with endorsement from the American Society of Anesthesiologists (ASA) for use of end-tidal capnography (EtCO₂) as a standard of care for moderate and deep procedural sedation [6] [7].

Although capnography has greater efficiency than pulse oximetry for effective detection of hypoventilation and apnea, accurate and consistent measurements of the EtCO₂ during minimally invasive procedures under deep sedation have historically been challenging [8]. This difficulty results from the capnography port of the nasal cannula being open to air, causing atmospheric gases to be entrained and sampled [9]. Additionally, delivery of supplemental oxygen to patients, particularly at flows >5 liters per minute (L/min), causes a “wash-out” or dilution of the sample of exhaled CO₂ and results in either a falsely low reading or no reading at all [10].

1.2. Supplemental Oxygenation

Recent prospective randomized controlled trials (RCTs) report up to 54% of all patients experience severe hypoxemia secondary to sedation-related UAO and respiratory depression [11]. Although passive oxygenating devices can provide higher concentrations of oxygen, they are incapable of generating positive pressure to maintain airway patency. Continuous Positive Airway Pressure (CPAP) equipment has been shown to relieve UAO by creating a pneumatic stent [12]. However, their utility is limited by the machine’s very large size and relatively greater expense, and the high oxygen flows required to maintain pressure also dilute EtCO₂ sampling [13] [14].

A recent RCT comparing the SuperNO₂VA^TM nasal PAP ventilation device (Vyaire Medical, Inc., United States) vs. nasal cannula with capnography during deep sedation documented a significantly higher minute ventilation and reduction in the incidence of severe hypoxemia in the SuperNO₂VA^TM nasal PAP ventilation device cohort compared to the nasal cannula with capnography cohort [15]. However, the design of the SuperNO₂VA nasal PAP ventilation device had the disadvantage of being unable to capture EtCO₂, especially in patients who exhale from their mouths, which also results in false apnea alarms.

1.3. SuperNO₂VA^TM Et Nasal Mask

A solution that offers the ability to monitor EtCO₂ and deliver supplemental oxygen is the novel SuperNO₂VA^TM Et Nasal Mask (Vyaire Medical, Inc., United States). This completely sealed nasal PAP device provides positive pressure to maintain upper airway patency without the use of capital equipment. The SuperNO₂VA^TM Et Nasal Mask (Figure 1) also is designed to capture EtCO₂ exhaled from both the patient’s mouth and nose. Combining capnography with positive pressure in a single device may prove to be a methodology to further improve patient outcomes in deep sedation as opposed to passive oxygenation techniques with capnography.

Figure 1. SuperNO₂VA Et Nasal Mask features an EtCO₂ Hood and EtCO₂ nasal sampling port (Source: Vyaire Medical).

The objectives of this study were to validate the capability of the SuperNO₂VA^TM Et to capture EtCO₂ exhaled from the nose and the mouth, provide 20 cm H₂O positive pressure, quantify leak rates, and summarize the performance testing compared to a predicate device.

2. Methods

2.1. Experimental Setup and Methods

A simulated patient setup was used to compare the accuracy of CO₂ measurements within the SuperNO₂VA Et Nasal Mask and a predicate device, the Smart CapnoLine® Plus, Adult/Intermediate CO₂ Oral-Nasal Set (Medtronic, United States).

The Device Under Test (DUT), either the SuperNO₂VA Et or Oral-Nasal Set, was placed on a face surrogate and breathing simulation was provided by a Large Animal Volume Controlled Ventilator Model 613 (Harvard Apparatus, United States). This device is suitable for humans up to 50 kg (110 lb) and enables an adjustable VT from 30 to 700 milliliters (ml) per stroke and an adjustable respiratory rate from 7 to 50 breaths per minute (BPM). The concentration of CO₂ flowing through the surrogate nose and mouth was set using a digitally controlled flow meter and CO₂ source, and verified using a CO₂ monitor (Dräger Narkomed 6400). A Datex-Ohmeda 5250 Respiratory Gas Anesthesia Monitor (General Electric Healthcare, United States) connected to the EtCO₂ sampling port was used to monitor CO₂. Testing assessed eight combinations of Input CO₂ (1% ± 0.25%; 5% ± 0.5%); breath rate and VT (12 BPM/500 ml; 20 BPM/300 ml); and O₂ flow rates (1 L/min; 5 L/min). Table 1 lists the combinations of Input CO₂, Breath Rate/VT, and O₂ Flows that were tested. After a 3-min stabilization period to reach steady-state, the CO₂ waveform of the sensor connected to the EtCO₂ sampling port was recorded for 16 seconds via an analog port of an oscilloscope (Tektronix TBS2000, United States).

Table 1. Test matrix listing the eight combinations of input CO₂, breath rate, tidal volume, and O₂ flow. Each test was repeated three times for the SuperNO₂VA Et and Oral/Nasal Sampling Set.

To evaluate the performance of the Oral-Nasal Set and SuperNO₂VA Et when a patient is breathing exclusively nasally or orally, the same set of eight tests were repeated while simulating nasal breathing and oral breathing. Three trials were performed for each of the eight test conditions and breathing type (i.e., nasal or oral).

In addition, leak rate and ability to hold a positive pressure for five minutes were tested for three SuperNO₂VA Et Nasal Masks and, as a comparator, a full-face anesthesia mask (Ventlab^TM inflatable anesthesia mask VR5100; SunMed, United States). The DUT was placed on a surrogate face and sealed with 10 pounds of force. To determine the leak flow rate, the O₂ flow rate was slowly reduced until a minimum flow was achieved while still maintaining a positive pressure of 20 cm H₂O.

2.2. Statistical Analysis

Absolute and relative errors between the CO₂Max, defined as maximum CO₂ during the 16-second trial, and the Input CO₂ were quantified for each DUT.

$AbsoluteError=C{O}_{2}MaxDUT-InputC{O}_2$

$RelativeError=\frac{\left(C{O}_{2}MaxDUT-InputC{O}_2\right)}{InputC{O}_2}\ast 100\%.$

Negative errors correspond to an underestimation of CO₂. Unpaired t-tests compared CO₂Max errors between the two devices for tests with Input CO₂ of 1% and 5%. Unpaired t-tests were also performed to compare CO₂Max errors between the two devices at O₂ Flows of 1 L/min and 5 L/min. Paired t-tests were performed to compare CO₂Max errors during Nasal Breathing and Oral Breathing trials for each of the two devices. As a comparator, DUT accuracy was measured against the specifications of the International Organization for Standardization (ISO 80601-2-55:2018) requirements for the basic safety and essential performance of a respiratory gas monitor intended for continuous operation with a patient, defined as ± (0.43%vol + 8% of gas level) [16].

3. Results

3.1. Accuracy of CO₂ Measurement

The SuperNO₂VA Et Nasal Mask had lower CO₂Max errors than the Oral-Nasal Set for all eight conditions (Figure 2).

For 1% Input CO₂, CO₂Max errors were significantly larger for the Oral-Nasal Set, −0.12%Vol ± 0.03%Vol (−12.2%Vol ± 3.3%Vol, mean ± SD), compared to the SuperNO₂VA Et Nasal Mask, −0.01%Vol ± 0.02%Vol (−1.3%Vol ± 2.2%Vol) (p = 0.0005). All 12 trials for the Oral-Nasal Set and the SuperNO₂VA Et Nasal Mask met the ISO accuracy specification.

For 5% Input CO₂, the Oral-Nasal Set significantly underestimated CO₂Max error, −0.93%Vol ± 0.16%Vol (−18.6%Vol ± 3.2%Vol), compared to the SuperNO₂VA Et Nasal Mask, −0.08%Vol ± 0.06%Vol (−1.5%Vol ± 1.2%Vol) (p < 0.0001). At 5% Input CO₂, eight of the 12 trials for the Oral-Nasal Set failed to meet the ISO accuracy specification, while all SuperNO₂VA Et Nasal Mask met the specification.

3.2. Effect of Supplemental Oxygen Flow Rate

To examine the effect of O₂ Flow on performance of the two devices, results from trials with O₂ Flow of 1 L/min were compared to trials with O₂ Flow of 5 L/min (Figure 3). Trials with the SuperNO₂VA Et had significantly lower errors than the Oral-Nasal Set with O₂ Flows of 1 L/min (0.01%vol vs. 0.11%vol, p = 0.0032) and 5 L/min (−0.03%vol vs. −0.14%vol, p = 0.0032). The difference in performance was even larger with an Input CO₂ of 5%. Specifically, the SuperNO₂VA Et errors were significantly less at both 1 L/min (−0.04%vol vs. 0.91%vol, p < 0.0001) and 5 L/min (−0.11%vol vs. −0.95%vol, p = 0.0002).

3.3. Nasal Breathing vs. Oral Breathing

The same set of eight tests were repeated while simulating Nasal Breathing and Oral Breathing for each of the two devices (See Figure 4). For the Oral-Nasal Set, CO₂Max measurements were significantly lower for the Oral Breathing compared to Nasal Breathing trials for Input CO₂ concentrations of 1% (paired t-test, p = 0.0005) and 5% (p = 0.0091). For the SuperNO₂VA Et, there was no

Figure 2. CO₂Max Error (in %vol) for the eight condition performance tests for Oral-Nasal Set (orange) and SuperNO₂VA Et Nasal Mask (blue). Horizontal shaded green areas correspond to the ISO 80601-2-55:2018 error limit (0.51% and 0.83% for 1% and 5% input CO₂ respectively). Filled circles are individual trials and bars represent mean error across the three trials for each condition test.

Figure 3. Comparison of maximum CO₂ measurements (i.e., CO₂Max) measurements during trials with O₂ Flow of 1 L/min and 5 L/min. CO₂Max with Oral-Nasal Set (orange) and SuperNO₂VA Et (blue) are compared to known Input CO₂ concentrations of 1% or 5% (horizontal dashed black lines). Shaded green areas correspond to the ISO 80601-2-55:2018 error limit (0.51% and 0.83% for 1% and 5% Input CO₂, respectively). Bars are the average measurements across all trials performed under those conditions and error bars are the standard deviation of measurements across these trials.

Figure 4. Comparison of maximum CO₂ measurements (i.e., CO₂Max) measurements during Nasal Breathing and Oral Breathing trials. CO₂Max with Oral-Nasal Set (orange) and SuperNO₂VA Et (blue) are compared to known Input CO₂ concentrations of 1% or 5% (horizontal dashed black lines). Shaded green areas correspond to the ISO 80601-2-55:2018 error limit (0.51% and 0.83% for 1% and 5% Input CO₂, respectively). Bars are the average measurements across all trials performed under each condition and error bars are the standard deviation of measurements across these trials.

significant difference in CO₂Max measurements for Nasal Breathing and Oral Breathing trials for both Input CO₂ concentrations (1%: p = 0.33, 5%: p = 0.064). At an Input CO₂ of 5%, the Oral-Nasal Set had 10 out of the 12 Nasal Breathing trials and 9 out of 12 Oral Breathing trials outside of the ISO error bound (shaded green region).

3.4. Flow Leak Rate

Both the SuperNO₂VA Et Nasal Mask and the full-face anesthesia mask successfully held a pressure of 20 cm H₂O for three, 5-minute trials. The SuperNO₂VA Et Nasal Mask had a leak rate of 2.0 L/min for all three samples compared to the mean leak rate of 2.7 (range: 2.5 - 3.0 L/min) for the anesthesia mask (Table 2).

4. Discussion

This performance test study compared the functionality of the SuperNO₂VA Et Nasal Mask and Oral-Nasal capnography in eight condition combinations with binary variations of input CO₂; respiratory rate and VT; and O₂ flow rates. Our results indicate that SuperNO₂VA Et Nasal Mask provided significantly greater accuracy in measuring EtCO₂ across a range of typical respiratory rates, tidal volume, O₂ flow, and CO₂ concentration, well within the error bounds specified by ISO (Figure 2). The error of CO₂ measurements within the SuperNO₂VA Et mask was less than 0.1%vol at both 1% and 5% CO₂ concentrations. In contrast, measurements from the Oral-Nasal Set did not meet the ISO standard for eight out of the twelve trials at a physiological CO₂ level of 5% (i.e., 38 mmHg) and underestimated CO₂ by −0.93%vol (−18.6%). Clinically, this dramatic underestimation of CO₂ could result in false positives of hypocapnia or apnea or missing true hypercapnic events.

Capnography has become standard-of-care during moderate and deep sedation in order to provide real-time feedback of the patient’s respiratory status and early detection of respiratory depression [6] [7] [17]. With good quality CO₂ sampling, capnography has been shown to significantly reduce adverse events, such as apnea and desaturation, during moderate and deep sedation [18] [19] [20]. However, EtCO₂ measurements using nasal cannula sampling are often not accurate during minimally invasive procedures under deep sedation [8]. The inaccuracy of EtCO₂ using nasal cannulas arises because they are exposed to

Table 2. Flow leak rate results for Full-Face Anesthesia Mask and SuperNO₂VA Et.

atmospheric gas [8] and supplemental O₂ washes out CO₂ in the sample [10] [21]. Both of these effects result in an underestimation in CO₂ measurements.

The SuperNO₂VA Et offers a solution to this CO₂ sampling problem by capturing all expired gases from the patient’s mouth and nose using an integrated flexible sampling hood over the patient’s mouth. The SuperNO₂VA Et also provides positive pressure to maintain upper airway patency. Use of the SuperNO₂VA results in increased minute ventilation and a reduction in severe hypoxemia compared to a nasal cannula [15]. Furthermore, in contrast to traditional anesthesia masks, the SuperNO₂VA Et does not cover the full face and therefore allows the clinician access to the oral cavity during a procedure while delivering air, oxygen, or anesthesia gases and simultaneously sampling expired gases.

Delivery of supplemental oxygen using traditional nasal cannulas results in an underestimation of CO₂ [10] and the error increases with the flow rate as more of the sampled gas is washed out with O₂ when using traditional nasal cannulas [21]. In this study, we saw no decrease in accuracy of CO₂ measurements when using the SuperNO₂VA Et (Figure 3). There was also no significant difference between 1 and 5 L/min O₂ flow rates using the Oral-Nasal Set. However, this dilution effect is typically observed for nasal cannulas at flow rates greater than 5 L/min which were not tested in this study.

Another source of capnography error arises when the patient breathes orally, which is common during respiratory distress and sedation, especially in obese patients with obstructive sleep apnea (OSA) [10]. For example, in non-intubated volunteers, mouth breathing resulted in a 2 mmHg decrease in EtCO₂ compared to nasal breathing [22]. In the present study, the accuracy of the CO₂ measurements within the SuperNO₂VA Et was similar for Nasal and Oral Breathing (Figure 4). The Nasal-Oral Set used in this study was engineered with an oral scoop intended to obtain gas samples from the mouth as well as the nose. Despite this design, CO₂ measurements were significantly lower during Oral Breathing compared to Nasal Breathing when using the Oral-Nasal Set.

Furthermore, the SuperNO₂VA Et Nasal Mask maintained a positive pressure of 20 cm H₂O within the mask with a low leak rate of 2.0 L/min, demonstrating superior fit to a full-face anesthesia mask. The majority of the leak from the SuperNO₂VA Et masks comes from the EtCO₂ sampling port. In order to achieve a sufficient seal for the full-face anesthesia mask, the balloon had to deflated and inflated in order to achieve a maximum seal.

The SuperNO₂VA Et Nasal mask is a sealed system around the nose that keeps all expired CO₂ within the system, preventing atmospheric dilution. The larger hood over the mouth increases capture of exhaled CO₂ from mouth. The size of the SuperNO₂VA Et nasal and oral apertures for EtCO₂ capture was designed based on fluid dynamic calculations to allow for an equal amount of capture.

5. Limitations

This study was conducted to determine specific performance features of the SuperNO₂VA Et Nasal Mask in a controlled setting using a face surrogate. The study results document the significantly better accuracy of the device and its potential to aid in providing optimal patient care during sedation. Future clinical work should be conducted to confirm if the use of the SuperNO₂VA Et improves clinical outcomes and decreases adverse events in patients under sedation.

6. Conclusions

The testing described in this report demonstrated that measurements of CO₂ within the SuperNO₂VA Et Nasal Mask are accurate for a range of respiratory rates, tidal volumes, O₂ flows, and CO₂ concentrations and meet ISO standards. The design of the SuperNO₂VA Et Nasal Mask allows for a good seal against a patient’s face to maintain positive pressure with minimal leak.

This performance and the positive pressure mechanism of the SuperNO₂VA Et Nasal mask to improve upper airway obstruction without sacrificing end-tidal measurements differentiate the device favorably from other methods of airway management. Additionally, its design and function improved airway management comparatively to passive devices that, because they cannot provide positive pressure to force airways open, lack the ability to maintain airway patency.

In practice, the performance of SuperNO₂VA Et Nasal Mask may help prevent patients from becoming hypoxemic and improve their overall outcomes in the settings of moderate or moderate and deep sedation.

Acknowledgements

The authors wish to thank Ryan Redford for his technical assistance with the study design and interpretation of data. We would also like to acknowledge Marion E. Glick and Edward A. Rose, M.D. for their assistance in editing the manuscript.

Funding

This work was supported by Vyaire Medical, Inc.

Declarations of Interest

Drs. Steven Cataldo and Michael Pedro are employees of Vyaire Medical, which supported the study. They also received payments for SuperNO₂VA Et Nasal Mask sales. None of the authors have any personal relationships with people or organizations that could inappropriately influence this work. The authors alone are responsible for the content of the paper.

Author Contributions

MJP: Conceptualization; Investigation; Data curation; Formal analysis, Methodology.

SHC: Writing—original draft, Writing—review & editing.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.

References

[1]	Qadeer, M.A., Lopez, A.R., Dumot, J.A. and Vargo, J.J. (2011) Hypoxemia during Moderate Sedation for Gastrointestinal Endoscopy: Causes and Associations. Digestion, 84, 37-45. https://doi.org/10.1159/000321621
[2]	Qadeer, M.A., Rocio Lopez, A., Dumot, J.A. and Vargo, J.J. (2009) Risk Factors for Hypoxemia during Ambulatory Gastrointestinal Endoscopy in ASA I-II Patients. Digestive Diseases and Sciences, 54, 1035-1040. https://doi.org/10.1007/s10620-008-0452-2
[3]	Yilmaz, M., Aydin, A., Karasu, Z., Gunsar, F. and Ozutemiz, O. (2002) Risk Factors Associated with Changes in Oxygenation and Pulse Rate during Colonoscopy. Turkish Journal of Gastroenterology, 13, 203-208.
[4]	Arakawa, H., Kaise, M., Sumiyama, K., Saito, S., Suzuki, T. and Tajiri, H. (2013) Does Pulse Oximetry Accurately Monitor a Patient’s Ventilation during Sedated Endoscopy under Oxygen Supplementation. Singapore Medical Journal, 54, 212-215. https://doi.org/10.11622/smedj.2013075
[5]	Burton, J.H., Harrah, J.D., Germann, C.A. and Dillon, D.C. (2006) Does End-Tidal Carbon Dioxide Monitoring Detect Respiratory Events Prior to Current Sedation Monitoring Practices? Academic Emergency Medicine, 13, 500-504. https://doi.org/10.1197/j.aem.2005.12.017
[6]	Lam, T., Nagappa, M., Wong, J., Singh, M., Wong, D. and Chung, F. (2017) Continuous Pulse Oximetry and Capnography Monitoring for Postoperative Respiratory Depression and Adverse Events: A Systematic Review and Meta-Analysis. Anesthesia & Analgesia, 125, 2019-2029. https://doi.org/10.1213/ANE.0000000000002557
[7]	Weaver, J. (2011) The Latest ASA Mandate: CO2 Monitoring for Moderate and Deep Sedation. Anesthesia Progress, 58, 111-112. https://doi.org/10.2344/0003-3006-58.3.111
[8]	Frasca, D., Geraud, L., Charriere, J.M., Debaene, B. and Mimoz, O. (2015) Comparison of Acoustic and Impedance Methods with Mask Capnometry to Assess Respiration Rate in Obese Patients Recovering from General Anaesthesia. Anaesthesia, 70, 26-31. https://doi.org/10.1111/anae.12799
[9]	Morimoto, K., Ogura, S., Shinohara, K. and Sunada, K. (2019) Respiratory Rate Is an Inadequate Parameter of Ventilation in Non-Intubated Sedation. Odontology, 107, 219-222. https://doi.org/10.1007/s10266-018-0404-z
[10]	Teng, W.-N., Ting, C.-K., Wang, Y.-T., et al. (2018) Oral Capnography Is More Effective Than Nasal Capnography during Sedative Upper Gastrointestinal Endoscopy. Journal of Clinical Monitoring and Computing, 32, 321-326. https://doi.org/10.1007/s10266-018-0404-z
[11]	Mehta, P.P., Kochhar, G., Albeldawi, M., et al. (2016) Capnographic Monitoring in Routine EGD and Colonoscopy with Moderate Sedation: A Prospective, Randomized, Controlled Trial. American Journal of Gastroenterology, 111, 395-404. https://doi.org/10.1007/s10877-017-0029-8
[12]	Mathru, M., Esch, O., Lang, J., Herbert, M.E., Chaljub, G., Goodacre, B. and Van Sonnenberg, E. (1996) Magnetic Resonance Imaging of the Upper Airway: Effects of Propofol Anesthesia and Nasal Continuous Positive Airway Pressure in Humans. Anesthesiology, 84, 273-279. https://doi.org/10.1097/00000542-199602000-00004
[13]	Chung, F., Nagappa, M., Singh, M. and Mokhlesi, B. (2016) CPAP in the Perioperative Setting: Evidence of Support. Chest, 149, 586-597. https://doi.org/10.1378/chest.15-1777
[14]	Schonhofer, B. and Sortor-Leger, S. (2002) Equipment Needs for Noninvasive Mechanical Ventilation. European Respiratory Journal, 20, 1029-1036. https://doi.org/10.1183/09031936.02.00404202
[15]	Bai, Y., Xu, Z., Chandrashekar, M., et al. (2019) Comparison of a Simplified Nasal Continuous Positive Airways Pressure Device with Nasal Cannula in Obese Patients Undergoing Colonoscopy during Deep Sedation: A Randomised Clinical Trial. European Journal of Anaesthesiology, 36, 633-640. https://doi.org/10.1097/EJA.0000000000001052
[16]	ISO (2018) 80601-2-55:2018 Medical Electrical Equipment. Part 2-55: Particular Requirements for the Basic Safety and Essential Performance of Respiratory Gas Monitors. https://www.iso.org/obp/ui/#iso.std.iso:80601:-2-55:ed-2:v1:en
[17]	Waugh, J.B., Epps, C.A. and Khodneva, Y.A. (2011) Capnography Enhances Surveillance of Respiratory Events during Procedural Sedation: A Meta-Analysis. Journal of Clinical Anesthesia, 23, 189-196. https://doi.org/10.1016/j.jclinane.2010.08.012
[18]	Beitz, A., Riphaus, A., Meining, A., et al. (2012) Capnographic Monitoring Reduces the Incidence of Arterial Oxygen Desaturation and Hypoxemia during Propofol Sedation for Colonoscopy: A Randomized, Controlled Study (Colocap Study). American Journal of Gastroenterology, 107, 1205-1212. https://doi.org/10.1038/ajg.2012.136
[19]	Qadeer, M.A., Vargo, J.J., Dumot, J.A., et al. (2009) Capnographic Monitoring of Respiratory Activity Improves Safety of Sedation for Endoscopic Cholangiopancreatography and Ultrasonography. Gastroenterology, 136, 1568-1576. https://doi.org/10.1053/j.gastro.2009.02.004
[20]	Saunders, R., Erslon, M. and Vargo, J. (2016) Modeling The Costs and Benefits of Capnography Monitoring during Procedural Sedation for Gastrointestinal Endoscopy. Endoscopy International Open, 4, E340-E351. https://doi.org/10.1055/s-0042-100719
[21]	Chang, K.C., Orr, J., Hsu, W.C., et al. (2016) Accuracy of CO2 Monitoring via Nasal Cannulas and Oral Bite Blocks during Sedation for Esophagogastroduodenoscopy. Journal of Clinical Monitoring and Computing, 30, 169-173. https://doi.org/10.1007/s10877-015-9696-5
[22]	Oberg, B., Waldau, T. and Larsen, V.H. (1995) The Effect of Nasal Oxygen Flow and Catheter Position on the Accuracy of End-Tidal Carbon Dioxide Measurements by a Pharyngeal Catheter in Unintubated, Spontaneously Breathing Subjects. Anaesthesia, 50, 695-698. https://doi.org/10.1111/j.1365-2044.1995.tb06096.x