Efficiency of oxygen delivery through different oxygen entrainment devices during sedation under low oxygen flow rate: a bench study

Evaluation of Venturi Adapters for CPAP

Background: CPAP therapy has been shown to effectively reduce the risk of obstructive apnea and oxygen desaturation in procedural sedation. An economical approach to administering CPAP is through a Venturi adapter, which amplifies oxygen flows to produce pressures suitable for CPAP. The objective of this study was to evaluate the performance of four Venturi adapters across clinically relevant metrics including pressure-generation efficiency, inspired oxygen concentration (FiO2), dilution of the end-tidal carbon dioxide (EtCO2) sample for capnometry, and noise levels produced. Methods: A benchtop simulator was used to evaluate Venturi adapters. The simulator was composed of a test lung, corrugated tubing to simulate a trachea, a silicone-molded face, an air-cushioned mask strapped to the face, a high-pressure oxygen source, and several Venturi adapters. The oxygen flows required to produce specific airway pressures were measured to evaluate pressure-generation efficiency, and the noise levels produced by the Venturi adapters at these pressures were recorded. CO2 was infused into the test lung while the lung was ventilated, and the EtCO2 measured at the mask was compared with a reference measurement taken from the trachea. FiO2 was evaluated by ventilating the test lung and observing the steady-state oxygen concentration in the lung. Results: Each of the Venturi adapter designs provides their unique strengths and weaknesses. There appears to be a direct trade-off between high pressure-generation efficiency and high FiO2. There also appears to be a direct trade-off between high FiO2 and the extent of dilution in the EtCO2 sample. Some Venturi adapters produce high noise levels, which might result in patient discomfort and clinician unwillingness to use. Conclusion: Variations in Venturi adapter designs create different clinical benefits. Clinicians should choose the Venturi adapter to best suit their present clinical needs.

True intratracheal oxygen concentration delivered by SentriO Oxy™ masks under various respiratory conditions: a bench study

SentriO Oxy™ is a newly available, Food and Drug Administration-approved oxygenation mask system that provides high oxygenation, even on low-flow (5-10 L/min) oxygen. This study aimed to accurately measure the intratracheal fraction of inspired oxygen (FiO2) using SentriO Oxy™ masks under relatively low oxygen flow rates. A manikin-ventilator-test lung simulation system was used. We measured FiO2 at the level of the carina, 5 minutes after applying 45 different respiratory parameter combinations using SentriO Oxy™ masks. Tidal volume (TV) was set to 300, 500, and 700 mL; respiratory rate (RR) was set to 8, 12, 16, 20, and 24 breaths per minute; and oxygen flow rate was set to 6, 8, and 10 L/min. Our hypothesis was that FiO2 would be proportional to the difference between oxygen flow rate and minute ventilation. FiO2 measured by smaller TV, lower RR, or higher oxygen flows revealed a significantly higher value, confirming our hypothesis. In addition, using linear regression analysis, we found that TV, RR, and oxygen flow were all significant factors influencing the measured FiO2. Our experiment proposed two prediction equations considering the oxygen flow rate, TV, and RR. The results of our study may provide information and prediction of FiO2 for clinicians to use SentriO Oxy™ masks during sedative anesthetic procedures under low oxygen flow rates.

Impact of High-Flow Nasal Cannula Oxygenation on the Prevention of Hypoxia During Endoscopic Retrograde Cholangiopancreatography in Elderly Patients: A Randomized Clinical Trial

BACKGROUND

Hypoxia is the most frequently occurring adverse effect during endoscopic retrograde cholangiopancreatography (ERCP) under sedation; thus, oxygen must be properly supplied to prevent a reduction of oxygen saturation. In this study, we intend to verify the preventive effect for hypoxia during ERCP, using a high-flow nasal cannula (HFNC), in elderly patients.

METHODS

As a multicenter prospective randomized trial, patients who underwent ERCP with propofol-based sedation were randomly assigned into two groups: Patients in the HFNC group were supplied with oxygen via an HFNC, and those in the standard nasal cannula group were supplied with oxygen via a low-flow nasal cannula. The co-primary end points were the lowest oxygen saturation rate and hypoxia during the overall procedure.

RESULTS

A total of 187 patients (HFNC group: 95; standard nasal cannula group: 92) were included in the analysis. Unexpected hypoxia events were more frequently observed among patients in the standard nasal cannula group than among patients in the HFNC group (13% vs. 4%, odds ratio 3.41, 95% confidence interval 1.06-11.00, p = 0.031). The mean of the lowest oxygen saturation rate during ERCP was significantly lower in the standard nasal cannula group than in the HFNC group (95% vs. 97%, p = 0.002).

CONCLUSION

Oxygen supplementation with an HFNC can prevent oxygen desaturation and hypoxia events in patients undergoing ERCP under sedation. Trial registration Clinical Research Information Service (CRIS; KCT0004960).

Fraction of Inspired Oxygen With Low-Flow Versus High-Flow Devices: A Simulation Study

Purpose: The fraction of inspired oxygen while administering oxygen to patients must be measured as it represents the alveolar oxygen concentration, which is important from a respiratory physiology viewpoint. Therefore, the purpose of this study was to compare the fractions of inspired oxygen obtained through different oxygen delivery devices.

Methods: A simulation model of spontaneous respiration was used. The fractions of inspired oxygen obtained through low- and high-flow nasal cannulas and a simple oxygen mask were measured. The fraction of inspired air was measured every second for 30 s after 120 s of oxygen administration. This was measured three times under each condition.

Results: With a low-flow nasal cannula, airflow reduced both the intratracheal fraction of inspired oxygen and extraoral oxygen concentration, indicating that exhalatory respiration occurred during rebreathing and may be involved in increasing the intratracheal fraction of inspired oxygen.

Conclusion: Oxygen administration during expiratory flow may lead to an increased oxygen concentration in the anatomical dead space, which may be involved in the increase in the fraction of inspired oxygen. With a high-flow nasal cannula, a high fraction of inspired oxygen can be achieved even at a flow rate of 10 L/min. When determining the optimum amount of oxygen, it is necessary to set an appropriate flow rate for patients and specific conditions without being bound by the fraction of inspired oxygen values alone. It might be difficult to estimate the fraction of inspired oxygen while using a low-flow nasal cannula and simple oxygen mask in clinical situations.

Impact of Oxygen Concentration Delivered via Nasal Cannula on Different Lung Conditions: A Bench Study

BACKGROUND

Measuring the fraction of inspired oxygen (FiO2) is challenging in spontaneously breathing patients with impaired respiratory mechanics during low-flow nasal cannula. Our study investigates the FiO2 with varied tidal volume (VT) and respiratory rate (RR) among different lung mechanics and provides equations to estimate the FiO2.

METHODS

Two training and test lungs were used in this study, and the three lung mechanics (normal (R5/C60), restrictive (R20/C80), obstructive (R5/C40)) were designed. Spontaneous breathing with VT (300, 500, and 700 mL) and RR (10, 20, and 30 breaths/min) was simulated. The flow rate of the nasal cannula was set to 1, 3, and 5 L per minute (LPM), and the FiO2 was measured at the carina.

RESULTS

The lowest and highest FiO2 were evident during high (700 mL) and low VT (300 mL), respectively, among normal, restrictive, and obstructive lung models. As RR increases, this decreases the FiO2. However, we found that VT and oxygen flow rate are the principal factors influencing measured FiO2 by multiple linear regression analysis.

CONCLUSIONS

Our data suggest that the actual FiO2 is never as high in spontaneously breathing patients as that estimated. VT and oxygen flow rate had a substantial impact on the FiO2.

Effect of high-flow vs. low-flow nasal plus mouthguard oxygen therapy on hypoxaemia during sedation: a multicentre randomised controlled trial

Whether high-flow vs. low-flow nasal oxygen reduces hypoxaemia for sedation during endoscopic retrograde cholangiopancreatography is currently unknown. In this multicentre trial, 132 patients ASA physical status 3 or higher, BMI > 30 kg.m^-2 or with known or suspected obstructive sleep apnoea were randomly allocated to high-flow nasal oxygen up to 60 l.min^-1 at 100% F_I O₂ or low-flow nasal oxygen at 4 l.min^-1 . The low-flow nasal oxygen group also received oxygen at 4 l.min^-1 through an oxygenating mouthguard, totalling 8 l.min^-1 . Primary outcome was hypoxaemia, defined as S_p O₂ < 90% regardless of duration. Hypoxaemia occurred in 7.7% (5/65) of patients with high-flow and 9.1% (6/66) with low-flow nasal oxygen (percentage point difference -1.4%, 95%CI -10.9 to 8.0; p = 0.77). Between the groups, there were no significant differences in frequency of hypoxaemic episodes; lowest S_p O₂ ; peak transcutaneous carbon dioxide; hypercarbia (transcutaneous carbon dioxide > 2.66 kPa from baseline); requirement of chin lift/jaw thrust; nasopharyngeal airway insertion; bag-mask ventilation; or tracheal intubation. Following adjustment for duration of the procedure, the primary outcome remained non-significant. In high-risk patients undergoing endoscopic retrograde cholangiopancreatography, oxygen therapy with high-flow nasal oxygen did not reduce the rate of hypoxaemia, hypercarbia or the need for airway interventions, compared with combined oral and nasal low-flow oxygen.

Novel mandibular advancement bite block with supplemental oxygen to both nasal and oral cavity improves oxygenation during esophagogastroduodenoscopy: a bench comparison

Drug-induced respiratory depression is a major cause of serious adverse events. Adequate oxygenation is very important during sedated esophagogastroduodenoscopy (EGD). Nasal breathing often shifts to oral breathing during open mouth EGD. A mandibular advancement bite block was developed for EGD using computer-assisted design and three-dimensional printing techniques. The mandible is advanced when using this bite block to facilitate airway opening. The device is composed of an oxygen inlet with one opening directed towards the nostril and another opening directed towards the oral cavity. The aim of this bench study was to compare the inspired oxygen concentration (FiO₂) provided by the different nasal cannulas, masks, and bite blocks commonly used in sedated EGD. A manikin head was connected to one side of a two-compartment lung model by a 7.0 mm endotracheal tube with its opening in the nasopharyngeal position. The other compartment was driven by a ventilator to mimic "patient" inspiratory effort. Using this spontaneously breathing lung model, we evaluated five nasal cannulas, two face masks, and four new oral bite blocks at different oxygen flow rates and different mouth opening sizes. The respiratory rate was set at 12/min with a tidal volume of 500 mL and 8/min with a tidal volume of 300 mL. Several Pneuflo resistors of different sizes were used in the mouth of the manikin head to generate different degrees of mouth opening. FiO₂ was evaluated continuously via the endotracheal tube. All parameters were evaluated using a Datex anesthesia monitoring system. The mandibular advancement bite block provided the highest FiO₂ under the same supplemental oxygen flow. The FiO₂ was higher for devices with oxygen flow provided via an oral bite block than that provided via the nasal route. Under the same supplemental oxygen flow, the tidal volume and respiratory rate also played an important role in the FiO₂. A low respiratory rate with a smaller tidal volume has a relative high FiO₂. The ratio of nasal to oral breathing played an important role in the FiO₂ under hypoventilation but less role under normal ventilation. Bite blocks deliver a higher FiO₂ during EGD. The ratio of nasal to oral breathing, supplemental oxygen flow, tidal volume, and respiratory rate influenced the FiO₂ in most of the supplemental oxygen devices tested, which are often used for conscious sedation in patients undergoing EGD and colonoscopy.