Identification of the Optimal Position of a Nasal Oxygen Cannula for Apneic Oxygenation: A Technical Simulation

Background: In a cannot-ventilate-cannot-intubate situation, careful preoxygenation with high FiO2 allowing subsequent apneic oxygenation can be life-saving. The best position for an oxygen supply line within the human airway at which oxygen insufflation is more effective than standard preoxygenation with a face mask is unknown. Methods: In this experimental study, we compared the effectiveness of preoxygenation by placing an oxygen cannula at the nose entrance, through the nose at the soft palatine, or at the base of the tongue; as a control we used ambient air. We connected a fully preoxygenated test lung on one side to an oximeter with a flow rate of 200 mL/min simulating the oxygen consumption of a normal adult on the other side of the trachea of an anatomically correctly shaped airway manikin over a 20 min observation period five times for each cannula placement in a random order. Results: The oxygen percentage in the test lung dropped from 100% in all groups to 53 ± 1% in the ambient air control group, to 87 ± 2% in the nasal cannula group, and to 96 ± 2% in the soft palatine group; it remained at 99 ± 1% in the base of the tongue group (p = 0.003 for the soft palatine vs. base of the tongue and p < 0.001 for all other groups). Conclusions: When simulating apneic oxygenation in a preoxygenated manikin, oxygen insufflation at the base of the tongue kept the oxygen percentage at baseline values of 99%, demonstrating a complete block of ambient air flowing into the airway of the manikin. Oxygen insufflation at the soft palatine or insufflation via a nasal cannula were less effective regarding this effect

The efficacy of apneic oxygenation during intubation using a prototype of an oxygenation laryngoscope - a technical simulation

Abstract Background Recently, a non-commercial oxygenation laryngoscope was able to maintain apneic oxygenation during simulated intubation efforts. Since that prototype was 3 mm wider than a standard Macintosh laryngoscope blade, the intubation performance of this device may differ from standard blades. A new prototype of an oxygenation laryngoscope was developed, consisting of a standard-size Macintosh blade and a fixed oxygen supply line to the side. Actually, it is unclear at which point of this blade the oxygen supply line should end to facilitate the best possible oxygen supply for apneic oxygenation. Methods In this simulation study using a standardized human airway manikin, the efficacy of apneic oxygenation by oxygen insufflation using standard and modified Macintosh blades was compared: a standard Macintosh blade without oxygen supply line as control, one with an additional oxygen supply line ending proximal near the handle, one with the line ending at the middle of the blade, and one with the line ending near the tip. A preoxygenated test lung was connected to an oximeter with a flow rate of 200ml/min, simulating oxygen consumption of a male adult, and to the trachea of an anatomically correctly shaped airway manikin. Apneic oxygenation was performed and oxygen content was measured over a 20-minutes observation period. Experiments were repeated five times for each laryngoscope blade. Results Oxygen percentage in the test lung dropped from 100 ± 0% at the start of the experiment to 53 ± 1.5% in the room air control group (p < 0.001 compared to all other groups), and to 74 ± 2.5% in the proximal oxygen line group, whereas oxygen percentage remained at 100% in both the medium and distal oxygen line groups (p = 1 between these groups; p < 0.001 between all other groups). Conclusions In this simulation study with a preoxygenated airway manikin, the use of a modified Macintosh laryngoscope blade with oxygen line attached at the tip or at the middle were able to maintain apneic oxygenation without measurable drop of oxygen content over 20 min. Proximal placement of the oxygen supply line still showed an advantage against room air, however it did not completely prevent room air from entering the airway. Trial registration Not applicable

Intubation using VieScope vs. Video laryngoscopy in full personal protective equipment - a randomized, controlled simulation trial

Background: VieScope is a new type of laryngoscope, with a straight, transparent and illuminated blade, allowing for direct line of sight towards the larynx. In addition,VieScope is disposed of after single patient use, which can avoid cross-contaminations of contagious material. This has gained importance especially when treating patients with highly contagious infectious diseases, such as during the SARS-CoV2 pandemic. In this context, VieScope has not been evaluated yet in a clinical study. Material and methods: This study compared intubation with VieScope to video-laryngoscopy (GlideScope) in normal and difficult airway in a standardized airway manikin in a randomized controlled simulation trial. Thirty-five medical specialists were asked to perform endotracheal intubation in full personal protective equipment (PPE). Primary endpoint was correct tube position. First-pass rate (i.e., success rate at the first attempt), time until intubation and time until first correct ventilation were registered as secondary endpoints. Results: For correct tracheal tube placement, there was no significant difference between VieScope and GlideScope in normal and difficult airway conditions. VieScope had over 91% fist-pass success rate in normal airway setting. VieScope had a comparable success rate to GlideScope in difficult airway, but had a significantly longer time until intubation and time until ventilation. Conclusion: VieScope and GlideScope had high success rates in normal as well as in difficult airway. There was no unrecognized esophageal intubation in either group. Overall time for intubation was longer in the VieScope group, though in an acceptable range given in literature. Results from this simulation study suggest that VieScope may be an acceptable alternative for tracheal intubation in full PPE

Safer employment of nitrous oxide in anesthesia machines—a technical simulation

Several incidents of anesthesia-attributed mortality in the past were caused by misconnection of gas pipelines resulting in ventilation with pure nitrous oxide. A simple safety feature may be to “mark” nitrous oxide with a lower pressure than oxygen and room air within the hospital’s gas pipeline system. Then, any misconnection of gas pipelines could be detected by pressure differences with a manometer in the anesthesia machine. To check technical suitability, we tested maximum achievable nitrous oxide flows of an anesthesia machine at different pressures in the nitrous oxide supply line. Using decreased pressures for nitrous oxide compared to oxygen did not result in decreased nitrous oxide flows, as long as pressure in the nitrous oxide supply line was >1500 hPa. A concept of different pressures for nitrous oxide and oxygen could be used to technically differentiate between those two gases, and to avoid potentially fatal misconnections

Comparison of the novel VieScope with conventional and video laryngoscope in a difficult airway scenario - a randomized, controlled simulation trial

Background Endotracheal intubation continues to be the gold standard for securing the airway in emergency situations. Difficult intubation is still a dreadful situation when securing the airway. Objective To compare VieScope with Glidescope and conventional Macintosh laryngoscopy (MAC) in a simulated difficult airway situation. Methods In this randomized controlled simulation trial, 35 anesthesiologists performed endotracheal intubation using VieScope, GlideScope and MAC in a randomized order on a certified airway manikin with difficult airway. Results For the primary endpoint of correct tube position, no statistical difference was found (p = 0.137). Time until intubation for GlideScope (27.5 +/- 20.3 s) and MAC (20.8 +/- 8.1 s) were shorter compared to the VieScope (36.3 +/- 10.1 s). Time to first ventilation, GlideScope (39.3 +/- 21.6 s) and MAC (31.9 +/- 9.5 s) were also shorter compared to the VieScope (46.5 +/- 12.4 s). There was no difference shown between handling time for VieScope (20.7 +/- 7.0 s) and time until intubation with GlideScope or MAC. Participants stated a better Cormack & Lehane Score with VieScope, compared to direct laryngoscopy. Conclusion Rate of correct tracheal tube position was comparable between the three devices. Time to intubation and ventilation were shorter with MAC and Glidescope compared to VieScope. It did however show a comparable handling time to video laryngoscopy and MAC. It also did show a better visualization of the airway in the Cormack & Lehane Score compared to MAC

Jaw thrust as a predictor of insertion conditions for the proseal laryngeal mask airway

We test the hypothesis that the response to jaw thrust is an effective predictor of insertion\ud conditions for the ProSeal laryngeal mask airway (ProSeal LMA). One hundred and sixty patients\ud (ASA grade 1-3, aged >18 yr) were studied. Five anesthetists blinded to the response to jaw thrust\ud participated in the study, each performed >30 insertions. Induction of anesthesia was with propofol\ud titrated to loss of lash reflex and apnea. A standard amount of jaw thrust was applied and any\ud motor response noted by three observers. The ProSeal LMA was inserted using the standard digital\ud technique. Insertion conditions were considered optimal if there was no motor or upper airway\ud reflex response to insertion. There was no response to jaw thrust in 86% (137/160) of patients and\ud insertion was optimal in 76% (121/160) of patients. A response to jaw thrust predicted suboptimal\ud insertion conditions in 74% (17/23) and a lack of response predicted optimal insertion conditions in\ud 84% (115/137). The accuracy, sensitivity and specificity were 0.82, 0.95 and 0.44, respectively. We\ud conclude that jaw thrust is a reliable predictor of insertion conditions for the ProSeal LMA with the\ud digital insertion technique after induction of anesthesia with propofol. We suggest that clinicians\ud learn how to apply the correct amount of jaw thrust and perform this test routinely

Temperature loss by ventilation in a calorimetric bench model

In intensive care medicine heat moisture exchangers are standard tools to warm and humidify ventilation gases in order to prevent temperature loss of patients or airway epithelia damage. Despite being at risk of hypothermia especially after trauma, intubated emergency medicine patients are often ventilated with dry and in winter probably cold ventilation gases. We tried to assess the amount of temperature-loss due to ventilation with cold, dry medical oxygen in comparison to ventilation with warm and humidified oxygen. We ventilated a 50-kg water-dummy representing the calorimetric capacity of a 60-kg patient over a period of 2 hours (tidal volume 6.6 mL/kg = 400 mL; respiratory rate 13/min). Our formal null-hypothesis was that there would be no differences in temperature loss in a 50 kg water-dummy between ventilation with dry oxygen at 10 degrees C vs. ventilation with humidified oxygen at 43 degrees C. After 2 hours the temperature in the water-dummy using cold and dry oxygen was 29.7 +/- 0.1 degrees C compared to 30.4 +/- 0.1 degrees C using warm and humidified oxygen. This difference in cooling rates between both ventilation attempts of 0.7 +/- 0.1 degrees C after 2 hours represents an increased cooling rate of similar to 0.35 degrees C per hour. Ventilation with cool, dry oxygen using an automated transport ventilator resulted in a 0.35 degrees C faster cooling rate per hour than ventilation with warm humidified oxygen in a bench model simulating calorimetric features of a 60-kg human body

Airway Management during Massive Gastric Regurgitation Using VieScope or Macintosh Laryngoscope&mdash;A Randomized, Controlled Simulation Trial

In this model of massive gastric aspiration, we compared two different laryngoscopes (VieScope and Macintosh) in a randomized, controlled simulation study. The primary endpoint was time to intubation; the secondary endpoints were intubation success (i.e., tracheal tube position) and amount of pulmonary aspiration. Thirty-four anesthetists performed endotracheal intubation using VieScope and Macintosh laryngoscopy in a randomized order on an airway manikin simulating massive regurgitation of gastric fluid. The primary endpoint &ldquo;time until intubation&rdquo; could be achieved significantly faster (mean &minus;12.4 s [95% confidence intervals (CI) &minus;19.7 s; &minus;7.3 s]) with Macintosh compared to VieScope (p &lt; 0.001). Concerning &ldquo;correct tube position&rdquo;, no statistical difference was found between the devices (p = 1.0). The mean time to first ventilation was &minus;11.1 s [95% CI &minus;18.3 s; &minus;5.3 s] when using Macintosh (p = 0.001). The mean volume of aspirated gastric fluid was lower in the Macintosh group: &minus;90.0 mL [95% CI &minus;235.0 mL; &minus;27.5 mL] (p = 0.011). Data from this simulation study suggest that in a model of massive gastric regurgitation, airway management can be achieved faster and with less gastric aspiration when using a Macintosh laryngoscope compared to a VieScope laryngoscope