In an apneic patient approximately 250 mL/minute of oxygen moves from the alveoli into the bloodstream. Conversely, only 8-20 mL/minute of carbon dioxide buffered in the bloodstream; this causes the net pressure in the alveoli to become slightly subatmospheric, generating a mass flow of gas from pharynx to alveoli via diffusion.Regarding CO2 concentrations, Patel et al., 2015 provided evidence of those concentrations during apnea. Figure 1 shows the rate of CO2 concentration levels rising in various forms of apnea.It’s interesting to note that traditional apneic oxygenation has a similar rate of CO2 concentration rise when compared to airway obstruction. High-flow oxygen therapy through a nasal cannula is a technique whereby oxygen is delivered to the nose at high flow rates. Higher flow rates generate low levels of positive pressure in the upper airways, and the fraction of FiO2 can be adjusted by changing the fraction of oxygen in the driving gas.The high flow rates may also decrease physiological dead space by flushing expired CO2 from the upper airway.The time period between becoming apneic and oxygenated via intubation is a vulnerable moment in the patient’s oxygen status, and can possibly be alleviated by using a nasal cannula. It was noted that traditional apneic oxygenation has a similar rise in CO2 concentration as an airway obstruction; so, can the use of nasal cannula during endotracheal intubation prevent oxygen desaturation? While various devices are used to preoxygenate patients, no standardized protocol exists. Despite the use of this technique by both anesthesiologists and EPs, to date implementing a nasal cannula during intubation has not been part of the standard of care in these procedures. The objective of this review was to evaluate studies that provide evidence for HFNC efficacy in preventing oxygen desaturation during intubation.Desaturation in apneic patients undergoing rapid sequence intubation procedures is predictable and reproduceable. In fact,cannabis drying racks desaturation rates are also determined by the patient’s underlying condition and body habitus.
In periods of apnea or a completely obstructedairway, the time to desaturation is much shorter in obese adults and in children, demonstrated by a precipitous drop of hemoglobin oxygen levels after only 2.5-3.5 minutes. Depending on the emergency such as cardiac arrest or a trauma, which can affect cardiac output, the time to desaturation in such populations will likely be even shorter. The effects of hypoxemia can take place rather quickly: thus the need for quick intervention.In this paper, we examined 18 studies through a standardized literature search. Methodologically, all studies were performed with the same protocol of preoxygenation prior to and followed by nasal cannula use during intubation, lending more credence to its favorable results. Of those 18, 14 studies pointed towards the use of nasal cannula during intubation carrying benefits to the patient undergoing intubation, while nine studies reported an increase or maintenance of oxygen saturation levels. Despite patients having various medical conditions, nasal cannula use during intubation extended the duration of safe apnea. The gaps in current research include the following: the use of varying levels of oxygen flow such as 5L vs. 15L O2 and whether or not it is efficacious in diverse presenting medical conditions such as trauma, anaphylaxis, or other comorbidities. Apneic oxygenation provides significant benefit in terms of improving SpO2 for most intubations. Miguel Montanes et al., 2005 concluded that HFNC was found to be more effective than a NRB mask for preoxygenation in intensive care unit patients by improving SpO2. It remains unclear how the use of HFNC compares with preoxygenation using a combination of standard nasal cannula and a NRB mask, or to the combination of standard nasal cannula and use of a BVM with a PEEP valve for apneic oxygenation. Although HFNC cannot compensate for ineffective preoxygenation, it may serve as a useful apneic oxygenation adjunct by extending safe apnea time.
Further research is required to solidify or refute this consistent evidence. While most studies concluded there was a benefit of apneic oxygenation to prevent desaturation during intubation, four studies found no benefit.Of these, three are high-quality, randomized control trials and do not show statistical support.One should note the characteristics of the patients. The study population in Semler et al., 2015 were ICU patients requiring intubation, while those in Vourc’h et al., 2015 were in respiratory failure; this points toward no benefit when hypoxic respiratory failure is the indication for intubation.Similarly, in Caputo et al., 2017 the majority of patients in both the apneic oxygenation group and standard-of-care group were intubated due to a “pulmonary” indication, totaling 60% of the patient population. Considering the majority of intubations were performed due to “pulmonary” related causes, one would expect a non-significant result, which is consistent with Semler et al., 2015 and Vourc’h et al., 2015. In contrast, the studies of patients undergoing elective surgery showed significant increases in time to oxygen desaturation, demonstrating that apneic oxygenation prior to intubation is only helpful in certain conditions, namely non-respiratory.While Caputo et al., 2017 analyzed apneic oxygenation from a broad mix of medical conditions and did not show statistical significance, it did not distinguish between the intervention’s efficacy in respiratory vs. non-respiratory causes as the results reflect all conditions. The reason that patients in respiratory failure or who are hypoxic prior to intubation do not benefit from apneic oxygenation is unclear. One hypothesis posits the development of pulmonary circulatory shunting, rendering passive ventilation ineffective.In light of Caputo et al., 2017, it continues to be confirmed that patients with respiratory failure or who are hypoxic prior to intubation are unlikely to benefit. White et al., 2017 provided strong evidence for the benefit of apneic oxygenation in terms of improved SpO2 in surgical patients, obese patients,hydroponic cannabis system and those undergoing emergency intubation without respiratory failure.
No significant benefit was found in patients with respiratory failure.Binks et al., 2017 found significant reduction in the incidence of desaturation and critical desaturation when apneic oxygenation was administered.There was also significant improvement in first-pass intubation success rate.Similarly, Pavlov et al., 2017 found that apneic oxygenation reduced the relative risk of hypoxemia, along with a significant trend toward lower mortality.From previous reviews of this intervention, we agree with their findings that there is strong evidence for the use of apneic oxygenation during intubation.There have been relatively few studies of apneic oxygenation in the emergency department ; thus, more investigation is warranted, particularly between apneic oxygenation prior to intubation in respiratory and non-respiratory causes.These often include acombination of auscultation, capnography, or ultrasound. However, there are inherent limitations with each of these methods. The potentially loud environment of the ED can make auscultation difficult, and quantitative capnography is not universally available at all centers.1 Ultrasound has been demonstrated to confirm ETT placement rapidly and accurately with recent meta-analyses demonstrating accuracy approaching that of capnography.Additionally, ultrasound offers the advantage of directly visualizing the location of the ETT in cases when capnography may be less reliable.However, studies have varied in the techniques described, with some using real-time, dynamic confirmation, while others use post-intubation, static imaging. The goal of this study was to determine whether there was a difference in the accuracy between the static and dynamic approaches when confirming ETT location. Secondary outcomes included time to identification and operator confidence.This was a blinded, randomized, controlled trial performed in the cadaver lab of an academic hospital located in Chicago, Illinois. Three cadavers with different neck circumferences were used to simulate the variations in live patient populations. Cadaver #1 had a neck circumference of 32 cm, cadaver #2 had a neck circumference of 34 cm, and cadaver #3 had a neck circumference of 37 cm. Local institutional review board approval was obtained for this study with waiver of informed consent. This study was conducted in accordance with the Standards for the Reporting of Diagnostic Accuracy studies criteria.Two attending emergency physicians with extensive intubation experience intubated each cadaver with a size 7.0 ETT using video laryngoscopy. Each cadaver was randomized a priori to either tracheal or esophageal intubation using a random number generator, with the goal of having equivalent numbers of tracheal and esophageal intubations in order to best define the test characteristics of each approach. The video screen was directed away from the sonographers and the intubating providers were instructed to look away after placement to avoid any potential reaction to bias the sonographers.
Two ultrasound fellowship-trained sonographers with prior experience in the use of ultrasound for ETT confirmation performed the assessments. A Zonare Z.One PRO ultrasound machine with an L14-5 linear transducer was used for all of the assessments. For each intubation, the dynamic technique was performed first by one sonographer. Then, the ETT was left in position while the other sonographer performed the static technique. Sonographers performed assessments in an alternating sequence of dynamic and static techniques to reduce the risk of shortening the learning curve with one technique. Each sonographer would leave the room after performing the sonographic assessment, so that neither sonographer was in the same room at the same time. For the dynamic technique, sonographers placed the ultrasound transducer across the neck at the suprasternal level to locate the trachea and surrounding tissues.Visualization of motion artifact within the trachea confirmed tracheal intubation. Visualization of a “second trachea” lateral to the true trachea confirmed esophageal intubation. For the static technique, sonographers placed the transducer in the same location post-intubation, while the intubator gently rotated the tube side-to-side to create a motion artifact.Presence of movement within the trachea confirmed tracheal intubation, while visualization of the “second trachea” confirmed esophageal intubation. A research assistant recorded the sonographer’s prediction of the ETT location, time to ETT prediction, and operator level of confidence after each intubation. Operator confidence was assessed using a Likert scale ranging from 1-5 with 1 signifying “not confident at all” and 5 signifying “very confident.” We performed a comparison between the predicted and actual location after study completion. With an estimated 120 readings each for static and dynamic techniques, 95% level of significance, and a moderate effect size , the expected power for the study was above 90%. We used Microsoft Excel and SPSS statistical software to conduct the analysis. We used descriptive statistics, chi-square test, andt-test to analyze the relationships between the ultrasound static and dynamic techniques with respect to the accuracy of correctly identifying location of intubation, operator time to identification, and operator confidence. In addition, we included moderating variables such as operators, cadaver number, and actual location of the intubations in the analysis.In the ED setting, it is essential to quickly and accurately confirm correct ETT placement. While there are many options for confirmation, each has its own limitations. In fact, even colorimetric capnography may have false positives and negatives, resulting in an accuracy as low as 67.9% during cardiac arrest.Ultrasound has been suggested to be particularly valuable in this application due to the ability to rapidly identify ETT location without requiring ventilations and the subsequent risk of gastric distention and aspiration if the ETT is incorrectly placed. However, current studies have used a variety of techniques, with some relying upon a static assessment, while others use dynamic assessments.This is one of the first studies to directly compare static with dynamic ultrasound for the identification of ETT location, demonstrating no statistically significant difference between techniques. This is an important finding, as there has been concern that performing dynamic sonography for ETT confirmation may be more challenging because it requires more than one trained provider to be available to perform the confirmation.This may prevent the use of this technique in locations where only one ultrasound-trained provider is present. By twisting the ETT in one’s fingers post-intubation, the provider is able to replicate the dynamic technique without the need for a second provider. Additionally, with the dynamic technique, placement is best assessed as the ETT is being inserted, and localization may be more limited if the ETT is not immediately identified during the intubation attempt. Finally, having the ultrasound probe on the neck may make the intubation attempt more difficult by providing extra pressure on the trachea and distorting upper airway anatomy. Alternatively, by performing the technique post intubation, the neck remains unencumbered, thereby allowing the intubating provider to also perform external laryngeal manipulation if needed. Interestingly, we found no difference in the confirmation time or operator confidence.