SpO2 at baseline and on induction were no different across study arms (Table). Thereafter, individual patient SpO2 profiles varied considerably (Figure 3). Patients in the buccal oxygenation arm were less likely to reach SpO2 < 95% in the first 750 seconds of apnea; hazard ratio 0.159, 95% confidence interval 0.044–0.226, P < .0001 (Figure 4). This manifested in a longer median (IQR) safe apnea time; 750 seconds (389–750) vs 296 seconds (244–314), P < .0001 (Figure 5). Of note, 11 of 20 patients in both arms had at least the first twitch (T1) of the train-of-four present 150 seconds after rocuronium administration. At the end of the study, no difficult airways were encountered. Median SpO2 values briefly dropped in the standard care arm before reoxygenation occurred – the median (IQR) of the lowest observed SpO2 values was higher in the buccal oxygenation arm; 97 (92–99) vs 91 (89–92), P < .001. Peak end-tidal CO2 levels remained within a safe range. All patients had uneventful surgery and met recovery discharge criteria in the expected time course.
This study demonstrates a median safe apnea time of 12.5 minutes in obese patients receiving buccal RAE tube oxygenation; a 2.5-fold increase compared with standard care and the longest safe apnea time reported in a randomized trial. In the only comparable study in obese patients (BMI 31), low-flow oxygen via Salter type nasal prongs extended safe apnea by 1.8 minutes, with only 8 of 15 patients maintaining SpO2 ≥ 95% for the duration of a 6-minute apnea test.3 The long duration of efficacy with buccal oxygenation is consistent with clinical studies in nonobese patients,16 animal experiments,21 and physiologic simulators.22
The benefits of an extended period of safe apnea with buccal oxygenation are multiple. First, sufficient time can be allowed for full neuromuscular junction blockade before intubation attempts, even if ventilation difficulties are encountered—an issue highlighted in the current study by rocuronium onset times slower than values accepted in the literature.23 Second, once the feasibility of facemask ventilation is established, the need for further ventilation can be eliminated even during prolonged intubation attempts. This is particularly relevant where facemask ventilation may encourage aspiration, eg, during rapid sequence induction. Third, mitigating the stress of evolving hypoxemia in the unanticipated difficult airway will likely improve operator performance.24 The buccal RAE tube system can deliver these benefits with equipment that is well tolerated, inexpensive, and widely available across standard anesthetic departments.
A number of alternative apneic oxygenation devices are employed in clinical practice. Nasopharyngeal catheters deliver oxygen close to the laryngeal inlet, maximizing efficacy by maintaining a high supralaryngeal oxygen fraction22 and yielding near-perfect oxygenation in randomized trials.7 , 16 , 17 However, if oxygen flows do not vent through the mouth or nose after induction of anesthesia, significant barotrauma can occur—19 such cases spanning 5 decades were recently described.19 The use of nasal prongs rather than nasal catheters has also been investigated. Moderate gains in apnea times have been reported with low-flow oxygen delivery,3 , 16 and efficacy may be limited in obese patients by retropalatal obstruction under anesthesia.25 In contrast, high-flow nasal cannulae (HFNC) deliver flows up to 70 L/min and in the process generate continuous positive airway pressure (CPAP)—a feature that can overcome retropalatal obstruction and augment functional residual capacity.26 Indeed, Patel and colleagues successfully used HFNC at 70 L/min in a case series of 25 patients undergoing ear, nose, and throat surgery with known difficult airways,18 reporting a median apnea time (range) with SpO2 ≥ 90% of 14 (5–65) minutes and enhanced carbon dioxide clearance. Nevertheless, randomized studies of HFNC during intubation of critically ill patients have not reported efficacy,27 , 28 pharyngeal pressures can rise when the oral29–31 and nasal32 escape routes are attenuated, and bag-mask ventilation necessitates equipment removal, potentially rendering this an intermittent technique.
The buccal approach was designed to integrate seamlessly with existing airway management algorithms,33 to eliminate the risk of barotrauma, and to offer a viable alternative when nasal instrumentation is contraindicated. Importantly, the RAE tube positioned within the left buccal space allows normal use of Guedel, nasopharyngeal, and laryngeal mask airways, minimal interruption of facemask seal and unimpeded laryngoscopy. This position also ensures that any rise of pharyngeal pressure is vented through the oral escape route, comprising the sum interdental gap area during facemask application and the open mouth during prolonged laryngoscopy. In a lung model for jet ventilation, we have previously shown end-expiratory lung pressures to be under 1 cm H2O when oxygen is applied to the trachea continuously at 15 L/min in the presence of a 1.1-cm2 surface area expiratory pathway (published as abstract).34 By reducing the flow rate to 10 L/min for buccal oxygenation, we aimed to generate negligible CPAP while maintaining a high supralaryngeal oxygen fraction and a patent airway through sustained laryngoscopy. In contrast to HFNC, the benefits of 10 L/min are likely restricted to pure apneic oxygenation with little contribution from CPAP or ventilatory exchange. Where sustained laryngoscopy is judged inappropriate, alternative techniques to maintain airway patency (eg, jaw thrust, Guedel airway) could be deployed and warrant further investigation.
A third of patients receiving buccal oxygenation did not maintain SpO2 ≥ 95% for the full study duration. Potential explanations include protocol deviations and a failure to maintain either a high supralaryngeal oxygen fraction or a patent airway, despite good views on video laryngoscopy. The observed incidence of early study termination is also consistent with the high incidence of atelectasis and subsequent pulmonary shunt that occurs in obese populations under general anesthesia.35 , 36 Even when apneic oxygenation techniques are perfectly implemented in animals, large shunt values associate with rapid desaturation at the onset of apnea.37 In such models of shunt, arterial oxygen values equilibrate at a higher plateau with apneic oxygenation,22 , 37 suggesting patients with shunt may still derive benefit from buccal oxygen delivery despite early desaturation below SpO2 of 95%. Minimizing atelectasis and pulmonary shunt on induction of anesthesia will likely maximize the efficacy of apneic oxygenation, highlighting the importance of the reverse Trendelenburg position and the potential advantages of techniques that generate CPAP.18 High shunt may also explain the apparent lack of utility of apneic oxygenation during intubation of critically ill patients.27 , 28
There are a number of limitations to the current work. First, this was a nonblinded, single-center study with associated risks of investigator bias. Given the hard end point of time to SpO2 < 95%, these risks were minimized. A blinded design was deemed impractical at this stage of investigation, because buccal oxygen administration is both audible and visible, and cannot easily be substituted with an alternative gas flow that is physiologically neutral. Blinding in future studies may be achievable by using sham RAE tubes or a concealed 3-way tap directing oxygen or air flow toward or away from the oral cavity. Second, the rationale for an oxygen flow rate of 10 L/min was based on limited data. Although this rate proved effective, experimental designs with measurement of pharyngeal pressure generation, oxygen fraction above the larynx, and carbon dioxide clearance are required to better inform optimal flow rates. Third, although apneic oxygenation is functional across very small apertures, the utility of buccal oxygenation in patients that develop severe airway obstruction cannot be inferred. Finally, our study population did not include super morbidly obese patients, a particularly at-risk group during the induction of anesthesia.
In conclusion, buccal oxygen delivery is an inexpensive, readily available, and effective method of apneic oxygenation during prolonged laryngoscopy in obese patients. Importantly, it offers a viable alternative to the nasal route. Future studies should focus on larger, multicenter designs, with reporting of extended safety profiles and clinically relevant outcomes in high-risk patients.
Name: Andrew Heard, FRCA.
Contribution:This author helped conceive and design the trial, collect the data, and write the manuscript.
Name: Andrew J. Toner, FRCA.
Contribution:This author helped collect and analyze the data, and write the manuscript.
Name: James R. Evans, FRCA.
Contribution:This author helped collect and analyze the data.
Name: Alberto M. Aranda Palacios, FRCA.
Contribution:This author helped design the trial and collect the data.
Name: Stefan Lauer, MD.
Contribution:This author helped design the trial, collect the data, and write the manuscript.
This manuscript is handled by: Richard C. Prielipp, MD.
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© 2017 International Anesthesia Research Society
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