Year: 2019
Type: article
Abstract: In this issue of EClinicalMedicine, Vourc'h and colleagues [[1]Vourc'h M. Baud G. Feuillet F. Blanchard C. Mirallie E. Guitton C. et al.High-flow nasal cannulae versus non-invasive ventilation for preoxygenation of obese patients: the PREOPTIPOP randomized trial.EClinicalMedicine. 2019; 13: 112-119Summary Full Text Full Text PDF PubMed Scopus (29) Google Scholar] report the results of the PREOPTIPOP trial, the first randomized trial to compare non-invasive ventilation (NIV) versus high flow nasal cannula (HFNC) during tracheal intubation in the operating room. The trial enrolled 100 obese adults undergoing elective intubation in the operating room of a single medical center. Patients randomized to NIV received 100% oxygen with an inspiratory positive airway pressure of 15 cm H2O and an expiratory positive airway pressure of 5 cm H2O from the start of pre-oxygenation until the patient developed apnea after induction. Patients randomized to HFNC received 60 L/min of 100% oxygen via nasal prongs from the start of pre-oxygenation until intubation of the trachea. Patients randomized to NIV had higher end-tidal oxygen concentrations following intubation (88%, inter-quartile range 82% to 90% vs. 76%, inter-quartile range 66% to 82%; P < 0.0001) and a lower incidence of arterial oxygen saturation less than 95% (30% vs. 12%; P = 0.03). The incidence of moderate or severe complications did not differ between groups. These results are consistent with those of other recent trials demonstrating the benefit of providing positive pressure during preoxygenation [2Baillard C. Fosse J.-P. Sebbane M. et al.Noninvasive ventilation improves preoxygenation before intubation of hypoxic patients.Am J Respir Crit Care Med. 2006; 174: 171-177Crossref PubMed Scopus (324) Google Scholar, 3Baillard C. Prat G. Jung B. et al.Effect of preoxygenation using non-invasive ventilation before intubation on subsequent organ failures in hypoxaemic patients: a randomised clinical trial.Br J Anaesth. 2018; 120: 361-367Summary Full Text Full Text PDF PubMed Scopus (33) Google Scholar] and during the period from induction to laryngoscopy [[4]Casey J.D. Janz D.R. Russell D.W. et al.Bag-mask ventilation during tracheal intubation of critically ill adults.N Engl J Med. 2019; 380: 811-821Crossref PubMed Scopus (94) Google Scholar]. High flow nasal cannula (HFNC) has been proposed for use in preoxygenation because it provides a high concentration of inhaled oxygen, decreases work of breathing, washes out anatomic dead space, and provides a low level of continuous positive airway pressure [5Mauri T. Turrini C. Eronia N. et al.Physiologic effects of high-flow nasal cannula in acute hypoxemic respiratory failure.Am J Respir Crit Care Med. 2016; (published online Dec 20)https://doi.org/10.1164/rccm.201605-0916OCCrossref Scopus (276) Google Scholar, 6Parke R.L. McGuinness S.P. Pressures delivered by nasal high flow oxygen during all phases of the respiratory cycle.Respir Care. 2013; 58: 1621-1624Crossref PubMed Scopus (180) Google Scholar]. Additionally, HFNC can be left in place after induction, providing “apneic oxygenation,” at a time when laryngoscopy requires removal of face masks used for bag-mask ventilation or non-invasive ventilation. Trials evaluating preoxygenation and apneic oxygenation with HFNC, however, have largely shown disappointing results [7Vourc'h M. Asfar P. Volteau C. et al.High-flow nasal cannula oxygen during endotracheal intubation in hypoxemic patients: a randomized controlled clinical trial.Intensive Care Med. 2015; 41: 1538-1548Crossref PubMed Scopus (184) Google Scholar, 8Simon M. Wachs C. Braune S. de Heer G. Frings D. Kluge S. High-flow nasal cannula versus bag-valve-mask for preoxygenation before intubation in subjects with hypoxemic respiratory failure.Respir Care. 2016; 61: 1160-1167Crossref PubMed Scopus (77) Google Scholar, 9Guitton C. Ehrmann S. Volteau C. et al.Nasal high-flow preoxygenation for endotracheal intubation in the critically ill patient: a randomized clinical trial.Intensive Care Med. 2019; (published online Jan 21)https://doi.org/10.1007/s00134-019-05529-wCrossref PubMed Scopus (65) Google Scholar], particularly when HFNC is compared against NIV [[10]Frat J.-P. Ricard J.-D. Quenot J.-P. et al.Non-invasive ventilation versus high-flow nasal cannula oxygen therapy with apnoeic oxygenation for preoxygenation before intubation of patients with acute hypoxaemic respiratory failure: a randomised, multicentre, open-label trial.Lancet Respir Med. 2019; 0https://doi.org/10.1016/S2213-2600(19)30048-7Summary Full Text Full Text PDF Scopus (86) Google Scholar]. The higher mean airway pressures achieved by non-invasive ventilation may outweigh the potential benefits of apneic oxygenation. Alternatively, non-invasive ventilation may assist ventilation, delivering highly oxygenated air to the distal alveolar spaces more effectively than apneic oxygenation. Although incomplete, the data currently available suggest that, for many patients, positive pressure ventilation with NIV may be more effective than HFNC for preventing hypoxemia during tracheal intubation. To our knowledge, this is the first airway management trial in which end-tidal oxygen concentration (EtO2) has been used as a surrogate outcome for patient oxygenation status during intubation. EtO2, the oxygen concentration at the end of an exhaled breath, reflects the oxygen concentration in the alveolar space, an important determinant of the arterial partial pressure of oxygen. Previous guidelines have suggested using EtO2 concentrations to ensure adequate preoxygenation [[11]Frerk C. Mitchell V.S. McNarry A.F. et al.Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults.Br J Anaesth. 2015; 115: 827-848Summary Full Text Full Text PDF PubMed Scopus (1150) Google Scholar]. Measuring EtO2 at induction, however, neglects the potential effects of preoxygenation device on functional residual capacity after induction or ongoing oxygen administration during apnea. In contrast, the PREOPTIPOP trial used the nadir in EtO2 that occurs following intubation as a measure of the lowest alveolar oxygen concentration during the entire intubation procedure. There are important reasons to explore additional measures of oxygenation during intubation beyond arterial blood gas (ABG) analysis and oxygen saturation by pulse oximetry (SpO2). ABG's are invasive, slow to provide results, and may miss the nadir in oxygen content as they cannot be obtained continuously. SpO2 has an upper threshold at 100% when all hemoglobin is saturated with oxygen, which occurs near an arterial partial pressure of oxygen (PaO2) of 100 mm Hg in most patients. This means that SpO2 cannot detect any changes in PaO2 occurring from 100 mm Hg to 650 mm Hg, the range of values that typically occur during intubation in the operating room. The nadir of EtO2 following intubation is related to the same variables that determine arterial oxygen content: 1) the alveolar oxygen concentration at the end of preoxygenation, 2) the volume of air in the lungs at the end of pre-oxygenation, 3) the rate of oxygen uptake (metabolic rate), and 4) the duration of apnea. As a surrogate for PaO2 unencumbered by the upper threshold experienced by SpO2, the nadir of EtO2 during intubation could be valuable as an outcome in populations with a low incidence of hypoxemia. However, unlike arterial measures of oxygenation, EtO2 concentrations are susceptible to measurement error from entrained air, and EtO2 concentrations at the end of intubation may be impacted by dead space to a much greater extent than EtO2 measured at the end of preoxygenation. Portions of the lung without perfusion (dead space) will not participate in gas exchange during the apneic period and will return highly oxygenated air that is not representative of the partial pressure of oxygen in the portions of the lung participating in gas exchange. In a trial comparing peri-intubation interventions, however, a higher EtO2 is still better, as the authors demonstrate by showing the correlation between end-tidal oxygen concentration and the incidence of oxygen saturation less than 95% by pulse oximetry. In summary, the authors of the PREOPTIPOP trial are to be congratulated for conducting a rigorous study, which adds to a growing body of literature outlining the potential benefits of positive pressure ventilation during tracheal intubation. While questions remain about the best surrogate outcome for airway management research, the nadir of end-tidal oxygen provides another method of monitoring patient oxygenation during this high-risk procedure. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported. High-flow Nasal Cannulae Versus Non-invasive Ventilation for Preoxygenation of Obese Patients: The PREOPTIPOP Randomized TrialCompared with NIV, preoxygenation with HFNC in obese patients provided lower EtO2 after intubation and a higher rate of desaturation <95%. Full-Text PDF Open Access
Source: EClinicalMedicine
Authors: Jonathan D. Casey, Matthew W. Semler
Institution: Vanderbilt University
Language: English
Subfield: Anesthesiology and Pain Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: gold
Estimated APC paid: $3,500
OpenAlex ID: W2963487817