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Dr. Sanders is Professor of Medicine and Drs. Strollo and Atwood are Associate Professors of Medicine, Division of Pulmonary, Allergy & Critical Care Medicine; Dr. Braun is Professor and Chair, Department of Oral Maxillofacial Surgery; and Dr. Johnson is Professor and Vice-Chairman, Department of Otolaryngology Head and Neck Surgery, University of Pittsburgh School of Medicine.
Correspondence to: Mark H. Sanders, MD, FCCP, University of Pittsburgh School of Medicine, 3550 Terrace St, 440 Scaife Hall, Pittsburgh, PA 15261
A patient has complaints of right-sided abdominal discomfort, fatty-food intolerance, bloating, and nonspecific physical findings. Gallstones are noted on ultrasonography, and the gall bladder is not visualized on a technically adequate cholecystogram. After there has been no response to medical therapy directed toward dyspepsia, the patient’s physician has reasonably localized the problem to the gall bladder. This site has obviously well-defined "margins" (when it is out, it is out), and following cholecystectomy, the surgeon is secure in the knowledge that he/she has addressed problems that are specifically related to this organ. If symptoms persist, one can definitively eliminate the gall bladder as the source, with the patient having undergone an effective operation that was directed at the wrong diagnosis. Unfortunately, the same cannot be said of the upper airway as it relates to patients with obstructive sleep apnea/hypopnea (OSA/H). As has been frequently noted in these pages as well as elsewhere, the upper airway serves many physiologic and functional masters, accommodating to the demands of speech, deglutition, and breathing. We are aware that each of these charges requires unique and potentially competing properties. Inappropriate synchronization of these services may have disastrous outcome (eg, choking), requiring rescue by built-in protective mechanisms.
The gall bladder is an obviously well-defined anatomic structure, the removal of which is well tolerated and resolves the consequences of dysfunction. Obviously unlike caring for a patient with gall bladder disease, a surgeon attending an OSA/H patient cannot excise the upper airway in its entirety. Unless the specific location of the upper airway dysfunction is identified, the problematic region may not be addressed, an issue that will only come to light following recovery from surgery. As a result, there is an advocacy for "site-specific" upper airway surgery for OSA/H patients, which is prompted by the imperative to treat only the dysfunctional aspects of airway control and to minimize the adverse impact that anatomic restructuring may have on the myriad of its other mandates.1 2 3 4 5 6 It is intuitively sensible that if the obstructing region can be identified in any given patient, the surgery should be designed accordingly and the problem solved after a single procedure, much like a cholecystectomy. However, instituting this scenario presupposes that we, as physiologists and clinicians, understand the normal mechanisms of upper airway function and dysfunctional sleep. Although there has been considerable progress over the last 2 decades, we challenge the contention that such knowledge is available. Efforts to identify the site, much less the mechanism of upper airway obstruction in a manner that assists surgeons, have lead to disappointing results. The Mueller maneuver performed during wakefulness with nasopharyngeal endoscopic observation, assessment of the level of obstruction using a multilevel pressure-sensor catheter, and fiberoptic evaluation of regional upper airway collapsibility during pharmacologically induced sleep have arguably not proven to be either useful or practical predictors of surgical outcome.7 8 9 10
There are many unique challenges to designing and evaluating optimal surgical paradigms for OSA/H. First, one may ask if, unlike gall bladder surgery, it is unrealistic to conceive of truly site-specific procedures on the upper airway. It may be naïve to think that surgical manipulation of one part of the airway has no impact on function in other locations. In the current issue of CHEST (see page 1519), Dr. Prinsell presents his approach to site-specific intervention. However, although maxillomandibular advancement (MMA) was performed in patients believed to have hypopharyngeal obstruction, postoperative cephalometric imaging revealed shortening of the soft palate. Additionally, a number of Dr. Prinsell’s patients had undergone concomitant surgery on structures that might be interactive in the pathogenesis of upper airway dysfunction, even though these structures may not have been located in the hypopharynx. In this light and in view of the likelihood that function and dysfunction across regions of the upper airway are interrelated, it may be prudent to conceive of "procedure-specific" outcomes instead of site-specific surgery.
Our current level of ignorance regarding the pathophysiology of OSA/H obfuscates assessment of treatment outcome and provides a unique challenge to those of us in the field of sleep medicine. Comparing the efficacy of different techniques for gall bladder surgery is relatively straightforward, with traditional and well-defined outcome measures. There are few critics who would find fault with assessment of hard end points such as postoperative vital signs, pulmonary mechanics, oxygenation, and radiographic abnormalities in comparing laparoscopic and open cholecystectomy.11 In contrast, the concept of hard measures of therapeutic outcome following OSA/H treatment (medical and surgical) is confounded by uncertainties regarding the physiologic and clinical significance of currently employed parameters of breathing during sleep (eg, what parameter is the appropriate measure of disease?). Even if there was agreement regarding the proper metric(s) of outcome, there remain important unresolved technical issues including variability in recording techniques and criteria used to define an abnormality for any given variable across studies.12 13 Attempts are underway to address these issues,14 15 but currently it remains difficult to determine if disparate results across investigations, even those examining what is putatively the same intervention, are biological or methodologic in nature. No solution is currently operational, and clinicians and researchers must continue to work around these shortcomings. It is nonetheless essential to consider the potential impact of these deficits in critically assessing the literature. In this context, interpreting the results of the current paper in CHEST is complicated by assessments utilizing data collected across a number of different laboratories. Dr. Prinsell appropriately points out that this must be considered when interpreting his results, despite the fact that all of these facilities used "conventional criteria." Other confounding elements such as weight change (Dr. Prinsell’s patients lost an average of 2 kg/m2 from the pre- to postoperative polysomnogram) must be considered and the data adjusted accordingly. Particularly in view of the limitations that we are currently unable to address, research studies must be designed to minimize methodologic variability and to adjust for confounding factors.
In addition to the above issues, which globally influence assessment of both surgical and medical treatment outcomes, some considerations uniquely challenge the surgeons in designing efficacy studies. It is clear that the highest level of evidence comes from prospective, randomized controlled trials. This may be relatively easy in assessing medical therapy (eg, positive pressure vs a "pill") that does not entail irreversible interventions. Randomizing OSA/H patients to one or another surgical procedure may be more technically and perhaps ethically vexing, but it has been done in other areas of surgery.11 Future patients benefit from optimally designed research. There also remains the even-more-difficult-to-resolve potential for subtle or not-so-subtle differences across surgeons with regard to technique in performing what is termed the "same procedure." This factor could conceivably complicate multicenter trials. Although technical differences could be a consideration in assessing the literature on gall bladder surgery outcome, it is doubtful that these would be as significant as are the potential variations in the degree to which the mandible is advanced, the volume of soft palate that might be resected, or the location from which the hyoid bone is resuspended. Finally, persistent symptoms after cholecystectomy indicates that the cause of the problem was not identified. On the other hand, if a patient fails to improve following upper airway surgery, it may be due to an otherwise effective procedure directed to the wrong location in the airway, an ineffective procedure directed toward the correct location, an ineffective procedure directed to the wrong location, or the presence of comorbid disease. Resolution of this dilemma depends on greater pathophysiologic insight to provide better matching of the patient and the procedure. We are not there yet.
In summary, we must conclude that the upper airway is not like the gall bladder, and in light of the above discussion (as well as for a variety of other reasons), it probably never will be. We admit to stretching our point. However, if surgery for OSA/H is going to evolve into a routinely successful treatment alternative, as it has for gall bladder disorders, rigorous attention to the Scientific Method must be applied in its development. If site-specific surgery is possible, and even if it is not, we must first have more "specific insight" into the mechanisms of upper airway function and dysfunction during sleep.
References
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