Evaluation of sleep apnea syndrome with low-field magnetic resonance fluoroscopy

Airways ultrasound in predicting difficult face mask ventilation

BACKGROUND

Unanticipated difficult airway is a potentially life-threatening event during elective surgery or management of critical conditions. Nevertheless, predicting difficult mask ventilation currently remains a challenge due to the poor sensitivity of available clinical tests. Our primary goal was to verify whether preoperative upper airway ultrasound measurements were useful to predict difficult face mask ventilation. Our secondary goal was to evaluate clinical characteristics and differences between patients who are difficult to ventilate and patients who are not.

METHODS

We performed a prospective observational study, enrolling 250 adult patients selected for colorectal, gastric, bariatric and pancreatic elective surgery between September 2017 and October 2018. We performed a preoperative US assessment of the airways, following a standardized protocol. We measured the hyomental distance (DIM), the thickness of the base of the tongue (SBL), the thickness of the soft tissues anterior to the hyoid bone (STTi), thyro-hyoid distance (DTI), the thickness of soft tissue anterior to the epiglottis (STTe), to the arytenoid (STTa) and to the commissure of the vocal cords (STTcv).

RESULTS

SBL had a predictive role of difficult mask ventilation in curarized and noncurarized patients for values higher than 50 mm. Hyomental distance with hyperextension of the head and subluxation of the mandible (DIMs) had a predictive role in the curarized patient (protective parameter).

CONCLUSIONS

Airways ultrasound evaluation could be an important tool to predict difficult mask ventilation. Further studies are necessary to validate the parameters found and correlate them to the preoperative clinical evaluation.

Obesity and obstructive sleep apnoea: mechanisms for increased collapsibility of the passive pharyngeal airway

Epidemiological evidence suggests there are significant links between obesity and obstructive sleep apnoea (OSA), with a particular emphasis on the importance of fat distribution in the development of OSA. In patients with OSA, the structure of the pharyngeal airway collapses. A collapsible tube within a rigid box collapses either due to decreased intraluminal pressure or increased external tissue pressure (i.e. reduction in transmural pressure), or due to reduction in the longitudinal tension of the tube. Accordingly, obesity should structurally increase the collapsibility of the pharyngeal airway due to excessive fat deposition at two distinct locations. In the pharyngeal airway region, excessive soft tissue for a given maxillomandibular enclosure size (upper airway anatomical imbalance) can increase tissue pressure surrounding the pharyngeal airway, thereby narrowing the airway. Even mild obesity may cause anatomical imbalance in individuals with a small maxilla and mandible. Lung volume reduction due to excessive central fat deposition may decrease longitudinal tracheal traction forces and pharyngeal wall tension, changing the 'tube law' in the pharyngeal airway (lung volume dependence of the upper airway). The lung volume dependence of pharyngeal airway patency appears to contribute more significantly to the development of OSA in morbidly obese, apnoeic patients. Neurostructural interactions required for stable breathing may be influenced by obesity-related hormones and cytokines. Accumulating evidence strongly supports these speculations, but further intensive research is needed.

Diagnostic imaging and sleep medicine

Obstructive sleep apnea syndrome (OSAS) is a relatively common disorder characterized by recurrent episodes of upper airway collapse and obstruction during sleep. It results in apneic events (or in the case of partial obstruction, hypopneic events) that lead to loud snoring, hypoxia, and arousals that interrupt the normal sleep cycle. Typically, these nocturnal arousals cause patients to complain of excessive daytime sleepiness, which may interfere with routine daily activities. More importantly, when moderate to severe, OSAS can lead to a wide variety of medical complications, some of which can result in severe consequences or even death.

Dynamic interaction between the tongue and soft palate during obstructive apnea in anesthetized patients with sleep-disordered breathing

Little is known about the mechanisms of persistence of obstructive apnea. Structurally, the dorsum of the tongue locates anterior to the soft palate. On the basis of the observation of posterior displacement of the tongue during obstructive apnea, we hypothesized that the dorsum of the tongue pushes the anterior wall of the soft palate posteriorly during inspiratory efforts, maintaining closure at the retropalatal airway. To test this hypothesis, we measured the pressure between dorsum of the tongue and anterior wall of the soft palate (PT&P) during experimentally induced obstructive apneas in anesthetized patients with sleep-disordered breathing. P(T&P) changes during the obstruction significantly depended on collapsibility of the retroglossal airway. Progressive increase in the P(T&P) during obstructive apnea was observed only in patients with highly collapsible retroglossal airways. Significant increase in the P(T&P) during inspiratory effort in accordance with positive deflection pattern of P(T&P) tracing was evident in the patients with highly collapsible retroglossal airways. The results indicate significant dynamic interaction between the tongue and soft palate during both obstructive apnea and each inspiratory effort, possibly maintaining closure at the retropalatal airway.

Sites of obstruction in obstructive sleep apnea

STUDY OBJECTIVE

The aim of this article was to identify the most common sites of obstruction in patients with obstructive sleep apnea (OSA) by a systematic review of published studies.

DESIGN

The review was conducted by a MEDLINE search of the English literature published during the years 1980 to 2002. The inclusion criteria were experiments involving five or more adult subjects, total rather than partial obstruction or narrowing of the upper airway, and techniques that were performed on the subjects while they were asleep.

CONCLUSION

Although there was considerable variability in the techniques and the results, the most common site of obstruction detected by these studies was at the level of the oropharynx, with extension to the laryngopharynx commonly observed.

Videoendoscopic Assessment of Uncommon Sites of Upper Airway Obstruction during Sleep

Patients with sleep-disordered breathing (SDB) suffer from repetitive upper airway occlusion. Various techniques have been described to assess the site of upper airway collapse. In most cases the soft palate or the base of tongue, or both, are the major levels of obstruction; rarely, the larynx, including the epiglottis, are found to be involved. We present five cases in which sleep videoendoscopy finally revealed the true mechanism of the inspiratory airway behavior. Two patients were sent to our service because of inefficacy of nasal ventilation therapy. One had a floppy epiglottis that was being sucked into the glottis. The other had a normal larynx during videoendoscopy. Instead, common pharyngeal collapse could be detected. Increasing the pressure normalized sleep, breathing, and videoendoscopy. The third patient showed apneas due to the adduction of the lateral parts of his omega-shaped epiglottis. In another case, inspiratory fluttering of the vocal cords caused snoring and arousals. The last case came in for bilateral vocal cord palsy with heavy nocturnal desaturations suggesting airway closure. Yet, the pharynx and larynx remained open throughout the night. Sleep videoendoscopy is a convenient method to define the level and mechanism of occlusion in obstructive SDB, particularly if the larynx is involved. It is useful to rule out airway compromise in case of recurrent nocturnal hypoxemias. Thus the results of sleep videoendoscopy have a strong therapeutical impact.