Discussion
Our study demonstrated significant increase in PIP with the use of simple NIV of “PhO2-NC” as an SPI technique. To the best of our knowledge, this is the first such study in the medical literature. Even with the frequent use of NIV worldwide, the types of device and the modes of delivery being used vary among countries and institutes. Clinically, this SPI is unique as it waives using other supplementary instruments, except a small oxygen catheter, and bronchoscopist himself can easily handle and control the whole procedure.
The PLS is a fibromuscular tube-like structure that is semicircular in cross section and relatively closed space. It serves as a continuation of the aerodigestive cavity, providing pathway from the nasal and oral cavities to the trachea, esophagus and the bilateral middle ears. PLS boundaries almost with soft tissues of the mouth and the nasal choanae anteriorly; the soft palate, velum, and portion of the skull base superiorly; the tonsils laterally; the inlets of larynx and esophagus inferiorly; and the pharyngeal constrictors posteriorly. Therefore, the PLS is a potential dynamic space which expands with increasing inside pressure.
FB examination via nasal track can offer real-time visualization and assessment of the whole PLS. FB is useful for detecting dynamic images that better demonstrate the presence, location, degree and extent of lesions. In this study, an optional action of SPI by PhO2-NC could create enough and controllable positive distending pressure which helps to open and expand the PLS, increase the cross-sectional area, and therefore allow accurate and precise inspection the anatomic structure with FB. Especially when there are pressure dynamic lesions which may lead to collapse or block airway path such as pharyngomalacia, adenoid hypertrophy, tonsil hypertrophy, vallecular cyst, laryngomalacia or glottis malacia laryngeal cleft, etc. as shown in the Figure 3 and Figure 4. While patients are sedated, these lesions may cause difficult breathing, hypoxia and desaturation. During FB interventions, these lesions may remain unrecognized when using traditional technique without appropriate or controllable pressure in the PLS. The PhO2-NC itself can provide simultaneous and optional PPV. This is not only safe for the patient, but also assists for the therapeutic intervention of FB such as doing laser partial adenoidectomy and tonsillectomy, check bleeding, marsupialization of vallecular cyst,11epiglottoplasty,16 etc. Our team has already been using this SPI modality successfully in many pediatric endoscopy interventions of airway9-16 and esophagus.17,18
Physiologically, this PhO2-NC has combinational effects of “apnea oxygenation” 19-23 and PPV. In the setting of PhO2, the continuous flow indeed fully fills the PLS with oxygen. For apnea oxygenation, randomized controlled trials have shown that it can extend the period of safe apnea, and reduce the unintended hypoxemia when used in patients after sedation or muscle paralysis, even with difficult airways. PhO2 with addition of optional NC as SPI, both PIP and PPV can be created and sustained for a demand period. This allows appropriate and controllable levels of pressure and times to expand the collapsed PLS for FB detail inspection, as well as performing diagnostic and therapeutic interventions. Furthermore, it may also promote the pressurized oxygen flow into the lower airways and lungs.20‐24
The modality of FB with this SPI offers several clinical advantages. First, transnasal approach of FB provides a good assessment for dynamic movements of airway lumens, as in small infants. Second, the ventilation interface of this SPI is in the PLS, near the larynx, which much reduces the respiratory dead-space. Third, this SPI is an easy PPV technique that can be performed with only a continuous gas (oxygen or air) flow and a soft catheter with distal tip sitting in the pharynx that minimizes impediment to airway access during FB procedures. FB operator can provide PPV himself while simultaneously execute FB interventions. Fourth, SPI can gradually and appropriately open and expand a collapsed PLS, as demonstrated in this study, which facilitates the passage of FB for thorough measurement of the PLS. This allows clear visualization of contents, structures and lesions that helps to yield more accurate diagnosis and subsequent effective management. All of these can be achieved without interference by artificial airway devices of facemask, nasal prong, LMA or ETT. Fifth, it is technically simple and readily available, therefore, can be used in resource‐limited scenarios. Sixth, it causes less distortion in PLS structure, less invasive, better‐tolerated and cost‐effective compared to the traditional techniques of PPV. In this study, the trend of long SPI presents more effective than short SPI to more expansion of airway space for better and detailed measurement which not easily be achieved in lower inflation levels. Furthermore, these positive and dynamic pressures of SPI may also transmit and facilitate tracheobronchial lumen expansion and lung ventilation. For patients with risk of compromised airway and oxygen desaturation, SPI may provide ventilation and reduce hypoxia, therefore, facilitate patient safety and FB procedures.
We observed that significant number of observations achieved very high PIP at SPI duration of 5 seconds. We did not observe any adverse effects of high PIP as it was used only transiently for our study. But safety of such high pressure cannot be confirmed due to small sample size of our cohort. We recommend SPI duration of 1-3 seconds for routine ventilation during FB and procedures, and 5 seconds inflation should be reserved for special situations where lesions are not adequately visible at lower inflation duration.
Some limitations may exist in this study. There might be variation of the tightness of the nose (mouth)-closure between, or even, in the same operators. This indeed may affect the level of measured PIP. A more prolonger duration of SPI, up to 15 seconds or more has been reported,3,8 but we restricted duration of SPI to 5 seconds as longer duration may create risky high PIP. In clinical practice, the real effort of SPI may be individualized which can be controlled by the operators.
Nonetheless, the findings of the present study are important and suggest the need for further investigations. The opening pressure of a collapse PLS or occult lesions can be measured and which helps to determine appropriate pressure of NIV support. The similar SPI effects may also be noted in the lower airway lumens, ventilation, and lung recruitment.