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.