Discussion
Over an 8-month period of 150 airway procedures, we were able to obtain
views by SL adequate for the procedure (grade S1-3) in all but one case
(in which failure had been predicted preoperatively and planned flexible
bronchoscopy back-up was successful) (8). This high success rate,
together with our low complication rates, compares well with series from
other centers specializing in laryngeal surgeries (Table 4), and is
likely multifactorial in nature. We are the UK referral service for
tertiary airway surgery - as such we have a high turnover of cases,
including many patients undergoing regular repeated procedures under our
care (albeit fewer in this time period due to COVID-19), and we have an
experienced surgical, anesthetic and nursing team who regularly work
together (1). Other factors which we feel contribute to this high
success rate include correct patient positioning (no shoulder roll and
head forward position), routine use of supraglottic jet ventilation,
infrequent endotracheal intubation and our predilection for the
Dedo-Pilling laryngoscope (although it must be stated that use of the
Lindholm laryngoscope was not correlated with increased complications)
(Figure 1).
Many other documented ‘laryngoscores’, whilst useful in research
contexts, are limited in their potential for widespread clinical
adoption by the need for multiple time-costly measurements of specific
head and neck movements (2-7). We suggest, given that we found
patient-demonstrated gross limitations to neck or chin movement to
correlate with the surgical view, that the absence of problems with
patients pre-operatively demonstrating the appropriate surgical position
(i.e. a forward head posture with or without neck extension) is
generally sufficiently predictive of procedural success without the need
to measure (3, 4, 7). A ‘Mini-Laryngoscore‘ predicting glottic exposure
was recently proposed by Incandela et al based solely on
thyromental distance, interincisor gap and upper jaw dentition (3).
However, interincisor distance and upper jaw dentition did not correlate
significantly with our grade of view in this series. The anesthetic
literature generally holds that BMI alone is not usually a strong
independent predictor of difficult intubation unless extremely high (9)
- although BMI and neck and head movement limitations were all
significantly correlated with higher grade view in our series,
intercorrelation of these variables could represent a confounding effect
(10).
Comparing anesthetic and surgical views can provide useful
management-changing information in the pre- to intra-procedure
transition, such as predicting the likelihood of requiring a senior
surgeon to perform the procedure, or to guide appropriate ventilatory
choices. We therefore adapted the widely-used MCLS anesthetic grading
system for our purposes to make the surgical score more relevant. The
anesthetic goal at laryngoscopy is somewhat different as the goal is
topicalization rather than to try and achieve the best view possible for
intubation; in cases where intubation is considered as first-line, a
video laryngoscope would usually be employed as a first choice in these
patients. The use of the straight-bladed Dedo, in contrast to the curved
anesthetic Mackintosh blade, may further explain the improved view of
the surgical team. If faced with a potentially difficult airway, the
anesthesia regimen would usually include higher doses of induction
agents and muscle relaxant to improve the view for the first attempt.
In this data collection period, we had no incidences of major
complications such as severe cardiovascular instability, esophageal
perforation or permanent tongue sequelae, incurring only mild temporary
complications (Table 3). Reassuringly, most large reported series also
report an absence of severe complications (1, 8, 11-19) and the
literature on these subjects is limited to isolated case reports (20).
The main complication experienced by our patients, in line with other
studies (18), was that of temporary sore throat (66% of patients). It
can be difficult to unpick complications associated with SL itself
versus the procedures that it enables (for example, ablative surgery is
likely to cause throat pain in its own right irrespective of SL). Our
results showed those patients with wider mouth opening had a
significantly lower correlation with sore throat, although age, which
also positively correlated with an increased interincisor gap, did not
have a significant association with sore throat. This leads us to
suggest that interincisor gap may be a useful independent clinical
indicator for sore throat, although it must be acknowledged that the
Spearman coefficient indicates a very modest effect only (21).
In this time period, 6.7% of patients experienced tongue symptoms, all
of which were followed up and seen to resolve by the end of the second
postoperative week. This is a relatively low incidence compared to other
reported series (8, 12, 13, 15, 17, 19, 22, 23). There was no
significant correlation between tongue symptoms and SL duration, however
as might be expected, there was a moderate significant positive
correlation with macroglossia (r=0.452, p=1.611x10-8).
Anecdotally, one patient reported that ‘they always get tongue numbness,
and it always resolves’. Given this patient was young with a low BMI, no
gross limitations to movement, an average interincisor gap and no
macroglossia, this leads us to hypothesize that some patients may be
more at risk of developing lingual nerve compression, perhaps due to
internal jaw anatomy as others have suggested (24). As with most other
reported studies, we saw non-significant associations with gender,
although others have suggested a female preponderance (11, 19). Detailed
further studies to investigate this could form the basis for future
cohort research. In this data collection period, we had no serious
dental complications, although there were two cases of temporary
exacerbation of existing dental/temporomandibular joint pain. Our team
are extremely careful not to lever the laryngoscope on the teeth, but
additional care is taken in patients who self-report painful teeth,
given this is a potential sign of underlying instability requiring
additional vigilance and care (12).
Reassuringly, there was no significant correlation between any
investigated complication rate and more difficult views or longer
procedural duration, both of which would imply greater cumulative
oropharyngeal tissue compression (11, 25). However, other series report
associations of longer procedural duration with increased complications
(8, 17, 19). Our airway unit treats predominantly benign pathologies and
is separate from the Head & Neck unit which manages malignant cases.
Our cases therefore tend to have shorter procedural times, and the
absence of adjuvant radiotherapy renders our patients’ oropharyngeal
tissues less stiff, and dentition more stable, than that seen by the
Head & Neck team. This makes comparison with other reported series
difficult (1, 8, 12, 15) as most report a mix of benign and malignant
cases and have much longer average procedural durations. Our findings of
common and uncommon procedural complications therefore pertain
specifically to benign laryngology and are not generalizable to mixed or
Head & Neck patient populations. In addition, rarer risks (i.e., those
with a <0.7% incidence) may not have occurred in our sample
size of 150 cases and the consent process should still contain mention
of more serious or long-lasting risks reported in the literature, such
as tongue weakness.
The major limitation of our work is that this is an unblinded snapshot
study, albeit one representative of our practice. Anesthesia regimes
also varied throughout the study by anesthetic consultant, and the
administered muscle relaxant dose was often incomplete on the electronic
documentation system - this factor was therefore subsequently excluded
from multivariate analysis. The relationships between relaxant dosage
and timing between administration and visualization, and between
relaxant type or dose and complication rates, are also important avenues
for further study.