Article Notes
In this review, Karmali & Rose challenge the dogma surrounding endotracheal tube sizing for adult anaesthesia, traditionally sizing based on sex.
What did they cover?
They explored both the functional consequences (good and bad) of ETT size, as well as airway trauma.
Noting that an ETT ≥ 6.0mm ID will accomodate most intraluminal devices, and in fact at these smaller sizes fibreoptic intubation or passage through an LMA is easier, however smaller tubes are more readily obstructed and deformed.
Ventilation through smaller ETTs
While smaller tubes may require slightly higher inspiratory pressures, these are generally not clinically significant with modern ventilators, and importantly do not translate to higher intra-tracheal or alveolar pressures experienced by the patient.
Similarly, expiratory gas flow is not significantly effected by a small ETT (6.0 mm) for most patients even at high minute ventilations (although use cautiously in patients with chronic airway limitation). Significant gas trapping at normal MV will start to occur with ETT < 5.0 mm.
Size and airway trauma?
While the internal diameter (ID) is important for anaesthesia conduct, it is the external diameter that matters for airway trauma (a standard 8.0 mm ID ETT has a 10.5 mm ED!).
They note while there is wide individual variation in tracheal dimensions, the trachea is narrowest at the subglottis – and thus adequate visualisation of the glottis at time of intubation is an incomplete indicator of the tube size suitability for the subglottis.
Not only do some adult women have an airway size at the lower-limit of acceptability for traditional 7.0-8.0 mm ETTs, but there is also correlation between ETT size and airway trauma, hoarseness and sore throat. A large ETT can result in mucosal ischaemia and ulceration after as little as 2 hours.
They conclude...
"Instead of opting for ‘the largest tube that the larynx will comfortably accommodate’, we perhaps should consider using the smallest tube which permits the safe conduct of anaesthesia."
For routine anaesthesia of ASA 1 & 2 patients, an ETT sized 6.0-7.0 mm is probably the best balance between ventilation needs and airway trauma.
Be smart
But remember, many of the concerns for tracheal tube trauma are based upon critical care experience, not anaesthesia. While a smaller tube is very likely beneficial for most elective adult patients, most benefit will simply be reduction in post-operative sore throat and hoarseness.
Daniel Jolley
While the reliability of this simple formula is interesting, the authors note the wide variability in nasal tubes from different manufacturers, particularly in length and guide markings for the same-sized tube. Thus although interesting, there is questionable utility in this formula.
Correct ETT depth is probably better determined clinically: visually observing the cuff pass the laryngeal inlet and cords, and auscultation to exclude endobronchial intubation. At best, a predictive-depth formula is a useful sanity-check.
Daniel Jolley
An editorial on pandemic information overload?
Yep. 😉
But setting aside the irony of adding 2,000 more words on COVID-19 information overload, Kearsley & Duffy neatly explore the challenge:
"Since the outbreak of this pandemic, our e-mail inboxes, social media feeds and even general news outlets have become saturated with new guidelines, revisions of guidelines, new protocols and updated protocols, all subject to constant amendments."
What's the thesis?
The authors' argument is that too much information in the era of COVID may be a bad thing: the marginal benefit of 'more' may be overwhelmed by the negative cost.
They acknowledge the tension between the pragmatic and perfect when it comes to information sources in the face of a rapidly advancing disease – and in particular the recurrent waves of shifting clinical guidelines.
Kearsley & Duffy mention the important role of rapid research, worryingly tempered by a surge in volume, but fall in quality, along with mainstream promotion of non-peer reviewed and pre-print investigations. They note how information technology in the pandemic climate exploits our biases: confirmation, anchoring, and novelty.
At an individual level they discuss the risk of pandemic 'alert fatigue', the growth of social media and excessive information sharing making quality assessment difficult, and the negative effect of both on well-being.
The take-home
We each have significant personal responsibility to consider the consequences when sharing information, especially if incomplete or risk of misunderstanding when stripped of context.
"As we learn to live with this virus it is important for us to be cognisant that we are all at risk of error; we need to work to reduce information overload and focus on unifying our approach to both information dissemination and presentation. We must go back to basics and apply the well-practiced human factors principles of good teamwork, communication and leadership.
...
We need to avoid a situation where a crisis is overmanaged and underlead; “Ipsa scientia potestas est" or 'knowledge itself is power' – from what COVID-19 is teaching us however, can too much knowledge be a bad thing?"
Daniel Jolley
Though these findings are in stark contrast to Kheterpal’s (2020) massive 45,000 subject matched cohort study that did show sugammadex reduced postop respiratory complications.
Daniel Jolley