There have been some interesting papers recently exploring all-things endotracheal, relevant to anaesthesiologists, intensivists and emergency physicians alike.
Here's a brief stroll through five articles that may challenge your practice.
First, Karmali & Rose challenge the dogma surrounding endotracheal tube sizing in adult anaesthesia. They explore both the functional consequences of ETT size, good and bad, as well as the implications for airway trauma.
They describe how a modern ETT ≥ 6.0mm ID will accomodate most intraluminal devices, and in fact smaller sizes might even facilitate some airway procedures. Similarly, inspiratory and expiratory flow dynamics of smaller ETTs are inconsequential for most fit and healthy patients.
Noting that there is wide individual variation in tracheal dimensions, such that some patients are poorly served by a traditional ETT-size choice, they highlight the correlation between ETT size and airway trauma, hoarseness and sore throat, noting that for many patients a 'large' ETT offers little practical benefit.
"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.
Yang et al.'s high quality meta-analysis explores the use of intravenous lidocaine/lignocaine to reduce a common, but potentially significant post-operative problem: coughing on extubation. Both coughing (reported incidence 15-94%) and post-operative sore throat (21-72%) are common among surgical patients.
This meta-analysis of 16 trials (though only 1,516 total subjects) showed a significant reduction in cough RR 0.64 (0.48-0.86 & NNT=5), and post-operative sore throat RR 0.46 (0.32-0.67), though no difference in laryngospasm, adverse events or time to extubation when using modern volatile agents.
However, they could make no clear recommendation of optimal timing or dose of lidocaine – although past reviews had found suggestion of a dose-effect, settling on 1.5 mg/kg as the best choice (Clivio et al. 2019).
Regardless, a simple intervention with peri-operative IV lidocaine reduces coughing on extubation and reduces post-operative sore throat, without any apparent increase in adverse events.
To cuff or not?
They challenge historical airway anatomy & physiology myths that once encouraged the use of uncuffed ETTs in children, and the questionable reliability of the widely-used Cole formula for tube size prediction (size = age/4 + 4; correct in only 50-75%).
More recently, Chamber's RCT compared cuffed and uncuffed ETTs in children undergoing elective general anaesthesia, and found that cuffed tubes improved ventilation and reduced short-term post-operative respiratory complications, in addition to decreasing tube changes.
Shah & Carlisle report on their updated meta-analysis, also showing that cuffed tracheal tubes in children result in fewer tube changes and less sore throat, but no difference in risk of laryngospasm.
Using a modern Microcuff™ or equivalent cuffed ETT that is 0.5 mm smaller in size than an equivalent uncuffed tube, offers functional, ventilation and safety benefits.
The ventral shift
Lumb and colleagues take us back to our physiological roots, confirming the well-known observation of a ventral ventilation shift under supine positive pressure ventilation, quantifying the contribution from the endotrachial tube itself (~16% of the change), versus from muscle relaxation and IPPV (noting some shift is also seen with an LMA under PSV).
While anaesthetists understand the detrimental effect of inadvertent endobronchial intubation, simply having the ETT tip close to the carina also worsens V/Q mismatch and is not as well appreciated. In these situations, tube withdrawal and/or 90o rotation may improve V/Q match.
Plumbing nasal tube depths
Finally, as a bonus, Massoth et al. demonstrate that nasolaryngeal distance can be reliably predicted using their derived formula:
NLD (mm) = 1.1 × body height (cm) – 13.2
Although the accuracy of this simple formula is interesting, the authors noted the wide variability in nasal tubes from different manufacturers, particularly in length and guide markings for the same-sized tube. Thus correct ETT depth is probably better determined clinically: visually observing the cuff pass the cords, and auscultation to exclude endobronchial intubation – although this predictive-depth formula may be a useful sanity-check.
For abstracts, article summaries and full-text links:
- Karmali S Rose P. Tracheal tube size in adults undergoing elective surgery - a narrative review. Anaesthesia. 2020 May 16.
- Yang SS, Wang NN, Postonogova T et al. Intravenous lidocaine to prevent postoperative airway complications in adults: a systematic review and meta-analysis. Br J Anaesth. 2020 Mar 1; 124 (3): 314-323.
- Shah A Carlisle JB. Cuffed tracheal tubes: guilty now proven innocent. Anaesthesia. 2019 Sep 1; 74 (9): 1186-1190.
- Lumb AB, Savic L, Horsford MR et al. Effects of tracheal intubation and tracheal tube position on regional lung ventilation: an observational study. Anaesthesia. 2020 Mar 1; 75 (3): 359-365.
- Massoth C, Schülke C, Köppe J et al. Nasolaryngeal Distances in the Adult Population and an Evaluation of Commercially Available Nasotracheal Tubes. Anesth. Analg. 2020 Apr 1; 130 (4): 1018-1025.