Forces applied by the laryngoscope blade onto the tongue during intubation attempts: a comparison between Mackintosh, AirTraq and Pentax AWS in a mannequin study (2011)

Editor, The most common post-intubation traumatic complications include trauma of the teeth, rupture of the tongue, tongue haematoma, vocal cords destruction, arytenoid cartilages trauma, larynx and related structures injuries.1 The objective of this study was to measure the pressure created by different intubation devices on the tongue during endotracheal intubation attempts in the mannequin model (Trauma Head, Woodstock, Vermont, USA). The study was approved by the University Ethics Committee (protocol number: RNN/703/10/KB, 14 December 2010, Chairperson: Professor Przedzislaw Polakowski). Fourteen specialists and 20 anaesthesiologists in training took part in the study. I connected the manometer with the line used for inflating the mannequin tongue to create simulated conditions of tongue oedema. For the study, the mannequin tongue was not inflated. I compared the standard Mackintosh (Timesco, London, England) laryngoscope with AirTraq (Prodol, Madrid, Spain) and Pentax AWS (Pentax, Tokyo, Japan) laryngoscopes. After a standard 20 min training with the three devices, every participant had one attempt at intubation with no time limit. The highest created pressure on the tongue was recorded in millimetres of mercury and then converted using the following formula: 1 mmHg = 133 Pa = 0.00132 kg cm−2. Statistical analysis was performed using Microsoft Office Excel (Microsoft SA, Warsaw, Poland) t-test for repeated pairs with different variations. I observed that the pressure created on the tongue was highest when the Mackintosh blade was used and was more than five times higher than with AirTraq and Pentax AWS (P < 0.05) (Table 1). When comparing the Pentax AWS and AirTraq, there was no statistical difference (P > 0.05).Table 1: Mean pressure onto tongue created by studied laryngoscopesAs expected, the pressure created on the tongue using the standard Mackintosh blade laryngoscope was the highest and may lead to traumatic complications. In my opinion, the size of the pressure anaesthesiologists create during intubation attempts, especially in difficult conditions, is underestimated. Two other devices – AirTraq and Pentax AWS – which were created for intubation attempts in patients with limited mouth opening caused much less pressure on the tongue and therefore should lead to significantly fewer traumatic complications compared with the standard Mackintosh laryngoscope. When comparing these two similar devices, I found that for the Pentax AWS the pressure on the tongue during intubation attempts was smaller but not significantly so. In the study performed by Hashemi et al.2 on 100 patients, the mean pressure on the base of the tongue created by intubation using a standard laryngoscope with a Mackintosh blade was smaller than in our study – about 160 mmHg (38.3 N). The authors found a positive correlation between force used during intubation attempts and incidence of complications such as sore throat intensity. In previous studies by Bucx et al.,3,4 the pressure on the tongue was even smaller (about 140 mmHg – 35 N). One of the recent studies performed by Evan et al.5 compared the forces exerted during laryngoscopy using disposable and non-disposable laryngoscope blades on a mannequin model. They found that the mean pressure was 30–41 N (about 110–170 mmHg) depending on the laryngoscopy blade. The difference in our study may be related to specific mannequin design which was constructed to simulate a difficult airway. The cited studies were performed under standard intubation conditions. As far as I know, there are no other mannequin or patient studies comparing AirTraq or Pentax AWS with the Mackintosh laryngoscope in terms of pressure on the tongue during intubation. In conclusion, I demonstrated that the use of Pentax AWS or AirTraq creates less pressure on the tongue when compared with the Mackintosh blade in a mannequin study. This may suggest that in patients at risk of tongue oedema and/or in expected difficult intubation conditions such as in obese patients, the Airtraq or the Pentax AWS may be a better option for intubation patient; however, further clinical studies are required to confirm these findings. Acknowledgements The author did not receive any financial support and sponsorship, and there is no conflict of interest.