Yasuhisa Okuda

Pentax-AWS, a new videolaryngoscope, is more effective than the Macintosh laryngoscope for tracheal intubation in patients with restricted neck movements: a randomized comparative study

BACKGROUND We studied whether laryngoscopy and tracheal intubation were easier when using the Pentax-AWS (Tokyo, Japan), a new videolaryngoscope, than when applying the Macintosh laryngoscope, during manual in-line neck stabilization. METHODS In 203 anaesthetized patients with manual in-line neck stabilization, we inserted the Pentax-AWS and a Macintosh laryngoscope, in turn, and recorded the view of the glottis and time taken to laryngoscopy. The success rate of tracheal intubation (within 120 s) and time to intubation were also recorded. RESULTS The view of the glottis was significantly better with the Pentax-AWS than with the Macintosh laryngoscope (P<0.001). For the Macintosh laryngoscope, the view was obscured in 22 of 203 patients (11%) (Grade 3 in 21 patients and Grade 4 in one patient), whereas for the Pentax-AWS, the glottis was always clearly seen (Grade 1). Time taken to see the glottis with the Pentax-AWS [mean (sd): 6.0 (3.1) s] was significantly shorter than with the Macintosh laryngoscope [11.0 (5.0) s] (95% CI for difference: 4-6 s). The success rate of tracheal intubation with the Pentax-AWS (all of 99 patients) was significantly higher than with the Macintosh laryngoscope (93 of 104 patients) (P=0.001). Time taken for intubation was similar between the Macintosh laryngoscope [51 (27) s] and the Pentax-AWS [54 (14) s] (95% CI for difference: -9 to 3 s). CONCLUSIONS In patients with stabilized neck, the Pentax-AWS provided a better view of the glottis and a higher success rate of tracheal intubation, compared with the conventional Macintosh laryngoscope.

Airway Scope for difficult intubation

The Airway Scope (AWS-S100, Pentax, Tokyo, Japan) (Fig. 1) is a new videolaryngoscope, currently available in Japan. The device consists of a disposable transparent blade, a 12-cm image channel (with a CCD camera at its tip), and a video screen. The blade is anatomically shaped and a tracheal tube can be attached to the right side. The image channel is inserted into the blade so that the tip is approximately 3 cm proximal to the tip of the blade. The image is displayed on a full colour screen. The device is battery operated. Because of the anatomically shaped blade it is unnecessary to place the patient’s head and neck into the Magill (sniffing) position, unlike with a Macintosh laryngoscope. We report four cases of difficult intubation in which the Airway Scope was useful. In the first case, a middle-aged woman with a small jaw and thyromental distance of 3.5 cm was scheduled for surgery. The view of the oropharynx was clear (Mallampati grade 2). Anaesthesia was induced and neuromuscular blockade achieved. At laryngoscopy with a size three Macintosh laryngoscope, it was impossible to see the glottis (Cormack and Lehane grade 3); pressure on the neck revealed only a part of the arytenoids. Insertion of the Airway Scope showed a full view of the glottis, and a 7.0-mm tracheal tube attached to the blade was easily advanced into the trachea. In the second case, a middle-aged man was scheduled for lumbar laminoplasty. He had a history of cervical spine disc herniation, and his neck movement was restricted, with Mallampati grade 1. In theatre his head was placed directly on to the trolley and his neck was stabilised. After induction of anaesthesia and neuromuscular blockade, a Macintosh laryngoscope was inserted, but it was impossible to see the glottis. With the Airway Scope a full view of the glottis was seen and trachea was intubated easily. In the third case, a middle-aged man with an unstable neck was scheduled for cervical laminectomy. Tracheal intubation using the Airway Scope was successful at the first attempt, while the head and neck were stabilised. In the final case, a middle-aged man with recurrent regurgitation and vomiting due to multiple antidepressants was scheduled for surgical fixation of a clavicular fracture. Anaesthesia was induced using a rapid sequence technique with cricoid pressure applied. Laryngoscopy did not reveal the glottis, and with pressure, only a part of the right arytenoid was seen. The trachea was easily intubated using the Airway Scope. We feel that the Airway Scope has a role in the patient with a difficult airway.

Effect of cricoid pressure on placement of the I‐gel™: a randomised study

We studied 40 adult patients to see if cricoid pressure affected placement of the I‐gel™. In a randomised crossover design, the i‐gel was placed with and without cricoid pressure, and we compared the success rate of adequate ventilation through the i‐gel, time to placement and the rate of optimal position of the device between the two circumstances. Cricoid pressure significantly decreased the success rate of adequate ventilation through the i‐gel (40 vs 34 patients) (p = 0.041, 95% CI for difference 4–26%), and significantly decreased the rate of the optimal position (39 vs 17 patients) (p < 0.001). The time to achieve adequate ventilation was significantly longer (p < 0.001) with cricoid pressure than without (median difference 8 s; 95% CI for median difference 3–12 s). Cricoid pressure significantly decreases the success rate of ventilation through the i‐gel, but the success rate of ventilation through the i‐gel is reasonably high.

In reply: efficacy of a new videolaryngoscope; what we should assess?

To the Editor: We thank Dr. Meng and colleagues for their constructive comments to our study [1]. Videolaryngoscopes have been shown to be useful in patients with and without difficult airways [2–5], but their efficacies may differ [2]. To assess the usefulness of each new device, we need to address three major factors: the device (efficacy), the patient (degree of difficult airway), and the performer (expertise). In addition to these major factors, as Meng and colleagues point out, we may need to assess the efficacy of supportive measures (such as pressure on the neck or use of a stylet). It would be ideal to assess all of these, but it is often impractical to standardize all factors (other than the device factor). We considered that because it would be difficult and may be unethical to standardize the patient factor in real patients, we chose to standardize the patient factor using a manikin with four different simulated difficult airways. Regarding the expertise of the performer, we stated the reasoning for choosing residents and their equal proficiency in our article [1]: It is known that the expertise of the anesthesiologist will affect the success rate of tracheal intubation. We considered that, for experienced anesthesiologists, they would be able to intubate the trachea using either a Macintosh laryngoscope or a fibreoptic bronchoscope, whereas for less experienced anesthesiologists (but with minimum skills), videolaryngoscopes may be regarded as the first choice when tracheal intubation using a Macintosh laryngoscope has failed. The participants had minimum skills with the Macintosh laryngoscopes, because in a manikin with normal airway, there were no significant differences in the success rate of tracheal intubation between the VLP-100, the AWS, and the Macintosh [1]. Meng and colleagues state that the difference in laryngoscopic views among three laryngoscopes was stated as a final endpoint of performance comparison, and comparing the views obtained with direct and video laryngoscopes is not an entirely appropriate comparison. We agree with their comments on the uncertainty regarding the use of the Cormack–Lehane score for assessing the efficacy of videolaryngoscopes, and this is why we did NOT use the view of the glottis as the primary endpoint. We clearly state that the main aim of our study was to compare success rates of tracheal intubation between the three laryngoscopes, and tracheal intubation was the primary endpoint [1]. As Meng and colleague imply, there are many factors that we did not study: for example, there is still insufficient evidence to judge whether tracheal intubation using a videolaryngoscope is less likely to traumatize the airway or to prolong apnea time [2]. We need to continue carrying out randomized controlled trials and reporting large case series, together with some tips for effective use, to establish the true role of each videolaryngoscope in patients with and without difficult airways.

Unilateral bronchospasm during one-lung ventilation

taken several minutes later with the patient in the supine position ruled out pneumothorax but showed decreased air entry to the right lung, indicating unilateral bronchospasm. With infusion of aminophylline 250 mg, it became possible to ventilate the right lung, and the EtCO2 waveforms reappeared. Auscultation of the chest showed weak wheezing. The causes of impossible ventilation during one-lung ventilation are various (see Table 1 in supplementary material). When ventilation becomes impossible during one-lung ventilation in the absence of the EtCO2, we should consider that unilateral bronchospasm is one possible cause.