Comparison of two Macintosh laryngoscope blades in 300 patients

BACKGROUND

There are two forms of Macintosh laryngoscope blade. Compared with the standard blade, the English blade is longer, its curve is more continuous across the entire length of the blade, the flange of the blade continues much closer to the blade tip, and the height of the flange is shorter.

METHOD

We studied 300 patients to compare the ease of laryngoscopy with each type of Macintosh laryngoscope blade. In a random crossover design, after induction of anaesthesia and neuromuscular block, the two blades were inserted in turn, and the views of the glottis at laryngoscopy (Cormack and Lehane scores) were compared.

RESULTS

There was a difference in the view of the glottis in 80 patients. Among these patients, the view was better for the English blade for 63 patients and the standard blade was better for 17 patients. Laryngoscopy was difficult (grade 3 or 4) for at least one blade in 42 of 300 patients (14%). In these 42 patients, there was a difference in the score between the blades in 28 patients; the view was better for the English blade in 25 patients (60%) and for the standard blade in three patients (7%). The view was significantly better for the English blade than for the standard blade (P<0.001; 95% confidence interval 45-74%).

CONCLUSIONS

In patients in whom laryngoscopy was unexpectedly difficult, the English blade provided a better glottic view significantly more frequently than the standard blade.

Effect of cricoid pressure on the ease of fibrescope-aided tracheal intubation

We studied the reasons for difficulty with tracheal intubation over a fibrescope, and whether cricoid pressure facilitated intubation, in 50 patients. After induction of anaesthesia and neuromuscular blockade in 10 patients (phase 1), we attempted to clarify the reasons for difficulty in advancing a tracheal tube over an orally-inserted fibrescope, by observing through another fibrescope that was inserted nasally into the pharynx. In the next 40 patients (phase 2), we studied the effect of cricoid pressure on the success rate of tracheal intubation over the fibrescope. After a fibrescope (with a tracheal tube over it) had been inserted orally into the trachea, patients were randomly allocated to receive either criocoid pressure or sham pressure, and the success rate of intubation within 60 s was assessed. In phase 1, the tube was advanced into the trachea without difficulty in three of 10 patients. In the remaining seven patients, the tube impacted on the epiglottis in one patient and on the arytenoid cartilage in another two patients, and the tube migrated into the hypopharynx in the remaining four patients. In phase 2, tracheal intubation was successful within 60 s in seven of 21 patients (33%) without cricoid pressure, compared with 12 of 19 patients (63%) when cricoid pressure was applied (95% CI for difference 2-59%; p = 0.04). We conclude that cricoid pressure facilitates fibrescope-aided tracheal intubation.

Evaluation of the disposable Vital View laryngoscope apparatus

The Vital View laryngoscope (Vital Signs, NJ, USA) consists of a plastic disposable blade containing a fibrelight and a non-disposable handle; there is therefore no need to sterilise the blade and no concern about disintegration of the fibrelight. In a random cross-over design, we compared the Vital View laryngoscope with a conventional metal fibrelight laryngoscope (Welch Allyn, NY, USA) in 100 patients. The Vital View laryngoscope produced a brighter field than the metal laryngoscope (p < 0.001), whereas there was no significant difference in the view of the glottis or the success rate of tracheal intubation. In no patient did any problem occur, such as damage to the laryngoscope blade or loss of light during laryngoscopy. In another 10 patients, prevention of light emission from the side of the laryngoscope blade reduced the brightness (p < 0. 01). This indicated that the brightness of the Vital View laryngoscope is produced by light emission not only from the tip of the blade but also from the side of the blade. Therefore, the disposable Vital View laryngoscope can be used as effectively as a conventional non-disposable laryngoscope.