Blood pressure and heart rate changes during intubation

We read with interest the paper from Xue et al. [1] comparing haemodynamic changes in fibreoptic and traditional nasotracheal intubation, which showed that fibreoptic intubation leads to a greater increase in heart rate and blood pressure. The authors referred to a similar study [2] conducted in our department which showed that the hypertensive response was marginally less with fibreoptic nasotracheal intubation compared with the conventional laryngoscopic technique. The authors suggest that these varying results occur because of the use of different anaesthetic techniques. Additional reasons could be the timing of the intubation, the time taken for intubation and the type of tracheal tube used. We ventilated the patients for 4 min with 50% oxygen, 50% nitrous oxide and 1% isoflurane after giving vecuronium, whereas the Xue and colleagues used 100% oxygen for 2 min. The purpose of the 4-min mask ventilation period was to allow the arterial pressure and heart rate to stabilise following induction, to standardise conditions and minimise pre-intubation data variance as much as possible. Moreover, the administration of isoflurane and the longer stabilisation period ensured complete neuromuscular blockade and better intubating conditions [3]. In our study, the mean fibreoptic intubation time was 30 s and the maximum intubation time allowed for inclusion in the trial was 60 s, as compared with a mean intubation time of 52.3 s and a time limit of 120 s used by the authors. The haemodynamic response is likely to be greater if the duration of mechanical stimulation during fibreoptic intubation is prolonged. Xue et al. used thermo-softened Portex nasal tubes, whereas we used red rubber tubes. Previous studies have shown that thermosoftened tubes rapidly cool to ambient room temperature and, consequently, become stiffer [4] if the time needed for intubation is prolonged. This could lead to greater stimulation, and therefore, might also contribute to the differences between the two studies.