From the Authors

From the authors:

We would like to thank A. Zamani for his comments concerning our article 1.

It seems that our methodology regarding the bronchoscopic procedure has been misunderstood. We intended to develop a bronchoscopic instrument that was basically a rigid, straight and hollow metallic tube, and followed the main bronchoscopic procedures. The instrument was connected to a three­way stopcock. An open system, one opening was then connected to the oxygen source, while the other accessed the atmosphere. The latter orifice precluded any unforeseen risk of excessive airway pressure and allowed to aspirate tracheobronchial secretion. The bronchoscopic instrument was inserted into the rat airway via the transoral route, certainly not outside the tracheobronchial tree. The lateral neck incision was performed to confirm whether the bronchoscopic instrument was in the trachea.

During the planning phase of this project, the upper airway anatomy, the trachea and the main stem bronchi of the rat had been carefully examined to construct our experimental design thoroughly. Meticulous dissection provided an excellent view of the anatomic structures of the airway. The length of the bronchoscope was 70 mm and the external diameter was 3 mm. The length of the bronchoscope was sufficient to reach the lower trachea and main stem bronchi. The bronchoscope was marked every 1 cm to estimate the anatomic localisation of the tip of the bronchoscope. The bronchoscope was inserted into the rat airway via the transoral route. The distance from the mouth to the epiglottis was approximately 30–32 mm. The larynx began at the opening bounded anteriorly by the free border of the epiglottis. The length of the larynx was ∼4–5 mm. The cricoid cartilage formed a complete ring at the inferior aspect of the larynx and was fixed to the tracheal rings. The trachea was entered after passing through the cricoid cartilage and ended at the division into the right and left main stem bronchi at the carina. The bronchoscope was introduced through the larynx and directed to the trachea. The length and internal diameter of the trachea was ∼25–27 mm and 3–4 mm, respectively. The angle between the longitudinal axis of the trachea and the bifurcation of the main bronchi was approximately 15–17°. The angle of the right main bronchus was only slightly less than that of the left main bronchus. Once the trachea was entered, the tip of the bronchoscope was gently slid along the right and left lateral wall of the trachea. This manoeuvre allowed both the right and left main bronchi to be entered easily. In addition, to enter the right and left main bronchi, the rat's head was turned and flexed slightly to the ipsilateral side and the proximal portion of the bronchoscope moved toward the contralateral corner of the mouth. The main stem bronchi was ∼6–7 mm in length and its internal diameter was 2–3 mm. The tip of the bronchoscope was advanced 4–5 mm into the right and left main bronchi. At this point, the distal progression of the instrument was halted. Overall, these attempts provided convincing results on proceeding tracheobronchial endoscopy. Thus, we strongly believe that our “simulated bronchoscopy” had the main physical properties of a rigid bronchoscope. The rat airway was not visualised in these experiment, yet, we think that this would not have changed the pathophysiological sequence leading to bacterial translocation following bronchoscopy.

There may some reports indicating that rigid bronchoscopy does not impair ventilation and oxygenation 2. However, what about clinical studies that do show that rigid bronchoscopy induces alterations in arterial blood gases, including hypoxaemia, respiratory acidosis and hypercarbia 3–5? Godden etal. 3 measured serial arterial blood gases in 10 patients during rigid bronchoscopy and showed carbon dioxide retention in nine patients even though ventilation was adequate in all. Mathisen and Grillo 4 observed 19 complications of 56 patients after rigid bronchoscope, in whom two of those complications were hypoxia and/or hypercarbia. It may intuitively appear that associated procedures during rigid bronchoscopy will increase resistance to ventilation and result in derangements in oxygenation 6. Overall, can we insist that rigid bronchoscopy is a 100% safe procedure regarding alterations of arterial blood gas parameters?

As mentioned above, at the beginning of this study, we examined the upper airway anatomy, trachea and main bronchi, and then prepared the instrument to be safely inserted into the trachea. The internal diameter of the trachea was 4–5 mm. The external diameter of the bronchoscope was 3 mm. In the present study, the bronchoscope was gently slid along the trachea. It was crucial not to damage the mucosa ofthe trachea during bronchoscopy, which was later also confirmed by histopathological examinations. As was stated in our article, bacterial translocation occurred from the damaged intestinal mucosa, not the tracheal mucosa.

In conclusion, the merit of our study is that it addresses the phenomenon of bacterial translocation in the specific settings of bronchoscopy. Bronchoscopy leading to impairment of arterial blood gas parameters may induce intestinal mucosal barrier dysfunction and bacterial translocation. However, further investigations aimed at understanding the clinical consequences of this phenomenon are warranted.