V-Gel® Guided Endotracheal Intubation in Rabbits

Abstract

Background: General anesthesia in rabbits is associated with higher morbidity and mortality relative to other mammalian species commonly anesthetized. Unique challenges related to endotracheal intubation (ETI) in rabbits contribute to this risk. Objective: To improve the safety of ETI in rabbits, we developed two new ETI methods using a supraglottic airway device (v-gel^®) to facilitate ETI and compared them to traditional "blind" technique. We hypothesized that relative to blind ETI, v-gel^® guided ETI provides more successful placement of the endotracheal tube (ETT) in a shorter time. Outcomes included number of intubation attempts, time for achievement of ETI, endoscopic findings, and serial arterial blood gas (ABG) analysis. Study Design: Prospective, randomized, and crossover study. Methods: Ten female, New Zealand White rabbits aged 1-2 years old, weighing 4.3 ± 0.4 kg, were anesthetized four times. Each time, ETI was performed with one of the following techniques: Method 1: v-gel^® guided, polypropylene catheter facilitated, intubation using a cuffed ETT; Method 2: v-gel^® guided intubation using an uncuffed ETT directly inserted through the device airway channel; Method 3 and 4: Blind intubation with uncuffed or cuffed ETT. Upper airway endoscopy was performed before intubation attempts and after extubation. Serial ABG analysis was performed during the peri-intubation process. Results: V-gel^® guided techniques allowed successful ETI on the initial attempt for 9/10 subjects using Method 1 and 10/10 using Method 2. Relative to the v-gel^® guided techniques, the blind techniques required more intubation attempts. A median of 2 attempts (range 1-4, p < 0.007) were required for the uncuffed ETT, and a median of 4 (range 1-4, p < 0.001) attempts were performed for the cuffed ETT. The time to perform successful ETI was positively correlated with the number of attempts (ρ = 0.82), while successful ETI was negatively correlated with number of attempts (ρ = -0.82). Endoscopic findings showed mild to moderate laryngeal trauma. In the absence of oxygen supplementation, ABG analysis demonstrated low PaO₂, while PaCO₂ remained consistent. Conclusions: Facilitated ETI using the v-gel^® guided techniques allows for the rapid establishment of a secure airway to provide ventilatory support for rabbits undergoing general anesthesia.

Keywords: anesthesia; blood gas; endoscopy; endotracheal tube; intubation; rabbit.

Figure 1

Representative pictures showing ETI performed with method 1. A size R4 v-gel^® is inserted (A) and correct placement is verified by capnography (B). A 3.5 Fr polypropylene guide catheter is then inserted through the v-gel^® airway channel (C). The v-gel^® is then removed and a ETT is threaded over the guide, with the head of the rabbit kept in a neutral position, without extension of the neck (D-F).

Figure 2

Representative picture showing a 2.5 mm internal diameter uncuffed ETT inserted through the v-gel^® airway channel (note the endotracheal portion of the tube circled in red).

Figure 3

(A) Representative pre-intubation image of normal endoscopic appearance of the laryngeal structures in one of the study animals. Note the two arytenoids (black asterisks), the epiglottis (white asterisk) and the soft palate (black arrows). (B) Representative post-intubation endoscopic image showing hyperemia of the pharyngeal walls. (C) Representative picture showing the scope insertion into the oral cavity with the rabbit maintained in sternal recumbency. One assistant gently pulls the tongue to facilitate the passage of the scope and head and neck are maintained extended. (D) Representative post-intubation endoscopic image showing bilateral hyperemia of the arytenoids (black arrows) and hyperemia of the epiglottis (white arrows).

Figure 4

Graph of the number of attempts for each intubation method. Data are presented as mean and statistically significant differences are indicated by lines and asterisks.

Figure 5

Graph displaying the ETCO₂ values measured for the different intubation techniques. Values are reported as mean (within columns) and standard deviation.

Figure 6

Arterial blood gas data. Graphs showing PaCO₂ (A) and PaO₂ (B) at different time points of the intubation procedure, in presence (T₁, T₃) or absence (T₀, T₂) of O₂ supplementation.