Video-Assisted Orotracheal Intubation in Rats Using a Low-Cost Smartphone-Connected Otoscope

Summary

This protocol describes a simple, low-cost, video-assisted method for orotracheal intubation, enabling rapid and visually guided intubation in adult rats under isoflurane anesthesia.

Abstract

Reliable endotracheal intubation is essential for experimental procedures in rats that require controlled ventilation, particularly during thoracic and cardiovascular surgeries. However, airway management in rats remains technically challenging due to anatomical constraints and limited accessibility of available intubation techniques. The goal of this protocol is to describe a simple, low-cost method for orotracheal intubation in rats using video-assisted direct laryngoscopy successfully applied in a cohort of 50 rats.

This protocol uses a commercially available video otoscope with an integrated light source and wireless smartphone connectivity to provide real-time visualization of the upper airway. The method does not require device modification or specialized imaging systems. Adult rats are anesthetized with xylazine and isoflurane, positioned on an inclined intubation platform, and intubated under continuous visual guidance using a flexible guide and an endotracheal tube. Correct tube placement is defined by bilateral thoracic expansion, stable oxygen saturation (SpO₂), and a consistent end-tidal CO₂ (capnography) waveform. Following intubation, mechanical ventilation is initiated without positive end-expiratory pressure, and the tidal volume was set at 7.5 mL/kg. In this cohort, the technique enabled rapid intubation with a high first-attempt success rate and was associated with a low incidence of peri-procedural complications. Continuous visualization may reduce the risk of esophageal intubation and airway trauma. These findings support the feasibility of this approach under the conditions tested, without extrapolation beyond this experimental setting.

Introduction

Rats are widely used in experimental and translational research, and endotracheal intubation may be required for procedures that necessitate controlled ventilation^1,2. However, reliable intubation in rats remains technically challenging due to their small oral cavity, narrow glottic opening, and anatomical angulation of the airway^3,4,5.

Several approaches have been proposed to overcome these constraints^6,7,8. Among them, blind intubation techniques have been refined in recent years and can improve success rates when specific positioning strategies are used; nevertheless, these methods remain highly operator-dependent and continue to carry a risk of failure or side-effects such as esophageal misplacement or airway injury³. Video-assisted techniques have been developed to improve visualization of the glottis and enhance procedural safety. While these approaches provide effective airway visualization, they often require specialized endoscopic equipment, external monitors, inhalation anesthesia systems, or custom-modified devices, which may limit accessibility and routine implementation^7,9,10.

Despite these advances, many methods remain constrained by technical complexity, invasiveness, or reliance on costly or modified equipment that is difficult to reproduce across laboratories. The primary advantage of the present approach is the provision of low-cost airway visualization without the need for device modification. This protocol is intended for laboratories requiring low-cost, visualization-assisted intubation without access to specialized endoscopic systems.

The present protocol describes a simple, reproducible, and low-cost method for orotracheal intubation in rats using a commercially available video otoscope equipped with an integrated light source and wireless smartphone connectivity. Unlike previously described video-assisted approaches, this technique requires no device modification (e.g., the addition of a blunt-tipped plastic blade fashioned from a modified 1 mL syringe cap)¹¹ and avoids the need for external imaging systems (e.g., computer-based displays)^9,12, while providing clear, real-time visualization of the glottic opening. This approach, therefore, represents an accessible alternative to higher-cost visualization systems and may facilitate airway management in settings where dedicated endoscopic equipment is not available.

Protocol

All animal procedures were approved by the Normand Ethics Committee for Animal Experimentation (CENOMEXA; project authorization no. 46008). Animals were acclimated for 9 days in the institutional animal facility prior to experimentation, with ad libitum. access to food and water.

1. Animals and anesthesia

1. Use male Wistar rats (>12 weeks old; 450–460 g). Record body weight, then administer xylazine (5 mg/kg, intraperitoneal) for anesthesia and buprenorphine (0.05 mg/kg, subcutaneous) for analgesia.
2. Place animals in an inhalation chamber and maintain anesthesia for 15 min using a mixture of air–isoflurane at 2% (2 L/min) and oxygen (0.4 L/min).
3. Confirm the depth of anesthesia by the absence of spontaneous movement and lack of withdrawal reflexes in the forelimbs, hind limbs, and tail in response to noxious stimulation.
   1. If sedation is inadequate, place the animal back into the isoflurane induction chamber for a few additional minutes until an appropriate level of sedation is achieved.

2. Orotracheal intubation

1. Place the rat in the supine position on the intubation platform inclined at 45° and maintain a ventilation mask over the airway throughout the procedure to preserve oxygenation (oxygen 0.4 L/min) and anesthesia (air 0.4 L/min and isoflurane 2%) (Figure 1A-C). Secure the animal by the upper incisors using a Velpeau band (Figure 1B). Scavenge excess isoflurane using an evacuation filter cartridge.
2. Gently extend the tongue and introduce the video otoscope (Figure 2) into the oral cavity to displace the tongue away from the palate and towards the floor of the mouth (Figure 3A). Advance the otoscope until the soft palate is visualized (Figure 3B), then apply gentle traction to expose the vocal cords (Figure 3C).
   1. If the vocal cords are not visualized, reposition the tongue by gently applying traction and displacing it toward the floor of the mouth.
   2. If esophageal intubation occurs, remove the guide and the endotracheal tube. Reposition the animal and ensure clear visualization of the vocal cords by applying gentle traction to the tongue. Ensure that the curvature of the flexible guide is oriented toward the vocal cords before reattempting intubation.
   3. If oxygen desaturation occurs (e.g., the tongue appears bluish or purple), pause the procedure and apply the nasal mask over the animal’s snout to restore oxygenation.
   4. If intubation attempts are unsuccessful (e.g., after two attempts) and desaturation occurs, place the animal back into the induction chamber and increase oxygen delivery to restore adequate oxygenation while maintaining isoflurane for an appropriate depth of anesthesia.
3. Insert the flexible guide between the vocal cords using its anterior curvature (Figure 3D).
4. Advance the endotracheal tube carefully over the guide into the trachea until a tactile resistance corresponding to the tracheal rings is perceived (Figure 3E).
   NOTE: In this protocol, the authors used a metallic tube with an approximate diameter of 2.8 mm, as specified in the Table of Materials.
5. Release the rat from the Velpeau band, remove the guide, connect the endotracheal tube to the ventilator, and secure it with adhesive tape (Figure 4A).

3. Verification of tube placement and ventilation

1. Before intubation, set the tidal volume to 7.5 mL/kg.
2. Confirm the absence of selective intubation by observing bilateral thoracic expansion, a stable capnography waveform, and adequate oxygen saturation (Figure 4B,C).
3. Ventilate the animal mechanically.
4. Adjust the respiratory rate to maintain end-tidal CO₂ values between 50 and 60 mmHg.
   1. If capnography (end-tidal CO₂) exceeds 60 mmHg, increase the respiratory rate to return values to the target range.

4. Animal periprocedural monitoring conditions

1. Monitor oxygen saturation continuously using a pulse oximeter. Maintain peripheral oxygen saturation (SpO₂) above 95%. If SpO₂ falls below this threshold, check for selective (endobronchial) ventilation and correct tube positioning as needed.
2. Monitor body temperature using a rectal thermal probe. Maintain body temperature at 37 °C throughout the procedure through a heating pad.

Results

Intubation success was defined as correct endotracheal tube placement confirmed after connection to the ventilator by bilateral chest expansion, stable oxygen saturation (SpO₂), and a consistent end-tidal CO₂ waveform.

Orotracheal intubation was performed by a single operator over 3 months in a consecutive cohort of 50 adult rats. Five additional animals were used during a preliminary phase to establish and refine the protocol and were not included in the final analysis. No animals were exclud...

Discussion

This study describes a video-assisted direct laryngoscopy technique for orotracheal intubation in rats using a commercially available video otoscope wirelessly connected to a smartphone. In this cohort, the method enabled successful intubation in all animals with a low rate of periprocedural complications, under the conditions tested.

Several technical features contributed to the observed procedural performance. The curved shape of the otoscope blade facilitated the displacement of oral debris...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
0.1 mL syringe for anaesthesia	Fischer	Not applicable	Subcutaneous injection of buprenorphine
1 mL syringe for anaesthesia	Fischer	Not applicable	Intraperitoneal injection of xylazine
22G needle for anaesthesia	TERUMO	Not applicable	Intraperitoneal injection of xylazine
Adjustable laptop stand	Amazon	Not applicable
Anesthesia induction chamber	Temsega	Not applicable
Animal ventilator	Physiosuite	Not applicable
Arterial catheter guide	Vygon	Not applicable
Buprenorphine	VIRBAC	Not applicable	0.05 mg/kg
Capnograph	Physiosuite	Not applicable
Endotracheal tube	INSTECH	FTSS-16S-76	Gavage tube of 2.8 mm diameter
Heating pad	Physiosuite	Not applicable
Induction chamber	Temsega	Not applicable
Isoflurane	IsoVet	Not applicable
Isoflurane  vaporizer’s	Temsega	Not applicable
Otoscope Vitococo	Amazon	Otoscope Oreille 1920P Camera
Saturation oxymeter	Physiosuite	Not applicable
Scavanger  system	F/air evacuation filter cartrigde	Not applicable
Smartphone	Samsung	Galaxy A52S
Temperature probe	Physiosuite	Not applicable
Velpeau band	Velpeau	Not applicable	Cotton crepe bandage, 10 cm × 4 m (approximately 120 cm used)
Ventilation mask	Temsega	Not applicable
Xylazine	VIRBAC	Not applicable	5 mg/kg