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Endotracheal Intubation in Mice via Direct Laryngoscopy Using an Otoscope

Published: April 5th, 2014



1Medical and Research Services, VA San Diego Healthcare System, 2Department of Medicine, University of California, San Diego, 3School of Medicine, University of California, San Diego

We have developed a simple, reliable, and relatively inexpensive method for endotracheal intubation in mice via direct laryngoscopy using an otoscope with a 2.0 mm speculum. This technique is atraumatic and can be used for repeated measurements in chronic experiments. We find it superior to tracheostomy or previously reported nonsurgical techniques.

Mice, both wildtype and transgenic, are the principal mammalian model in biomedical research currently. Intubation and mechanical ventilation are necessary for whole animal experiments that require surgery under deep anesthesia or measurements of lung function. Tracheostomy has been the standard for intubating the airway in these mice to allow mechanical ventilation. Orotracheal intubation has been reported but has not been successfully used in many studies because of the substantial technical difficulty or a requirement for highly specialized and expensive equipment. Here we report a technique of direct laryngoscopy using an otoscope fitted with a 2.0 mm speculum and using a 20 G intravenous catheter as an endotracheal tube. We have used this technique extensively and reliably to intubate and conduct accurate assessments of lung function in mice. This technique has proven safe, with essentially no animal loss in experienced hands. Moreover, this technique can be used for repeated studies of mice in chronic models.

The laboratory mouse has supplanted virtually all species as the principal mammalian model of biology and pathobiology. The laboratory mouse is the smallest mammalian species that has been clearly and extensively shown to be of value as a model of human disease and has proven invaluable in advances of our understanding of human biology and disease. The short gestation time and substantially lower cost has allowed the development and study of null and transgenic mice as a commonplace tool in biomedical research. However, the size of the average laboratory mouse (20-25 g) has limited their study in physiologically or surgically based studies and, consequently, some inve....

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1. Animal Preparation

  1. Obtain mice that are older than 8 weeks and more than 20 g (smaller mice can be intubated by an expert).
  2. Anesthesia
    1. Inject mice with  20 mg/kg, each, of ketamine and xylazine intraperitoneally as a preanesthetic. (This dose is insufficient to fully anesthetize the mouse, but facilitates the safe transfer, after intubation, to mechanical ventilation.) However, adjustment of the dosages may be necessary according to the anesthetic response in consultati.......

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Intubation with the above technique is reliable and fast. The appropriate placement of the endotracheal tube is most easily verified by observing expired gas bubbling from the submerged expiratory limb of the of the ventilator circuit (usually in a PEEP trap) and negative deflections on an airway pressure tracing (Figure 1). The negative deflections on airway pressure tracing are the most reliable. Others have used movement of a small fluid droplet in intravenous tubing connected to the expiratory ventil.......

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In this report we describe a simple, reliable technique to intubate mice that is nontraumatic and can be used repeatedly in the same animal. This technique can be accomplished with simple laboratory or medical equipment that can be purchased for a modest sum. The technique of direct laryngoscopy, originally reported by Hastings and colleagues4, can also be used for a variety of purposes, but mainly to accurately deliver test substances to the lower respiratory tract. We have found this technique superior to th.......

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A Merit Grant from the Department of Veteran Affairs and a T32-HL098062 grant from the NHLBI of the National Institutes of Health supported this work. We wish to gratefully acknowledge the advice of Randolph H. Hasting, M.D., Ph.D. and the advice and support of the Veterinary Medical Unit of the VA San Diego Healthcare System.


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Name Company Catalog Number Comments
Operating Otoscope Head Welch Allyn 21700  $188.98
Otoscope Handle Welch Allyn 71000  $112.20
Reuseable Speculum Welch Allyn 22002  $ 3.98
Fine Forceps Miltex 18-779  $107.18
Small clamp stand to hold otoscope
Optional Equipment
Isoflurane Vaporizer (multiple circuit with vacuum waste gas handling) Summit Medical $3,000
Flexivent (Animal Ventilator) SCIREQ $35,000
Intravenous catheter (20 ga x 1 inch) BD 381233  $  9.62
Polyethylene tubing (PE10) (0.011 inch I.D., 0.024 inch O.D.) 100 ft Intramedic, Clay-Adams 427401  $115.70
Ketamine 100 mg/ml (10 ml bottle) Butler 23061  $10.00
Xylazine (100 ml bottle) Vedco 24105  $20.00
Isoflurane (250 ml bottle)  $15.00
vecuronium bromide 10 mg/10 ml Pfizer NDC 0069-0094-01 $15.00

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