Laryngeal mask airway for urine collection in anesthetized rats

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Rats have been used extensively as research subjects in experimental science and medicine for over a century. Quantification of urinary output is an important variable for pharmacological and physiological studies. Accurate collection of urine from rats poses a great challenge especially during the acute phase of an experiment. Several excellent means of collecting urine from study animals, including rats and mice, have been reported in a review by Kurien et al. (Kurien, Everds, & Scofield, 2004). These include free catch, methods with mild intervention, surgical methods, modified restraint and metabolism cage methods for 24‐hr urine collection.
In this report, we propose use of a simple device, a modified infant size laryngeal mask airway (Figure 1), which collects urine from an anesthetized rat continuously over time. The laryngeal mask airway is a supraglottic airway device which anaesthesiologists have used for management of various airway indications for more than 30 years (Brain, 1983). The laryngeal mask airway features a unique one‐piece moulded, natural spoon shape design. The laryngeal mask airway consists of two parts, the mask with inflatable cuff that conforms to the shape of larynx and airway tube (Figure 1). It comes in various sizes, ranging from infant to large adult (size 1 to 5, respectively).
For purposes of urine collection, the airway tube is cut short, and the cuff is inflated slightly to maintain the oval shape of the mask and to achieve a nice seal with the skin. Rats are placed in a natural prone position with the tail end about 3 inches from the edge of a padded platform. The laryngeal mask airway cuff is oriented facing upwards and fitted over the urethral opening (Figure 2). To collect urine, the shortened laryngeal mask airway tube is inserted in a calibrated collecting tube and supported by the table and padding (Figure 3). By gravity, urine falls into the laryngeal mask airway cuff and flows through airway tube into the collecting receptacle (Figure 4).
We have used this method of collecting rat urine in our earlier studies (Toung, Nyquist, & Mirski, 2008; Wang, Panpangelou, Lin, & Mirski, 2013). This technique was successfully applied to all animals tested. On rare occasion, there was minor dislodgement of the laryngeal mask airway, which was easily corrected and did not result in any appreciable loss of urinary volume. In these studies (Toung et al., 2008; Wang et al., 2013), the observation period for urinary volume ranged between 1.25 and 5.75 hr (mean 3.38 hr). The overall mean animal weight was approximately 350 g (n = 446), and urinary output ranged from 0.39 to 8.04 ml/100 g body weight, reflecting large variations in observation time and diuretic potency of the study solution utilized. In conclusion, this technique appears to be a novel, simple and effective method for urinary volume quantification in experimental rat studies.
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