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January - March 2006: 
Volume 19, Issue 1

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ARCHIVE

Pulmonary artery catheterization in rabbits - Our experience
Abstract
Pulmonary artery catheterization in small mammals contributes to more precise monitoring of hemodynamic parameters studied in experimental models. In addition, it allows drugs to be administered locally in the lungs through the inserted catheter, thus minimizing systemic adverse reactions. A refined technique for insertion of a Swan-Ganz catheter in the pulmonary artery of New Zealand rabbits through right external jugular artery is described. The catheter is bended before the insertion; when the right ventricle is reached, a minimal inflation of the balloon helps its advancement in the pulmonary artery carried along by the blood flow. Pneumon 2006,19(1):42-45.
Full text
INTRODUCTION

Monitoring of hemodynamic parameters of cardiac and pulmonary function in rabbits through pulmonary artery catheterization contributes to a more comprehensive understanding of hemodynamic disturbances in various conditions, as well as to the study of the actions of certain drugs. In addition, measurements of hemodynamic parameters, including pulmonary capillary wedge pressure and cardiac output, are made possible by the presence of a catheter in the pulmonary artery and the application of the principles of thermodilution.

Kydd is referred to as the first investigator in the literature to have measured pulmonary artery pressures in rats with a closed-chest method (i.e. without sternotomy)1. Later, several catheterization techniques appeared in the literature; some of which included the use of a bent-tip PE- 50 catheter, while in others, a slightly larger in diameter curved catheter was used as a guide through which a Swan-Ganz catheter was inserted into the pulmonary artery2-5.

In the following sections, we present a pulmonary artery catheterization method in New Zealand rabbits which, having tried all methods described in the literature to date, we believe is the easier to perform.

MATERIAL AND METHODS

A Swan-Ganz catheter No 4 Fr. is used for the catheterization of the pulmonary artery in rabbits. The catheter is immersed in cold normal saline at a temperature of 4 oC after its tip has been bent to a ¾ circle with a diameter of 1 cm.

The rabbit is anesthetized with ketamine 25 mg/kg IM in combination with xylazine 5 mg/kg IM; atropine 0.08 mg/kg IM is also administered in order to prevent bradycardia induced by xylazine. Doses are repeated every half an hour or so. After the administered drugs have began to exert their actions, which occurs in about 10 minutes, the rabbit is shaved and a venous catheter (25 G) is inserted in an aural vein for the intravenous administration of fluids or drugs.

After subcutaneous small-dose infusion of a xylocaine solution 2%, a transverse skin incision about 2 cm long is made in the right cervical area; the right external jugular vein is identified and isolated from the surrounding tissues using two stitches, one proximal and one distal. The catheter is flushed with cold (4 oC) slightly heparinized normal saline and then connected to a recording device. Cold saline makes catheter stiff and thus its shape is preserved. The catheter is inserted in the jugular vein through a small incision made in the front wall of the vein with its bent tip directed superiorly, and advanced while simultaneously clockwise rotated by approximately 30o. Changes in recorded pressures are monitored during the advancement of the catheter. Figure 1 shows the pressures recorded as the catheter is advanced toward the pulmonary artery.

Figure 1. Pressure waveforms that appear on the monitoring device as the catheter is advanced toward a terminal branch of the pulmonary artery.




When the catheter has reached the right ventricle, the balloon of the catheter is slightly inflated (not distended) and then advanced very gently. After the catheter has entered the trunk of the pulmonary artery, the balloon is deflated, and the catheter is further advanced in a lobar artery and more distally with gentle semicircular clockwise and counterclockwise maneuvers until the typical wedge waveform (which is dependent upon the breathing of the rabbit) appears on the monitor.

Figure 2. Catheterization of the left lower lobar pulmonary artery.


RESULTS

Of 30 rabbits included in our experimental study, we successfully cannulated a peripheral pulmonary artery branch in 28. Two rabbits passed away right after the completion of the catheterization procedure; one after an episode of arrhythmia and the other after a repeat intravenous administration of the anesthetic drugs that was necessary for the continuation of the experiment. The left pulmonary artery seemed to be slightly superior compared to the right pulmonary artery. Radiographic confirmation of the position of the catheter was not deemed necessary after the first few procedures, since monitoring of the recorded waveforms provided reliable information as to the position of the catheter.

Figure 3. Catheterization of the right lower lobar pulmonary artery.


DISCUSSION

The technique of pulmonary artery catheterization in small mammals was first described by Kydd1. Since then, several techniques have been developed by experimental laboratory groups2-5. The success of all techniques relies heavily upon adequate experience and technical skill.

Having studied all techniques described by other investigators in this field and having applied them in our experimental model, we were faced with two major difficulties associated with the advancement of the catheter in the pulmonary artery of the rabbits. The first difficulty regards the passage of the catheter from the right atrium to the right ventricle, since many times the catheter is advanced in the inferior vena cava. The second difficulty is the rotation of the catheter inside the right ventricle in order to be directed toward the trunk of the pulmonary artery. In these small mammals, the cavity of the right ventricle is proportionately small and, as a result, the catheter is quite frequently wedged in the ventricular wall.

JB Forest et al have solved both of these problems using a sheath with a bent tip forming a 90o angle they designed. The catheter is inserted and fixed in this sheath, which is advanced in the right ventricle of the animal; then the catheter is advanced in the trunk of the pulmonary artery3.

The rationale of bending the catheter prior to its insertion was also adopted by our team. In an attempt to simplify the Forest technique, the bent tip sheath was left out; before the insertion of the catheter, the desired curvature was formed and fixed through immersing the catheter in cold normal saline. Our technique worked out successfully, although it required adequate training and skill. Hence, we believe that our modified technique is safe and relatively easy to be learnt. In the first catheterizations, a chest radiograph was obtained to confirm the right position of the catheter. Nevertheless, our experience indicates that monitoring the pressure waveform on the recording device is a reliable way to ascertain that the catheterization has been successful, while chest radiograph adds only the information of which side of the lung, right or left, has been cannulated.

CONCLUSION

The catheterization of the pulmonary artery in a rabbit is easy to perform using the above-described method. The method is quite simple; learning to perform this method is relatively easy too. Radiographic confirmation of the catheter position may be omitted, since monitoring the pressure waveforms is a reliable guide during the advancement of the catheter.

REFERENCES

1. Kydd GH. Pressure in the pulmonary circulation of the rat. Physiologist 1966; 9:224.
2. Hayes BE, Will JA. Pulmonary artery catheterization in the rat. Am J Physiol 1978; 235(4):H452-H454.
3. Forrest JB, Todd MH, Cragg DJ. A simple method of percutaneous cannulation of the pulmonary artery in small mammals. Can Anaesth Soc J 1979; 26(1):58-60.
4. Stinger RB, Iacopino VJ, Alter I, Fitzpatrick TM, Rose JC, Kot PA. Catheterization of the pulmonary artery in the closed-chest rat. J Appl Physiol 1981; 51(4):1047- 50.
5. Chang SW, Morris KG, McMurtry IF, Voelkel NF. Pulmonary artery catheterization in the rat. Am J Physiol 1988; 255(3 Pt 2):H691-2.

References