Abstract

1. A method of inducing spinal anesthesia in the rabbit has been described.

2. The dosage of local anesthetics injected intraspinally in the rabbit has been shown to be more closely correlated with the spinal length, than with the weight of the animal. This is confirmation of the findings of Co Tui in the dog.

3. The subarachnoidal space of a rabbit can be filled with a volume dose of 0.02 cc. per centimeter of spinal length. This constant volume dose has been used throughout these experiments.

4. The modified method for sensory stimulation, of Hirschfelder and Ridges has been shown to be well adapted for the study of spinal anesthesia in the rabbit.

5. The intraspinal minimal sensory anesthetic concentrations of the six local anesthetics have been found to be: pantocaine, 0.05 per cent; nupercaine, 0.07 per cent; panthesine, 0.5 per cent; tutocaine, 0.5 per cent; metycaine, 0.86 per cent; and procaine HCl, 0.9 per cent.

6. The intraspinal minimal lethal concentrations of the six local anesthetics have been found to be: nupercaine, 0.8 per cent; pantocaine, 1.5 per cent; metycaine, 3.5 per cent; panthesine, 4.0 per cent, tutocaine, 6.0; and procaine HCl, 6.0 per cent.

7. From these percentage figures the following therapeutic ratios have been determined: metycaine, 4.0; procaine HCl, 6.6; panthesine, 8.0; nupercaine, 11.4; tutocaine, 12.0; and pantocaine, 30.0.

8. The order of incidence of irritation, beginning with the most irritant anesthetic, has been found to be: nupercaine, pantocaine, tutocaine, metycaine, panthesine, and procaine HCl.

9. Acute or immediate death during spinal anesthesia in the rabbit appeared to be due, primarily, to respiratory depression.

10. Delayed death was associated with permanent motor paralysis, and, for pantocaine, also, with permanent sensory anesthesia.