THE EFFECTS OF ANESTHETIC DOSES OF SODIUM THIO-PENTOBARBITAL, SODIUM THIO-ETHAMYL AND PENTOTHAL SODIUM UPON THE RESPIRATORY SYSTEM, THE HEART AND BLOOD PRESSURE IN EXPERIMENTAL ANIMALS

¹ From the Department of Pharmacology, Jefferson Medical College, Philadelphia

1. Thio-pentobarbital, pentothal and thio-ethamyl usually decrease the rate and depth of respiration in rabbits, cats, dogs and monkeys. Large doses slowly injected or small doses rapidly injected produce cessation of respiration before the heart ceases to beat. In the monkey and in some dogs accelerated respiration may occur during the injection of the drug.

2. Evipal, ortal, pentobarbital, thio-pentobarbital, pentothal and thio-ethamyl, if rapidly injected intravenously cause marked falls in general blood pressure. The recovery is most rapid with evipal and the thio-barbiturates.

3. Thio-pentobarbital and thio-ethamyl if injected intravenously slowly in five and ten per cent solutions, a pure rise in blood pressure may occur. This rise may be as much as 50 mm. of mercury.

4. The heart rate is increased in the unanesthetized dog by the intravenous administration of the thio-barbiturates. In the ether anesthetized dog in which the heart is already rapid the thio-barbiturates tend to decrease the rate. In cats, rabbits and monkeys the thio-barbiturates tend to slow the already rapid heart.

5. Like the barbiturates the thio-barbiturates tend to dilate the heart.

6. Thio-barbiturates cause alternate ventricular rhythm in the dog. Similar changes are noted in some rabbits, cats and monkeys. In this rhythm there is a premature ventricular contraction alternated with a normal beat.

7. Morphine sulphate definitely increases the toxicity of the thio-barbiturates. This was most noticeable in the monkey.

8. In dogs the P-R interval as shown by the electrocardiogram is definitely shortened. This effect is very slight in the cat, rabbit and monkey.

9. Stimulation of the vagus nerve may bring about cardiac arrhythmia if not present, after the injection of the thio-barbiturate. If the arrhythmia is present vagus nerve stimulation may cause temporary and in some instances permanent recovery.

10. Atropine sulphate has no effect upon the cardiac arrhythmia produced by the thio-barbiturate.

11. Epinephrine restores either temporarily or permanently, the normal rhythm in animals hearts rendered arrhythmic by thio-barbiturates.

12. Some terrapin hearts become irregular in rhythm when exposed to high concentrations of the thio-barbiturates.

13. Thio-ethamyl appears to be less toxic to the dog's heart than is thio-pentobarbital.

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