Effect of Some Short Acting Barbiturates on the Patency of the Glottis

Abstract

Experiments were conducted on normal cats with the following barbituric acid derivatives: sodium N-methyl-cyclohexanyl barbiturate (evipal), sodium iso-amyl ethyl barbiturate (amytal), sodium iso-amyl ethyl thio-barbiturate (sodium thio-ethamyl∗), sodium N-ethyl-l-methyl butyl barbiturate (nembutal), and sodium N-ethyl-l-methyl butyl thio-barbiturate (pentothal). In each case a 2% aqueous solution, freshly prepared, was injected intravenously at a constant rate of a milligram per second. The quantities injected ranged between the minimum anesthetic dose and the minimum lethal dose.

It was noticed that most of the animals would cough, sneeze, or hiccup considerably during the course of anesthesia and that these animals would quickly develop cyanosis and dyspnea regardless of whether a large or small dose had been administered. Inspection of the glottis in these cases showed spastic adduction of the vocal cords. In the cases where there was no spontaneous coughing, inspection of the glottis showed hyper-active adducted vocal cords and lifting the epiglottis would elicit complete spastic closure of the glottis; cyanosis then developed rapidly and unless tracheal intubation was performed cardiac arrest would ensue. These results are illustrated in Table I.

Since artificial stimulation of the superior laryngeal nerve 1 causes reflex closure of the glottis by contraction of the adductor muscles, it is possible that the symptoms here observed are of parasympathetic origin. In order to test the validity of this assumption experiments were performed to study the modification of this symptom-complex by drugs affecting the sympathetic and parasympathetic divisions of the autonomic nervous system and by section of the vagi. The results may be summarized thus:

Atropin sulphate (3 to 5 mg. per kilo intravenously) always caused immediate relaxation of the vocal cords, a return of normal respiration, disappearance of cyanosis, a shortening of anesthesia time, and an increase in tolerance to the M.L.D.