The effect of thiopental sodium, methoxyflurane and halothane on the acid-base status in sheep.

Experiments have been carried out on 20 adult fat-tailed ewes to determine the effects of thiopental sodium, methoxyflurane and halothane on acid-base status of the saliva loss during prolonged surgical anaesthesia. The rate of loss of base in saliva depends on the volume of saliva produced, which fell sharply at the onset of anesthesia with the volatile anaesthesia. Plasma pH and plasma pvCO2 excess were both increased by the volatile anaesthetics but fell sharply during thiopental anaesthesia. Plasma pH and plasma PvCO2 showed no consistent relationship.

Effects of thiopentone sodium, methoxyflurane and halothane on haematological parameters in sheep during prolonged anaesthesia.

1. Satisfactory surgical anaesthesia in sheep was achieved by i.v. injection of thiopentone sodium per se (20 mg/kg); and also with thiopentone/methoxyflurane and thiopentone/halothane anaesthetics (2--3% and 1.5--2%, respectively). 2. Cardiac arrhythmias were not observed during thiopentone sodium, thiopentone/methoxyflurane and thiopentone/halothane anaesthesia. However, during thiopentone anaesthesia, one sheep displayed a high degree of sinus tachycardia followed with ventricular tachycardia. 3. Pneumograms recorded during thiopentone sodium and thiopentone/methoxyflurane anaesthesia showed no irregularity, but in thiopentone/halothane anaesthesia, 30% of the sheep developed Cheyne-Stokes periodic respiration. 4. Packed cell volume (PCV) and haemoglobin (Hb) were significantly decreased in thiopentone/methoxyflurane and thiopentone anaesthetized sheep, but not in animals anaesthetized by thiopentone/halothane. 5. White blood cell count (WBC) was significantly decreased only in thiopentone/methoxyflurane anaesthetized sheep, but was not remarkable in thiopentone and thiopentone/halothane anaesthetized animals. 6. A significant lymphocytopenia occurred in thiopentone/methoxyflurane and in thiopentone/halothane anaesthetized sheep, but not in the thiopentone anaesthetized animals. This was accompanied with an increase in neutrophils. 7. Clotting time fell, but the extent and time course was different in thiopentone, thiopentone/methoxyflurane and thiopentone/halothane anaesthesia. 8. From these data, it is suggested that thiopentone sodium, thiopentone/methoxyflurane and thiopentone/halothane have different effects on different blood parameters during prolonged anaesthesia, and may be clinically significant.

Acute urea toxicity in sheep.

Twenty-seven sheep were assigned to three groups in order to study acute urea toxicity. Groups I, II and III were dosed with 0.5, 0.6 annd 0.75 g/kg of urea, respectively. The mean survival times were 165, 109 and 60 minutes, respectively. The following clinical signs such as pronounced muscle fasciculation, trembling, grinding teeth, ataxia, lateral recumbency, bloating, regurgitation, hyperesthesia, mydriasis and convulsions were observed. Anuria and lack of salivation were also present. The primary cause of death in this study was due to respiratory arrest and not cardiovascular collapse. Plasma examinations showed a marked increase in glucose, ammonia and urea levels but no change in ketone body concentration.

Prevention of thiopental and thiopental/halothane cardiac sensitization to epinephrine in the sheep.

The effects of epinephrine (5 microgram/kg of body weight) on ten unanesthetized sheep were experimentally tested: all sheep displayed serious arrhythmias. Sheep anesthetized with thiopental and thiopental/halothane combination displayed cardiac arrhythmias of the order of 10% and 20% respectively. Challenge injections of epinephrine (5 microgram/kg of body weight) to ten sheep anesthetized with thiopental, and to the same number of animals after 45 minutes of anesthesia with thiopental/halothane, produced serious arrhythmias. However, following preanesthetic treatment with acepromazine maleate (0.5 mg/kg) to 15 sheep, serious arrhythmias were prevented in all of them when they were given arrhythmic doses of epinephrine.

Biosynthesis of noradrenaline in organ cultured hearts.

In hearts of newborn mice, maintained in organ culture in an in vitro environment, noradrenaline levels were reduced after 24 h but subsequently recovered, reaching at three days values significantly greater than those found at birth. The increased synthesis of noradrenaline was blocked by the inhibitor of tyrosine hydroxylase, alpha-methyl tyrosine methyl ester. The site and control of noradrenaline biosynthesis in cultured newborn hearts are discussed.