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

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.