Blood gas and acid–base status during tiletamine/zolazepam anaesthesia in dogs

Abstract

ObjectiveTo evaluate the effect of the tiletamine/zolazepam (TZ) combination (Zoletil 100; Virbac, Carros, France) with and without atropine on blood gas values and acid–base status in dogs. Study designRandomized cross-over experimental study. AnimalsSix healthy adult cross-bred dogs, weighing 11.0–18.5 kg. Materials and methodsEach dog received four different drug treatments at intervals of at least 15 days: (i) 5 mg kg−1 intravenous (IV) TZ (TZ.IV); (ii) 10 mg kg−1 intramuscular (IM) TZ (TZ.IM); (iii) atropine, 20 μg kg−1 IV, followed 5 minutes later by 5 mg kg−1 TZ IV (A.TZ.IV); and (IV) atropine (same dose) given 5 minutes before 10 mg kg−1 TZ IM (A.TZ.IM). Arterial blood samples were collected from each dog before drug administration (baseline) at induction of anaesthesia (time 0) and 2, 5, 10 and 30 minutes thereafter. ResultsTransient hypoxaemia and respiratory acidosis were observed just after induction. PaO2 and SaO2 dropped, while H+ concentration and PaCO2 rose significantly above baseline values. In groups TZ.IV and A.TZ.IV, PaO2 values as low as 6.0–6.4 kPa (45–48 mm Hg) were recorded. However, there was no significant difference in blood gas variables among the groups encountered during the evaluation period. The overall change in [HCO3−] and base excess (BE) was not significant among groups. Atropine did not affect the above variables. Conclusions and clinical relevanceTiletamine/zolazepam injection may induce transient hypoxaemia and respiratory acidosis, but acid–base status changes are clinically unimportant. Particularly, close observation of dogs is recommended during the first 5–10 minutes after induction with TZ, especially in animals with cardiopulmonary disease. TZ should perhaps not be used in animals intolerant of tachycardia.