Endocrine, haematological and metabolic responses to sevoflurane anaesthesia in lambs

Objective To compare the magnitude and duration of the peri-operative haematological, endocrine and metabolic effects of surgery performed under sevoflurane anaesthesia. Study Design Prospective randomized study. Animals Ten, 55-day-old lambs of both sexes, mean weight 20.8 ± 0.3 kg (range 18.5-23.6 kg). Methods Animals were randomly allocated to two equal groups. All were anaesthetized with sevoflurane for 3 hours. Surgery (end-to-end anastomosis of the right carotid artery and right jugular vein) was performed in animals of Group 1 only. The electrocardiogram, pulse oximetry, cardiac output and noninvasive arterial blood pressure (NIBP) were monitored. Venous blood samples (5 mL) were taken 30 minutes before induction of anaesthesia (T = 0) and 1 (T1), 24 (T2), 48 hours (T3) and 7 days (T4) after anaesthesia in order to measure plasma cortisol, ACTH, insulin, cyclic adenosine monophosphate (cAMP), glucose, protein concentrations and haematological variables. Results Sevoflurane decreased NIBP (minimum mean value: 64 ± 3 mm Hg) in both groups. Plasma cortisol and ACTH concentration increased in Group 1 (maximum mean values: cortisol: 136.2 nmol L^-1, ACTH: 54.5 pmol L^-1) and Group 2 (maximum mean values: cortisol: 128.7 nmol L^-1, ACTH: 44.0 pmol L^-1). Cyclic AMP increased only in Group 1 (9.3 nmol) 1 hour after anaesthesia. Neutrophilia, lymphopaenia and a decreased PCV were observed in both groups 1 hour after anaesthesia. Plasma protein and glucose concentrations did not change. Conclusions Increased ACTH and cortisol concentrations recorded 1 hour after anaesthesia suggest that sevoflurane induces a stress response in lambs. Clinical relevance The study did not identify the mechanism by which sevoflurane induces a stress response although hypotension is implicated.