Effects of anaesthesia on blood gases, acid-base status and ions in the toad Bufo marinus

It is common practice to chronically implant catheters for subsequent blood sampling from conscious and undisturbed animals. This method reduces stress associated with blood sampling, but anaesthesia per se can also be a source of stress in animals. Therefore, it is imperative to evaluate the time required for physiological parameters (e.g. blood gases, acid -base status, plasma ions, heart rate and blood pressure) to stabilise following surgery. Here, we report physiological parameters during and after anaesthesia in the toad Bufo marinus. For anaesthesia, toads were immersed in benzocaine (1 g 1(-1)) for 15 min or until the corneal reflex disappeared, and the femoral artery was cannulated. A 1-ml blood sample was taken immediately after surgery and subsequently after 2, 5, 24 and 48 h. Breathing ceased during anaesthesia, which resulted in arterial Po-2 values below 30 mmHg, and respiratory acidosis developed, with arterial Peo(2) levels reaching 19.5 +/- 2 mmHg and pH 7.64 +/- 0.04. The animals resumed pulmonary ventilation shortly after the operation, and oxygen levels increased to a constant level within 2 h. Acid-base status, however, did not stabilise until 24 It after anaesthesia. Haematocrit doubled immediately after cannulation (26 +/- 1%), but reached a constant level of 13% within 24 h. Blood pressure and heart rate were elevated for the first 5 It, but decreased after 24 h to a constant level of approximately 30 cm H2O and 35 beats min(-1), respectively. There were no changes following anaesthesia in mean cellular haemoglobin concentration, [K+], [Cl-], [Na+], [lactate] or osmolarity. Toads fully recovered from anaesthesia after 24 h. (C) 2002 Elsevier Science Inc. All rights reserved.