Prolonged (12 hours) intravenous anesthesia in the rat.

A method is described for prolonging anesthesia in the rat for periods of up to 12 h, with subsequent recovery. Ketamine and xylazine in a ratio of 30 to 1 were infused intravenously by use of an adjustable syringe pump at rates of 40 to 50 microliters/min (1,000 to 1,250 micrograms/kg of body weight/min for ketamine and 32 to 40 micrograms/ kg/min for xylazine), and the rate of infusion was adjusted to maintain a stable depth of anesthesia. Primary assessment of the depth of anesthesia was provided by observation of the respiratory rate, which was maintained between 80 and 100 breaths/min. Rectal temperature was maintained between 35 and 36 degrees C. Blood pressure, pulse, and blood pH and bicarbonate concentration were stable during the 12-h period. The PCO2 increased slightly to 53 mm Hg; PO2 decreased gradually to 59 mm Hg at the last measurement. Plasma glucose concentration decreased progressively; supplemental glucose was given to maintain plasma concentration > 5 mM. After anesthetic administration was discontinued, the animals recovered promptly.