To determine dose-dependent cardiovascular effects of dobutamine and phenylephrine during anesthesia in horses, increasing doses of dobutamine and phenylephrine were infused to 6 healthy Thoroughbred horses. Anesthesia was induced with xylazine, guaifenesin and thiopental and maintained with sevoflurane at 2.8% of end-tidal concentration in all horses. The horses were positioned in right lateral recumbency and infused 3 increasing doses of dobutamine (0.5, 1.0 and 2.0 µg/kg/min) for 15 min each dose. Following to 30 min of reversal period, 3 increasing doses of phenylephrine (0.25, 0.5 and 1.0 µg/kg/min) were infused. Cardiovascular parameters were measured before and at the end of each 15-min infusion period for each drug. Blood samples were collected every 5 min during phenylephrine infusion period. There were no significant changes in heart rate throughout the infusion period. Both dobutamine and phenylephrine reversed sevoflurane-induced hypotension. Dobutamine increased both mean arterial blood pressure (MAP) and cardiac output (CO) as the result of the increase in stroke volume, whereas phenylephrine increased MAP but decreased CO as the result of the increase in systemic vascular resistance. Plasma phenylephrine concentration increased dose-dependently, and these values at 15, 30 and 45 min were 6.2 ± 1.2, 17.0 ± 4.8 and 37.9 ± 7.3 ng/ml, respectively.

ABSTRACT. To determine hemodynamic effects of hydroxyethyl starch (HES) infusion during anesthesia in horses, incremental doses of 6% HES were administered to 6 healthy Thoroughbred horses. Anesthesia was induced with xylazine, guaifenesin and thiopental and maintained with sevoflurane at 2.8% of end-tidal concentration in all horses. The horses were positioned in right lateral recumbency and administered 3 intravenous dose of 6% HES (5 ml/kg) over 15 min with 15-min intervals in addition to constant infusion of lactated Ringer's solution at 10 ml/kg/hr. Hemodynamic parameters were measured before and every 15 min until 90 min after the administration of 6% HES. There was no significant change in heart rate and arterial blood pressures throughout the experiment. The HES administration produced significant increases in mean right atrial pressure, stroke volume, cardiac output (CO) and decrease in systemic vascular resistance (SVR) in a dose-dependent manner. There was no significant change in electrolytes (Na + , K + , Cl − ) throughout the experiment, however, packed cell volume, hemoglobin concentration, and total protein and albumin concentrations decreased in a dose-dependent manner following the HES administration. In conclusion, the HES administration provides a dose-dependent increase in CO, but has no impact upon arterial blood pressures due to a simultaneous decrease in SVR. Anesthetic-induced hypovolemia and hypotension reduce blood flow to peripheral tissues [11], which increases the risk of postanesthetic complications and death [5,17,18]. Intravenous administration of fluids is a useful method for the treatment of hypovolemia and hypotension during anesthesia in horses. Crystalloid solutions, in particular lactated Ringer's solution (LRS), are frequently administered for the improvement of anesthetic-induced hypovolemia and hypotension. It is reported that less than 33% of the infused volume of a crystalloid solution is retained within the vascular compartment during infusion, and less than 20% of the infused volume is retained after 30 min [6,10,13]. Therefore, large volumes of crystalloids must be required to treat hypovolemia and hypotension. However, it is clinically difficult to administer large volumes of fluids in a short duration in large animals. Moreover, rapid administration of large volumes of crystalloids can result in hemodilution of blood constituents and increase the risk of interstitial and pulmonary edema [7,15].The administration of colloidal solutions, in particular 6% hydroxyethyl starch (HES) solution, for the treatment of hypovolemia and hypotension is becoming increasingly popular in veterinary practice. Colloid solutions are retained within the vascular compartment after administration, thereby reducing the total fluid requirement, prolonging volume expansion and improving peripheral blood flow [3,13]. It is reported that the administration of colloid fluid, compared with administration of LRS, is significantly effective in expanding the intravascular volume in isoflurane-ane...

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A total of 20 racehorses with longitudinal fractures underwent internal fixation surgery under sevoflurane anesthesia combined with infusion of medetomidine (3 µg/kg/hr) alone (10 horses, group M) or medetomidine and fentanyl (7 µg/kg/hr) (10 horses, group FM). In group FM, the end-tidal sevoflurane concentration during surgery was maintained significantly lower than in group M (2.8–2.9% for group M vs. 2.2–2.6% for group FM, P<0.01). The mean arterial blood pressure was maintained over 70 mmHg using dobutamine infusion (group M, 0.36–0.54 µg/kg/min; group FM, 0.27–0.65 µg/kg/min), and the recovery qualities were clinically acceptable in both groups. In conclusion, co-administration of fentanyl and medetomidine by constant rate infusion may be a clinically useful intraoperative anesthetic adjunct for horses to reduce the requirement of sevoflurane when they undergo orthopedic surgery.

Summary In order to define allergen‐induced bronchial responses, sixteen asthmatics, assessed as mild (twelve cases) and moderate (four cases) were tested by inhalation of small doses of house dust allergen. The minimum dose was first determined in each patient. It caused no abnormal respiratory sensation, while a fall of V̇max50 air with no change or slight decrease of V̇max50 He‐O2 and a rise of density dependence ratio were observed. Inhalation tests with multiples of the minimum dose were made and showed that the minimum dose was dependent on the individual, his condition and induced airflow obstruction in a dose‐related fashion.