Background and Purpose: Guinea pigs are one of the most difficult rodents to anesthetize safely, and as a consequence, there is a paucity of reports regarding the effects of anesthesia on their cardiorespiratory variables. We used long-term indwelling cannulas for studying the guinea pig in the conscious state, and subsequently investigated the effects of four types of injectable anesthetic regimens on cardiorespiratory variables. Methods: Using barometric plethysmography (conscious: long-term cannulated, n = 11; no cannulation, n = 28) or trachea-out plethysmography (anesthetized: n = 7 for each of the four groups), we recorded ventilatory, cardiovascular, metabolic, and arterial gas variables during air breathing and in response to 10 min of hypoxia (8% O2) and 10 min of hypercapnia (8% CO2). The four anesthetic regimens tested were: Saffan (infused at 9.75 mg/kg of body weight/h, i.v.); ketamine/xylazine (14.6/3.7 mg/kg/h, i.v.); pentobarbitone (8.3 mg/kg/h, i.v.) plus Innovar Vet (0.15 mg/kg every 1 to 1.5 h, s.c.); or pentobarbitone alone (22 mg/kg/h, i.v.). Results: The least depressive anesthetic with regard to ventilation (VE) was ketamine/xylazine. Air breathing was depressed by only 17% (cf. approx 50 to 60% for all other regimes), and the VE responses to hypoxia and hypercapnia were attenuated the least. All anesthetics equally depressed mean arterial blood pressure (from 70 mmHg to 56 mmHg) and ketamine/xylazine was the only anesthetic to reduce heart rate (from 260 beats/min to 198 beats/min). Conclusion: Although all anesthetics induce cardiorespiratory depression to some extent, the use of ketamine/xylazine is recommended for future use in respiratory studies of the guinea pig where anesthesia cannot be avoided.
Department of Physiology, University of Otago, Dunedin School of Medicine, PO Box 56, Dunedin, New Zealand
Publication date: February 1, 2004
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Comparative Medicine (CM), an international journal of comparative and experimental medicine, is the leading English-language publication in the field and is ranked by the Science Citation Index in the upper third of all scientific journals. The mission of CM is to disseminate high-quality, peer-reviewed information that expands biomedical knowledge and promotes human and animal health through the study of laboratory animal disease, animal models of disease, and basic biologic mechanisms related to disease in people and animals.
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