Comparison of the depressive effects of four anesthetic regimens on ventilatory and cardiovascular variables in the guinea pig.
OBJECTIVE
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).


CONCLUSIONS
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.
Schwenke
Daryl O
DO
Department of Physiology, University of Otago, Dunedin School of Medicine, PO Box 56, Dunedin, New Zealand.
Cragg
Patricia A
PA
D000530:Alfaxalone Alfadolone Mixture / Q000009:adverse effects; D000758:Anesthesia / Q000009:adverse effects* / Q000379:methods*; D000777:Anesthetics / Q000009:adverse effects*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004329:Droperidol / Q000009:adverse effects; D004359:Drug Therapy, Combination; D005260:Female; D005283:Fentanyl / Q000009:adverse effects; D006168:Guinea Pigs; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D007649:Ketamine / Q000009:adverse effects; D010424:Pentobarbital / Q000009:adverse effects; D010991:Plethysmography / Q000662:veterinary*; D012119:Respiration / Q000187:drug effects*; D014991:Xylazine / Q000009:adverse effects
D000777:Anesthetics; D014991:Xylazine; D007649:Ketamine; C001451:Innovar; D000530:Alfaxalone Alfadolone Mixture; D010424:Pentobarbital; D004329:Droperidol; D005283:Fentanyl