Indirect monitoring methods are used to ensure adequate oxygen delivery to vital organs during anesthesia.2 Technologies not commonplace in veterinary medicine can provide additional information. One such technology is near-infrared spectroscopy (NIRS), a non-invasive method of assessing regional tissue perfusion.1 In a randomized crossover design, nine impala (Aepyceros melampus) were anesthetized twice each with protocol EA [15 µg/kg etorphine (Captivon 98, Wildlife Pharmaceuticals Ltd., White River, South Africa) and 0.15 mg/kg acepromazine (Calmivet solution injectable, Vétoquinol, Magny-Vernois, Lure, France)] and protocol MK [110 µg/kg medetomidine (Zalopine 30 mg/ml, Orion Pharma, Espoo, Finland) and 4.3 mg/kg ketamine (Ketaminol Vet, MSD Animal Health, AN Boxmeer, Holland)]. As anticipated, EA animals had lower mean arterial blood pressures (EA 72±21, MK 118±8 mm Hg) and respiratory rates (EA 8±3, MK 27±23 bpm) but higher heart rates (EA 107±11, MK 47±18 bpm) at 20 min post-darting. NIRS values, reflecting muscle oxygenation, were consistently higher for EA than for MK animals. Mean values at 20 min were EA 70.8% and MK 56.0% and at 40 min EA 66.3% and MK 60.4%. The lower muscle oxygenation levels seen with MK animals at 20 min were likely a result of reduced perfusion caused by medetomidine. Further work is required to establish the relationship between perfusion/oxygenation of muscle and that of vital organs. However, NIRS uniquely allows assessment of tissue oxygenation reflecting perfusion, and in this case demonstrated better muscle oxygenation with EA than with MK.
The authors thank Helle Flaga, Mari-ann Da Silva, and Mette Halck for their help in conducting this project.
1. Scott JP, Hoffman GM. Near-infrared spectroscopy: exposing the dark (venous) side of the circulation. Paediatr Anaesth. 2014;24:74–88.
2. Ozeki L, Caulkett N. Monitoring. In: West G, Heard D, Caulkett N, eds. Zoo Animal and Wildlife Immobilization and Anesthesia. Ames, IA: Wiley-Blackwell; 2014:43–51.