Use of the Bispectral Index (BIS) in Avian and Reptilian Anesthesia: Preliminary Results
This presentation describes the use of a wakefulness measuring device called the bispectral (BIS) monitor (Aspect Medical Systems International B.V., de Meeren, The Netherlands) in avian and reptilian patients. The index of wakefulness is calculated by an empirically derived algorithm on the complex waveforms of an electroencephalogram (EEG) in humans. BIS measurements have also been published from horses,3 pigs,7 goats,1 dogs,2 cats,5 rabbits,6 and dolphins,4 but to our knowledge not from birds and reptiles.
In nine feral pigeons (Columba livia) anesthetized with medetomidine, butorphanol and ketamine, no correlation between reflex score and BIS score (BIS A-2000 XP®) was found. In a red kite (Milvus milvus) anesthetized with butorphanol and isoflurane, BIS scores increased from a intraoperative average score of 51±7 to 84 within 3 minutes following extubation, indicating that the animal was fully conscious, although the bird remained in sternal recumbency, probably feigning death.
BIS values were recorded from a Hermann’s tortoise (Testudo graeca) which underwent lung lavage after midazolam and butorphanol premedication, propofol induction and isoflurane maintenance. BIS scores during the procedure were 25±15, arising to 54±4 for extubation and showing the first movements at 33±8 BIS value. This was considered to be an effect of hypothermia (29°C mean rectal temperature).
Our observations show that BIS signals can be obtained from avian and reptile species. BIS monitoring in these species may prove to be useful to monitor the degree of wakefulness in view of depth of anesthesia.
1. Antognini, J.F., X.W. Wand and E. Carstens. 2000. Isoflurane anaesthetic depth in goats monitored using the bispectral index electroencephalogram. Vet. Res. Commun. 24: 361–370.
2. Greene, S.A., W.J. Tranquilli, G.J. Benson and K.A. Grimm. 2003. Effect of medetomidine administration on bispectral index measurements in dogs during anesthesia with isoflurane. Am. J. Vet. Res. 64: 316–320.
3. Haga, H.A. and N.I. Dolvik. 2002. Evaluation of the bispectral index as an indicator of degree of central nervous system depression in isoflurane-anesthetized horses. Am. J. Vet. Res. 63: 438–442.
4. Howard, R.S., J.J. Finneran and S.H. Ridgway. 2006. Bispectral index monitoring of unihemispheric effects in dolphins. Anesth Analg. 103: 626–632.
5. Lamont, L.A., S.A. Greene, K.A. Grimm and W.J. Tranquilli. 2004. Relationship of bispectral index to minimum alveolar concentration multiples of sevoflurane in cats. Am. J. Vet. Res. 65: 93–98.
6. Martín-Cancho, M.F., J.R. Lima, L. Luis, V. Crisóstomo, M.S. Carrasco-Jiménez and J. Usón-Gargallo. 2006. Relationship of bispectral index values, haemodynamic changes and recovery times during sevoflurane or propofol anaesthesia in rabbits. Lab. Anim. 40: 28–42.
7. Martín-Cancho, M.F., J.R. Lima, L. Luis, V. Crisóstomo, L.J. Ezquerra, M.S. Carrasco and J. Usón-Gargallo. 2003. Bispectral index, spectral edge frequency 95%, and median frequency recorded for various concentrations of isoflurane and sevoflurane. Am. J. Vet. Res. 64: 866–873.