Abstract

Accurate monitoring of oxygenation in reptiles, especially snakes, is challenging for multiple reasons, but vital for assessment of physiologic state, especially during anesthesia. Traditional pulse oximetry (SpO₂) is limited by the unique anatomy and physiology of reptiles, and monitoring trends is generally considered the most clinically relevant use.² Transcutaneous oxygen monitoring utilizes near-infrared spectroscopy to assess a mixture of arterial, venous, and capillary flow to measure regional oxygen saturation (rSO₂).⁴ Uses in human medicine include assessment of cerebral oxygenation during anesthesia and assessment of soft tissues, specifically during wound healing.^1,3 In the present study, nine Louisiana pine snakes (Pituophis ruthveni) were monitored through four phases of an anesthetic event: breathing room air, supplied with supplemental oxygen, during sedation, and recovery. rSO₂, measured over both the liver (rSO₂^Liver) and at the midpoint of the body (rSO₂^Half), and SpO₂, were compared to the venous partial pressure of oxygen (PvO₂) at the end of each phase. Strong positive associations were found between PvO₂ and both rSO₂^Liver (r=0.72) and rSO₂^Half (r=0.63) irrespective of phase, but not with SpO₂ (r=0.3). Strength of correlation varied with each phase but was universally strongest for rSO₂^Liver. Strengths of associations were further increased when rSO₂^Liver values of <60% were excluded from analyses. The use of rSO₂ in snakes appears to have merit in assessing oxygenation levels of snakes, particularly when compared to traditional pulse oximetry.

Acknowledgments

The authors would like to thank the herpetology staff of Zoo Knoxville, in particular Michael Ogle. In addition, statistical assistance from Joshua Price was appreciated, and Mitch Sandifer at Masimo corporation for the use of the equipment.

Literature Cited

1.  Brazy JE, Lewis DV, Mitnick MH, Jöbsis vander Vliet FF. Noninvasive monitoring of cerebral oxygenation in preterm infants: preliminary observations. Pediatrics. 1985;75(2):217–225.

2.  Hernandez-Divers SM, Schumacher J, Stahl S, Hernandez-Divers SJ. Comparison of isoflurane ad sevoflurane anesthesia after premedication with butorphanol in the green iguana (Iguana iguana). J Zoo Wildl Med. 2005;36(2):169–175.

3.  Tobias JD. Cerebral oxygenation monitoring: near-infrared spectroscopy. Expert Rev Med Devices. 2006;3(2):235–243.

4.  Watzman H, Kurth C, Montenegro L, Rome J, Steven J, Nicolson S. Arterial and venous contributions to near-infrared cerebral oximetry. Anesthesiology. 2000;93(4):947–953.