Abstract

Plethysmographic variability index (PVI) is an effective, noninvasive method to help evaluate central venous pressure and guide fluid therapy in humans and dogs.^1,2 PVI is calculated via measuring dynamic changes in perfusion index during respiratory cycles, which mimics the amplitude of the pulse oximeter waveform. PVI changes also reflect vascular tone and circulating blood supply. The primary objective of this study was to investigate the applicability of PVI in monitoring anesthetized tigers (Panthera tigris). Eight adult, healthy tigers were anesthetized and mechanically ventilated. PVI, direct blood pressure (BP), capnography, and ECG were measured. Mean arterial pressure (MAP) was controlled and maintained at three different states (normotensive [MAP=70±5 mm Hg], hypotensive [MAP=50±5 mm Hg], and hypertensive [MAP=90±5 mm Hg]) for 20 min each, using changes in isoflurane concentration and administration of dobutamine. Arterial blood gas analysis was performed at the beginning of anesthesia and during each BP state. Mean PVI values were 8.44, 10.69, and 16.11 for hypertensive, normotensive, and hypotensive states, respectively; PVI in the hypotensive state was significantly different than PVI in normotensive and hypertensive states. PVI values were significantly correlated with MAP (r=0.657, p<0.0001), similar to the results of a hemorrhagic model in dogs.² PaO₂ values were greater (p<0.05) in all BP states when compared to baseline, and there were no differences in other blood gas variables amongst BP states. PVI is a highly portable, noninvasive method for predicting the BP status in tigers under general anesthesia.

Acknowledgments

The authors wish to thank the staff at Tiger Haven for their unparalleled care and dedication to these animals; Andrew Tepe (LVT) from the anesthesia service and other technicians, interns, and residents of the anesthesia and zoological medicine services at the University of Tennessee for their assistance in data acquisition.

Literature Cited

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2.  Klein AV, Teixeira-Neto FJ, Lagos-Carvajal AP, Diniz MS, Becerra-Velasquez DR. Changes in pulse pressure variation and plethysmographic variability index caused by hypotension-inducing hemorrhage followed by volume replacement in isoflurane-anesthetized dogs. Am J Vet Res. 2016;77(3):280–287.